Low-pressure shunt 'malfunction' following lumbar puncture in children with shunted obstructive hydrocephalus.

Most shunt malfunctions present with signs and symptoms of high intracranial pressure, and computed tomography scans demonstrate ventricular enlargement. However, several authors have described a rare 'low-pressure' hydrocephalic state in which ventricular enlargement can occur in the face of low, or even negative, intracranial pressures. We report 2 children with obstructive hydrocephalus in whom this 'low-pressure state' followed a lumbar puncture; in both children, the shunts were functioning properly despite increased ventricular size on computed tomography scans, and all symptoms resolved (and the ventricles returned to baseline) following a period of enforced recumbency without shunt revision. We hypothesize that subarachnoid cerebrospinal fluid leakage through the puncture site in the lumbar theca decreases the intracranial pressures globally to a point below the opening pressures of the shunt valves. The ventricular cerebrospinal fluid, unable to be drained through either the subarachnoid space or the shunt, accumulates within the ventricular system under low pressure. One consistent feature in our 2 patients has been the postural nature of the headaches. We recommend enforced recumbency and, if necessary, a blood patch to seal the lumbar leakage. Shunt revision or prolonged external ventricular drainage appears to be unnecessary in these patients. Finally, neurosurgeons should be aware of this potential complication.