Fibrohistiocytic tumors containing zebra body-like inclusions and fibripositors

Plexiform fibrohistiocytic tumor (PFH) and cellular neurothekeoma (CN) are dermal neoplasms that present many histological and immunophenotype similarities as well as unknown histogenesis. Recently, the ultrastructural detection of zebra body-like inclusions in lesional histiocytes has been considered crucial to favor the diagnosis of PFH over that of CN. Here we report two examples of dermal tumors that were diagnosed as CN. Electron microscopy revealed cytoplasmic collections of myelin and zebra body-like inclusions in tumor cells; these inclusions focally merged together or with multivesicular bodies; tumor cells also showed collagen secretion granules and fibripositors, i.e., channels containing single, double or multiple copies of collagen fibrils. These observations support the view that PFH and CN have a common histogenesis and consists of cells sharing phagocityc and fibrillogenic abilities.