The use of an adjustable valve to treat over-drainage of a cyst-peritoneal shunt in a child with a large sylvian fissure arachnoid cyst.

INTRODUCTION: The cyst-peritoneal shunt is a recognised surgical alternative in the management of sylvian fissure arachnoid cysts. Shunt overdrainage is well described in literature on ventriculo-peritoneal shunts, but not often appreciated as a complication of cysto-peritoneal shunts. CASE REPORT: A 5-year-old boy presented with a symptomatic left sylvian fissure arachnoid cyst. This was initially treated by craniotomy and membrane fenestration in the carotid cistern. Recurrence led to insertion of a valveless cyst-peritoneal shunt 5 months later. Initial progress was followed by persistent headaches 18 months after shunt insertion. CT scan revealed a significant reduction in the cyst size, enlargement of the ipsilateral lateral ventricle, collapse of the contra-lateral ventricle and midline shift towards the side of the shunt. These findings were interpreted as over-drainage of the cyst-peritoneal shunt. RESULT: A Codman Medos adjustable valve was inserted, with the intention of gradually increasing the pressure until the midline shift was restored and the contra-lateral ventricle was reconstituted. This was achieved with the valve set at 90 mm H(2)O, verified by CT scan. Radiological improvement was associated with dramatic symptomatic improvement.
CONCLUSION: Over-drainage of cyst-peritoneal shunts is often not appreciated, especially when the main manifestation is headaches. As it is difficult to predict the required valve pressure setting, it may be advisable to consider the use of an adjustable valve.