This pathology case review focuses on the key features of Chordoma, a rare malignant tumor typically found at the ends of the spine (clivus and sacrum). The video details the classic morphology, characterized by cords and chains of epithelioid cells set within an abundant blue myxoid background. A highly characteristic, though not always present, finding is the physaliferous cell (multi-vacuolated cytoplasm). The discussion heavily emphasizes the differential diagnosis with Myoepithelial neoplasms, which share overlapping morphology and often co-express Keratin and S100. The presenter concludes by stressing the importance of the nuclear marker Brachyury, which is highly specific and sensitive for Chordoma and is necessary to definitively distinguish it from its primary imitators.
Pathology of Chordoma: Location, Morphology, and Key Markers
0:04 Location and Presentation: Chordomas are tumors most commonly found in bone at the ends of the spine—specifically, the clivus (where the spine meets the cranium) or the sacrum (inferior end). Occurrence outside these locations is extremely rare.
0:41 Classic Morphology: The characteristic presentation is a multi-nodular, multi-lobulated tumor featuring an abundant blue myxoid background.
0:53 Cords and Chains: Within the myxoid background are cords and chains of epithelioid cells (nests, islands) running throughout the tissue, which is highly diagnostic.
1:08 Cellular Features: The epithelioid cells show a wide range of features, including eosinophilic or clear cytoplasm, sometimes appearing spindled or rhabdoid.
1:27 Differential Diagnosis (DDx): The main differential diagnosis is Myoepithelial Neoplasm (e.g., myoepithelioma, myoepithelial carcinoma), which also tends to form cords and chains in a myxoid background. Extraskeletal Myxoid Chondrosarcoma is also noted as having overlapping features.
2:00 Immunohistochemistry (IHC) Profile: Chordoma exhibits a unique IHC profile, typically positive for Keratin, EMA, and S100.
2:27 Diagnostic Challenge: Historically, Myoepithelial tumors were difficult to differentiate because they also tend to be Keratin and S100 co-expressors.
2:33 Key Diagnostic Marker (Takeaway): The definitive marker is the nuclear stain Brachyury, which is highly specific and sensitive for Chordoma and will be negative in Myoepitheliomas, enabling accurate separation.
3:26 Physaliferous Cells (Buzzword): A very common and classic feature (though not mandatory for diagnosis) is the presence of physaliferous cells, characterized by prominent, multi-vacuolated (bubbly) cytoplasm. The speaker advises relying on the cords/chains and myxoid background for diagnosis, rather than solely on the presence of these cells.