Primary epithelioid angiosarcoma of the mediastinum, cytomorphologic features of a rare entity-A case report and literature review.

Epithelioid angiosarcoma (EA) is a highly aggressive vascular neoplasm. Primary mediastinal EA is extremely rare with only few cases reported in the English literature. We herein present a case of a 78-year-old patient, who was found to have a right superior mediastinal mass associated with mediastinal and hilar lymphadenopathy. Endobronchial ultrasound guided fine needle aspiration cytology of a station 4R lymph node revealed a cellular, discohesive malignant neoplasm displaying primarily epithelioid morphology with occasional spindled, plasmacytoid, and tumor giant cells. The tumor cells had ample eosinophilic cytoplasm with pleomorphic nuclei and prominent nucleoli. Vasoformative features were noted, exemplified by widespread cytoplasmic vacuoles containing neutrophils and rare red blood cells (hemophagocytosis) and vascular channels identified solely in the cell block. By immunohistochemistry, the tumor cells stained strongly positive for vimentin, positive for ERG, CD-31, FLI-1, and focally positive for pan-cytokeratin. The cytomorphological features and immunostaining patterns were diagnostic of EA. No history of malignancy was reported, and no other lesions were identified on imaging. The diagnosis of primary mediastinal EA on cytology and small biopsy specimens may be challenging due to the rarity of this tumor, limited diagnostic material, and overlapping morphologic features with other entities in the differential diagnosis. A high index of suspicion, especially in cases with vasoformative features, and utilization of ancillary studies can help establish the diagnosis.