To estimate the prevalence of CSF pleocytosis and hyperproteinorrachia after neurological surgery and evaluate their duration and time to normalization.

Post-surgical CSF pleocytosis and protein elevation are often attributed to inflammatory responses, but data supporting this are limited, and the time course for normalization is unknown.

We retrospectively reviewed 221 patients with medulloblastoma treated between 2013 and 2023. Demographic, surgical, and clinical data were abstracted from medical records. CSF samples were analyzed for pleocytosis and protein abnormalities at baseline (first sample after initial surgery) and during follow-up. Primary outcomes included prevalence and time to normalization of CSF indices. Associations with extent of resection, ventriculoperitoneal (VP) shunting, cytology, and metastases were evaluated.

Of 221 patients (63% male, median age 9.5 years, range 3.2–38.6), gross total resection was achieved in 83%, near-total in 11%, and subtotal in 6%; 28% required repeat surgery. Median time from surgery to baseline CSF was 20.0 days (range 6-63). Distant metastases were present in 40%. CSF management included external ventricular drain placement in 46% and VP shunting in 18%. CSF cytology was positive for tumor cells in 15%, and infectious meningitis occurred in 3%. At baseline, 69% demonstrated pleocytosis, more frequent after gross total resection (p=0.039). Of these, 97% normalized (median 150 days, range 4–686), with delayed return to normal associated with VP shunting (p=0.0056) and positive cytology (p=0.0209). Elevated baseline protein occurred in 35%, associated with metastasis (p=0.009), shunting (p=0.001), and positive cytology (p=0.018). Among these, 61% normalized (median 147 days, range 5–1254), with delayed normalization linked to metastasis (p=0.0042), shunting (p<0.0001), and positive cytology (p=0.0099).

Postoperative CSF pleocytosis and protein abnormalities are frequent but usually resolve. Delayed normalization is associated with VP shunt, positive cytology, and metastasis. Abnormal CSF may persist in some patients for many months.