Epithelioid Angiosarcoma Presenting as a Huge Cystic Mass in the Right Hemithorax: A Rare Case Report and Diagnostic Pitfall

Abstract

Epithelioid angiosarcoma (EAS) is a rare, highly aggressive vascular malignancy arising from endothelial cells, characterized by variable morphology and challenging diagnosis. Involvement of the chest wall or hemithorax was uncommon and posed diagnostic difficulties due to morphological heterogeneity and overlap with other epithelioid tumors. This case report described the clinical and histopathological features of a malignant vascular tumor occurring in the right hemithorax. Clinical data were collected from electronic medical records using the electronic public health information system (e-Phis) of Chonburi Hospital. The patient was a 42-year-old man who presented with right-sided chest pain and pleural effusion. Imaging revealed a large cystic and hemorrhagic lesion occupying the right hemithorax. The initial thoracotomy specimen demonstrated a fibrous-walled pseudocyst with organized hematoma and calcification, without evidence of malignancy. After a two-year follow-up, repeat biopsy revealed epithelioid cells with abundant amphophilic cytoplasm, vesicular pleomorphic nuclei, and prominent nucleoli, accompanied by hemorrhage, necrosis, and high mitotic activity. Immunohistochemistry showed diffuse positivity for CD31, CD34, FLI-1, AE1/AE3, Vimentin, and cytoplasmic WT1, and negativity for D2-40, calretinin, SALL4, and TTF-1, confirming high-grade EAS. After diagnosis, the patient deteriorated rapidly, and he died despite aggressive management. This case highlighted the diagnostic pitfalls of EAS presenting as a benign-appearing cystic lesion. Initial sampling may have miss the malignant component, delaying diagnosis. Thorough histopathological evaluation, repeat biopsy, and comprehensive immunohistochemistry were essential to distinguish EAS from morphologically similar epithelioid neoplasms. Early recognition and prompt pathological diagnosis were crucial, but prognosis remained poor even with aggressive management.