SAT0452 Distribution Pattern of MRI Abnormalities Within the Knee and Wrist of Juvenile Idiopathic Arthritis Patients; MRI made Easy

Background MRI plays an increasingly important role in the assessment and monitoring of disease activity in juvenile idiopathic arthritis (JIA). Awareness of the incidence and distribution pattern of MRI abnormalities in JIA is a valuable tool in the daily practice of the reading radiologist and the treating clinician. Preferred locations for pathology within target joints are facilitated by knowledge on common distribution patterns of MRI abnormalities, enabling rapid differentiation between JIA abnormalities and normal variants. Objectives To determine (1) incidence and (2) distribution pattern of soft-tissue- and osseous abnormalities upon MRI of the two of the most affected joints in JIA (i.e. the knee and wrist) Methods MRI datasets of 166 active JIA patients (123 with knee and 43 with wrist involvement) were analyzed. Two readers evaluated presence of 4 literature-based items per joint. Common items included synovial hypertrophy (SH), bone marrow changes (BMC), and bone erosions (BE). Joint-specific features were additionally evaluated: cartilage lesions (CL) for the knee and tenosynovits (TS) for the wrist. Scoring locations in these two joints were also literature-based. Incidence of each scored item was defined separately. Involvement per location, analyzed as percentage of the total amount of affected locations, was determined. Results SH showed the highest incidence in both the knee and wrist (56.9-65.1% of the patients). Besides BMC (34.1%), the incidence of osteochondral features was low in the knee (CL 6.5%; BE 4.9%). In contrast, the incidence of these features in the wrist were relatively high (BMC 37.2% and BE 30.2%) and TS was present in 46.5% of the patients with wrist involvement. In order to make MRI easy, ‘top-3-location’ per feature was constituted. Below, the ‘number 1’ or most frequently affected location per feature is mentioned. In the knee these locations consisted of cruciate ligaments (25.1% in SH), medial patella (28.1% in BMC, 33.3% in CL) and lateral femur trochlea (50% in BE). In the wrist, the radiocarpal joint (32.8% in SH), extensor-tendon-group (83.3% in TS), lunate (15.2% in BMC) and capitate/triquetrum (21.4% in BE) were mostly affected. Being the most important feature in JIA, SH in the knee showed preferred presence in the central locations, which accounted for >85% of the total affected locations. Less obvious demarcation for SH was found in the wrist. Both in the knee and wrist the three least affected locations