Cytological diagnosis of cystic brain tumors: a retrospective study of 88 cases.

The stereotaxic aspiration of cystic brain tumors is performed to provide cyst decompression and/or to facilitate surgical resection. The purpose of our study was to determine the diagnostic value of brain cyst fluid cytology, especially in clinically suspected recurrent tumors with no histological follow-up (HF), when a diagnosis is most needed. We reviewed the cytological diagnoses of 88 aspirates from 70 patients with cystic brain tumors between 1995 and 2001, of which 31 had a prior known malignancy including 18 primary brain tumors (PBTs) and 13 adenocarcinomas (ACAs). Sixty-nine of 88 aspirates were obtained intraoperatively. Nineteen of 88 aspirates were obtained from 10 patients with recurrent or persistent cystic brain tumors (8 patients with PBT and 2 patients with ACA), with available clinicoradiological correlation (magnetic resonance imaging/computed tomography [MRI/CT] scans) in 13 of them. The 88 aspirates were classified in three categories: 28 positive (32%), 15 atypical (17%), and 45 negative (51%). Eight of 28 positive cases (5 case of PBT, 2 cases of ACA, and 1 case of melanoma) were given a nonspecific diagnosis of malignant neoplasm (9% of all cases). Fifteen of 28 positive cases (6 cases of PBT, 8 cases of ACA, and 1 case of melanoma) were diagnosed correctly and confirmed by HF (17% of all cases). Four of 28 cases were ACA diagnosed solely by cytology (<4% of all cases). One neurocytoma (1/28) case was mistaken for an oligodendroglioma despite cell blocks (CBs) and immunophenotyping (IPT) (<1% of all cases). Eleven of 15 atypical cases were 8 cases of PBT, 2 cases of ACA, and 1 case of postoperative change (PC). Four of 15 atypical cases (from three patients with suspected PBT recurrence) could not be further characterized by CB/IPT and had no HF. Twenty-seven of 45 negative cases were falsely negative (23 cases of PBT, 3 cases of ACA, and 1 case of malignant neoplasm); 11/45 cases were PC, and 7/45 (from five patients with clinically suspected tumor recurrence) cases had no HF. Cytological evaluation of brain cyst fluid is not a reliable means of diagnosing cystic brain neoplasms (including recurrences) due to a high false negative rate and a low sensitivity. Most of the negative or atypical cases (68% of all cases) were recurrent PBT of glial origin that may not be prone to exfoliate. These cytological specimens consisted of lysed blood, obscuring inflammatory cells, and degenerated diagnostic cells if any, yielding inconclusive results.