Journal of Postgraduate Medicine Medknow Publications and Staff Society of Seth GS Medical College and KEM Hospital, Mumbai, India ISSN: 0022-3859 EISSN: 0972-2823 Vol. 56, Num. 3, 2010, pp. 213-215

Journal of Postgraduate Medicine, Vol. 56, No. 3, July-September, 2010, pp. 213-215

Case Report

Normal pressure hydrocephalus after gamma knife radiosurgery for vestibular schwannoma

Mohammed TA, Ahuja MS¹ , Ju SS, Thomas J²

Departments of Neurology, ¹ Diagnostic Radiology and ² Neurosurgery, National Neuroscience Institute, Singapore General Hospital, Singapore

Correspondence Address: Dr. Mohammed Tauqeer Ahmad, Department of Neurology, National Neuroscience Institute, Singapore General Hospital, Singapore, tauqeer.ahmad@sgh.com.sg

Date of Submission: 08-Jan-2010
Date of Decision: 17-May-2010
Date of Acceptance: 19-May-2010

Code Number: jp10059

PMID: 20739769

DOI: 10.4103/0022-3859.68634

Abstract

Keywords: Acoustic schwannoma, gamma knife surgery, normal pressure hydrocephalus

Introduction

Hydrocephalus is an uncommon and controversial complication of gamma knife radiosurgery for vestibular schwannomas. We present a rare case of normal pressure hydrocephalus (NPH) after gamma knife radiosurgery of a vestibular schwannoma in which the timeline of events strongly suggests that gamma knife played a contributory role in the development of hydrocephalus.

Case Report

A 63-year-old previously healthy woman presented with sudden onset hearing loss in left ear. Her neurological examination revealed left sensorineural deafness. Magnetic resonance imaging (MRI) study [Figure - 1] demonstrated a 1.5 x 1.4 cm enhancing mass that was closely associated with the left vestibular nerve, with extension into the left internal auditory canal causing widening of porus acousticus. The appearance was consistent with vestibular schwannoma. After reviewing options, the patient opted for gamma knife radiosurgery and she received 15 Gy of radiation to her acoustic schwannoma. One year after the gamma knife procedure, the patient presented with triad of NPH. Another MR scan was obtained, which demonstrated severe ventriculomegaly, with enlargement of the lateral, third, and fourth ventricles [Figure - 2]. No intraventricular point of obstruction of cerebrospinal fluid (CSF) flow was identified. The 1.5 ΄ 1.4 cm vestibular schwannoma was again demonstrated. A lumbar puncture procedure was performed, the opening pressure was 16 cm of water (14-18 cm of water) and CSF demonstrated a normal protein level of 0.3 g/l (0.1-0.4g/l). White blood cells were absent and glucose levels were 3.8 mmol/l (capillary sugar 5.6mmol/l). Gram smear and culture results were negative, and there was no clinical evidence of infection. A ventriculoperitoneal shunt was placed with normalization of gait and improvement in memory over six weeks.

Discussion

Cerebellopontine-angle (CP-angle) tumors account for about 8-10% of all intracranial tumors. ^[1] Acoustic neuromas account for 80-90% of all CP-angle tumors. ^[1],[2],[3] Among the non-acoustic neuromas, meningiomas account for about 60% all CP-angle tumors with; epidermoid cysts, cholesteatomata, and glioma accounting for the rest. ^[4] Hydrocephalus is a known complication of an acoustic schwannoma, occurring in approximately 14% of cases and in 4-6% of cases after gamma knife treatment. ^[5],[6] Although it has been reported that gamma knife radiosurgery may contribute to the development of hydrocephalus, a causal relationship has not been established and remains controversial. ^{[6],[7],[8],[9],[10]} The time course of events in this case suggests a contributory role of gamma knife treatment in the development or exacerbation of hydrocephalus. Indeed, in the few reported cases in which a timeline is documented, the time course of events is similar, with hydrocephalus developing four to 18 months after radiosurgery. ^[6],[7]

Our patient did not have elevated CSF protein level; it has been proposed that communicating hydrocephalus accompanying an acoustic schwannoma is caused by tumor necrosis, with subsequent elevation of CSF protein concentration. Elevated CSF protein levels are thought to then obstruct CSF resorption at the level of the arachnoid granulations. ^[5] These events are reported to occur in acoustic schwannomas without radiosurgical treatment, though radiosurgery may exacerbate these events in some patients.

Hydrocephalus after a gamma knife procedure is an infrequent event and likely reflects subtle differences in the tumor rather than differences in radiosurgical technique. It is generally accepted that vestibular schwannomas demonstrate variable growth rates. ^[11] Our case is unusual with regards to the small size of tumor, normal CSF protein developing NPH which has not been reported to date. The incidence of hydrocephalus, including nonobstructive hydrocephalus, has been shown to be greater with larger tumors. ^[12] Acoustic schwannomas typically present in the sixth decade of life. ^[12] Although histological examination is not available in such cases, tumor necrosis and hydrocephalus may arise from faster-growing tumors, possibly correlating with patient age. Although not all studies corroborate, two of them suggest that faster growth rates are seen in younger female patients. ^[13] Radiosurgery does play an important role in the development of hydrocephalus, however it is independent of the dose of radiotherapy ^[14] and till date, the mechanism of development of hydrocephalus remains controversial. ^[15] Faster growth rates and larger tumors are likely at increased risk for post-treatment tumor necrosis and the development of hydrocephalus.

Once MR features are consistent with communicating hydrocephalus and CSF pressure is normal, as in our case, a ventriculo-peritoneal or caval shunt should be the treatment of choice. ^[15] However, third ventriculostomy is an option for the treatment of a non-communicating hydrocephalus. ^[16]

Conclusions

We presented a rare case of normal pressure hydrocephalus with clinical and MR evidence after gamma knife treatment of acoustic schwannoma. Gamma knife treatment may exacerbate the development of hydrocephalus in some cases of acoustic schwannoma. However, the underlying mechanism is still unclear. Close monitoring for development of hydrocephalus after gamma knife surgery is essential to prevent irreversible cerebral damage.

References

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