Member Login March 2009 Case of the Month     Compiled by: SalvadorB. Trinidad, M.D.                                                                                                        History: A 55-year-old female developed swelling and locking of the knee. Her symptoms began ten months ago. Exam: MRI of the knee was performed. T1, T2, and T2 fat-suppressed sequences were performed in multiple planes. Arrows denote lesions.   Findings: On the coronal PD-FS sequence (Fig. 1), multiple mixed hypointense bodies are identified. Arrow 1A identifies one of the mixedhypointense bodies. Arrow 2A denotes a low-density body/structure that follows the subcutaneous fat signal on Fig. 1A.   On the coronal T1-weighted sequence (Fig. 1A),Arrow 1 denotes a barely visible hypointense body just slightly higher in signal than the adjacent effusion. Arrow 2 denotes a high-intensity structure correlating with fat and not to be confused with a body.   On axial PD-FS sequence (Fig. 2), Arrow 3A denotes the effusion.   On sagittal T2-weighted sequences (Fig. 3),Arrow 4 denotes a  hypointense body very low  in signal. The body is lower in signal than the fat and the adjacent effusion.   Onthe coronal T1-weighted sequence (Fig. 5), Arrow5 denotes a subchondral erosion. Arrow 5A denotes a marginal osteophyte. Figure 1 Figure 1A Figure 2  Figure 3 Figure 5 Diagnosis: Secondarysynovialosteochondromatosisfrom osteoarthritis   Discussion: Synovial chondromatosis is benign andmay occur as either a primary or secondary form. Itis considered a metaplasia. When calcified, it is known as synovial osteochondromatosis. Malignant dedifferentiation into chondrosarcoma is rare.   Primarysynovialchondromatosisoccurs in the setting of no identifiable etiology.   Secondary synovial chondromatosis can occur from trauma, osteonecrosis, rheumatoid arthritis, neuropathic arthropathy, and tuberculous arthritis.   The underlying pathology involves loose bodies of cartilage or bone that undergo metaplasia. The bodies are slow-growing and may cause locking and pressure erosions.   Involvement is typically monoarticular, with the large joints being most frequently affected.The knee joint is involved in the majority of cases; the shoulder,elbow, and hip are the next most frequently involved joints.   On T1-weighted sequences, the bodies are higher in signal than the effusion.    On T2-weighted sequences, the bodies are lower insignal than both the subcutaneous fat and effusion.   Synovial chondromatosis can be distinguished from pigmented villous nodular synovitis (PVNS) by the lack of blooming on gradient echoimaging. PVNS is typically associated with bone erosions.     Lipomatous arborescens, which are intra-articular areas of fat signal, may also mimic synovial chondromatosis.The aggressive nature ofsynovial sarcoma and chondrosarcoma typically preclude themselves from the differential diagnosis. Treatment: Synovectomy or radiation treatment References: 1. Stoller, DW. Magnetic Resonance Imaging in Orthopaedics and Sports Medicine.  3rd Ed., Vol. 2, Baltimore, MD: Wolters Kluwer-Lippincott Williams and Wilkins, 2007. Terms of Use Privacy Statement HIPAA Privacy Practices Careers Site Map Copyright © 2010 by ProScan Imaging