Intra-articular venous malformations of the knee: a diagnostic challenge

Background: Intra-articular venous malformations (IAVM) are rare benign vascular anomalies that usually affect young patients and most common locate in the knee. The terminology of these lesions is still ill-defined, as they are often termed in the literature as synovial hemangiomas. Early diagnosis can be difficult, because they usually present with nonspecific clinical manifestations that are similar those of other rheumatic diseases, especially juvenile idiopathic arthritis (JIA). Case series: We conducted a retrospective analysis of five pediatric patients admitted to our units for recurrent swelling of the knee, and compared their characteristics with those of literature reports. The average age at first symptom and time from onset to diagnosis was 3.9 years (range 18 months-7 years) and 3.5 years (range 1-7 years), respectively. In our patients, an initial misdiagnosis of JIA, bleeding disorder or traumatic arthropathy was made. On MRI imaging, the features of the lesion were similar in all patients, and were marked by isointense-to-hypointense signal in T1-weighted images, and hyperintense signal in T2-weighted images. When performed, arthrocentesis led to aspiration of bloody fluid. The diagnosis was confirmed with a biopsy and histopathologic assessment in all patients. Open surgery enabled complete excision of the mass and was followed by stable remission over time in all cases. Conclusions: Our report highlights the challenges that may be posed by the detection of knee IAVM and the frequent long delay between onset of symptoms and diagnosis. The key elements for early recognition include careful assessment of patient history, demonstration of bloody fluid on arthrocentesis, and proper interpretation of MRI scanning.