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

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.

A rare case of multifocal pseudomyogenic hemangioendothelioma, involving soft tissues and bone, misdiagnosed as a rhabdomyosarcoma: Diagnostic and treatment implications.

Pseudomyogenic hemangioendothelioma (PHE) is an uncommon, but distinctive soft tissue tumor, characterized by multifocality. A 17‑year‑old male referred to us with progressively increasing multiple subcutaneous nodular lesions over his left leg and foot, reported elsewhere as a spindle cell rhabdomyosarcoma. On review, microscopy showed a cellular tumor comprising plump spindle cells arranged in loose fascicles with interspersed inflammatory cells. Tumor cells exhibited mild nuclear variation. Immunohistochemically, tumor cells expressed AE1/AE3, CD31, Fli‑1, and smooth muscle actin (SMA), confirming diagnosis of PHE. Whole‑body positron emission tomography–computed tomography (PET‑CT) scan revealed multiple, metabolically active, subcutaneous nodular lesions over the left lower leg and in the distal tibia. Subsequently, resection specimens from the various lesions and bone curettage also revealed features of PHE. Three months later, the patient developed multiple lesions over his fourth toe and left foot, for which he underwent tumor resections. At present, he is disease‑free. PHE is a locally aggressive soft tissue tumor characterized by multifocality, rarely bony involvement and can be misdiagnosed as a high‑grade sarcoma.