This video presents a detailed pathological analysis of a rare vascular tumor, Case Number 9: a 30-year-old female presenting with a medial thigh nodule. Intraoperative examination revealed the mass was located entirely within the lumen of the femoral vein, initially mimicking a thrombus or nerve sheath tumor on MRI. Microscopic examination shows the tumor filling the vein lumen with an outer wall infiltrated by a prominent chondromixoid/sclerotic background. The tumor cells are epithelioid, arranged in cords, nests, and chains, and exhibit classic features such as cytoplasmic vacuoles, some containing fragments of erythrocytes (classic "blister cells"). The diagnosis is confirmed as Epithelioid Hemangioendothelioma (EHE), a vascular tumor with intermediate malignant potential capable of metastasis, distinguishing it from both benign hemangiomas and highly aggressive angiosarcomas. The presenter emphasizes the importance of differentiating EHE from metastatic carcinoma due to its epithelioid morphology and frequent positivity for Keratin, recommending workup for internal primaries in soft tissue cases and long-term follow-up for excise tumors due to metastatic risk.
Pathological Review: Epithelioid Hemangioendothelioma in the Femoral Vein
00:00:09 Case Introduction: A 30-year-old female presented with a 2.5 cm medial thigh nodule that intraoperatively was found to be entirely within the lumen of the femoral vein.
00:00:41 Gross Pathology Description: The specimen shows thickened, fibrotic, and myxoid/mucinous intima surrounding a lumen mostly plugged by a nodule. The background matrix is described as chondromixoid/sclerotic collagen.
00:01:38 Tumor Cell Morphology: The cells are epithelioid, arranged as single units, small nests, or cords/chains, mimicking metastatic carcinoma initially.
00:02:49 Blister Cells: Key diagnostic feature: some epithelioid cells show cytoplasmic vacuoles containing fragments of degenerative erythrocytes, termed "blister cells."
00:03:33 Diagnosis: Epithelioid Hemangioendothelioma (EHE): This is a vascular tumor with intermediate malignant potential; it can metastasize, often slowly, unlike highly malignant angiosarcoma.
00:03:47 EHE Classification: EHE is not a single entity but a category of tumors, some leaning closer to angiosarcoma on the spectrum.
00:04:35 Primary Sites: EHEs are often first described in the lungs or liver, sometimes presenting as multiple nodules.
00:05:05 Immature Vascular Formation: The characteristic "blisters" are the cells' attempt to form intracytoplasmic lumens, not well-connected vascular channels.
00:05:48 Immunostaining Notes: EHE cells stain with endothelial markers and often stain positive for Keratin, necessitating caution not to misdiagnose them as carcinoma.
00:06:01 Presentation in Soft Tissue: When occurring in soft tissue, EHE commonly arises in the lumen of a vein and invades the adjacent soft tissue.
00:07:17 Clinical Management Advice: For peripheral EHEs, workup to rule out lung or liver primaries is recommended, and soft tissue tumors require complete excision and long-term follow-up due to metastasis risk (often to the lungs).
00:08:08 Molecular Testing: The conventional type usually shows a $WWTR1-CAMT1$ fusion; a rare subtype with Yap1/TFE3 fusions tends to form actual vascular channels (unlike the case shown).
00:09:02 Key Takeaway: Always consider a vascular tumor in the differential diagnosis when presented with an unusual, keratin-positive epithelioid tumor that mimics carcinoma.