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Show Journal oj'N'euro- Ophthalmology 20( 4): 266- 267, 2000. © 2000 Lippincott Williams & Wilkins, Inc., Philadelphia Chiasmal Compression Due to Obstructive Hydrocephalus Marko D. Bogdanovic, MRCP, and Gordon T. Plant, FRCP A 25- year- old man sought treatment for an 8- month history of blurred vision. It began in the nasal field OS and progressed to affect both eyes severely. Visual acuity was 6/ 60 OD and counting- fingers on the left. There was mild chronic disc swelling and pallor bilaterally ( atrophic papilledema). Visual field testing ( Fig. 1A, B) indicated generally depressed visual fields with maximal loss in the lower temporal hemifields bilaterally. Central vision was lost on the left. Magnetic resonance imaging ( MRI) showed ventricu-lomegaly caused by aqueduct stenosis ( Fig. 2), congenital in origin. There is an associated Chiari malformation. The ballooning lamina terminalis of the third ventricle is displacing the optic chiasm anteroinferiorly ( Fig. 3). The visual field loss is explained by a combination of chiasmal compression, bilateral optic nerve damage, and chronic papilledema. Cerebrospinal fluid ( CSF) examination showed a normal protein content and cell count. Manuscript received March 28, 2000; accepted June 27, 2000. From The National Hospital for Neurology and Neurosurgery, London, England. Address correspondence and reprint requests to Gordon T. Plant, FRCP, The National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, U. K. Third ventriculostomy was attempted but abandoned because the interventricular foramen could not be visualized, and an external ventricular drain was sited. A modest reduction in ventricular size occurred, but an Acinetobacter infection prevented any further attempt at ventriculostomy under image guidance. Once the infection had been treated, a ventriculo- peritoneal drain was inserted through a right parietal burr- hole. The left lateral ventricle and third ventricle remained markedly enlarged, however, and an additional ventriculo- peritoneal drain was required on the left. The ventricles were of normal size after this procedure, but unfortunately visual function did not improve. The papilledema resolved, and at follow- up optic atrophy was observed with no change in visual acuity or fields. Enlargement of the third ventricle can cause many different field defects ( 1,2). These include unilateral and bilateral scotomata, binasal and bitemporal hemianopia, unilateral upper temporal quadrantanopia, homonymous hemianopia, and unilateral blindness. Maximal loss in the lower temporal quadrants might be expected because the relevant fibers lie posterosuperiorly in the chiasm, in the direct path of the enlarging ventricle. This field defect does not appear to be reported more commonly than the others, however. KHSTB1U FIG. 1. Goldmann perimetry of A: left and B: right eyes. The visual fields are generally depressed with maximal loss in the temporal hemifields bilaterally. 266 CHIASMAL COMPRESSION DUE FIG.. 2. T1- weighted MRI scan showing enlarged ventricles. The floor of the III ventricle balloons antero- inferiorly, displacing the chiasm. The aqueduct is dilated proximal to the site of obstruction ( arrow), and there is a Chiari malformation. In some cases of hydrocephalus in adults, ventricu-lomegaly and neurologic dysfunction persist despite the presence of a functioning shunt. It has been suggested that in established cases there can be a loss in the elastic properties of the brain, which may prevent resolution of ventriculomegaly despite normalization of CSF pressure ( 3,4). It is hypothesized that ventricular enlargement is directly responsible for neurologic dysfunction. Increased CSF removal by adopting subatmospheric pressure levels in the shunt system has be reported to lead to resolution of ventriculomegaly and neurologic improvement. This persisted when standard pressure levels were reinstituted and may reflect reversal of the changes in brain compliance ( 3,4). In our patient, irreversible neurologic damage is likely to have occurred to the visual pathways, because reduction of ventricular size to nor- OBSTRUCTIVE HYDROCEPHALUS 267 FIG. 3. T2- weighted MRI scan showing downward displacement of the chiasm ( arrow) by the enlarged III ventricle. mal did not lead to clinical improvement. The need for a second shunt may have been related to the infection that occurred after the first procedure. REFERENCES 1. Humphrey PRD, Moseley IF, Ross Russell RW. Visual field defects in obstructive hydrocephalus. J Neurol Neurosurg Psychiatry 1982; 45: 591- 7. 2. Osher RH, Corbett JJ, Schatz NJ, et al. Neuro- ophthalmological complications of enlargement of the third ventricle. Br J Ophthalmol 1978; 62: 536- 42. 3. Bergsneider M, Peacock WJ, Mazziotta JC, et al. Beneficial effect of siphoning in treatment of adult hydrocephalus. Arch Neurol 1999; 56: 1224- 9. 4. Pang DP, Altschuler E. Low- pressure hydrocephalic state and vis-coelastic alterations in the brain. Neurosurgery 1994; 35: 643- 56. J Neuro- Ophthalmol, Vol. 20, Mo. 4, 2000 |
