PSEUDOMYOGENIC HEMANGOENDOTHELIOMA: A CASE REPORT

Abstract

Pseudomyogenic hemangioendothelioma (PMH) is a rare, intermediate-grade vascular neoplasm with distinctive clinicopathological features. Also termed epithelioid sarcoma-like hemangioendothelioma due to its histological resemblance to epithelioid sarcoma, PMH typically presents as multiple discontinuous cutaneous or subcutaneous nodules, intramuscular masses, and occasionally lytic bone lesions. The lower limbs are most frequently affected, followed by upper limbs, trunk, and head and neck. Despite its infiltrative nature, PMH demonstrates low metastatic potential, and only a limited number of cases are reported annually in the literature. We report the case of a 17-year-old male with a slow-growing chest wall mass present for eight years. MRI revealed a solitary, ill-defined subcutaneous lesion in the right pectoralis region measuring 5.5×4.5×3.5 cm, hypointense on T1 and hyperintense on T2-weighted images. Gross examination showed a lobulated lesion with a homogeneous white cut surface. Histology demonstrated sheets and fascicles of plump spindle cells with eosinophilic cytoplasm, vesicular nuclei, and small nucleoli infiltrating skeletal muscle, accompanied by neutrophilic infiltrates, reactive bone formation, osteoclast-like giant cells, and low mitotic activity. Differential diagnoses included rhabdomyoma, inflammatory myofibroblastic sarcoma, and epithelioid sarcoma. Immunohistochemistry revealed focal CD31, diffuse FLI1, and cytokeratin positivity, with retained INI-1 and negative CD34, supporting PMH diagnosis. Although demonstration of FOSB gene rearrangement is recommended by WHO for definitive confirmation, this was not available in our setting. Molecular studies or FOSB immunohistochemistry were advised for further validation. This case highlights the diagnostic challenges of PMH and emphasizes the importance of integrating morphology, immune-profile, and molecular studies for accurate diagnosis.