PMC4296266_01
45-year-old male presented with recurrent lateral knee pain and movable nodule.. A. Coronal fat suppressed proton density weighted image (repetition time [TR] 1700 ms, echo time [TE] 10 ms) shows thickened iliotibial band (ITB), high signal intensity (SI) fatty abnormalities deep to ITB, and slight high SI nodule with thin rim (arrow). B. Coronal T1-weighted image (TR 400 ms, TE 20 ms) reveals low SI lesion (arrow) compared to adjacent fat and iso-SI compared to knee muscle. C. Axial T2-weighted image (TR 3200 ms, TE 100 ms) shows high SI nodule (arrow). D, E. Arthroscopic examination shows presence of inflamed lateral synovial recess (D) and whitish polypoid intraarticular nodule (E) attached to joint capsule. F, G. Resected fibrous nodule (F, H&E staining, x 10) composes of collagen fibers and scattered fibroblasts (G, H&E staining, x 200). H. Resected adjacent tissues show fibrosis, marked hemorrhage, and prominent capillary proliferation (H&E staining, x 30).
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F1
The MRI showed a thickened ITB and poorly defined high signal intensity abnormalities in a compartment-like space bounded laterally by the ITB on coronal fat suppressed proton density weighted images (repetition time [TR] 1700 ms, echo time [TE] 10 ms) (Fig. 1A). The T1-weighted image (TR 400 ms, TE 20 ms) showed a decreased signal intensity lesion compared to adjacent fat, deep to the ITB (Fig. 1B). T1-weighted image, high signal intensity on T2-weighted images (TR 3200 ms, TE 100 ms), and a slightly higher signal intensity with thin rim on fat suppressed proton density weighted images (Fig. 1A-C). The initial diagnosis based on the MRI findings, clinical history, and physical examination was ITB friction syndrome. During an arthroscopic examination, the surgeon found an inflamed lateral synovial recess, which is typically observed in ITB friction syndrome (Fig. 1D). After a sequential arthroscopic inflamed synovial recess resection with synovial shaver, a whitish intraarticular polypoid nodule was observed, attached to the lateral joint capsule (Fig. 1E). The nodule did not contain necrosis, mitotic activity, or cellular atypia (Fig. 1F, G). The resected tissues showed fibrosis, marked hemorrhage, prominent capillary proliferation, and mild chronic inflammation that was consistent with ITB friction syndrome (Fig. 1H).