Cellular schwannoma: a variety of schwannoma sometimes mistaken for a malignant tumor.

Fourteen cellular schwannomas, a variety of peripheral nerve sheath tumor showing a predominantly compact cellular growth, no formed cellular palisades or Verocay bodies, but the ultrastructure of schwannomas, are reported. A presumed nerve of origin was identified in three instances. The tumor had no sex predeliction; the mean age was 48. The neoplasm is usually well encapsulated and most commonly presents in the neck, posterior mediastinum, or pelvis. Because of a variety of confusing histologic features, including dense cell bundles and fascicles, storiform areas, a moderate mitotic activity and moderate nuclear atypia, six of 14 cases were mistaken for either fibrous histiocytoma, leiomyoma, malignant peripheral nerve sheath tumor, or sarcoma of uncertain type. In two instances the false impression of a malignant tumor was reinforced by clinical evidence of bony erosion and destruction. Follow-up thus far has shown the tumor to be benign.