Tumours and tumour-like lesions of joints: Differential diagnoses in a paediatric population compared to adults

Objective: To determine the differential diagnosis of intra-articular tumours and tumour-like lesions in a paediatric population compared to adults. Methods: Retrospective review of children up to the age of 18 years with suspected intra-articular tumours and tumour-like lesions referred to a specialist musculoskeletal oncology service from January 2019 to August 2020. Data recorded included patient age and gender, lesion location and morphology (based on the classification system of Adams et al.), and the final diagnosis made either by image-guided biopsy/resection or by clinical and imaging features. Comparison was then made with a group of adults presenting during the same period. Results: 28 paediatric patients were included (12 males and 16 females with mean age 11.2 years, range 3–18 years). Joints involved were the knee (n = 22; 78.6%), ankle (n = 4; 14.3%), hip (n = 1; 3.6%) and elbow (n = 1; 3.6%). Lesion morphology was Type 1 (n = 18; 64.3%), Type 2 (n = 3; 10.7%), Type 3 (n = 1; 3.6%) and Type 4 (n = 5; 17.9%). Final diagnosis was made by image-guided biopsy/resection in 18 (64.3%) patients. The commonest neoplastic lesion was tenosynovial giant cell tumour (n = 11; 39.3%), followed by synovial haemangioma (n = 5; 17.9%). There was only a single malignant lesion, a case of synovial sarcoma. Of eight (28.6%) non-neoplastic lesions, three were diagnosed as juvenile idiopathic arthritis and three as non-specific synovitis. There was no difference compared to adults regarding gender, joint involved or lesion morphology, but there was a significant difference in final diagnoses (p < 0.001). The range of intra-articular tumours and tumour-like lesions in children differs from that in adults, although tenosynovial giant cell tumour is the commonest diagnosis in both groups and malignant lesions are rare. Advances in knowledgeart: In our series, ~16% of tumours and tumour-like lesions of joints occur in the paediatric population. Tenosynovial giant cell tumour remains the commonest diagnosis in children as in adults. Synovial haemangioma and juvenile idiopathic arthritis were the next commonest diagnoses in children, while primary synovial chondromatosis and reactive synovitis were the next commonest diagnoses in adults. Malignant lesions are rare in both groups.