This video presents a detailed pathological case review focusing on Epithelioid Hemangioendothelioma (EHE), a rare vascular tumor with intermediate malignant potential. The case involves a 30-year-old female with a medial thigh nodule, initially mistaken for a nerve sheath tumor or vascular malformation on MRI. Intraoperatively, the mass was discovered to be arising entirely within the lumen of the femoral vein, subsequently perforating the wall and invading adjacent soft tissue. Histologically, the tumor is characterized by epithelioid cells forming cords, nests, and chains embedded in a prominent chondromyxoid/sclerotic background. A key diagnostic feature observed under higher magnification is the presence of intracytoplasmic vacuoles, sometimes containing fragments of red blood cells (classic "blister cells"). The presenter emphasizes that EHE is distinct from other hemangioendotheliomas and angiosarcoma, noting its potential (though slower than angiosarcoma) to metastasize, often to the lungs. Immunohistochemically, these tumors are typically positive for endothelial markers and often aberrantly express keratin, necessitating caution not to confuse them with metastatic carcinoma. The diagnosis can be confirmed molecularly by detecting the common WWTR1-CAMT1 fusion.
Pathology Deep Dive: Recognizing Epithelioid Hemangioendothelioma (EHE)
0:00 Case Presentation: Introduction to Case 9: a 30-year-old female with a 2.5 cm medial thigh nodule initially suspected to be a nerve sheath tumor or vascular malformation based on MRI proximity to the femoral artery/vein.
0:31 Intraoperative Finding: The mass was found not adjacent to, but inside the lumen of the femoral vein, expanding and perforating the wall into the soft tissue.
0:58 Histological Background: The background tissue is described as highly fibrous, sclerotic, and chondromyxoid/mucinous, surrounding the tumor cells.
1:38 Tumor Cell Morphology: Epithelioid cells arranged in single units, small nests, cords, and chains, mimicking metastatic carcinoma initially.
2:50 Classic Diagnostic Feature: Observation of cells forming cytoplasmic vacuoles, often containing fragments of degenerated erythrocytes—the "classic blister cells" indicating attempts at forming intracytoplasmic lumens.
3:33 Diagnosis: Epithelioid Hemangioendothelioma (EHE): Identified as a vascular tumor with intermediate malignant potential, distinct from benign hemangiomas or aggressive angiosarcomas.
4:20 Malignant Potential: EHE has the potential to metastasize and cause death, though it progresses much slower than angiosarcoma.
5:02 Vessel Formation: Typically, EHE lacks well-formed, interconnecting vascular channels, instead showing immature vascular formation via the blister cells.
5:48 Immunohistochemistry: EHE cells usually stain positive for endothelial markers and frequently express Keratin, which can cause diagnostic confusion with carcinoma.
7:20 Clinical Recommendation: If EHE arises in the skin or soft tissue, a workup to rule out internal primaries (lung/liver) is often recommended due to metastatic risk.
7:45 Metastasis Risk: Approximately 10% of soft tissue EHEs eventually give rise to distant metastases, usually in the lungs, requiring long-term follow-up.
8:02 Molecular Confirmation: The most common molecular finding is the $WWTR1-CAMT1$ fusion; a minority subtype shows $YAP1-TFE3$ fusions, which are more likely to form true vascular channels.