In primary cerebral cortex brain tumor, the CSF usually is clear and colorless, although xanthochromia may be present. Spinal fluid pressure is elevated in 70% of patients. Seventy percent show increased protein levels, with about one half of these more than 100 mg/100 ml (1.0 g/L). CSF glucose levels are normal. The majority (70%) of brain tumor patients have normal cell counts. Of the remainder, about two thirds have counts less than 25/mm3 consisting mostly of lymphocytes. In the few patients with high cell counts, there may be appreciable numbers of neutrophils, and the spinal fluid pattern then resembles that of brain abscess. Most metastatic tumors have CSF findings similar to primary neoplasms.

In occasional instances, metastatic carcinoma may spread widely over the meninges. In such cases, the findings are similar to those of tuberculous meningitis (elevated cell count, lymphocytes predominating; elevated protein concentration, and decreased glucose level). Cell blocks and cytologic smears of spinal fluid sediment are helpful for diagnosis. Cytology of CSF yields malignant cells in 55%-83%. Malignant lymphoma may involve the meninges in 5%-30% of cases, with CSF cytology said to be positive in 60%-80% of these cases. Acute lymphocytic leukemia in childhood is reported to involve the meninges at some time in up to 50% of cases. CSF cytology is not helpful in the majority of metastatic carcinomas to the brain, which most often do not involve the meninges. However, some investigators cytologically detected as many as 20%-40% of cases. In primary tumors of the brain, the meninges are uncommonly involved, so that CSF cytology detects fewer than 10% of cases.

CT or MRI is the most helpful procedure for demonstrating either primary or metastatic brain tumors. As noted previously, detection rate is reported to be approximately 90%-95% for primary intracerebral tumors. Radionuclide brain scans are useful if CT is not available; sensitivity is 5%-10% less than that of CT, and nonuniformity of technical details makes results more variable between different institutions.