Plexiform Fibrohistiocytic Tumor: Ultrastructural Studies May Aid in Discrimination from Cellular Neurothekeoma

Department of Pathology, The Children's Hospital, Aurora, Colorado 80045, USA.
Ultrastructural Pathology (Impact Factor: 1.08). 12/2009; 33(6):286-92. DOI: 10.3109/01913120903348860
Source: PubMed


Plexiform fibrohistiocytic tumor is a low-grade soft tissue malignancy that can at times be difficult to differentiate from the less biologically aggressive cellular neurothekeoma. The two entities, which may display identical clinical and histological features, cannot be distinguished by immunohistochemical or molecular diagnostic means. Electron microscopy may enable the accurate identification of problematic examples and thus aid in resolving these occasionally occurring diagnostic dilemmas. To illustrate typical variations in the ultrastructural appearance of plexiform fibrohistiocytic tumor, the authors present two diagnostically noncontroversial examples, and to demonstrate the potential diagnostic utility of electron microscopy in this setting, they present an example of plexiform fibrohistiocytic tumor that could not otherwise have been distinguished from cellular neurothekeoma.

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    ABSTRACT: 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.
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