This video presents the detailed histopathological analysis of a mixoid ankle mass (Case #4) from a 50-year-old patient. Microscopic review identified separate mixoid nodules interspersed with fibrous tissue, confirmed to be background tendon/ligament exhibiting the "Ramen Noodle Sign"βa hyper-wavy appearance of dense regular connective tissue caused by contraction during fixation. The initial differential diagnosis favored myoepithelioma, but the final diagnosis was Extraskeletal Myxoid Chondrosarcoma (EMCS). Key features of EMCS include round to epithelial-looking cells arranged in classic "cords and chains" meandering through a mixoid background. The presenter details the diagnostic difficulty between EMCS and myoepithelioma, noting EMCS's defining EWSR1-NR4A3 translocation, its keratin-negative staining profile, and its aggressive clinical behavior (slow growth, high persistence, potential late metastasis). The case is noted to have required amputation due to extensive local infiltration.
Summary of Extraskeletal Myxoid Chondrosarcoma (EMCS) Case Analysis
0:00 Case Introduction: The subject is case number four: an ankle mass from a 50-year-old patient.
0:29 Initial Histology and Tendon Identification: The mass consists of separate mixoid nodules separated by fibrous bands. These bands were identified as dense regular connective tissue (tendon/fascia) from the background soft tissue.
0:51 The "Ramen Noodle Sign": The presenter introduces this descriptive sign (named after Ed Fulton) for the super wavy, accordion-like appearance of dense regular connective tissue (tendon, fascia, ligament) resulting from contraction during fixation.
1:51 Differential Diagnosis (DDx): The initial close differential included Myoepithelioma (considered a very legitimate and closest differential) and Calcifying Aponeurotic Fibroma.
2:27 Final Diagnosis: The actual diagnosis is Extraskeletal Myxoid Chondrosarcoma (EMCS).
2:56 Key Histological Feature: EMCS displays round cells in a mixoid background with a strong tendency to run in cords and chains, often in single-file rows that meander through the matrix.
3:30 Tumor Characteristics: Despite the name, EMCS is usually not a true chondrosarcoma, rarely exhibits real cartilage, and almost always occurs in soft tissue (not bone).
4:03 Molecular Diagnostics: EMCS is characterized by a translocation between the EWSR1 gene and the NR4A3 gene. Dual break-apart FISH can be used for confirmation.
4:24 DDx Challenges (EMCS vs. Myoepithelioma): Myoepitheliomas can look extremely similar, often having chondroid areas, cords and chains, and can also share EWSR1 rearrangements, making the differential challenging.
5:53 Immunostaining Clues: Myoepitheliomas are typically characterized by the co-expression of S100 with Keratin and/or EMA. EMCS, conversely, tends to be Keratin-negative.
6:33 Clinical Takeaway: EMCS is a problematic tumor, characterized by slow growth but high persistence and the ability to metastasize years after diagnosis.
6:49 Case Outcome: Due to extensive infiltration around the foot and ankle mass, this specific patient necessitated an amputation.
7:17 Chordoma DDx: Chordoma is also added to the differential as it produces cords and chains and stains with S100/Keratin. It can be distinguished using Brachyury (positive in Chordoma, negative in Myoepithelioma and EMCS).