Venous Malformations Masquerading as Episodic Knee Monoarthritis

Background: Vascular malformations are abnormal arterial, venous, lymphatic, capillary, or mixed vessels. They can be intra-articular, present as recurrent arthritis, and misdiagnosed as infection or juvenile idiopathic arthritis (JIA).

Aim: To characterize patients with knee venous malformations and offer key clinical features leading to diagnosis.

Methods: Medical & imaging files were reviewed and analyzed.

Results: Over 1 year, 4 patients were diagnosed with venous malformations of the knee. Age at diagnosis was 3-8.5 years. Time to diagnosis was 0.7-6.5 years. Episodic swelling of the knee of a few days to >2 months, with tenderness and limping, began during the first or second year of life, without systemic or extra-articular manifestations. Episodes were spontaneous or after mild trauma. Physical exam revealed swollen, mildly tender knee, with slightly limited range of motion. Bloody fluid was aspirated from the knees of 2 patients. Only MRI was diagnostic. Anti-inflammatory drugs and intra-articular steroid injections in 3 had no effect. Currently, 2 patients were treated with sclerotherapy with no recurrence over 1 year of follow-up.

Conclusions: Differential diagnosis of recurrent, episodic monoarthritis included JIA, familial Mediterranean fever, mechanical disorders, and pigmented villonodular synovitis. Intra-articular vascular malformation should be suspected in patients with dermal vascular malformations, without extra-articular involvement, with normal inflammatory markers, aspiration of bloody synovial fluid, or when anti-inflammatory treatment fails. MRI is the diagnostic modality of choice, revealing high T2 and low T1 signal intensity and patchy enhancement after intravenous contrast.