Tumefactive synovial thickening mimicking synovial chondromatosis in the setting of oligoarticular juvenile idiopathic arthritis in a toddler

Juvenile idiopathic arthritis (JIA) is the most common cause of arthritis in children. It is characterized by inflammatory cell infiltration of synovial membranes leading to synovitis and synovial membrane thickening. Synovial chondromatosis is rare sequela of synovitis in which foci of cartilage develop within the synovial membrane of a joint capsule. We report a case of a 35-month old boy who developed tumefactive synovial hypertrophy and hyperplasia that mimicked synovial chondromatosis on MRI. The reactive synovium was arthroscopically excised and the patient's arthritis improved. Tumefactive synovial hypertrophy and hyperplasia mimicking synovial chondromatosis on MRI in the setting of JIA, has not been reported in this young of a patient in the literature to date. A discussion on imaging in oligoarticular JIA and synovial chondromatosis is presented herein. Keywords: Juvenile idiopathic arthritis, Synovial chondromatosis, Tumefactive synovium