Abstract

Pseudomyogenic hemangioendothelioma (PMH) is a rare vascular neoplasm with intermediate malignant potential. This case study describes a 26-year-old male presenting with a non-healing nodule at the site of a previous "lipoma" excision. Physical examination revealed a 7mm well-defined, firm papule with overlying hemorrhagic crust on the left abdomen. Clinical considerations included keloid/scar and traumatized dermatofibroma. Histological evaluation showed a dermal proliferation of spindled to epithelioid cells arranged in short intersecting fascicles surrounding central keloid-like areas. The tumor cells had deeply eosinophilic cytoplasm, frequently vesicular nuclei, and conspicuous nucleoli, with scattered admixed neutrophils. The tumor cells exhibited strong reactivity for cytokeratin AE1/AE3, ERG, and FOSB, with variable intensity for CD31. Nuclear reactivity for INI1 was retained, and the tumor cells were negative for CK 8/18, p63, p40, SMA, desmin, S100 protein, CD34, and TFE3. While PMH is often multifocal, arising in the extremities, and involving multiple tissue planes, the presented lesion developed as a solitary nodule on the trunk within the site of a prior excision scar. Prior pathology is unavailable for review, so it is unclear if features of PMH were present in the original biopsy or if the tumor arose in association with the biopsy scar. Diagnosing PMH can be challenging due to its similarities with epithelioid sarcoma, including its predilection for the extremities of young adults, epithelioid cytomorphology, and keratin positivity. Accurate diagnosis relies on a high index of suspicion and thorough immunohistochemical workup. Molecular detection of the characteristic FOSB rearrangement can be helpful in difficult cases.