Extraventricular neurocytomas - Pathologic features and clinical outcome

Neurocytic neoplasms usually arise within the lateral ventricles, generally as circumscribed, slowly growing masses curable by total resection. Both s ubtotal resection and histologic atypia are associated with an increased ri sk of recurrence. In contrast, neurocytic neoplasms situated within brain p arenchyma, so-called "extraventricular neurocytomas" (EVNs), are not as wel l characterized. The relationships between histologic features and extent o f resection versus clinical behavior have not been defined. We evaluated pa thologic features, clinical data, and neuroimaging of 35 examples. The tumo rs occurred in 18 males and 17 females, age 5-76 years (median 34 years). A ll tumors involved the cerebrum. On imaging, EVNs were solitary, variably c ontrast-enhancing, and often (57%) cystic. Tumor cells were arranged in she ets, clusters, ribbons, or rosettes, in association with fine neuropil disp ersed in broad zones that separated cell aggregates. Ganglion cell differen tiation was seen in 66%. All tumors showed strong synaptophysin immunoreact ivity. Despite the lack of apparent astrocytes in hematoxylin and eosin-sta ined sections, focal glial fibrillary acidic protein reactivity was seen in 46%. Eleven EVNs were designated "atypical" based on the presence of necro sis, vascular proliferation, or elevated mitotic activity (greater than or equal to3 mitoses/10 high power fields). Nineteen tumors were subtotally re sected or biopsied, whereas 14 were totally resected grossly. Seventeen pat ients underwent radiotherapy (mean 55 Gy). In 30 cases with follow-up, 10 t umors recurred, 3 causing death at 6, 14, and 43 months. All 10 recurrences followed subtotal resection. No totally resected tumors recurred. Thus, th e majority of EVNs are well differentiated and appear unlikely to recur aft er gross total resection. Subtotal resection, atypical histologic features, and high cell proliferation rates correlate with recurrence.