AUTHOR(S): Horton, Jonathan C., M.D., Ph.D.; Seiff, Stuart R., M.D.; Pitts, Lawrence H., M.D.; Weinstein, Philip R., M.D.; Rosenblum, Mark L., M.D.; Hoyt, William F., M.D. Neuro-Ophthalmology Unit (JCH, WFH), Department of Neurosurgery (LHP, PRW, MLR), and Department of Ophthalmology (SRS), University of California, San Francisco, San Francisco, California Neurosurgery 31; 203-212, 1992 ABSTRACT: OBSTRUCTION OF THE dural sinuses produces a clinical syndrome that resembles pseudotumor cerebri. In these patients, unremitting papilledema can cause blindness. We performed decompression of the optic nerve sheath in four patients who had occlusion of the dural sinuses. The operation achieved rapid relief of papilledema and recovery of vision. In three patients, fenestration of the nerve sheath of only one eye resulted in resolution of papilledema in both eyes. The procedure appears to relieve papilledema by filtering small quantities of cerebrospinal fluid into the orbit. It did not lower cerebrospinal fluid pressure in three patients who underwent lumbar puncture after surgery. Optic nerve sheath decompression is an effective operation for salvage of vision in patients with obstruction of the dural sinuses. KEY WORDS: Dural sinus obstruction; Magnetic resonance angiography; Optic nerve sheath decompression; Papilledema Incision of the optic nerve sheath for the relief of papilledema was first performed in 1872 by Louis de Wecker (8). He operated, without anesthesia, by inserting a guarded neurotome into the orbit through a conjunctival incision to slit the optic nerve sheath. Recognizing the hazards of such a blind technique, Carter later modified de Wecker's procedure by exposing the optic nerve directly from a lateral subconjunctival approach. In 1889, Carter (4) reported the cure of papilledema in four patients by fenestration of the optic nerve sheath. Despite this remarkable result, the operation never became popular, and it was performed only sporadically thereafter (16,18). Eventually it disappeared from the surgical repertoire. In 1964, Hayreh (10) developed an animal model for the study of papilledema by inflating balloons within the intracranial cavity of the monkey. He found that fenestration of the optic nerve sheath behind the globe prevented the subsequent development of papilledema. This experiment proved that papilledema is caused by transmission of elevated cerebrospinal fluid pressure along the optic nerve
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sheath to the eye. It also suggested that incision of the optic nerve sheath in patients might relieve papilledema refractory to treatment by conventional neurosurgical means. In 1969, applying Hayreh's animal studies, Davidson (6) and Smith et al. (24) reported the surgical treatment of optic disc edema by decompression of the optic nerve sheath. Since then, de Wecker's forgotten operation has enjoyed a renaissance, and numerous studies have described optic nerve sheath decompression for treatment of papilledema in patients with pseudotumor cerebri (2,3,5,7,9,11,12,15,19,23, 25) . It remains unclear which operation, optic nerve sheath decompression or lumboperitoneal shunting, provides the best relief of papilledema caused by pseudotumor cerebri. A clinical syndrome mimicking pseudotumor cerebri occurs from obstruction or thrombosis of the cerebral venous sinuses (17,20,26). For this subset of patients, the pathogenesis of the elevated intracranial pressure is different. The elevated pressure is produced by cerebral venous hypertension, not by defective filtration of cerebrospinal fluid across the arachnoid villi (26). A lumboperitoneal shunt will fail to relieve papilledema if cerebral venous hypertension maintains intracranial pressure at high levels. In these patients, optic nerve sheath decompression has an advantage over lumboperitoneal shunting: it works without producing or requiring a drop in intracranial pressure. This report describes the successful treatment of papilledema by decompression of the optic nerve sheath in four patients who had obstruction of the cerebral dural sinuses. REPORT OF CASES Patient 1 In 1988, a 53-year-old man reported loss of vision in his right eye. For several years, he had been experiencing transient blackouts of vision in the eye. The left eye had been enucleated after trauma in 1969. On examination, the vision in the right eye was 20/50 with the best optical correction. A Humphrey computerized perimeter showed severe depression of the visual field (Fig. 1A). The optic disc appeared pale, gliotic, and mildly elevated from chronic papilledema. A magnetic resonance scan revealed a lesion abutting the right transverse sinus that enhanced after administration of gadolinium (Fig. 2). The ventricles were normal in size. A lumbar puncture yielded an opening pressure of 250 mm H2O. A cerebral venogram showed compression of the right transverse sinus by an extrinsic mass (Fig. 3, arrows). Only a trickle of contrast material filled the left transverse sinus; it was thought to be hypoplastic on a congenital basis. A pressure reading of 33 mm Hg was obtained in the torcular herophili by retrograde cannulation with a pressure-transducing catheter. After the catheter was retracted into the right transverse sinus, beyond the sinus obstruction, the pressure fell abruptly to 3 mm Hg. To halt the progression of visual loss, the patient underwent decompression of the right optic nerve
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Neurosurgery 1992-98 August 1992, Volume 31, Number 2 203 Decompression of the Optic Nerve Sheath for Vision-Threatening Papilledema Caused by Dural Sinus Occlusion Clinical Study
Patient 2 In 1984, a 34-year-old woman began experiencing recurrent headaches and intermittent blurred vision. The acuity was 20/20 in both eyes. Mild papilledema was evident on examination of the fundus. The findings of a contrast-enhanced computed tomographic scan were within normal limits. Lumbar puncture gave an opening pressure of 260 mm H2O. The patient was treated for presumed pseudotumor cerebri for the next 6 years with acetazolamide. In early 1990, the patient was referred for examination because her vision had worsened. The acuity was 20/25 in the right eye and 20/40 in the left eye. The blind spots were enlarged when plotted at the tangent screen. She had chronic papilledema with chorioretinal folds extending into the maculae (Fig. 4, A and B). The opening pressure on lumbar puncture was 290 mm H2O. A gadolinium-enhanced magnetic resonance scan showed a posterior fossa mass at the junction of the left transverse and sigmoid sinuses (Fig. 5). A cerebral venogram demonstrated occlusion of the left drainage system by the lesion (Fig. 6A). In addition, the right transverse sinus appeared focally stenotic (Fig. 6A, arrow). This impression was verified by direct pressure measurements within the dural sinuses. In the right transverse sinus near the torcular herophili, the mean pressure was greater than 18 mm Hg (Fig. 6B). The pressure fell to less than 8 mm Hg when the catheter was moved beyond the apparent constriction of the sinus. A magnetic resonance angiogram also showed absent flow in the left transverse and sigmoid sinuses (Fig. 7). The right transverse sinus appeared normal near the torcular herophili, but narrowed suddenly at the junction with the sigmoid sinus. The combination of total occlusion of the left transverse sinus and partial occlusion of the right transverse sinus explained the patient's increased intracranial pressure. We never determined why the right transverse sinus was partially occluded. In May 1990, the lesion was removed from the left posterior fossa. It was a meningioma. Despite removal of the tumor, it was impossible to restore the patency of the left transverse and sigmoid sinuses. After surgery the patient continued to note transient
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visual obscurations and blurred vision. In August 1990, fenestration of the left optic nerve sheath was performed. Following this operation, the papilledema in both eyes gradually resolved. By May 1991, the optic discs appeared completely flat (Fig. 4, C and D) and the visual acuity had returned to 20/20 in each eye. The intracranial pressure remained persistently elevated: lumbar puncture in June 1991 yielded an opening pressure of 260 mm H2O. Patient 3 A 40-year-old woman noticed difficulty hearing with her left ear while using the telephone. A magnetic resonance scan showed a left acoustic neuroma measuring 3 cm. On examination the day before surgery, the visual acuity was 20/20 in both eyes, and the optic discs were normal. In February 1991, the tumor was removed completely via a translabryinthine approach. The tumor cavity was packed with abdominal fat. The patient made a routine recovery from surgery, although before discharge she complained of headache. Six weeks after surgery, the patient noted blurred vision while trying to read. Her visual acuity was 20/60 in the right eye and 20/200 in the left eye. The computerized Humphrey perimeter showed enlarged blind spots and severe, irregular depression of the visual field (Fig. 8, A and B). The optic discs appeared massively swollen, with florid hemorrhages and exudates (Fig. 9, A and B). The opening pressure on lumbar puncture was 330-350 mm H2O. We concluded that papilledema had developed from occlusion of the left transverse and sigmoid sinuses during surgery to remove the acoustic neuroma. A magnetic resonance angiogram confirmed our suspicion (Fig. 10). No flow was detected in the left transverse and sigmoid sinuses. In addition, the distal right transverse sinus appeared severely narrowed (Fig. 10, arrow). Standard spinecho magnetic resonance images showed no lesion to explain the partial occlusion of the right transverse sinus. On March 26, 1991, the patient underwent fenestration of the left optic nerve sheath. After surgery, she reported relief of her headaches. She also noted rapid improvement in the vision in each eye. By July 23, 1991, the acuity had improved to 20/30 in the right eye and 20/40 in the left. The visual fields recovered almost entirely (Fig. 8, C and D), and the optic discs became virtually flat (Fig. 9, C and D). The opening pressure on lumbar puncture performed 2 months after the optic nerve sheath decompression was still 350 mm H2O. Patient 4 A 56-year-old woman saw her physician for a complaint of intermittent dizziness. She had no visual symptoms. Bilateral papilledema was discovered on routine inspection of the ocular fundi (Fig. 11, A and B). The acuity was 20/20 in each eye, and the blind spots were enlarged. A magnetic resonance scan showed a mass arising from the falx cerebri that compressed the superior sagittal sinus. The lesion enhanced with
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sheath in October 1988 via a medial subconjunctival approach. At surgery, the optic nerve sheath appeared massively dilated. Shifting fluid within the subarachnoid space could be detected by gentle ballottement of the nerve sheath. A gush of cerebrospinal fluid issued forth when the nerve sheath was incised. A fenestration of 2 × 4 mm was made in the perioptic nerve sheath. After surgery, the patient reported a steady improvement in vision. On our last examination in April 1990 the visual acuity was 20/25. The visual field showed marked improvement in retinal sensitivity (compare Figs. 1A and1B). The papilledema resolved completely, leaving an atrophic, flat disc. The lesion in the right posterior fossa has never been excised. It is probably a meningioma.
DISCUSSION Obstruction of the cerebral dural sinuses produces a syndrome that simulates pseudotumor cerebri. Blindness from unrelieved papilledema constitutes a major threat to the patient. We describe the successful treatment of papilledema by surgical fenestration of the optic nerve sheath in four patients who had partial occlusion of the cerebral venous sinuses. After surgery, the visual acuity and the visual fields improved rapidly in each patient. In addition, headache was relieved in one patient. We do not understand why headache is relieved by optic nerve sheath decompression in some patients, but others have reported the same finding (2,4-7,9,23). In three patients, we remeasured the lumbar opening pressure after surgery. It was still high, despite the satisfactory resolution of papilledema. Previous studies have documented that intracranial pressure remains elevated after optic nerve sheath decompression (1,3,5,12,15). However, other reports have noted a drop in intracranial pressure after fenestration (2,14) . These contradictory results are difficult to interpret. It seems safe to conclude that in some patients, at least, optic nerve sheath fenestration works without a major decrement in cerebrospinal fluid pressure as measured by lumbar puncture. This result suggests that relief of papilledema by sheath decompression is due to a local effect at the optic nerve head, not to a global reduction in intracranial pressure. Keltner (13) has proposed that optic nerve sheath fenestration works by filtering small quantities of cerebrospinal fluid into the orbit. This fluid egress may produce a local reduction of pressure within the subarachnoid space immediately behind the optic nerve head. Several investigators have attempted unsuccessfully to demonstrate leakage of cerebrospinal fluid through the optic sheath window. In 1975, Billson and Hudson (1) injected a radioisotope into the cerebrospinal fluid after performing an optic nerve sheath decompression.
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They were unable to show appearance of the radioactive label in the orbit. More recently, Brourman et al. (2) injected iopamidol intrathecally in four patients and performed axial and coronal computed tomographic scans 1 day after surgery. No dye was seen in the orbit. Either these techniques are not sensitive enough to show leakage of cerebrospinal fluid into the orbit, or the operation works by some other mechanism. Recently, we obtained evidence pertaining to this issue in the course of treating a 23-year-old woman for pseudotumor cerebri. A magnetic resonance image of the left orbit after optic nerve sheath decompression showed a cystic structure contiguous with the globe at the site of the fenestration. The signal characteristics of the cyst contents were compatible with cerebrospinal fluid (Fig. 14A). With fat saturation, enhancement of the cyst rim could be seen after gadolinium administration (Fig. 14B). We believe that this image shows a filtering bleb that formed after fenestration of the optic nerve sheath. If correct, it provides direct evidence in favor of Keltner's theory (13) for the mechanism of optic nerve sheath decompression. Our first patient had lost one eye many years before developing papilledema in his remaining eye. Obviously, the effect of optic nerve sheath decompression upon the contralateral eye could not be ascertained. In the other three patients, surgery upon the optic nerve sheath of one eye resulted in the resolution of papilledema in both eyes. This remarkable result, namely, the improvement of papilledema on the unoperated side, has been reported previously (4,5,7,8,14,23). The mechanism is not well understood. One possibility is that unilateral fenestration of the optic nerve sheath lowers intracranial pressure by a small amount--enough to relieve papilledema in the contralateral eye--but not enough to be measured clearly with a manometer in the lumbar subarachnoid space. An alternative possibility is that fluid communication at the chiasm lowers cerebrospinal fluid pressure in the contralateral perioptic subarachnoid space without a significant reduction in intracranial pressure. The latter mechanism has been explored in a recent laboratory model (22). Whatever the correct explanation, decompression of just one optic nerve sheath is sufficient to achieve bilateral relief of papilledema in the majority of patients. We make a window of approximately 2 × 4 mm in the optic nerve sheath to obtain adequate filtration of cerebrospinal fluid into the orbit. A large rectangular opening, rather than a slit, may be less likely to heal closed with time. It is important during surgery to identify and preserve the posterior ciliary arteries supplying the optic nerve head. With observation of these precautions, the operation is safe. During the operation, the medial rectus muscle is disinserted temporarily. Rarely, this may cause transient diplopia after surgery. The most common complication, present in a third of our patients after surgery, is an irregular, mildly dilated pupil. This pupil abnormality is caused by injury to the short ciliary nerves that enter the globe on the medial side of the optic nerve
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administration of gadolinium (Fig. 12). A standard dye-injection arteriogram confirmed partial obstruction of the sinus, with prominent venous collateral circulation to the sphenoparietal sinus (Fig. 13). A meningioma was removed at surgery in May 1991. After the operation, the patient developed transient visual obscuration. The acuity fell to 20/25 in the right eye and 20/40 in the left eye, and the papilledema appeared worsened (Fig. 11, C and D). A lumbar puncture gave an opening pressure of 240 mm H2O. Removal of the meningioma was thought to have exacerbated the papilledema by disrupting the venous collaterals draining the superior sagittal sinus. In July 1991, the patient underwent fenestration of the right optic nerve sheath. A month after surgery, the visual acuity had improved to 20/20 in each eye, and the visual fields had returned to normal. By September 1991, the papilledema in each eye had largely resolved (Fig. 11, E and F). A lumbar puncture in September 1991 yielded an opening pressure of 230 mm H2O.
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to intervene surgically before chronic, atrophic changes appear in the optic disc (5,25). If atrophic papilledema is allowed to develop, the restoration of visual function will be incomplete, as in our first patient. Once it becomes evident that surgery is required, there are two principal alternatives: lumboperitoneal shunt or optic nerve sheath decompression. No comparative study has attempted to determine which operation provides the best relief of papilledema with the fewest complications and relapses. For patients with dural sinus obstruction, optic nerve sheath decompression deals effectively with the threat to vision. It provides rapid relief of papilledema even though cerebrospinal fluid pressure remains elevated after surgery. Received, October 18, 1991. Accepted, January 15, 1992. Reprint requests: Jonathan C. Horton, M.D., Ph.D., Neuro-Ophthalmology Unit, U-125, University of California, San Francisco, San Francisco, CA 94143-0350. REFERENCES: (1-27) 1. 2.
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Billson FA, Hudson RL: Surgical treatment of chronic papilledema in children. Br J Ophthalmol 59:92-95, 1975. Brourman ND, Spoor TC, Ramocki JM: Optic nerve sheath decompression for pseudotumor cerebri. Arch Ophthalmol 106:1378-1383, 1988. Burde RM, Karp JS, Miller RN: Reversal of visual deficit with optic nerve decompression in long-standing pseudotumor cerebri. Am J Ophthalmol 77:770-771, 1984. Carter RB: Operation of opening the sheath of the optic nerve for the relief of pressure. BMJ 1:399-401, 1889. Corbett JJ, Nerad JA, Tse DT, Anderson RL: Results of optic nerve sheath fenestration for pseudotumor cerebri. Arch Ophthalmol 106:1391-1397, 1988. Davidson SI: A surgical approach to plerocephalic disc edema. Trans Ophthalmol Soc UK 89:669-690, 1969. Davies G, Zilkha KJ: Decompression of the optic nerve in benign intracranial hypertension. Trans Ophthalmol Soc UK 96:427-429, 1976. De Wecker, L: Sur l'incision du nerf optique dans certains cas de nevro-rétinite. Int Ophthalmol Congr Rep 4:11-14, 1872. Galbraith JEK, Sullivan JH: Decompression of the perioptic meninges for relief of papilledema. Am J Ophthalmol 76:687-692, 1973. Hayreh SS: Pathogenesis of oedema of the optic disc. Br J Ophthalmol 48:522-543, 1964. Hupp SL, Glaser JS, Frazier-Byrne S: Optic nerve sheath decompression. Arch Ophthalmol 105:386-389, 1987. Kaye AH, Galbraith JEK, King J: Intracranial
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to supply the nasal sector of the iris sphincter muscle. In most patients, the nerves recover and the pupil returns to normal within a few months. In three of our patients, papilledema developed after an acquired lesion blocked only one transverse sinus. Ordinarily, when flow is interrupted in the transverse sinus, the transverse sinus on the other side can provide sufficient venous drainage to avoid elevation of the intracranial pressure (26). However, variations in the anatomy of the dural venous sinuses are not uncommon. Woodhall (27) dissected the venous sinuses in 100 consecutive autopsies and found one of the lateral sinuses absent in four cadavers. In addition, he found a major disproportion in the caliber of the lateral sinuses in 24 cadavers. Patients with an anomaly of one transverse sinus-often congenital--are more liable to develop symptoms when a lesion encroaches on the remaining patent transverse sinus. For this reason, patients who come to medical attention from an acquired transverse sinus lesion will frequently be found to have preexisting stenosis or hypoplasia of the other sinus. In two patients, noninvasive magnetic resonance angiography readily demonstrated impaired flow in the lateral sinuses (Figs. 7 and 10). After obtaining the magnetic resonance stereoangiogram in Patient 3 (Fig. 10), we decided that an invasive catheter study was unnecessary. Although our experience with magnetic resonance angiography is still limited, the technique appears to be sensitive and reliable for assessing flow in the cerebral dural sinuses (21). In the future, as this imaging method is used more widely, it may be discovered that some cases previously diagnosed as pseudotumor cerebri are in fact caused by disease of the dural sinuses. Before recommending optic nerve fenestration, the surgeon should recall that some patients can tolerate a mild degree of papilledema for years with no adverse effect on visual function. In such patients, the function of the optic nerve must be monitored regularly. We have found computerized perimetry invaluable because it tests the visual field in a precise and quantitative fashion that allows accurate comparison of serial examinations (19). If the visual field is depressed, the patient can be treated with drugs like acetazolamide that lower intracranial pressure by reducing the production of cerebrospinal fluid. Surgery is reserved for patients with visionthreatening papilledema that cannot be controlled with medical therapy. When the dural sinuses are obstructed suddenly, as in our third patient, papilledema and visual loss can be fulminant. This occurs most often in patients with dural sinus thrombosis. In such patients, immediate decompression of the optic nerve is required to salvage visual function. In other patients, if papilledema is less severe, surgery can be delayed in the hope that adequate collateral venous channels will develop around the blocked sinus. In some patients, we have avoided surgery by allowing time for spontaneous improvement in papilledema that occurs as a result of the development of venous collaterals. In caring for patients with papilledema, it is crucial
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COMMENTS Papilledema long has had a reputation for being a visually benign condition, despite the fact that it is now well documented that vision is regularly
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affected. Constriction of the visual fields and central loss of vision have been reported in 49 to 75% of cases reported in three large series (2,5,7). The introduction of fenestration of the optic nerve sheath in 1872 provided the first treatment for this condition (4) . This procedure has been recently resurrected with excellent results in the treatment of papilledema caused by idiopathic intracranial hypertension (pseudotumor cerebri) (1,3,6). The paper by Horton et al. documents the effectiveness of fenestration of the optic nerve sheath in the subgroup of patients who have symptomatic intracranial hypertension with unremitting high pressure, such as that associated with large cerebral venous occlusions. There are two other potential uses of fenestration of the optic nerve sheath. First, prophylactic optic nerve sheath fenestration before surgery for posterior fossa tumors may prevent the terrible, bilateral, sudden blindness that occasionally occurs. These disasters are almost always seen in patients with severe, chronic papilledema and probably result from brief drops in blood pressure. The compound effect of chronic disc swelling and superimposed disc ischemia can destroy vision. A second potential use for optic nerve sheath fenestration is for the person with a terminal intracranial malignancy whose vision is being lost as a result of chronic papilledema. These patients frequently live long enough to end their days blind. This may be prevented with optic nerve sheath fenestration. To be effective, fenestration of the optic nerve sheath should be done before the disc has become atrophic and only scraps of vision remain. Optic nerve sheath fenestration is an effective, technically easy-to-perform surgical procedure that rarely requires another operation, and it protects the optic disc from the damaging effects of papilledema. James J. Corbett Jackson, Mississippi REFERENCES: (1-7) 1.
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Brourman ND, Spoor TC, Ramocki JM: Optic nerve sheath decompression for pseudotumor cerebri. Arch Opthalmol 196:1378- 1383, 1988. Corbett JJ, Savino PJ, Thompson HS, Kansu T, Schatz NJ, Orr LS, Hopson D: Visual loss in pseudotumor cerebri: Follow-up of 57 patients from five to 41 years and a profile of 14 patients with permanent severe visual loss. Arch Neurol 39:461-474, 1982. Corbett JJ, Nerad JA, Tse DT, Anderson RL: Results of optic nerve sheath fenestration for pseudotumor cerebri. Arch Ophthalmol 106:1391-1397, 1988. De Wecker L: Sur l'incision du nerf optique dans certains cas de nevro-rétinite. Int Ophthalmol Congr Rep 4:11-14, 1872. Orcutt JC, Page NGR, Sanders MD: Factors affecting visual loss in benign intracranial hypertension. Ophthalmolmology 91:13031312, 1984.
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pressure following optic nerve decompression for benign intracranial hypertension. J Neurosurg 55:453-456, 1981. Keltner JL: Optic nerve sheath decompression. Arch Ophthalmol 106:13651368, 1988. Keltner JL, Albert DM, Lubow M, Fritsch E, Davey LM: Optic nerve decompression. Arch Ophthalmol 95:97-104, 1977. Knight RSG, Fielder AR, Firth JL: Benign intracranial hypertension: Visual loss and optic nerve sheath fenestration. J Neurol Neurosurg Psychiatry 49:243-250, 1986. Marburg O: Einiges über Grundlagen, Komplikationen und Erfolge der Sehnervenscheiden-Trepanation nach Muller. Graef Arch Ophthalmol 105:591-598, 1921. Marr WG, Chambers JW: Occlusion of the cerebral dural sinuses. Am J Ophthalmol 61:45-49, 1966. Muller L: Die Trepanation der Optikusscheide. Wien Klin Wochenschr 29:1001-1003, 1916. Pearson PA, Baker RS, Khorram D, Smith TJ: Evaluation of optic nerve sheath fenestration in pseudotumor cerebri using automated perimetry. Ophthalmology 98:99-105, 1991. Repka MX, Miller NR: Papilledema and dural sinus occlusion. J Clin Neuro Ophthalmol 4:247-250, 1984. Rippe DJ, Boyko OB, Spritzer CE, Meisler WJ, Dumoulin CL, Souza SP, Heinz ER: Demonstration of dural sinus occlusion by the use of MR angiography. Am J Neuroradiol 11:199-201, 1990. Seiff SR, Shah L: A model for the mechanism of optic nerve sheath fenestration. Arch Ophthalmol 108:1326-1329, 1990. Sergott RC, Savino PJ, Bosley TM: Modified optic nerve sheath decompression provides long-term visual improvement for pseudotumor cerebri. Arch Ophthalmol 106:1384-1390, 1988. Smith JL, Hoyt WF, Newton TH: Optic nerve sheath decompression for relief of chronic monocular choked disc. Am J Ophthalmolmol 68:633-639, 1969. Spoor TC, Ramocki JM, Madion MP, Wilkinson MJ: Treatment of pseudotumor cerebri by primary and secondary optic nerve sheath decompression. Am J Ophthalmolmol 112:177-185, 1991. Walsh FB: Ocular signs of thrombosis of the intracranial venous sinuses. Arch Ophthalmol 17:46-65, 1937. Woodhall B: Variations in the cranial venous sinuses in the region of the torcular herophili. Arch Surg 33:297-314, 1936.
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Pseudotumor cerebri is a syndrome of increased intracranial pressure, papilledema, normal or small ventricles, and normal cerebrospinal fluid composition occurring in patients with no focal neurological signs (2). It may occur as an isolated finding in over 50% of patients or in association with various conditions, such as cerebral venous obstruction or impairment, endocrine and metabolic dysfunction, exposure to exogenous agents, and systemic illness (8). Although the mechanism of intracranial hypertension in most forms of pseudotumor cerebri is not adequately understood (3), patients with venous occlusion are believed to develop increased intracranial pressure by either increased cerebrospinal fluid outflow resistance or by direct transmission of cerebral venous hypertension to the cerebrospinal fluid, or both (4). The result is that obstructed venous drainage, as described in this paper, may result in increased intracranial hypertension and papilledema, which may have an impact on the patient's vision (5, 9-11,13) . Optic nerve sheath fenestration continues to find applications in the treatment of optic nerve swelling. Although we cannot fully explain its mechanism of action through current models (1,7,12), it clearly has improved or halted the progression of visual field and visual acuity loss in a variety of patients. One only need read this past year's journal articles, particularly in ophthalmology, to understand its popularity and apparent success. As noted by the authors, not everyone with papilledema will require surgical intervention. However, when visual function progressively declines despite medical management, then surgery such as optic nerve sheath fenestration should be considered. Visual improvement may occur even in the presence of optic atrophy, but it is better to perform this procedure earlier, when progressive field loss is noted (6). Optic nerve sheath fenestration may not be a panacea in itself, and papilledema along with visual dysfunction may recur and may necessitate repeated fenestration of one or both optic nerves. Thus, it is critical that these patients be followed postoperatively on a regular basis for changes in visual acuity and in the visual fields. Craig E. Geist Washington, District of Columbia REFERENCES: (1-13) 1.
Bazarian RA, Burde, RM: Mechanism of optic
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Figure 1. Patient 1. Pre- (A) and postoperative (B) visual field examinations of the central 30 degrees of vision in the right eye, performed using a computerized Humphrey perimeter. In this gray scale representation of retinal sensitivity, dark areas indicate regions of vision loss. Before surgery (A) the mean deviation (MD) was -24.06 dB, indicating an average depression in retinal sensitivity of 2.4 log units, as compared with normal reference control values. After surgery, the mean deviation improved to -12.49 dB. The abbreviations FL (fixation losses), FP (false positives), and FN (false negatives) are indices of patient reliability on visual field testing.
Figure 3. Patient 1. Venogram showing focal narrowing (arrows) of the right transverse sinus caused by the lesion illustrated in Figure 2. There is also minimal flow in the left transverse sinus.
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Figure 2. Patient 1. T1-weighted magnetic resonance image showing a gadolinium-enhanced lesion involving the right transverse sinus.
Figure 5. Patient 2. T1-weighted magnetic resonance scan revealing a gadolinium-enhancing mass at the junction of the left transverse and sigmoid sinuses.
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Figure 4. Patient 2. A-B, preoperative pictures showing bilateral papilledema and retinal folds. C-D, after fenestration of the left optic nerve sheath, the papilledema resolved in both eyes.
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Figure 6. Patient 2. A, venogram demonstrating absent flow in the left sigmoid sinus caused by the lesion shown in Figure 5. The distal right transverse sinus is also focally narrowed (arrow). B, direct measurements with a pressure-transducing catheter in the right transverse sinus yielded a pressure greater than 18 mm Hg near the torcular herophili. The pressure dropped to less than 8 mm Hg after the catheter was retracted past the partial obstruction within the sinus.
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Figure 7. Patient 2. Three-dimensional time-of-flight magnetic resonance angiogram confirming occlusion of the left transverse sinus and partial occlusion of the right transverse sinus. The arrow indicates the site of unexplained focal narrowing of right transverse sinus.
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Figure 8. Patient 3. A-B, preoperative central 30degree visual fields tested with a computerized Humphrey perimeter. Retinal sensitivity is severely diminished, with a mean depression of -15.88 dB in the left eye and -15.63 dB in the right eye. C-D, postoperative visual fields show almost complete return of retinal function to normal.
Figure 10. Patient 3. Stereopair of magnetic resonance angiogram images showing occlusion of the left transverse sinus and focal obstruction of the right transverse sinus (arrow). To appreciate the stereo effect, the reader should overlap the two images by allowing the eyes to cross.
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Figure 9. Patient 3. A-B, preoperative pictures demonstrating exudates, hemorrhages, and massive optic disc elevation in both eyes. C-D, after the left optic nerve was decompressed, the papilledema showed rapid improvement in both eyes.
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Figure 11. Patient 4. A-B, preoperative fundus pictures showing bilateral papilledema. C-D, after resection of a meningioma, hemorrhages appeared and the papilledema worsened. E-F, 2 months after fenestration of the right optic nerve sheath, the papilledema in both eyes showed major improvement.
Figure 13. Patient 4. Late phases of arteriogram showing partial obstruction (arrow) of the superior sagittal sinus by the mass pictured in Figure 12. Collateral venous drainage to the sphenoparietal sinus is visible (arrowheads).
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Figure 12. Patient 4. T1-weighted magnetic resonance scan showing a gadolinium-enhanced lesion compressing the superior sagittal sinus (arrow).
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Figure 14. Axial magnetic resonance scan through the orbits of a 23-year-old patient with pseudotumor cerebri, revealing a filtering bleb formed by cerebrospinal fluid drainage after decompression of the left optic nerve sheath: A, T1-weighted image, in which a dark cystic structure (between arrows) behind the left eye is outlined by the bright signal of orbital fat; B, after supression of the orbital fat signal using a fat supression technique, the rim of the cyst can be seen to enhance with gadolinium.
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sheath to the eye. It also suggested that incision of the optic nerve sheath in patients might relieve papilledema refractory to treatment by conventional neurosurgical means. In 1969, applying Hayreh's animal studies, Davidson (6) and Smith et al. (24) reported the surgical treatment of optic disc edema by decompression of the optic nerve sheath. Since then, de Wecker's forgotten operation has enjoyed a renaissance, and numerous studies have described optic nerve sheath decompression for treatment of papilledema in patients with pseudotumor cerebri (2,3,5,7,9,11,12,15,19,23, 25) . It remains unclear which operation, optic nerve sheath decompression or lumboperitoneal shunting, provides the best relief of papilledema caused by pseudotumor cerebri. A clinical syndrome mimicking pseudotumor cerebri occurs from obstruction or thrombosis of the cerebral venous sinuses (17,20,26). For this subset of patients, the pathogenesis of the elevated intracranial pressure is different. The elevated pressure is produced by cerebral venous hypertension, not by defective filtration of cerebrospinal fluid across the arachnoid villi (26). A lumboperitoneal shunt will fail to relieve papilledema if cerebral venous hypertension maintains intracranial pressure at high levels. In these patients, optic nerve sheath decompression has an advantage over lumboperitoneal shunting: it works without producing or requiring a drop in intracranial pressure. This report describes the successful treatment of papilledema by decompression of the optic nerve sheath in four patients who had obstruction of the cerebral dural sinuses. REPORT OF CASES Patient 1 In 1988, a 53-year-old man reported loss of vision in his right eye. For several years, he had been experiencing transient blackouts of vision in the eye. The left eye had been enucleated after trauma in 1969. On examination, the vision in the right eye was 20/50 with the best optical correction. A Humphrey computerized perimeter showed severe depression of the visual field (Fig. 1A). The optic disc appeared pale, gliotic, and mildly elevated from chronic papilledema. A magnetic resonance scan revealed a lesion abutting the right transverse sinus that enhanced after administration of gadolinium (Fig. 2). The ventricles were normal in size. A lumbar puncture yielded an opening pressure of 250 mm H2O. A cerebral venogram showed compression of the right transverse sinus by an extrinsic mass (Fig. 3, arrows). Only a trickle of contrast material filled the left transverse sinus; it was thought to be hypoplastic on a congenital basis. A pressure reading of 33 mm Hg was obtained in the torcular herophili by retrograde cannulation with a pressure-transducing catheter. After the catheter was retracted into the right transverse sinus, beyond the sinus obstruction, the pressure fell abruptly to 3 mm Hg. To halt the progression of visual loss, the patient underwent decompression of the right optic nerve
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Neurosurgery 1992-98 August 1992, Volume 31, Number 2 203 Decompression of the Optic Nerve Sheath for Vision-Threatening Papilledema Caused by Dural Sinus Occlusion Clinical Study
Patient 2 In 1984, a 34-year-old woman began experiencing recurrent headaches and intermittent blurred vision. The acuity was 20/20 in both eyes. Mild papilledema was evident on examination of the fundus. The findings of a contrast-enhanced computed tomographic scan were within normal limits. Lumbar puncture gave an opening pressure of 260 mm H2O. The patient was treated for presumed pseudotumor cerebri for the next 6 years with acetazolamide. In early 1990, the patient was referred for examination because her vision had worsened. The acuity was 20/25 in the right eye and 20/40 in the left eye. The blind spots were enlarged when plotted at the tangent screen. She had chronic papilledema with chorioretinal folds extending into the maculae (Fig. 4, A and B). The opening pressure on lumbar puncture was 290 mm H2O. A gadolinium-enhanced magnetic resonance scan showed a posterior fossa mass at the junction of the left transverse and sigmoid sinuses (Fig. 5). A cerebral venogram demonstrated occlusion of the left drainage system by the lesion (Fig. 6A). In addition, the right transverse sinus appeared focally stenotic (Fig. 6A, arrow). This impression was verified by direct pressure measurements within the dural sinuses. In the right transverse sinus near the torcular herophili, the mean pressure was greater than 18 mm Hg (Fig. 6B). The pressure fell to less than 8 mm Hg when the catheter was moved beyond the apparent constriction of the sinus. A magnetic resonance angiogram also showed absent flow in the left transverse and sigmoid sinuses (Fig. 7). The right transverse sinus appeared normal near the torcular herophili, but narrowed suddenly at the junction with the sigmoid sinus. The combination of total occlusion of the left transverse sinus and partial occlusion of the right transverse sinus explained the patient's increased intracranial pressure. We never determined why the right transverse sinus was partially occluded. In May 1990, the lesion was removed from the left posterior fossa. It was a meningioma. Despite removal of the tumor, it was impossible to restore the patency of the left transverse and sigmoid sinuses. After surgery the patient continued to note transient
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visual obscurations and blurred vision. In August 1990, fenestration of the left optic nerve sheath was performed. Following this operation, the papilledema in both eyes gradually resolved. By May 1991, the optic discs appeared completely flat (Fig. 4, C and D) and the visual acuity had returned to 20/20 in each eye. The intracranial pressure remained persistently elevated: lumbar puncture in June 1991 yielded an opening pressure of 260 mm H2O. Patient 3 A 40-year-old woman noticed difficulty hearing with her left ear while using the telephone. A magnetic resonance scan showed a left acoustic neuroma measuring 3 cm. On examination the day before surgery, the visual acuity was 20/20 in both eyes, and the optic discs were normal. In February 1991, the tumor was removed completely via a translabryinthine approach. The tumor cavity was packed with abdominal fat. The patient made a routine recovery from surgery, although before discharge she complained of headache. Six weeks after surgery, the patient noted blurred vision while trying to read. Her visual acuity was 20/60 in the right eye and 20/200 in the left eye. The computerized Humphrey perimeter showed enlarged blind spots and severe, irregular depression of the visual field (Fig. 8, A and B). The optic discs appeared massively swollen, with florid hemorrhages and exudates (Fig. 9, A and B). The opening pressure on lumbar puncture was 330-350 mm H2O. We concluded that papilledema had developed from occlusion of the left transverse and sigmoid sinuses during surgery to remove the acoustic neuroma. A magnetic resonance angiogram confirmed our suspicion (Fig. 10). No flow was detected in the left transverse and sigmoid sinuses. In addition, the distal right transverse sinus appeared severely narrowed (Fig. 10, arrow). Standard spinecho magnetic resonance images showed no lesion to explain the partial occlusion of the right transverse sinus. On March 26, 1991, the patient underwent fenestration of the left optic nerve sheath. After surgery, she reported relief of her headaches. She also noted rapid improvement in the vision in each eye. By July 23, 1991, the acuity had improved to 20/30 in the right eye and 20/40 in the left. The visual fields recovered almost entirely (Fig. 8, C and D), and the optic discs became virtually flat (Fig. 9, C and D). The opening pressure on lumbar puncture performed 2 months after the optic nerve sheath decompression was still 350 mm H2O. Patient 4 A 56-year-old woman saw her physician for a complaint of intermittent dizziness. She had no visual symptoms. Bilateral papilledema was discovered on routine inspection of the ocular fundi (Fig. 11, A and B). The acuity was 20/20 in each eye, and the blind spots were enlarged. A magnetic resonance scan showed a mass arising from the falx cerebri that compressed the superior sagittal sinus. The lesion enhanced with
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sheath in October 1988 via a medial subconjunctival approach. At surgery, the optic nerve sheath appeared massively dilated. Shifting fluid within the subarachnoid space could be detected by gentle ballottement of the nerve sheath. A gush of cerebrospinal fluid issued forth when the nerve sheath was incised. A fenestration of 2 × 4 mm was made in the perioptic nerve sheath. After surgery, the patient reported a steady improvement in vision. On our last examination in April 1990 the visual acuity was 20/25. The visual field showed marked improvement in retinal sensitivity (compare Figs. 1A and1B). The papilledema resolved completely, leaving an atrophic, flat disc. The lesion in the right posterior fossa has never been excised. It is probably a meningioma.
DISCUSSION Obstruction of the cerebral dural sinuses produces a syndrome that simulates pseudotumor cerebri. Blindness from unrelieved papilledema constitutes a major threat to the patient. We describe the successful treatment of papilledema by surgical fenestration of the optic nerve sheath in four patients who had partial occlusion of the cerebral venous sinuses. After surgery, the visual acuity and the visual fields improved rapidly in each patient. In addition, headache was relieved in one patient. We do not understand why headache is relieved by optic nerve sheath decompression in some patients, but others have reported the same finding (2,4-7,9,23). In three patients, we remeasured the lumbar opening pressure after surgery. It was still high, despite the satisfactory resolution of papilledema. Previous studies have documented that intracranial pressure remains elevated after optic nerve sheath decompression (1,3,5,12,15). However, other reports have noted a drop in intracranial pressure after fenestration (2,14) . These contradictory results are difficult to interpret. It seems safe to conclude that in some patients, at least, optic nerve sheath fenestration works without a major decrement in cerebrospinal fluid pressure as measured by lumbar puncture. This result suggests that relief of papilledema by sheath decompression is due to a local effect at the optic nerve head, not to a global reduction in intracranial pressure. Keltner (13) has proposed that optic nerve sheath fenestration works by filtering small quantities of cerebrospinal fluid into the orbit. This fluid egress may produce a local reduction of pressure within the subarachnoid space immediately behind the optic nerve head. Several investigators have attempted unsuccessfully to demonstrate leakage of cerebrospinal fluid through the optic sheath window. In 1975, Billson and Hudson (1) injected a radioisotope into the cerebrospinal fluid after performing an optic nerve sheath decompression.
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They were unable to show appearance of the radioactive label in the orbit. More recently, Brourman et al. (2) injected iopamidol intrathecally in four patients and performed axial and coronal computed tomographic scans 1 day after surgery. No dye was seen in the orbit. Either these techniques are not sensitive enough to show leakage of cerebrospinal fluid into the orbit, or the operation works by some other mechanism. Recently, we obtained evidence pertaining to this issue in the course of treating a 23-year-old woman for pseudotumor cerebri. A magnetic resonance image of the left orbit after optic nerve sheath decompression showed a cystic structure contiguous with the globe at the site of the fenestration. The signal characteristics of the cyst contents were compatible with cerebrospinal fluid (Fig. 14A). With fat saturation, enhancement of the cyst rim could be seen after gadolinium administration (Fig. 14B). We believe that this image shows a filtering bleb that formed after fenestration of the optic nerve sheath. If correct, it provides direct evidence in favor of Keltner's theory (13) for the mechanism of optic nerve sheath decompression. Our first patient had lost one eye many years before developing papilledema in his remaining eye. Obviously, the effect of optic nerve sheath decompression upon the contralateral eye could not be ascertained. In the other three patients, surgery upon the optic nerve sheath of one eye resulted in the resolution of papilledema in both eyes. This remarkable result, namely, the improvement of papilledema on the unoperated side, has been reported previously (4,5,7,8,14,23). The mechanism is not well understood. One possibility is that unilateral fenestration of the optic nerve sheath lowers intracranial pressure by a small amount--enough to relieve papilledema in the contralateral eye--but not enough to be measured clearly with a manometer in the lumbar subarachnoid space. An alternative possibility is that fluid communication at the chiasm lowers cerebrospinal fluid pressure in the contralateral perioptic subarachnoid space without a significant reduction in intracranial pressure. The latter mechanism has been explored in a recent laboratory model (22). Whatever the correct explanation, decompression of just one optic nerve sheath is sufficient to achieve bilateral relief of papilledema in the majority of patients. We make a window of approximately 2 × 4 mm in the optic nerve sheath to obtain adequate filtration of cerebrospinal fluid into the orbit. A large rectangular opening, rather than a slit, may be less likely to heal closed with time. It is important during surgery to identify and preserve the posterior ciliary arteries supplying the optic nerve head. With observation of these precautions, the operation is safe. During the operation, the medial rectus muscle is disinserted temporarily. Rarely, this may cause transient diplopia after surgery. The most common complication, present in a third of our patients after surgery, is an irregular, mildly dilated pupil. This pupil abnormality is caused by injury to the short ciliary nerves that enter the globe on the medial side of the optic nerve
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administration of gadolinium (Fig. 12). A standard dye-injection arteriogram confirmed partial obstruction of the sinus, with prominent venous collateral circulation to the sphenoparietal sinus (Fig. 13). A meningioma was removed at surgery in May 1991. After the operation, the patient developed transient visual obscuration. The acuity fell to 20/25 in the right eye and 20/40 in the left eye, and the papilledema appeared worsened (Fig. 11, C and D). A lumbar puncture gave an opening pressure of 240 mm H2O. Removal of the meningioma was thought to have exacerbated the papilledema by disrupting the venous collaterals draining the superior sagittal sinus. In July 1991, the patient underwent fenestration of the right optic nerve sheath. A month after surgery, the visual acuity had improved to 20/20 in each eye, and the visual fields had returned to normal. By September 1991, the papilledema in each eye had largely resolved (Fig. 11, E and F). A lumbar puncture in September 1991 yielded an opening pressure of 230 mm H2O.
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to intervene surgically before chronic, atrophic changes appear in the optic disc (5,25). If atrophic papilledema is allowed to develop, the restoration of visual function will be incomplete, as in our first patient. Once it becomes evident that surgery is required, there are two principal alternatives: lumboperitoneal shunt or optic nerve sheath decompression. No comparative study has attempted to determine which operation provides the best relief of papilledema with the fewest complications and relapses. For patients with dural sinus obstruction, optic nerve sheath decompression deals effectively with the threat to vision. It provides rapid relief of papilledema even though cerebrospinal fluid pressure remains elevated after surgery. Received, October 18, 1991. Accepted, January 15, 1992. Reprint requests: Jonathan C. Horton, M.D., Ph.D., Neuro-Ophthalmology Unit, U-125, University of California, San Francisco, San Francisco, CA 94143-0350. REFERENCES: (1-27) 1. 2.
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Billson FA, Hudson RL: Surgical treatment of chronic papilledema in children. Br J Ophthalmol 59:92-95, 1975. Brourman ND, Spoor TC, Ramocki JM: Optic nerve sheath decompression for pseudotumor cerebri. Arch Ophthalmol 106:1378-1383, 1988. Burde RM, Karp JS, Miller RN: Reversal of visual deficit with optic nerve decompression in long-standing pseudotumor cerebri. Am J Ophthalmol 77:770-771, 1984. Carter RB: Operation of opening the sheath of the optic nerve for the relief of pressure. BMJ 1:399-401, 1889. Corbett JJ, Nerad JA, Tse DT, Anderson RL: Results of optic nerve sheath fenestration for pseudotumor cerebri. Arch Ophthalmol 106:1391-1397, 1988. Davidson SI: A surgical approach to plerocephalic disc edema. Trans Ophthalmol Soc UK 89:669-690, 1969. Davies G, Zilkha KJ: Decompression of the optic nerve in benign intracranial hypertension. Trans Ophthalmol Soc UK 96:427-429, 1976. De Wecker, L: Sur l'incision du nerf optique dans certains cas de nevro-rétinite. Int Ophthalmol Congr Rep 4:11-14, 1872. Galbraith JEK, Sullivan JH: Decompression of the perioptic meninges for relief of papilledema. Am J Ophthalmol 76:687-692, 1973. Hayreh SS: Pathogenesis of oedema of the optic disc. Br J Ophthalmol 48:522-543, 1964. Hupp SL, Glaser JS, Frazier-Byrne S: Optic nerve sheath decompression. Arch Ophthalmol 105:386-389, 1987. Kaye AH, Galbraith JEK, King J: Intracranial
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to supply the nasal sector of the iris sphincter muscle. In most patients, the nerves recover and the pupil returns to normal within a few months. In three of our patients, papilledema developed after an acquired lesion blocked only one transverse sinus. Ordinarily, when flow is interrupted in the transverse sinus, the transverse sinus on the other side can provide sufficient venous drainage to avoid elevation of the intracranial pressure (26). However, variations in the anatomy of the dural venous sinuses are not uncommon. Woodhall (27) dissected the venous sinuses in 100 consecutive autopsies and found one of the lateral sinuses absent in four cadavers. In addition, he found a major disproportion in the caliber of the lateral sinuses in 24 cadavers. Patients with an anomaly of one transverse sinus-often congenital--are more liable to develop symptoms when a lesion encroaches on the remaining patent transverse sinus. For this reason, patients who come to medical attention from an acquired transverse sinus lesion will frequently be found to have preexisting stenosis or hypoplasia of the other sinus. In two patients, noninvasive magnetic resonance angiography readily demonstrated impaired flow in the lateral sinuses (Figs. 7 and 10). After obtaining the magnetic resonance stereoangiogram in Patient 3 (Fig. 10), we decided that an invasive catheter study was unnecessary. Although our experience with magnetic resonance angiography is still limited, the technique appears to be sensitive and reliable for assessing flow in the cerebral dural sinuses (21). In the future, as this imaging method is used more widely, it may be discovered that some cases previously diagnosed as pseudotumor cerebri are in fact caused by disease of the dural sinuses. Before recommending optic nerve fenestration, the surgeon should recall that some patients can tolerate a mild degree of papilledema for years with no adverse effect on visual function. In such patients, the function of the optic nerve must be monitored regularly. We have found computerized perimetry invaluable because it tests the visual field in a precise and quantitative fashion that allows accurate comparison of serial examinations (19). If the visual field is depressed, the patient can be treated with drugs like acetazolamide that lower intracranial pressure by reducing the production of cerebrospinal fluid. Surgery is reserved for patients with visionthreatening papilledema that cannot be controlled with medical therapy. When the dural sinuses are obstructed suddenly, as in our third patient, papilledema and visual loss can be fulminant. This occurs most often in patients with dural sinus thrombosis. In such patients, immediate decompression of the optic nerve is required to salvage visual function. In other patients, if papilledema is less severe, surgery can be delayed in the hope that adequate collateral venous channels will develop around the blocked sinus. In some patients, we have avoided surgery by allowing time for spontaneous improvement in papilledema that occurs as a result of the development of venous collaterals. In caring for patients with papilledema, it is crucial
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COMMENTS Papilledema long has had a reputation for being a visually benign condition, despite the fact that it is now well documented that vision is regularly
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affected. Constriction of the visual fields and central loss of vision have been reported in 49 to 75% of cases reported in three large series (2,5,7). The introduction of fenestration of the optic nerve sheath in 1872 provided the first treatment for this condition (4) . This procedure has been recently resurrected with excellent results in the treatment of papilledema caused by idiopathic intracranial hypertension (pseudotumor cerebri) (1,3,6). The paper by Horton et al. documents the effectiveness of fenestration of the optic nerve sheath in the subgroup of patients who have symptomatic intracranial hypertension with unremitting high pressure, such as that associated with large cerebral venous occlusions. There are two other potential uses of fenestration of the optic nerve sheath. First, prophylactic optic nerve sheath fenestration before surgery for posterior fossa tumors may prevent the terrible, bilateral, sudden blindness that occasionally occurs. These disasters are almost always seen in patients with severe, chronic papilledema and probably result from brief drops in blood pressure. The compound effect of chronic disc swelling and superimposed disc ischemia can destroy vision. A second potential use for optic nerve sheath fenestration is for the person with a terminal intracranial malignancy whose vision is being lost as a result of chronic papilledema. These patients frequently live long enough to end their days blind. This may be prevented with optic nerve sheath fenestration. To be effective, fenestration of the optic nerve sheath should be done before the disc has become atrophic and only scraps of vision remain. Optic nerve sheath fenestration is an effective, technically easy-to-perform surgical procedure that rarely requires another operation, and it protects the optic disc from the damaging effects of papilledema. James J. Corbett Jackson, Mississippi REFERENCES: (1-7) 1.
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Brourman ND, Spoor TC, Ramocki JM: Optic nerve sheath decompression for pseudotumor cerebri. Arch Opthalmol 196:1378- 1383, 1988. Corbett JJ, Savino PJ, Thompson HS, Kansu T, Schatz NJ, Orr LS, Hopson D: Visual loss in pseudotumor cerebri: Follow-up of 57 patients from five to 41 years and a profile of 14 patients with permanent severe visual loss. Arch Neurol 39:461-474, 1982. Corbett JJ, Nerad JA, Tse DT, Anderson RL: Results of optic nerve sheath fenestration for pseudotumor cerebri. Arch Ophthalmol 106:1391-1397, 1988. De Wecker L: Sur l'incision du nerf optique dans certains cas de nevro-rétinite. Int Ophthalmol Congr Rep 4:11-14, 1872. Orcutt JC, Page NGR, Sanders MD: Factors affecting visual loss in benign intracranial hypertension. Ophthalmolmology 91:13031312, 1984.
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pressure following optic nerve decompression for benign intracranial hypertension. J Neurosurg 55:453-456, 1981. Keltner JL: Optic nerve sheath decompression. Arch Ophthalmol 106:13651368, 1988. Keltner JL, Albert DM, Lubow M, Fritsch E, Davey LM: Optic nerve decompression. Arch Ophthalmol 95:97-104, 1977. Knight RSG, Fielder AR, Firth JL: Benign intracranial hypertension: Visual loss and optic nerve sheath fenestration. J Neurol Neurosurg Psychiatry 49:243-250, 1986. Marburg O: Einiges über Grundlagen, Komplikationen und Erfolge der Sehnervenscheiden-Trepanation nach Muller. Graef Arch Ophthalmol 105:591-598, 1921. Marr WG, Chambers JW: Occlusion of the cerebral dural sinuses. Am J Ophthalmol 61:45-49, 1966. Muller L: Die Trepanation der Optikusscheide. Wien Klin Wochenschr 29:1001-1003, 1916. Pearson PA, Baker RS, Khorram D, Smith TJ: Evaluation of optic nerve sheath fenestration in pseudotumor cerebri using automated perimetry. Ophthalmology 98:99-105, 1991. Repka MX, Miller NR: Papilledema and dural sinus occlusion. J Clin Neuro Ophthalmol 4:247-250, 1984. Rippe DJ, Boyko OB, Spritzer CE, Meisler WJ, Dumoulin CL, Souza SP, Heinz ER: Demonstration of dural sinus occlusion by the use of MR angiography. Am J Neuroradiol 11:199-201, 1990. Seiff SR, Shah L: A model for the mechanism of optic nerve sheath fenestration. Arch Ophthalmol 108:1326-1329, 1990. Sergott RC, Savino PJ, Bosley TM: Modified optic nerve sheath decompression provides long-term visual improvement for pseudotumor cerebri. Arch Ophthalmol 106:1384-1390, 1988. Smith JL, Hoyt WF, Newton TH: Optic nerve sheath decompression for relief of chronic monocular choked disc. Am J Ophthalmolmol 68:633-639, 1969. Spoor TC, Ramocki JM, Madion MP, Wilkinson MJ: Treatment of pseudotumor cerebri by primary and secondary optic nerve sheath decompression. Am J Ophthalmolmol 112:177-185, 1991. Walsh FB: Ocular signs of thrombosis of the intracranial venous sinuses. Arch Ophthalmol 17:46-65, 1937. Woodhall B: Variations in the cranial venous sinuses in the region of the torcular herophili. Arch Surg 33:297-314, 1936.
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Pseudotumor cerebri is a syndrome of increased intracranial pressure, papilledema, normal or small ventricles, and normal cerebrospinal fluid composition occurring in patients with no focal neurological signs (2). It may occur as an isolated finding in over 50% of patients or in association with various conditions, such as cerebral venous obstruction or impairment, endocrine and metabolic dysfunction, exposure to exogenous agents, and systemic illness (8). Although the mechanism of intracranial hypertension in most forms of pseudotumor cerebri is not adequately understood (3), patients with venous occlusion are believed to develop increased intracranial pressure by either increased cerebrospinal fluid outflow resistance or by direct transmission of cerebral venous hypertension to the cerebrospinal fluid, or both (4). The result is that obstructed venous drainage, as described in this paper, may result in increased intracranial hypertension and papilledema, which may have an impact on the patient's vision (5, 9-11,13) . Optic nerve sheath fenestration continues to find applications in the treatment of optic nerve swelling. Although we cannot fully explain its mechanism of action through current models (1,7,12), it clearly has improved or halted the progression of visual field and visual acuity loss in a variety of patients. One only need read this past year's journal articles, particularly in ophthalmology, to understand its popularity and apparent success. As noted by the authors, not everyone with papilledema will require surgical intervention. However, when visual function progressively declines despite medical management, then surgery such as optic nerve sheath fenestration should be considered. Visual improvement may occur even in the presence of optic atrophy, but it is better to perform this procedure earlier, when progressive field loss is noted (6). Optic nerve sheath fenestration may not be a panacea in itself, and papilledema along with visual dysfunction may recur and may necessitate repeated fenestration of one or both optic nerves. Thus, it is critical that these patients be followed postoperatively on a regular basis for changes in visual acuity and in the visual fields. Craig E. Geist Washington, District of Columbia REFERENCES: (1-13) 1.
Bazarian RA, Burde, RM: Mechanism of optic
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6.
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Figure 1. Patient 1. Pre- (A) and postoperative (B) visual field examinations of the central 30 degrees of vision in the right eye, performed using a computerized Humphrey perimeter. In this gray scale representation of retinal sensitivity, dark areas indicate regions of vision loss. Before surgery (A) the mean deviation (MD) was -24.06 dB, indicating an average depression in retinal sensitivity of 2.4 log units, as compared with normal reference control values. After surgery, the mean deviation improved to -12.49 dB. The abbreviations FL (fixation losses), FP (false positives), and FN (false negatives) are indices of patient reliability on visual field testing.
Figure 3. Patient 1. Venogram showing focal narrowing (arrows) of the right transverse sinus caused by the lesion illustrated in Figure 2. There is also minimal flow in the left transverse sinus.
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Figure 2. Patient 1. T1-weighted magnetic resonance image showing a gadolinium-enhanced lesion involving the right transverse sinus.
Figure 5. Patient 2. T1-weighted magnetic resonance scan revealing a gadolinium-enhancing mass at the junction of the left transverse and sigmoid sinuses.
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Figure 4. Patient 2. A-B, preoperative pictures showing bilateral papilledema and retinal folds. C-D, after fenestration of the left optic nerve sheath, the papilledema resolved in both eyes.
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Figure 6. Patient 2. A, venogram demonstrating absent flow in the left sigmoid sinus caused by the lesion shown in Figure 5. The distal right transverse sinus is also focally narrowed (arrow). B, direct measurements with a pressure-transducing catheter in the right transverse sinus yielded a pressure greater than 18 mm Hg near the torcular herophili. The pressure dropped to less than 8 mm Hg after the catheter was retracted past the partial obstruction within the sinus.
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Figure 7. Patient 2. Three-dimensional time-of-flight magnetic resonance angiogram confirming occlusion of the left transverse sinus and partial occlusion of the right transverse sinus. The arrow indicates the site of unexplained focal narrowing of right transverse sinus.
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Figure 8. Patient 3. A-B, preoperative central 30degree visual fields tested with a computerized Humphrey perimeter. Retinal sensitivity is severely diminished, with a mean depression of -15.88 dB in the left eye and -15.63 dB in the right eye. C-D, postoperative visual fields show almost complete return of retinal function to normal.
Figure 10. Patient 3. Stereopair of magnetic resonance angiogram images showing occlusion of the left transverse sinus and focal obstruction of the right transverse sinus (arrow). To appreciate the stereo effect, the reader should overlap the two images by allowing the eyes to cross.
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Figure 9. Patient 3. A-B, preoperative pictures demonstrating exudates, hemorrhages, and massive optic disc elevation in both eyes. C-D, after the left optic nerve was decompressed, the papilledema showed rapid improvement in both eyes.
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Figure 11. Patient 4. A-B, preoperative fundus pictures showing bilateral papilledema. C-D, after resection of a meningioma, hemorrhages appeared and the papilledema worsened. E-F, 2 months after fenestration of the right optic nerve sheath, the papilledema in both eyes showed major improvement.
Figure 13. Patient 4. Late phases of arteriogram showing partial obstruction (arrow) of the superior sagittal sinus by the mass pictured in Figure 12. Collateral venous drainage to the sphenoparietal sinus is visible (arrowheads).
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Figure 12. Patient 4. T1-weighted magnetic resonance scan showing a gadolinium-enhanced lesion compressing the superior sagittal sinus (arrow).
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Figure 14. Axial magnetic resonance scan through the orbits of a 23-year-old patient with pseudotumor cerebri, revealing a filtering bleb formed by cerebrospinal fluid drainage after decompression of the left optic nerve sheath: A, T1-weighted image, in which a dark cystic structure (between arrows) behind the left eye is outlined by the bright signal of orbital fat; B, after supression of the orbital fat signal using a fat supression technique, the rim of the cyst can be seen to enhance with gadolinium.
