CT and MRI imaging manifestations of uncommon type of chondrosarcoma

Objective To explore the CT and MRI findings of uncommon type of chondrosarcoma (uCHS), and improve the diagnosis and treatment of uncommon type of chondrosarcoma. Methods CT and MRI imaging features of 14 cases of uCHS confirmed by surgery or needle biopsy and pathological examination were retrospectively analyzed. The imaging data included plain CT (n=6) and contrast enhanced CT (n=4), as well as plain and contrast enhanced MRI (n=9). Results Total 14 lesions were respectively located in posterior peritoneum, anterior mediastinum, posterior mediastinum, left thigh, atlas, left ischium, left pubis, right parasellar region, right petrosum, right cotyle, thoracic vertebras, left parietal bone, left rib, left scapula respectively. ①Myxoid chondrosarcoma in 5 cases:Mild expansive or osteolytic bone destruction accompanies extraosseous lobulated or irregular soft tissue masses with few calcifications were showed on CT imaging. MRI scanning showed obviously heterogeneous long T₁ long T₂ signal and heterogeneous enhancement after contrast administration. One case associated hemorrhage. ②Mesenchymal chondrosarcoma in 4 cases:All of the lesions were located outside bones accompany soft tissue masses with scattered grit calcification. Two cases exhibited open-herding appearance. ③Clear cell chondrosarcoma in 3 cases:The lesions showed osteolytic bone destruction combined with extraosseous tissue masses included rarely calcification on CT imaging. The hypo-intense septa were seen on T₂WI and the peripheral and septal enhancement with wreath- or shell-like appearance was showed on post-contrasted MRI. Two cases demonstrated fluid-fluid level because of hemorrhage. ④Dedifferentiated chondrosarcoma in 2 cases:Two lesions showed "bimorphic features" with different tumors features mixed within the lesion. The tumors constituted by low-grade chondrosarcoma and high-level sarcomas variability, demonstrated osteolytic destruction with unmineralized soft-tissue mass. Conclusion CT and MR imaging features of uCHS have no obvious specificity, but the examinations play important roles in depicting the location, internal structure and its correlation with the adjacent structures, as well as in formulating the plan of treatment and assessing the efficacy of treatment. The final diagnosis should be relied on pathologic and immunohistochemical examinations.