Abstract

Glomus tumors are benign tumors comprised of glomus cells most commonly presenting in young adults (< 40 years) as a solitary and painful papulonodule on the extremities, especially subungual sites. Glomus tumors can appear blue-red-purple in color and are classically tender and sensitive to temperature and pressure changes. The hand (palm and nailbeds) is most frequently affected, however, rare cases of extracutaneous glomus tumors have been reported. Histologically, glomus tumors demonstrate dense collections of uniform and rounded glomus cells primarily located around vasculature. Glomus cells have eosinophilic cytoplasm and dark staining round nuceli with notable lack of cytologic atypia and pleomorphism. Glomus tumor variants have been reported including atypical, malignant, and oncocytic subtypes. We report a 48-year-old male with a mass on his left upper arm present for years which had previously been diagnosed as a vascular malformation on imaging. Cold weather made the mass more painful and he underwent radiological embolization of the lesion without improvement. Surgical excision was performed and the lesion was successfully removed. Microscopic examination revealed a multinodular lesion which extended throughout the dermis into the subcutis. It was composed of two cell populations (uniform rounded cells in small nodules with associated vasculature and larger epithelioid cells with oncocytic cytoplasm). Rare mitoses were noted but overt cytologic atypia was lacking. The lesional cells were positive for smooth muscle actin, but pan-keratin and epithelial membrane antigen were negative. The patient was diagnosed with a glomus tumor displaying oncocytic change, a very uncommon variant. This case is notable because it contributes to the paucity of existing literature, highlights key histopathologic features, and supports the previously reported observation that while rare, oncocytic glomus tumors display similar clinical behavior to conventional glomus tumors.

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