Soft tissue perineurioma of the finger: expanding the differential diagnosis of a soft tissue tumor presenting on a digit

Peripheral nerves are surrounded by an external sheath, which contains concentric layers of thin perineurial cells. Perineuriomas are rare nerve sheath tumors composed of well-differentiated perineurial cells that have a distinct ultrastructural and immunochemical phenotype. We review the histologic characteristics and staining patterns, reported variants, and salient features that differentiate this entity from other soft tissue tumors that may present on a digit. Because of the nonspecific clinical appearance and varying histology on hematoxylin-eosin stain, perineuriomas are likely to be confused with more common tumors of the hand and, therefore, should be included in the differential diagnosis of a soft tissue tumor presenting on a digit.