This transcript provides a detailed pathology discussion of a case of epithelioid sarcoma (ES), a rare but aggressive soft tissue tumor, presenting as a wrist nodule in a 30-year-old man. Histologically, ES often presents as multiple nodules in the subcutis with central coagulative necrosis, frequently mimicking benign conditions such as rheumatoid nodules or deep granuloma annulare. The speaker emphasizes key microscopic features, including epithelioid cells with large nuclei exhibiting characteristic chromatin clearing, and dense, keratin-rich eosinophilic cytoplasm. Diagnostic confirmation relies heavily on immunohistochemistry, specifically the expression of epithelial markers (Keratin, EMA) and, most critically, the loss of nuclear staining for INI1/SMARCB1. The video concludes by highlighting the tumor’s aggressive clinical course, tendency for recurrence, and notable propensity for metastasis to lymph nodes and distant sites, especially in young adult patients.
Epithelioid Sarcoma: Pathology, Diagnosis, and Clinical Features
0:11 Case Presentation: A 30-year-old man presented with a skin-colored wrist nodule, diagnosed as Epithelioid Sarcoma (ES).
0:30 Classic Low-Power Finding: ES often displays multiple subcutaneous nodules with red, necrotic centers, which can resemble fibrinoid necrosis seen in a rheumatoid nodule or deep granuloma annulare (GA).
1:13 Distinguishing Histology: Closer examination reveals greater nuclear atypia and size than seen in rheumatoid nodules/GA. The center contains coagulative tumor necrosis (ghost tumor cells), rather than smudgy fibrinoid necrosis.
1:57 Cytological Features (Key Pearl): The tumor nuclei tend to have "clearing" or "cracking" in the chromatin, giving them a "shiny" appearance. The cytoplasm is dense, pink, and squamoid-like.
2:37 Immunohistochemistry (IHC) Screening: The dense cytoplasm is due to packed keratin filaments; therefore, ES cells are positive for Cytokeratin and EMA (Epithelial Membrane Antigen).
2:58 Confirmatory IHC: Diagnosis is typically confirmed by INI1 (SMARCB1) loss of staining in the tumor nuclei, requiring careful observation of normal internal controls (like inflammatory or vascular cells) which must stain positive.
4:46 Clinical Presentation: ES conventionally affects the distal extremities (hands, wrists, feet, ankles) in young adults, though it can occur at any age.
5:08 Proximal Type ES: A more aggressive form exists (proximal type ES) which occurs closer to the trunk (groin, shoulder) and presents with much more atypical, rhabdoid cells.
5:26 Aggressive Course: ES is an aggressive tumor prone to recurrence and metastasis, sometimes tracking up the limb in a sporotrichoid pattern.
5:57 Metastatic Pattern: ES is a notable exception among sarcomas as it frequently metastasizes to lymph nodes, in addition to the lungs.
6:36 Terminology Caution: The term "Epithelioid Sarcoma" is reserved for this specific tumor type; other sarcomas with epithelioid morphology must be carefully distinguished.