Concurrence of subependymoma and heterotopic leptomeningeal neuroglial tissue.

Heterotopic neuroglial tissues in the leptomeninges are generally regarded as developmental malformations. They are uncommon in the general population (1%) but are more often found in patients with other CNS maldevelopments (25%). Of the 22 cases of subependymoma available for our study, four (18.2%) had concurrent heterotopic neuroglial tissue. The great majority of these neuroglial heterotopias were located over the brain stem and were topographically close to the subependymomas. Since the histogenetic nature of subependymoma, whether it represents a local maldevelopment (hamartoma) or a true neoplasm, is still uncertain, the concurrence of subependymoma and heterotopic leptomeningeal neuroglial tissue seems to support the concept that the tumor is a maldevelopment rather than a true neoplasm.