Hybrid Granular Cell Tumor/Perineurioma

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Hybrid peripheral nerve sheath tumors (PNSTs), which show hybrid features of more than one cell type normally found in a peripheral nerve sheath, are recently recognized clinical entities. Various composite tumors have been reported; however, granu-lar cell tumor/perineurioma is a rare combination. Since peri-neurial cells may be found in other types of PNSTs, it is important to determine if those are reactive, remnantal, or true neo-plastic when a perineurial component of the PNST is identified. Main differential diagnoses include granular perineurioma and granular cell tumor with reactive perineurial cell hyperplasia, which show a lack of immunopositivity for S-100 in the granu-lar cells and prominent perineurial cell proliferation throughout the tumor, respectively. A 54-year-old man presented with a 2-year history of a well-circumscribed movable mass in the posterior aspect of the right axilla. He did not complain of tenderness or neuropathic pain. He had no specific familial or medical history of neurogenic tumors , including neurofibromatosis. Laboratory test results, including electrolyte levels and blood cell counts, were all within the normal ranges. The magnetic resonance imaging revealed a well-circumscribed mass in the subcutaneous fat layer of the right posterior axilla (Fig. 1A). The patient underwent an exci-sional biopsy of the mass. Macroscopically, the lesion was a well-circumscribed nodular mass measuring 5.5×5 cm in the greatest dimension. It was tan to gray in color and rubbery to firm in consistency (Fig. 1B). No hemorrhage or necrosis was evident. There were no macro-scopic associations with a nerve. Microscopically, the neoplasm was a well-circumscribed but nonencapsulated deep soft tissue mass. At first glance, there were nests or rounded aggregations of granular cells and prominent encircling spindle cells. Because the spindle cells showed a whorl-ed and storiform growth pattern, the overall appearance of the lesion looked like whorls or eddies (Fig. 1C, D). Although the proportion of granular cells and spindle cells was variable depending on the location of the tumor, the overall proportion was similar (Fig. 1C-E). Two components of the lesion had no transition area and were intimately admixed throughout the le-sion. Occasionally, mature adipose tissue was admixed with the lesion, which may have constituted a third component of the lesion (Fig. 1F). Although it occupied …