Neoplastic meningitis. Marked variations of cerebrospinal fluid composition in the absence of extradural block.

Cerebrospinal fluid levels of protein, glucose, and malignant cells may differ markedly at different levels of the neuraxis in patients with neoplastic meningitis, even in the absence of an extradural blockage to cerebrospinal fluid flow. The pathogenesis of these differences is unclear, but is probably related to focal disruption of the blood-cerebrospinal fluid barrier produced by neoplastic involvement of the meninges. The clinical implications of this new observation are important. When the diagnosis of neoplastic meningitis is strongly suspected, but malignant cells cannot be demonstrated by repeated examination of lumbar cerebrospinal fluid, samples should be obtained by cisternal tap if the neurologic deficits are manifestations from involvement of the cranial nerves or cerebrum. Similarly, response to intrathecal chemotherapy should be monitored with serial examinations of cerebrospinal fluid obtained from the site of most marked pretreatment abnormality.