PMC5803675_01
Hybrid schwannoma and perineurioma. Nodular lesion of the scalp (a). Whole-mount of the lesion: a multinodular dermal growth with heterogenous areas (b, scanning magnification), including a schwannomatous component with plump-spindled cells arranging in Antoni A and Antoni B areas (c, original magnification x100), and hypocellular myxoid areas with slender-spindled cells corresponding to the perineurial component (d, original magnification x100). Diffuse S100 protein expression in the schwannomatous component (e, original magnification x50). Focal epithelial membrane antigen expression in the perineurial component (f, original magnification x400).
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F1
At gross examination, the lesion was a nodular mass measuring 2 cm in its largest diameter (Fig. 1a). Microscopic analysis revealed a well-circumscribed but unencapsulated dermal lesion covered by normal-appearing skin (Fig. 1b) and represented by a biphasic proliferation of cellular areas in the center (Fig. 1c) and hypocellular to myxoid areas at the periphery (Fig. 1d). Alternating hyper- and hypocellularity resembling Antoni A and Antoni B areas were observed in the center (Fig. 1c). The myxoid areas at the periphery of the lesion exhibited slender spindle cells with delicate nuclei and elongated bipolar cytoplasm (Fig. 1d). The first component was diffusely S100 positive but negative for epithelial membrane antigen (EMA), corresponding to a schwannoma (Fig. 1e). The second component exhibited the opposite immunophenotype and was consistent with a perineurioma (Fig. 1f).
PMC5803675_02
Hybrid schwannoma and neurofibroma. Nodular lesion of the ankle (a). Scanning magnification showing a multinodular dermal lesion (b), with a schwannomatous component in the center of one nodule (right) surrounded by a neurofibromatous component (left) (c, original magnification x100). Diffuse S100 protein expression in the schwannomatous component, with only partial expression in the neurofibroma (d, original magnification x50). CD34 highlighting the neurofibromatous component but negative in the schwannomatous nodule (e, original magnification x50). Epithelial membrane antigen highlighting the capsule at the periphery of the lesion (f, original magnification x200).
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F2
A 24-year-old man presented with a cutaneous lesion on the right ankle (Fig. 2a) diagnosed clinically as a lipoma versus cyst or benign fibrous histiocytoma. Histological examination showed a multilobular well-circumscribed plexiform dermal lesion with a biphasic proliferation (Fig. 2b) mostly represented by lobules of myxoid hypocellular areas. A second distinct cellular nodular component was found in the center of one lobule (Fig. 2c). The two components were clearly separated with an abrupt transition (Fig. 2c). The peripheral areas were consistent with a neurofibroma composed of spindle cells with heterogenous cytology arranged in a myxoid stroma, intermingled with some collagen bundles and some mast cells (Fig. 2c). By immunohistochemistry, these cells expressed CD34 (Fig. 2e) and partially S100 protein (Fig. 2d). A slender capsule positive for EMA could be identified at the periphery of the lobules (Fig. 2f). The central nodular area was consistent with a schwannoma represented by a plump spindle cell population with a palisading disposition (Verocay bodies) and expressed diffusely S100 protein by immunohistochemistry (Fig. 2d), but was negative for EMA and CD34 (Fig. 2e).