Synovial hemangioma is a rare benign tumor that is most likely found in the knee in children and adolescents. It was first described by Bouchut in 1856 ^[1]. Synovial hemangioma typically occurs in adolescents and young adults, with the average age of onset reported to be 10 years in girls and 12 years in boys ^[2]. Patients usually present with recurrent non-traumatic knee swelling with pain that often subsides by taking rest and immobilization ^[3]. Intraarticular hemangioma of the knee in young children is rare, making it difficult to diagnose thus leading to delayed diagnosis and subsequent arthrosis and destruction of joints ^[4]. Herein, we report the case of a 4-year-old girl who was diagnosed with intraarticular hemangioma at our center and discusses the management of her condition.

A 4-year-old girl presented to us with a complaint of recurrent swelling of the left knee in the last 6 months, the last episode 7 days back before visiting us. The swelling was insidious in onset, with no history of trauma or injury to the knee, and swelling was associated with pain and affecting the gait of the patient; the patient was previously treated elsewhere with an aspiration of the knee done twice, followed by a short course of antibiotics after which patient was stable for some time, the hematological investigation was inconclusive. Magnetic resonance imaging (MRI) is suggestive of synovitis along with soft-tissue swelling in the left knee in all compartments, differential being pigmented villonodular synovitis or hemangioma of the knee (Fig. 1).

On clinical examination, there was no palpable swelling present over the knee. The range of motion was terminally restricted and painful; there was no sign of meniscus or ligament injury, no local warmth, and no gross deformity of the left knee with this MRI finding, we subjected the patient to an open excision of the mass. Intraoperatively, it was found that in cherry red color mass in all compartments of the knee, all abnormal tissue was excised, and the sample was sent for histopathological examination (Fig. 2-5).

Histological features were suggestive of the proliferation of vascular spaces in synovial tissue, synovial vascular congestion, and variable caliber of lumen seen filled with red blood cells. Histopath Impression – Features consistent with clinicoradiological diagnosis of benign lesions more in favor of synovial hemangioma (Fig. 6).

Synovial hemangioma of the knee was first described by Bouchut in 1856 ^[1]. It is most commonly found in adolescents and young adults ^[2]. It presents in the form of swelling, pain, recurrent hemarthrosis, stiffness, and a palpable mass. In 35% of cases, prior trauma history was noted, the average age of onset is 10.9 years for girls and 12.5 years for boys, and 75% of patients are symptomatic before the age of 16 years ^[3]. Intra-articular hemangioma of the knee in young children is very rare, resulting in an average delay of 8.7 years in the diagnosis and treatment of the condition ^[4]. In the present case, the patient was referred for further management only after a 6-month delay following the onset of symptoms, despite numerous medical consultations. Other disease entities that should be included in the differential diagnosis are pigmented villonodular synovitis, synovial sarcoma, juvenile idiopathic arthritis, hemophilia, and sickle cell disease ^[5]. MRI is the preferred imaging modality if an intraarticular vascular lesion such as synovium hemangioma is suspected ^[6]. The lesion will have a low-to-moderate signal intensity on T1-weighted images but will have a high signal intensity on T2-weighted images ^[8]. MRI also allows visualization of the extent of the lesion, as well as the presence of any chondral degeneration. In our patient, the MRIs clearly showed an enhancing lesion with high T2 signal intensity over the infrapatellar region. However, no chondral degeneration was seen. Treatment of intraarticular hemangioma should be commenced as soon as possible to prevent degenerative changes of the cartilage. Treatment modalities include open surgical resection, arthroscopic excision, or arthroscopic ablation ^[7]. However, arthroscopic excision may be complicated due to excessive bleeding or difficulty in complete resection of the hemangioma, and open surgical resection may result in a limited range of motion of the knee secondary to fibrosis and scarring ^[9]. In the present case, our patient was treated with open surgical excision, and neither excessive bleeding nor limitation in the knee range of motion occurred postoperatively. As the recurrence of intraarticular hemangioma following open resection has been reported ^[10], we continue to follow up on our patient to monitor for any recurrence of symptoms. At 12 months following the initial resection of the hemangioma, our patient remained disease-free. To summarize, we report the case of a 4-year-old girl with 6 month history of recurrent swelling and pain in the left knee in the absence of preceding trauma, who was diagnosed with intra-articular hemangioma and treated with open surgical excision. As misdiagnosis is common, intraarticular hemangioma should be considered in skeletally immature patients who present with recurrent swelling and pain in the knee. Clinicians should exercise a high index of suspicion, as prompt diagnosis and treatment can prevent progressive arthropathic changes in the joint. MRI is essential for definitive diagnosis. Following treatment, extended follow-up with regular biopsies should be undertaken for early detection of any recurrence of disease.

Synovial hemangioma is rare in children below 10 years, it is difficult to diagnose in the outpatient department, a high index of suspicion is required for prolonged knee pain and swelling without significant trauma, and MRI is the investigation of choice. Early treatment is recommended in the form of open or arthroscopic excision, as delay can lead to joint destruction and stiffness. Regular follow-up after excision is required as the disease has a high chance of recurrence.

Synovial hemangioma is rare in children; a detailed study should be done on non-traumatic swelling of the knee.