Cytopathologic diagnosis of cerebrospinal fluid metastasis from solid tumors: a 10-year institutional review

Leptomeningeal metastasis is a rare and poor prognostic factor in patients with solid malignancies. Cerebrospinal fluid (CSF) cytology is a reliable method for diagnosing CSF metastasis. This study aims to evaluate the reliability of CSF cytology for detection and subclassification of CSF metastasis and to report the different types of solid malignant CSF metastasis at our institution.

Laboratory information system was queried over a 10 year period (2014-2024) to identify all CSF cytology cases with metastatic disease. Only metastatic solid malignancies were included. Hematologic malignancies and "Atypical" or "Suspicious for malignancy" cases were excluded.

Total of 286 specimens from 171 patients were identified. This was reduced to 150 patients following consolidation and exclusion criteria, and included 39 breast carcinoma, 26 lung adenocarcinoma, 15 melanoma, 6 urothelial carcinoma, 3 serous carcinoma, 5 gastric adenocarcinoma, 3 esophageal adenocarcinoma, 2 GE junction adenocarcinoma, 1 cholangiocarcinoma, 1 small cell carcinoma, 1 pulmonary large cell carcinoma, 1 pancreatic adenocarcinoma, 1 metastatic nuclear protein in testis carcinoma of the orbit, and 1 bladder signet ring adenocarcinoma. There were 30 (20%) metastatic carcinomas NOS and 15 (10%) metastatic adenocarcinomas NOS whereby limited cellularity and inability to perform ancillary testing precluded further subclassification.

Cytology can provide a reliable and accurate method for diagnosing solid malignant CSF metastasis. Similar to literature, the most common tumor origins at our institution were breast, lung and melanoma. Although further subclassification could not be performed on 30% of our cases, rare tumors were detected including metastatic bladder signet ring adenocarcinoma and metastatic nuclear protein in testis carcinoma.