Child's Nerv Syst (1992) 8:317-321

RGNS 9 Springer-Verlag 1992

Retroflexion of holoprosencephaly: report of two cases Chifumi Kitanaka *, Yasuo Iwasaki, and Hisashi Yamada Department of Neurosurgery, Japanese Red Cross Medical Center, 4-1-22, Hiroo, Shibuya-ku, Tokyo, 113 Japan Received June 4, 1991

Abstract. Two cases o f retroflexed h o l o p r o s e n c e p h a l y are presented. R e p o r t s o f nine cases o f retroflexion were available in the literature. Case analysis indicates that retroflexion results f r o m subdural fluid collection. The incidence o f retroflexion in h o l o p r o s e n c e p h a l y was apparently higher t h a n that o f o r d i n a r y subdural hygromas. Possible explanations for this high incidence are given. The clinical significance and m a n a g e m e n t o f retroflexion are t o u c h e d upon.

Key words: Retroflexion - D o r s a l sac - Subdural hyg r o m a - Cranio-cerebral d i s p r o p o r t i o n - A r a c h n o i d a l tear

Retroflexion is a condition in h o l o p r o s e n c e p h a l y in which the brain is posteriorly flexed (retroflexed) a w a y f r o m the calvaria. A l t h o u g h its incidence in holoprosencephaly is relatively high, there have been few papers [1, 4, 5, 7 - 9 ] discussing retroflexion since D e M y e r and Zem a n discussed three cases in 1963 [3]. As to the m a j o r cause ofretroflexion, the only suggestion has been maldevelopment o f the midline structures such as the falx cerebri and the superior sagittal sinus [9]. In this report, two o f o u r o w n cases and nine cases taken f r o m other relevant published reports are analyzed. The findings suggested that retroflexion was principally constituted by the unusually high incidence o f spontaneous subdural hygromas. As the previous theory could n o t explain this, we p u t f o r w a r d some hypotheses as to its pathogenesis. The clinical significance and m a n a g e m e n t o f retroflexion are also described.

days). Her facial appearance showed hypotelorism (Fig. 1). Postpartum computerized tomography (CT) scan revealed alobar-type holoprosencephaly (Fig. 2, top). No surgery was performed and the patient received follow-up at an outpatient clinic. At 4 months she was admitted to our hospital because of frequent seizures and increasing head circumference. CT scanning on admission (Fig. 2, middle) revealed retroflexion &the holoprosencephalic brain. Cerebral angiography (Fig. 3) did not reveal an azygous anterior cerebral artery, but the superior sagittal sinus was poorly developed with only a single bridging vein. Abnormal veins drained the deep cerebrum into the lateral sinus. Deep venous systems such as the straight sinus and the vein of Galen were absent. CT cisternography (Fig. 2, bottom left) showed that the contrast medium stayed in the subarachnoid space and did not enter either of the large cerebrospinal fluid (CSF) spaces existing in the anterior and posterior cerebrum. At 5 months, the patient's anterior CSF space and peritoneal cavity were shunted. In order to make clear whether there was any communication between the two CSF spaces, contrast medium was injected into the anterior CSF space through the ventricular catheter, but its dilution rendered the study inadequate. The

Case reports Case 1

This female infant was found to be hydrocephalic by ultrasonography in utero and was delivered by Cesarean section (33 weeks, 6 * Present address and address for correspondence: 215-10 Sagata, Shin-ichi-chou, Ashina-gun, Hiroshima Pref., 729-31 Japan

Fig. 1. Case 1: an enlarged head and hypotelorism are noticeable

318

Fig. 2. Case 1: computerized tomography (CT) scans. Top: Postpartum CT scan reveals alobar type holoprosencephaly. Middle: CT scan on admission. The brain stays away from the calvarial bones. Bottom left: CT cisternography (7 h after injection of contrast medium). The contrast medium has not entered either of the large CSF spaces. Bottom right: CT scan at 17 months. The ventricular catheter is placed in the subdural space

Fig. 3. Case 1: cerebral angiography. Top: Right carotid angiogram. Middle: Left carotid angiogram. Arterial phase. A n azygous anterior cerebral artery is not present. Bottom: Venous phase. The superior sagittal sinus is poorly seen. The brain is "hanging from" a single bridging vein

patient is now receiving follow-up care at our outpatient clinic. The mental retardation is severe. A recent CT scan done at 17 months (Fig. 2, b o t t o m right) reveals a persistent anterior CSF space. The cerebral mantle has not thickened.

examination revealed that both optic nerves were atrophic and left palpebral ptosis was present (Fig. 4). Ultrasonography revealed a dysgenetic brain and a large CSF space. CT scanning showed that a dysgenetic, monoventricular brain floated within the enlarged calvaria. There were large CSF spaces on b o t h sides, the left one of which seemed to be communicating with the monoventricle. These findings were compatible with those of retroflexed holoprosencephaly. CT cisternography (Fig. 5, lower left and middle) showed that the contrast medium stayed in the subarachnoid space and did not enter either of the large CSF spaces. Cerebral angiography (Fig. 6) revealed an azygous anterior cerebral artery. Double superior sagittal sinuses fused posteriorly into a single superior sagittal sinus. A couple of bridging veins were found on the right. The vein of Galen and the straight sinus were absent, and cerebral

Case 2 This female infant was delivered in an ambulance on the way to our hospital. The infant had reached full term. On admission she had an enlarged head. The major fontanel was tense. The infant was not active but sucking was well developed. A normal M o r o reflex was present and there were no superficial anomalies. Ophthalmological

319 veins drained into the bridging veins or the lateral sinus. The left CSF space was shunted into the peritoneal cavity 12th day after birth. Left palpebral ptosis disappeared after surgery. The electrolyte imbalance that appeared was corrected. The patient is now 17 months old and is being followed-up at our outpatient clinic. Her head circumference has been well monitored, but she is severely mentally retarded. A recent CT scan (Fig. 5, lower right) shows no change in the proportion of the CSF spaces. The cerebral mantle has not thickened.

Discussion In addition to the two cases presented above, nine other reported cases of holoprosencephaly from the literature were available for analysis [1, 3 - 5 , 7-9]. Six of these cases were alobar, two were semilobar, and one was of

Fig. 4. Case 2. Normal facial appearance except for left palpebral ptosis

the lobar type. Increased intracranial pressure was noted in two alobar cases, in both semilobar, and the one lobar case. In these five cases ventriculoperitoneal shunting was done. None of the 11 cases had clear evidence of head trauma or meningitis. In retroflexed holoprosencephaly, two large CSF spaces exist in the anterior and posterior retroflexed brain. The posterior space is called the dorsal sac, which is thought to be an extension of the ventricular space. As to the anterior space, it is considered to be a subdural space [1, 7, 9]. It is at any rate apparent from CT cisternography that it is not an enlarged subarachnoid space. H o n d a et al. [4] believe that the anterior space is really an anterior dorsal sac (or an extension of the dorsal sac) on the basis of histological wall specimens from the anterior CSF space. However, DeMyer et al. [3] and Kurlander et al. [5] confirmed in necropsy that the anterior CSF space had been separated from the dorsal sac-ventricular system. The precise incidence of retroflexion has still not been demonstrated. The incidence of retroflexion reported in neurological practice is thought to be biased, because most patients needing neurosurgical care are hydrocephalic and thus are "selected" cases. In this sense, the reports of DeMyer et al. [3] and Kurlander et al. [5] are valuable. In their reports, five cases out of eight showed retroflexion. In terms of neurosurgical series, Osaka et al. [8] reported 26 cases of holoprosencephaly, 2 of which showed retroflexion. In our hospital, during the 5-year period between 1984 and 1988, six patients with holoprosencephaly diagnosed by CT, ultrasonography, or postmortem examination were admitted, and two of them showed retroflexion. Thus, the incidence seems to be rather high: retroflexion is not at all rare in holoprosencephaly. What is most noteworthy is that neither of our two cases had in their histories clear evidence of head trauma or meningitis, the most frequent causes of subdural hy-

Fig. 5. Case 2: CT scans. Top: CT scan on admission. Semilobar type holoprosencephaly with dysgenetic appearance. Large spaces exist on both sides of the brain. Lower left and middle: CT cisternography (7 h after injection of contrast medium). The contrast medium has not entered either of the two large spaces. Lower right: CT scan at 17 months. The ventricular catheter is placed in the dorsal sac

320

Fig. 6. Case 2: right carotid angiogram. Upper: Arterial phase. An azygous anterior cerebral artery is present. Lower: Venous phase. There is a dysgeneticsuperior sagittal sinus, and the brain is "hanging from" a couple of bridging veins groma (excluding patients who underwent shunt operations). Also, none of the cases obtained from the literature are reported to have had head trauma or meningitis. This means that retroflexion is caused by spontaneous subdural hygroma in most cases, and it is unusual for spontaneous subdural hygroma to occur so frequently. This unusually high incidence has led us to believe that holoprosencephaly may have some features that facilitate the development of subdural hygromas. The importance of the paucity of bridging veins due to maldevelopment of the falx and the superior sagittal sinus has often been stressed as a causative factor of retroflexion [9]. It is indeed possible that the paucity of bridging veins is responsible for the characteristic appearance of retroflexion, because the absence of the bridging veins allows unusual expansion of the subdural space, but it seems unlikely that it plays a major role in the primary developmental process of subdural hygroma. Thus, we had to seek another theory. For this purpose, the pathogenesis of subdural hygroma was reviewed first. Several causes have been considered in relation to the pathogenesis of subdural hygromas, the most popular cause for noninfectious subdural hygromas being head

trauma. In the development of traumatic subdural hygroma, it is thought that arachnoidal tear plays a major role and that CSF in the subarachnoid space moves into the subdural space through the torn arachnoid membrane [6, 10]. However, how the arachnoid membrane is torn without disruption of surrounding structures in cases of minor head injury is not elucidated (in severe head injury it may be that external forces directly break both the arachnoid membrane and the surrounding tissue). One possible explanation is that negative pressure is created either generally or locally within the cranium (e.g., overdrainage after shunt operations, contrecoup injury) and works to tear off the arachnoid border membrane from the dural layer. Seen this way, generation of negative pressure is essential and the traumatic process not always necessary for the development of subdural hygromas. On the basis of the pathogenesis described above, the increased frequency of subdural hygroma in holoprosencephaly (retroflexion) may be explained by the presence of the dorsal sac, a characteristic of holoprosencephaly. The dorsal sac and the communicating ventricles occupy a large space within the cranium. Their content is CSF, and they communicate with the subarachnoid space through the narrow openings of the IV ventricle. When they are rapidly compressed, their internal pressure will rapidly rise at first, and then the CSF within them will flow out through the narrow openings into the infratentorial subarachnoid space; the internal pressure will decrease sufficiently but gradually due to the impedance of the CSF pathway. In this sense, the ventricle-dorsal sac (V-D) system has a poor dynamic and a high static compliance. Under negative external pressure, the volume of the system will show little change for a brief period and then gradually increase by CSF regurgitation. To apply this consideration practically, let us consider the head of a resting infant. It is constantly subject to varying degrees of external force. In other words, external pressure is always being given and removed. Pressure on the head of an infant easily bends the soft calvarial bones (also, the bones are mobile at the sutures) and considerably compresses the head. This pressure is conveyed to the V-D system, resulting in its diminution. When the pressure is removed, the calvarial bones begin to return to their previous state without delay. This means that the cranium begins expanding immediately. However, the V-D system falls behind, and the brain expands scarcely at all because of its poor compliance. Thus, negative pressure is created at the initial moment between the cranium and the brain. This negative pressure would be expected to increase as the proportion of the ventricular system grows. Thus, in holoprosencephaly, in which the V-D system occupies a large space, the negative pressure would be great. However, it must be kept in mind that cases of obstructive hydrocephalus are different. Another factor, craniocerebral disproportion, is also important in the development of subdural hygromas in infants, especially in microcephalic cases. Craniocerebral disproportion is a discrepancy between the size of the cranium and the volume of the brain, due to relative maldevelopment (failure to expand) of the brain [11]. In

321

our second case, the apparently dysgenetic brain with its bizarre contours seems to have failed to conform to the growing cranium; continuous negative pressure might have been created locally. In hydrocephalic (either obstructive or communicating) holoprosencephaly, like in our first case, the small and thin cerebral mantle is pressed against the cranium by the internal pressure. When the internal pressure is sufficiently reduced, the holoprosencephalic brain will fail to expand, and this will result in subdural fluid collection. Thus, it is assumed that procedures that reduce the internal pressure of the CSF space, such as ventriculoperitoneal shunting and lumbar tapping, easily cause retroflexion. Reviewing the cases again, these two factors seem successfully to explain the pathogenesis of retroflexion. Actually, out of eight cases of spontaneous retroflexion (retroflexion not caused by ventriculoperitoneal shunt), six were of the alobar type with a large V-D system and two were of the semilobar type with bizarre contours. It is not yet shown how the presence of retroflexion affects the clinical course of a case of holoprosencephaly. It may be a matter of a benign subdural hygroma and not need treatment [2]. However, when retroflexion is complicated by increased intracranial pressure, a subduroperitoneal shunt should be considered, as in our first case, since theoretically, a ventriculoperitoneal shunt can aggravate retroflexion. However, subduroperitoneal shunting does not always obviate subdural hygromas, probably due to communication between the subdural space and the V-D system. In addition, care is necessary in selecting the valve system in shunt operations for hydrocephalic holoprosencephaly, because overdrainage may easily cause retroflexion. Excessive retroflexion is undesirable because it would be expected that an abnormal configuration of the brain could effect torsion, tension, or pressure upon intracranial vessels, and this should naturally be avoided.

Although it is possible that the stretched bridging veins may be torn even in minor head injuries, no cases of hemorrhage into the subdural space have yet to be reported.

Acknowledgements. We are grateful to the Department of Neonatology and Department of Pediatrics for referring patients to us.

References 1. Altman NR, Altman CH, Sheldon JJ, Leborgne J (1984) Holoprosencephaly classified by computed tomography. AJNR 5:433 -437 2. Carolan PL, McLaurin RL, Towbin RB, Egelhoff JC (1986) Benign extra-axial collections of infancy. Pediatr Neurosci 12:140-144 3. DeMyer W, Zeman W (1963) Alobar boloprosencephaly (arhinencephaly) with median cleft lip and palate: clinical, electroencephalographic and nosologic considerations. Confin Neurol 23:1-36 4. Honda E, Hayashi Z, Shojima K, Shojima T, Kuramoto S (1986) A case of atypical holoprosencephaly (in Japanese). Shoni No Nosinkei 11:117-122 5. Kurlander GJ, DeMyer W, Campbell JA, Taybi H (1966) Roentgenology of holoprosencephaly (arhinencephaly). Acta Radiol Diagn 5:25-40 6. Matsumoto S, Tamaki N (1986) Subdural hygromas. In: McLaurin RL (ed) Extracerebral collections. (Advances in neurotraumatology, vol 1). Springer, Berlin Heidelberg New York, pp 157-172 7. Nagano O, Ohno K, Masaoka H, Fukai N, Matsushima Y (1987) Retroflexed holoprosencephaly - X-ray, CT findings and MRI findings (in Japanese). CT Kenkyu 9:100-104 8. Osaka K, Ohta T (1983) Holoprosencephaly (in Japanese). Neurosurgeons 3:53-64 9. Probst FP (1979) The prosencephalies. Springer, Berlin Heidelberg New York, pp 77-78 10. Stone JL, Lang RG, Sugar O, Moody RA (1981) Traumatic subdural hygroma. Neurosurgery 8:542-559 11. Yamada H (1984) Craniocerebral disproportion: a review (in Japanese). Shoni No Nosinkei 9:1-8

Retroflexion of holoprosencephaly: report of two cases.

Two cases of retroflexed holoprosencephaly are presented. Reports of nine cases of retroflexion were available in the literature. Case analysis indica...
2MB Sizes 0 Downloads 0 Views