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Case Reports

Abstract

Glomus tumors are mesenchymal neoplasms arising from modified smooth muscle cells. These lesions are generally painful as they arise from neuromyoarterial glomus cells, and commonly occur in the subcutaneous tissue of the extremities. Glomus tumors account for less than 2% of all soft tissue tumors and are commonly treated with wide excision. Generally, glomus tumors are benign, however, malignancy should be considered in lesions larger than 2.0 cm, deep-seated lesions (under the muscular fascia), or in the presence of atypical histologic features such as nuclear atypia, necrosis, and increased mitoses. Malignant glomus tumors are exceptionally rare, accounting for approximately 2.9% of all glomus tumors, and are defined by marked nuclear atypia or atypical mitotic figures. Herein we present a case of a 67-year-old man who presented with a 0.7 cm painful soft tissue lesion on the volar aspect of his right thumb distal phalanx. An excision was performed, and histologic sections revealed a nodular, well-circumscribed proliferation consisting of sheets and cords of profoundly pleomorphic round cells with abundant eosinophilic cytoplasm. Mitotic figures were readily identified, including atypical forms. Additionally, this was in a background of prominent vascular spaces and variably hyalinized stroma. Immunohistochemical staining was positive for Calponin, smooth muscle actin and approximately a 2-5% proliferative index on Ki-67 staining. The diagnosis of a malignant glomus tumor was made and three months later the patient underwent a distal amputation of their right thumb.  No evidence of recurrence or metastasis has been found after a 5-month follow-up.