Subependymomas: clinicopathologic study of 14 tumors, including comparative MIB-1 immunohistochemical analysis with other ependymal neoplasms.

BACKGROUND: Subependymomas are uncommonly encountered ependymal tumors, which are important to distinguish from ordinary ependymomas because of their generally better prognosis.
OBJECTIVE: To review the clinicopathologic features and MIB-1 labeling indices (marker of cell proliferation) of 14 subependymomas.
DESIGN: Retrospective review of 14 subependymomas encountered in a tertiary care setting.
RESULTS: Fourteen ependymomas presenting in 8 men and 6 women between the ages of 18 and 78 years (mean, 53.6 years) comprise the study group. The most common clinical presentations included ataxia (n = 4), dizziness/vertigo (n = 3), nausea/vomiting (n = 3), headaches (n = 3), and incidental finding at autopsy (n = 2). Tumor locations included fourth ventricle (n = 7), lateral ventricle (n = 4), third ventricle (n = 2), and thoracic spinal cord (n = 1). Eight patients underwent gross total resection, and 4 had subtotal resection. Tumors were characterized by clustering of cell nuclei arranged against a fibrillary background. Focal cystic degeneration was seen in 10 tumors, hemosiderin deposition in 8 tumors, sclerotic vessels in 8 tumors, calcifications in 5 tumors, and focal nuclear pleomorphism in 2 tumors. Mitotic figures, vascular endothelial proliferation, and necrosis were not seen in any of these tumors. Cell proliferation marker MIB-1 labeling indices (percentage of positive staining tumor cells) ranged from 0 to 1.4 (mean, 0.3). In comparison, 13 myxopapillary ependymomas had labeling indices ranging from 0 to 5.5 (mean, 1.1). Thirty-nine low-grade ependymomas had MIB-1 labeling indices of 0.1 to 5.4 (mean, 1.1). Fourteen anaplastic/malignant ependymomas had MIB-1 labeling indices ranging from 0.4 to 34.0 (mean, 12.8). One subependymoma was treated with radiation therapy. Six patients were alive with no evidence of tumor at a mean follow-up of 94.4 months. Two patients were alive with residual tumor (follow-up of 4 and 53 months). Two patients died with tumor at 0.67 and 43.4 months. One patient was lost to follow-up, 1 is a recent case, and 2 were incidental findings at autopsy. None of the patients developed tumor recurrence.
CONCLUSIONS: Subependymomas are generally low-grade lesions, as evidenced by their benign clinical course and low MIB-1 labeling indices. Compared with other ependymal tumors, subependymomas have the lowest rate of cell proliferation as evidenced by MIB-1 immunostaining.