Epithelioid schwannoma of soft tissue: unusual morphological variant causing a diagnostic dilemma

Abstract

Epithelioid variant of peripheral nerve sheath tumors is a rare but, at the same time, a well-known entity especially in the malignant counterpart. However, peculiar epithelioid morphology in soft tissue schwannomas is unusual and has been defined recently. These tumors may cause diagnostic errors owing to their increased cellularity and epithelioid morphology. Typical histologic features of classic schwannoma such as Antoni A and B areas, Verocay bodies, and hyalinized vessels are either absent or only present in focal areas. Furthermore, strong and diffuse S-100 protein expression is seen in both benign and malignant counterparts of epithelioid schwannoma. The findings that are suggestive of the benign nature of the lesion are long-term clinical history, small size, superficial localization, encapsulation, bland morphology, lack of mitosis and necrosis, and a benign clinical course after complete excision. Pathologists should be aware of the epithelioid variant of schwannoma to avoid false diagnosis of malignancy. We hereby report 3 cases of unusual benign epithelioid schwannoma of the soft tissue with special regard to problems in differential diagnosis.