Symptomatic subependymoma. Report of 21 cases with review of the literature.

Of 48 cases of subependymoma reported to date, 22 were associated with symptoms. In a personal series of 47 additional cases of subependymoma reviewed by the author, 21 were symptomatic. The mean age of patients with symptom-producing subependymomas was 39 years, that is, 20 years younger than that of patients with asymptomatic tumors. Symptoms were most often produced by large tumors, particularly those arising from the septum pellucidum (100%), the floor of the fourth ventricle (65%), and the lateral ventricular walls (55%). The majority of symptomatic tumors displayed the classic gross and microscopic features of subependymomas; however, large tumors more frequently demonstrated cyst formation, microcalcification, and vessel degeneration accompanied by hemorrhage. Of all subependymomas, 15% were microscopically composed of an admixture of classic subependymoma and cellular ependymoma; of these, one-half occurred within the first decade, all were situated in the fourth ventricle, and 80% were symptomatic. In contrast to pure subependymomas, the mortality rate of patients with mixed tumors was 80%, reflecting their growth potential, large size, and dangerous location.