Overdrainage phenomena in shunt treated hydrocephalus.

In addition to the high rate of shunt complications due to obstruction and infection there is a considerable number of undesirable side effects caused by excessive drainage of CSF. Four hundred shunt treated patients are analyzed for overdrainage signs: acute decompression symptoms produced by upward shifting of the brain stem, low pressure headaches (mostly transient), and microcephaly and head deformities like scaphocephaly in infants. Skull X-ray changes reflect adjustment to reduced intracranial content. Slit ventricles and a marked intolerance to minimal pressure rises may be quite troublesome. Subdural haematomas are only exceptionally space-occupying; in most instances they are space-filling. Causes, incidence, management, and prevention are discussed.