Differentiation between Chondrosarcoma and Synovial Chondromatosis of the Temporomandibular Joint Using CT and MR Imaging

CS of the right TMJ in 54-year-old woman. Axial MDCT with bone and soft-tissue windows (A and B). T2-weighted MR (C) and contrast-enhanced T1-weighted MR (D) images demonstrate a large mass infiltrating the tendon of the lateral pterygoid muscle (asterisk) in the pterygoid fovea and show septalike internal enhancement. Stippled calcification and severe destruction of the mandibular condyle with a spiculate periosteal reaction are revealed (A and B). Note the lesion center on the mandibular condyle. Sagittal MDCT (E) and T2-weighted MR images (F) show the eroded mandibular condyle and the intact articular eminence. Note the disc (arrow) located between them. This mass showed all 9 high-risk imaging features for CS and received a composite score of 9.

CS of the left TMJ in 44-year-old woman. Axial MDCT (A), fat-suppressed T2-weighted MR (B), and contrast-enhanced T1-weighted MR (C) images reveal a mass surrounding the mandibular condyle. Sagittal MDCT (D) and contrast-enhanced T1-weighted MR images (E) demonstrate the mass center in the joint space. Lesion centered on the superior joint space (arrows), destruction and sclerosis of the articular eminence/glenoid fossa, absence of periosteal reaction, and the relatively small lesion size favor SC. On the other hand, destruction of the mandibular condyle, infiltration into the tendon (arrowhead) of the lateral pterygoid muscle (asterisk), stippled calcification, and internal enhancement favor CS. A histopathologic examination after mass resection resulted in a diagnosis of CS. This TMJ mass revealed 4 high-risk imaging features and a composite score of 4. It was not easy to differentiate CS from SC by imaging features.

SC of the left TMJ in 52-year-old man. Axial MDCT (A and B) and fat-suppressed T2-weighted MR images (C) show a mass surrounding and eroding the mandibular condyle. Sagittal MDCT (D) and contrast-enhanced T1-weighted MR images (E) reveal the mass to be centered on the joint space. Ring-and-arc calcification, intact attachment of tendon (blue arrowheads) of the lateral pterygoid muscle (red asterisk), lesion center on the joint space, and a relatively small lesion size favor an imaging diagnosis of SC. The result of a preoperative incisional biopsy was CS, but the final histopathologic diagnosis was changed to SC after mass resection. This TMJ mass showed 3 high-risk imaging features and received a composite score of 3.

ROC curves for qualitative and quantitative variables show that the best discriminating values for differentiating CS from SC are the following: Mandibular condyle for lesion center, Presence for destruction of the mandibular condyle, Absence for destruction of the articular eminence/glenoid fossa, Absence for sclerosis of the articular eminence/glenoid fossa, Presence for infiltration into the tendon of lateral pterygoid muscle, Stippled pattern of calcification, Presence for periosteal reaction, Presence for internal enhancement, and 30.5 mm for lesion size. Of the 9 variables, except for pattern of calcification and mean lesion size, the remaining 7 variables were dichotomous qualitative variables with discriminating values determined at 1 of the 2 characteristics. On the other hand, mean lesion size was a quantitative variable, and the discriminating value was determined at the point of 30.5 mm, which revealed the maximum Youden index among multiple points. Last, the pattern of calcification, the 5 patterns, namely absence, stippled, flocculent, ring-and-arc, and popcorn, were considered as a dimensional continuum in ascending order and converted into an ordinal quantitative variable. The ROC curve was then constructed, and the discriminating value was derived at the point of stippled calcification, which indicates that CS showed a higher prevalence in absence or stippled calcification, and SC, in the other calcification patterns.