Pseudomyogenic (epithelioid sarcoma-like) hemangioendothelioma - a rare vascular neoplasm with deceptive morphology and distinctive immunophenotype

ABSTRACT

Pseudomyogenic (epithelioid sarcoma-like) hemangioendothelioma is a rare, low grade vascular(endothelial) neoplasm typically presenting as multicentric, superficial to deep nodules in extremitieswith a slight tendency of affecting young adult males. We report a case of pseudomyogenichemangioendothelioma in a 15-year-old boy presenting initially with a 1 cm right thigh painlesscutaneous lump. The lump was excised with the clinical impression of a sebaceous cyst. On microscopy,a poorly circumscribed, mild to moderately atypical spindle cell lesion in fascicular and storiformpatterns with strikingly myoid-like eosinophilic cytoplasm was identified. The spindle cells werehighlighted by pancytokeratin AE1/AE3, CD31, and ERG with retained INI-1, while being negativefor MNF116, S100, CD34, EMA, desmin, SMA, caldesmon, myogenin, MyoD1, HHV-8 and CD163.Following the first diagnostic report, a positron emission tomography–computed tomography(PET-CT) scan revealed another 4 cm ill-defined nodule accompanied by a smaller adjacent 0.7cm ipsilateral satellite nodule within the right psoas muscle that displayed similar morphologyand immunophenotype as the cutaneous lump, supporting the multicentric feature of this uniqueentity. It is an uncommon yet increasingly recognised neoplasm of endothelial origin possessing amisleading myoid morphology and distinctive immunophenotype worth notifying.