Case Report

Isolated, Transient, Pneumocephalus-Induced Oculomotor Neuropathy After Microvascular Decompression of the Trigeminal Nerve William J. Steele III1, Sean M. Barber1, Andrew G. Lee2, George A. West1

Key words Craniotomy - Microvascular decompression - Neuropathy - Neurosurgery - Oculomotor - Pneumocephalus - Trigeminal neuralgia -

Abbreviations and Acronyms CSF: cerebrospinal fluid FIO2: Fraction of inspired oxygen MRI: Magnetic resonance imaging From the Departments of 1Neurological Surgery and 2 Neuroophthalmology, Houston Methodist Neurological Institute, Houston, Texas, USA To whom correspondence should be addressed: William J. Steele III, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2016) 88:690.e17-690.e22. http://dx.doi.org/10.1016/j.wneu.2015.11.090 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2016 Elsevier Inc. All rights reserved.

INTRODUCTION Pneumocephalus occurs commonly after cranial or spinal procedures in which the dura is breached. After supratentorial craniotomies or posterior fossa craniotomies in the sitting position, postoperative pneumocephalus is seen without exception.1,2 In most cases, postoperative pneumocephalus without a tension component is of little clinical significance, although symptoms such as headache, nausea, vomiting, general malaise, or even seizures may occasionally be seen. Several reports exist in the literature of isolated cranial mononeuropathies emerging after cranial or spinal procedures for which no cause other than pneumocephalus could be found. Most of these reports describe isolated oculomotor or trigeminal neuropathies occurring after trauma or lumbar puncture. Only 3 reports exist in the literature3-5 of isolated, pneumocephalus-related cranial neuropathies occurring after craniotomy.

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- BACKGROUND:

Pneumocephalus is a common radiographic finding after posterior fossa craniotomy. In contrast, cranial neuropathies related to pneumocephalus are extremely rare, with only a handful of previous reports.

- CASE

DESCRIPTION: We present the rare case of a right partial oculomotor mononeuropathy occurring in a 26-year-old woman 4 hours after a microvascular decompression of her right trigeminal nerve. Postoperative imaging revealed pneumocephalus in the interpeduncular cisterns with an air bubble close to the cisternal segment of the right oculomotor nerve, trapped by a fetal right posterior cerebral artery. The patient was placed on 100% FIO2 (fraction of inspired oxygen) and encouraged to remain in the Trendelenburg position. She was discharged with only modest improvement in her pupil-involved partial oculomotor palsy, but she improved over the course of clinical follow-up and her deficit had completely resolved at 6 months.

- CONCLUSIONS:

Cranial neuropathy secondary to pneumocephalus is a rare and usually self-limiting condition. Although high-concentration oxygen therapy hastens resolution of pneumocephalus, recovery from pneumocephalus-related neuropathies may take weeks to months. To properly treat pneumocephalusinduced cranial neuropathies, further studies into the mechanism of injury are needed.

We present a case of an isolated oculomotor nerve palsy occurring after microvascular decompression of the trigeminal nerve and provide a review of the relevant literature to better understand the pathophysiology of this disease.

CASE PRESENTATION A 26-year-old woman presented with a 3year history of intermittent right-sided facial pain. She had previously been seen by dentistry, oral surgery, and otolaryngology and had undergone numerous procedures including a root canal and 2 teeth extractions before her diagnosis of trigeminal neuralgia. She underwent multiple cranial imaging studies, which revealed a retention cyst in her right maxillary sinus but were otherwise negative. She continued to have intermittent right-sided lancinating sensations in a V3 distribution, which were triggered by eating, touch, or brushing her teeth, consistent with trigeminal neuralgia. The

pain became more progressive in terms of severity and frequency. She was placed on carbamazepine up to 2400 mg daily without significant relief. She was seen in the clinic and high-resolution magnetic resonance imaging (MRI) of the brain was ordered, which revealed a vessel loop superior to the cisternal segment of the right trigeminal nerve (Figure 1). After discussing treatment options including Gamma Knife (Elekta, Stockholm, Sweden) radiosurgery, and percutaneous rhizotomy, as well as microvascular decompression and exploration, the decision to proceed with microsurgical vascular decompression was agreed on. The patient was taken to the operating room and placed in the left lateral decubitus position with her head in pin fixation. The right retromastoid area was shaved, prepared, and draped in sterile fashion. The patient was given perioperative antibiotics. No osmodiuretic therapy was administered. A curvilinear incision was then made in the retromastoid area and dissection was

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PNEUMOCEPHALUS-INDUCED OCULOMOTOR NEUROPATHY

Figure 1. Fast imaging using steady-state acquisition magnetic resonance images of the brain of a 26-year-old woman with right facial pain. A small vessel loop can be seen superior to the right trigeminal nerve.

carried down to the level of the skull. Using standard landmarks, a burr hole was fashioned over the junction between the transverse and sigmoid junctions. A small craniotomy was then turned. The underlying sinuses were visualized and additional bone was then removed over the sigmoid sinus to improve the exposure. The bone edges were waxed. The dura was then opened with a curvilinear incision and was flapped laterally. Under the microscope, with gentle retraction on the cerebellum and release of cerebrospinal fluid (CSF), the trigeminal nerve was identified and found to be heavily encased with arachnoid adhesions. After opening these adhesions, an arterial vessel could be seen impinging on the trigeminal nerve near the root entry zone. This artery was carefully dissected away from the nerve and a good plane between the 2 established. Two Teflon pledget sponges were then inserted between the artery and nerve such that there was no longer contact between them. No significant bleeding was seen. The retractors were removed, the wound was irrigated with normal saline, and the dura was closed in a watertight fashion that was confirmed with Valsalva maneuvers. The bone edges were rewaxed and Gelfoam (Pfizer, Kalamazoo, Michigan, USA) and Duragen (Plainsboro, New Jersey) were

placed overlying the dura. The bone flap was then resecured using cranial plates and screws. The wound was then closed in standard layered fashion (Figure 2). The patient was extubated without incident and transferred to the recovery unit, where she was examined and found to have no focal neurologic deficits. She was transferred to the neurologic intensive care unit. Her facial pain had largely resolved. Approximately 4 hours postoperatively, the patient began to complain of headache, nausea, and binocular diplopia. She was examined again and found to have right-sided ptosis, a fixed and dilated right pupil, and an inability to adduct her right eye, consistent with a pupil-involving oculomotor nerve palsy. An immediate computed tomography scan of the head was ordered that revealed only a moderate amount of air within the lateral ventricles and anterior cranial fossa as well as the perimesencephalic cisterns. There was no evidence of hemorrhage, infarction, venous sinus thrombosis, or other acute abnormality (Figure 3). The patient was placed on a 100% FIO2 (fraction of inspired oxygen) nonrebreather mask and given antinausea medication. Follow-up MRI without contrast and magnetic resonance angiography of the brain was performed 2 hours

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later because the patient’s oculomotor nerve palsy persisted. High-resolution MRI of the brain revealed a susceptibility artifact from pneumocephalus within the ventricles, along the bilateral frontal convexities, and in the right prepontine cisterns. No acute infarct, hemorrhage, or mass lesion was seen. The patient did harbor a partial fetal-type right posterior cerebral artery with a prominent right posterior communicating artery and a small right P-1 segment that extended inferiorly close to the cisternal segment of the right oculomotor nerve. A small pneumatocele was seen here, apparently trapped by this confluence. Magnetic resonance angiography was negative for aneurysm (Figures 4 and 5). On postoperative day 1, the patient’s nausea and diplopia persisted. The neuroophthalmology service was consulted and found that her visual acuity was normal. The right pupil was 7 mm dilated and nonreactive to light. The left pupil was 4 mm and reactive. There was partial lid ptosis (4e5 mm) on the right along with exotropia of 25 prism diopters in primary position that increased on attempted adduction of the right eye. Her abduction remained normal and in right gaze was straight. She had 1 underaction of elevation and 3 to 4 underaction of depression in the right eye. Intorsion in downgaze remained intact. Her disk and macula were normal bilaterally with no disk edema or optic atrophy. Because of her radiographic findings, ophthalmology recommended continued oxygen therapy and placement of the patient in the Trendelenburg position in an attempt to treat her pneumocephalus. The patient was monitored in the intensive care unit for 1 day and then transferred to the floor. She was maintained on non-rebreather oxygen therapy and was intermittently placed in the Trendelenburg position, but she did not tolerate this position for extended periods. Her examination results improved by postoperative day 2 and she was able to adduct her right eye slightly, although her pupil remained fixed and dilated. She was given an eye patch and discharged home on postoperative day 3 with only marginal improvement in her partial pupil-involving oculomotor nerve palsy. When seen in follow-up at 3 months, her deficit had improved substantially, and by 6 months, it had completely resolved.

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Figure 2. Postoperative coronal T2 magnetic resonance images of the brain of a 26-year-old woman who underwent microvascular decompression of the right trigeminal nerve. Teflon pledgets can be seen displacing a vessel loop of the superior cerebellar artery superiorly and laterally.

DISCUSSION Pneumocephalus is a common finding after neurosurgical procedures in which the dura is violated. The incidence of pneumocephalus on postoperative days 0e2 has been reported to be 100% after supratentorial craniotomy and 57%, 72.5%, or 100% after posterior fossa craniotomy or

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upper cervical spinal cord surgery in the prone, park-bench, and sitting positions, respectively.1,2 Some investigators suggest that the incidence of postoperative pneumocephalus is higher in patients with preoperative hydrocephalus or those undergoing lengthier operative procedures.2

Clinical symptoms attributable to pneumocephalus are rare. Headache is often cited as the most common symptom related to pneumocephalus and is seen in approximately 39% of pneumocephalic patients.6 Other commonly cited symptoms of pneumocephalus include nausea/vomiting, seizures, dizziness, encephalopathy, or general malaise. A characteristic bruit hydro-aérique (a splashing sound perceived by patient or examiner with movement of the patient’s head; said to be the only symptom pathognomonic for pneumocephalus) is reportedly seen in only 7% of cases.6 Some investigators suggest that postoperative patient positioning influences the incidence of symptoms related to pneumocephalus; keeping a patient’s head elevated (e.g., at 30 ) decreases the incidence of symptoms related to pneumocephalus by reducing intracranial pressure.2 In our case, the patient was placed intermittently in the Trendelenburg position in an attempt to dislodge the pneumatocele from its undesired location, and her oculomotor neuropathy improved only marginally by the time of discharge. What effect postoperative positioning had in this case is not clear. Other perioperative factors contribute to pneumocephalus. Intraoperative use of gravity (i.e., sitting position), CSF evacuation, hyperventilation, and diuretics act together to produce a slack brain with concomitant enlargement of the subdural space. When CSF fluid is drained, air is permitted to enter the cranial subdural space. Postoperatively, persistent CSF leakage can create a negative pressure gradient over the dura, allowing CSF to be replaced with air. Valsalva maneuvers, frequently performed after closure of the dura, increase pressure in the middle ear via the Eustachian tube. This creates a positive pressure gradient, allowing air to enter the intracranial space.7 Other risk factors including nitrous oxide anesthesia, barotrauma, continuous CSF drainage via lumbar drain, epidural anesthesia, hydrocephalus, infection, and neoplasms have been previously reported with the development of pneumocephalus.8 Our patient, in addition to CSF evacuation, did undergo a Valsalva maneuver after closure of the dura to ensure a watertight closure. These maneuvers, in addition to encountering air cells that were

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Figure 3. Postoperative computed tomography scan of the brain of a 26-year-old woman with right facial pain who underwent microvascular decompression of the right trigeminal nerve and developed a pupil-involving right oculomotor nerve palsy 4 hours postoperatively. No hemorrhage, infarct, or other abnormality to account for a right oculomotor nerve palsy can be seen. A small amount of pneumocephalus can be seen scattered throughout the subarachnoid space, including a small amount in the interpeduncular cistern.

thoroughly waxed at the time of the operation, could have provided the necessary bony defect to allow extracranial air under positive pressure to enter the intracranial space. Tension pneumocephalus (in which gas is trapped within the cranial vault under increased pressure) may be more likely to produce clinical symptoms and may require reoperation for evacuation. Tension pneumocephalus may develop because of 1) the

use of nitrous oxide anesthesia, 2) a ballvalve effect, wherein a soft tissue component covers an opening to the intracranial, air-containing compartment, allowing air to enter the compartment but not to leave, 3) room-temperature air being trapped within the cranial vault and expanding after warming to body temperature, or 4) gasproducing organisms. The incidence of isolated cranial neuropathy related to pneumocephalus is

exceedingly low and has been documented in only a few case reports, only 2 of which are related to craniotomy.4,9 An isolated abducens nerve palsy was documented in a single case, and an oculomotor nerve palsy was seen in another case. These neuropathies resolved postoperatively in both patients (time to resolution ranged from 3 hours to 6 months postoperatively in these 2 cases). Other reports exist of isolated cranial neuropathies emerging in the setting of posttraumatic pneumocephalus or postlumbar puncture pneumocephalus, but these are similarly uncommon.3,10 The isolated cranial neuropathies in the above cases are theorized to be related to direct compression of the involved cranial nerves by postoperative intracranial air.4,9 However, it is not clear why pneumocephalus-related cranial neuropathies are seen so rarely after craniotomies, particularly when pneumocephalus is known to occur so commonly. Why the deficit in this case was absent immediately postoperatively but then emerged 4 hours later is not clear. Other investigators have reported pneumocephalusrelated cranial neuropathies occurring as much as 4 days after craniotomy.9 This may be related to body temperature increase occurring after surgery, because others have noted that room-temperature air trapped within the cranial vault may expand on warming to body temperature.11 Expansion

Figure 4. Fast imaging using steady-state acquisition axial magnetic resonance images of the brain of a 26-year-old woman who underwent microvascular decompression of the right trigeminal nerve and developed a pupil-involving right oculomotor nerve palsy 4 hours postoperatively. A small pneumatocele can be seen underlying the confluence of a prominent right posterior communicating artery and the right posterior cerebral artery. The oculomotor nerve can be seen coursing close to this pneumatocele.

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Figure 5. Coronal T2 magnetic resonance images of the brain of a 26-year-old woman who underwent microvascular decompression of the right trigeminal nerve and developed a pupil-involving right oculomotor nerve palsy 4 hours postoperatively. A small pneumatocele can be seen underlying the confluence of a prominent right posterior communicating artery and the right posterior cerebral artery. The oculomotor nerve can be seen coursing close to this pneumatocele.

of trapped intracranial air has also been attributed to the use of nitrous oxide anesthesia,12 but nitrous oxide was not used in this case. Increased pressures in the middle ear cavity secondary to nose blowing, sneezing, swallowing, coughing, or Valsalva maneuver can also contribute to the development of pneumocephalus7 and could have occurred while the patient was in the recovery unit. Although these actions were not so repetitive or excessive in our patient to raise clinical concern, they could have nonetheless occurred and contributed to the development of pneumocephalus in a delayed fashion. Also interesting is that the pneumocephalus-induced oculomotor neuropathy reported by Marupudi et al.4 did

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not present with pupillary dilation, implying that the neuropathy in this case did not have a compressive cause. It is unclear whether this postoperative, pupil-sparing oculomotor neuropathy was simply related to a highly coincidental microvascular ischemic cause, or whether another, non-compressive mechanism (e.g., desiccation) by which intracranial air may lead to abnormal cranial nerve transmission exists. Furthermore, several investigators have reported pneumocephalus-induced cranial neuropathies as resolving clinically in concert with the resolution of pneumocephalus on imaging,10 and others4,9 have reported a more prolonged course of recovery that appears to be largely

independent of the resolution of pneumocephalus itself. Although no further postoperative imaging was performed in our case to confirm resolution of pneumocephalus, literature evidence suggests that pneumocephali do not typically persist longer than 2 weeks postoperatively,1 and our patient’s deficit did not completely resolve until 6 months postoperatively. Asymptomatic pneumocephalus of a small to moderate volume is often treated conservatively, and resorption of the intracranial air occurs spontaneously within 2e3 weeks. Symptomatic pneumocephalus may be treated with 100% FIO2 (which has been shown to hasten absorption via randomized controlled clinical trials)13,14 or by surgical evacuation of the air. The mechanism by which 100% FIO2 increases the rate of pneumocephalus resolution is controversial but it is believed to be caused by a reduction of the partial pressure of N2 within the blood and brain parenchyma. Although oxygen is highly soluble in the blood and is rapidly absorbed, nitrogen gas (which comprises 78% of atmospheric air) is relatively insoluble, and its absorption depends on a variety of factors. One of these factors is the partial pressure of N2 in blood and brain tissue (a factor that is inversely related to the FIO2 concentration). Administration of 100% FIO2 is thus believed to decrease the concentration of N2 within the blood and brain parenchyma, thereby increasing the concentration gradient for nitrogen absorption and hastening the resolution of pneumocephalus.13 CONCLUSIONS Cranial neuropathy secondary to pneumocephalus is a rare complication of a craniotomy. Although high-concentration oxygen therapy can resolve the radiographic findings of pneumocephalus, clinical improvement may take weeks to months. Further studies are needed to elucidate the mechanism by which neuropathy develops from pneumocephalus to more appropriately tailor treatments and improve outcomes. REFERENCES 1. Reasoner DK, Todd MM, Scamman FL, Warner D. The incidence of pneumocephalus after

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supratentorial craniotomy. Observations on the disappearance of intracranial air. Anesthesiology. 1994;80:1008-1012. 2. Toung TJ, McPherson RW, Ahn H, Donham RT, Alano J, Long D. Pneumocephalus: effects of patient position on the incidence and location of aerocele after posterior fossa and upper cervical cord surgery. Anesth Analg. 1986;65:65-70. 3. Cosio F, Bermejo-Alvarez MA, Fervienza P, Jiménez LJ, Castañón E, Díaz ML. Temporary trigeminal disorder as a result of pneumocephalus after subarachnoid block. Br J Anaesth. 2003;91: 430-432. 4. Marupudi NI, Mittal M, Mittal S. Delayed pneumocephalus-induced cranial neuropathy. Case Rep Med. 2013;2013:105087. 5. Schirmer CM, Heilman CB, Bhardwaj A. Pneumocephalus: case illustrations and review. Neurocrit Care. 2010;13:152-158. 6. Markham JW. The clinical features of pneumocephalus based upon a survey of 284 cases with report of 11 additional cases. Acta Neurochir (Wien). 1967;16:1-78.

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7. Schrijver HM, Berendse HW. Pneumocephalus by Valsalva’s maneuver. Neurology. 2003;60:345-346. 8. Standefer M, Bay JW, Trusso R. The sitting position in neurosurgery: a retrospective analysis of 488 cases. Neurosurgery. 1984;14:649-658. 9. Stevens QE, Colen CB, Ham SD, Kattner KA, Sood S. Delayed lateral rectus palsy following resection of a pineal cyst in sitting position: direct or indirect compressive phenomenon? J Child Neurol. 2007;22:1411-1414. 10. Aygun D, Doganay Z, Baydin A, Akyol M, Senel A, Nural MS, et al. Posttraumatic pneumocephalusinduced bilateral oculomotor nerve palsy. Clin Neurol Neurosurg. 2005;108:84-86. 11. Bilginer B, Ziyal IM, Celik O, Ayhan S, Akalan N. Enlargement of postoperative aqueductal air due to elevated body temperature. Case report. Turk Neurosurg. 2007;17:37-39. 12. Toung T, Donham RT, Lehner A, Campbell J. Tension pneumocephalus terior fossa craniotomy: report of four cases and review of postoperative cephalus. Neurosurgery. 1983;12:164-168.

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Alano J, after posadditional pneumo-

13. Gore PA, Maan H, Chang S, Pitt AM, Spetzler RF, Nakaji P. Normobaric oxygen therapy strategies in the treatment of postcraniotomy pneumocephalus. J Neurosurg. 2008;108:926-969.

14. Hong B, Biertz F, Raab P, Scheinichen D, Ertl P, Grosshennig A, et al. Normobaric hyperoxia for treatment of pneumocephalus after posterior fossa surgery in the semisitting position: a prospective randomized controlled trial. PLoS One. 2015;10: e0125710.

Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received 6 September 2015; accepted 26 November 2015 Citation: World Neurosurg. (2016) 88:690.e17-690.e22. http://dx.doi.org/10.1016/j.wneu.2015.11.090 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2016 Elsevier Inc. All rights reserved.

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Isolated, Transient, Pneumocephalus-Induced Oculomotor Neuropathy After Microvascular Decompression of the Trigeminal Nerve.

Pneumocephalus is a common radiographic finding after posterior fossa craniotomy. In contrast, cranial neuropathies related to pneumocephalus are extr...
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