Spontaneous swelling of the ankle in a child : a difficult diagnosis.

The authors present a case of monoarticular localized pigmented villonodular synovitis (PVNS) in a 7-year old girl. PVNS is a rare benign disease of the synovial tissue. It is especially rare in ankles of children, with only 15 cases reported in literature. The girl presented with swelling and pain in the left ankle since 4 weeks. The tentative diagnosis was made after a joint puncture and a MRI scan. A synovial mass with a brown-yellowish appearance was seen during the excisional biopsy. After removing the entire mass and without adjuvant therapy, no recurrence was detected after 12 months. As it is very rare in children, PVNS is easily misdiagnosed. Early diagnosis is important to prevent bone and cartilage damage. A review of the clinical, radiological and therapeutical features of PVNS are presented.