This pathology video examines a case of Chordoma arising in the sacrococcygeal region. Utilizing two pieces from the same tumor, the speaker first highlights the remarkable anatomical section of the coccyx, illustrating the tumor's origin within the bone and subsequent growth into the soft tissue. The discussion then focuses on the classic features of chordoma, including its multi-nodular, mixoid architecture and the presence of physaliferous cells. Crucially, the video explores the differential diagnosis, specifically Myoepithelioma, which can be distinguished using the specific nuclear marker Brachyury, alongside the common co-expression of Keratin and S100 seen in both tumors. The tumor’s problematic clinical course and management challenges are also addressed, concluding with a memorable visual aid: the "bicycle chain" analogy for describing the characteristic arrangement of chordoma cells.
Chordoma of the Coccyx: Pathology and Diagnosis
0:03 Case Presentation: The discussion centers on a tumor presented in two pieces (10 and 11) from the same patient. Piece 2 is remarkable for its anatomical relationship to the bone.
0:43 Fascinating Anatomy: The bone shown in Piece 2 is the coccyx (the very tip of the sacrum), displayed in a sagittal section, illustrating the tumor emanating from the bone itself and forming a large soft tissue mass.
1:38 Tumor Diagnosis: The tumor is identified as a Chordoma, classically found at the proximal (clivus) or distal (sacrococcygeal) ends of the axial spine, originating from remnants of the embryonic notochord.
2:14 Rare Locations: While classic sites are axial, chordomas can rarely be found in extra-axial locations, such as soft tissue or extremities.
2:45 Differential Diagnosis: Chordomas must be distinguished from other tumors that look similar, specifically Myoepithelioma (which includes tumors historically called "paracordomas" found in peripheral sites).
3:33 Classic Histology: Features helpful for diagnosing chordoma include:
A multi-nodular growth pattern separated by fibrous septations.
A prominent mixoid background.
Cells arranged in chains and chords (rows).
The characteristic presence of multi-vacuolated, bubbly physaliferous cells (3:56).
4:56 Clinical Challenge: Chordomas are highly problematic due to their location, difficulty of removal, high rate of recurrence, and potential for metastasis, often requiring extensive procedures like sacrectomy.
5:52 Immunophenotype (IHC): The classic co-expression markers for chordoma are Keratin (or EMA) and S100. This co-expression is also typical of myoepitheliomas, highlighting the diagnostic challenge.
6:03 Specific Marker: The definitive diagnostic marker for chordoma is the nuclear stain Brachyury (T Brachyury), which is sensitive and specific and helps resolve the differential diagnosis with Myoepithelioma.
8:07 Visual Aid: A visual analogy, credited to Dr. Seung-Mi Zheng, likens the curving, cord-like arrangement of the chordoma cells to a "bicycle chain."