CPC07 An unusual vascular neoplasm of the foot: pseudomyogenic haemangioendothelioma

Abstract

Pseudomyogenic haemangioendothelioma (PMH) is a rare vascular neoplasm of intermediate malignant potential, predominantly affecting young male patients and commonly involving the distal extremities. We report a case of PMH in a 17-year-old boy who presented with progressively enlarging, painful nodules over the medial aspect of the left midfoot and little toe for 6 months, associated with ulceration, bleeding and spontaneous nail avulsion. Clinical examination revealed firm, deep-seated nodules with crusting and ulceration, without lymphadenopathy or systemic involvement. Histopathological examination showed a dermal tumour composed of plump spindle-to-epithelioid cells arranged in loose fascicles, with interspersed ganglion-like cells and prominent neutrophilic inflammation. The tumour cells exhibited moderate eosinophilic cytoplasm and vesicular nuclei with conspicuous nucleoli, without significant mitotic activity or necrosis. Immunohistochemistry revealed tumour cell positivity for pancytokeratin, muscle-specific actin and ERG, and strong nuclear FosB expression, with retained INI-1 expression. Tumour cells were negative for melanocytic, myogenic and vascular markers including HMB-45, melan-A, desmin, myogenin, MyoD1 and CD31. Magnetic resonance imaging demonstrated ill-defined subcutaneous nodular lesions with abnormal marrow signals involving multiple bones of the left foot, suggestive of a neoplastic process. Based on these findings, a diagnosis of PMH was established. The patient underwent amputation of the left little toe followed by adjuvant chemotherapy with gemcitabine and docetaxel due to margin involvement and radiological evidence of bone invasion, resulting in significant clinical improvement. This case highlights the importance of recognizing PMH and distinguishing it from epithelioid sarcoma and other histological mimickers due to differences in prognosis and management.