Abstract:

Hybrid peripheral nerve sheath tumors (HPNST) are benign proliferations with combined features of more than one type of benign peripheral nerve sheath tumor including schwannoma, perineuroma or neurofibroma. We, herein, present a case of this uncommon proliferation with features of plexiform schwannoma and neurofibroma. A 44 year-old female presented with subcutaneous nodule on the scalp that was sensitive to touch present since childhood. Physical examination revealed a 3.0x2.0 cm soft subcutaneous nodule with an overlying skin-colored umbilicated papule. The nodule was surgically excised. Histopathology demonstrated a well-circumscribed and encapsulated dermal proliferation with a multinodular growth pattern. The nodules were interconnected, enclosed in thin fibrous capsules and composed of spindle cells with nuclei palisading consistent with Antoni A tissue. Interspersed between the nodules were areas composed of loosely arranged spindle cells with wavy elongated nuclei resembling neurofibroma, and distinct areas with loose edematous, myxoid stroma consistent with Antoni B tissue. Cellular atypia and mitotic figures were not identified. The schwannomatous component was S100+ (diffuse, strong) and CD34-, while the neurofibromatous component was S100 + (partial) and CD34+. The patient did not have a personal or family history of neurofibromatosis. HPNST with features of neurofibroma and schwannoma have been reported in genetic syndromes such as neurofibromatosis. Recurrence and malignant transformation have rarely been described. We present a unique and interesting case of a hybrid plexiform schwannoma and neurofibroma in an otherwise healthy patient with no history of neurofibromatosis.

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