Synovial Hemangioma: A rare cause of chronic anterior knee painAbstract: Synovial hemangioma is an uncommon cause of chronic anterior knee pain. The non-specific clinical presentation leads to delay in diagnosis. MRI is diagnostic and should be considered early in evaluation to plan treatment and prevent functional disability. We present a case of unilateral synovial hemangioma of the knee in a child with pain, swelling and restricted knee mobility. Arthroscopy can be diagnostic and therapeutic in such cases.Introduction: Anterior knee pain is the pain occurring in the anterior and central part of the knee resulting in varying degrees of functional disability1. Evaluation of such pain is challenging as the symptoms are non-specific and the differential diagnosis is quite extensive. Patellofemoral pain syndrome (PFPS), chondromalacia patellae, Osgood-Schattler disease, Plica syndrome, patellar tendonitis and knee bursitis are amongst the common etiology of anterior knee pain2. Although bony tumors are commonly seen around the knee, tumors of the synovium are rarely seen and pose a diagnostic challenge in the evaluation of knee pain.Pigmented Villo Nodular Synovitis, Giant cell tumor, lipoma arborescence, synovial chondromatosis and Synovial Hemangioma are some of the proliferative lesions of the synovial tissue presenting as synovial tumor or tumor-like lesions.Synovial Hemangioma is a rare benign vascular tumor of the synovial membrane. It frequently affects adolescents and young adults and presents as unilateral chronic knee pain and swelling. The clinical diagnosis is often not possible due to non-specific clinical presentation and a wide array of differentials often leading to delayed diagnosis.We present as case of synovial hemangioma of the knee in a child presenting as chronic knee pain and swelling over a period of 1 year. We highlight the clinical presentation, radiological findings, management and expectant follow-up of this disease.Case ReportA 12-year-old child presented to us with a history of anterior knee pain for 1 year and swelling in the anterior aspect of knee for 6 months. The pain was progressive, localized to anterior and antero-medial aspect of the knee, sharp pin like character and aggravated with knee movements especially with squatting and climbing stairs. There were no history of trauma or constitutional symptoms. The knee pain had significantly affected the daily activities of the child including absence from school.On examination, a small tender swelling was present on the antero-medial aspect of knee joint adjacent to patellar tendon. The knee movements were painful with restricted terminal 30 degrees of knee flexion. There was no flexion deformity. Quadriceps wasting was noted.The child was evaluated with complete blood count, erythrocyte sedimentation rate, C- reactive protein, radiograph and an ultrasound of the knee. The reports were unremarkable (Figure 1).MRI was requested which revealed a well-defined, lobulated T1 hypointense, T2, PDFS and STIR hyperintense lesion in the infra patellar compartment of the knee measuring 3.2 X 4.1 X 3 cm. There were multiple tiny lobulated phleboliths within the lesion. The lesion was predominantly posterior to the patellar tendon with no obvious bony erosions or invasions (Figure 2,3).Based on these clinico-radiological features, synovial hemangioma was diagnosed.The child underwent arthroscopic excision and ablation. The tissue was sent for histopathology which confirmed Synovial Hemangioma. Post-operatively, follow-up was done at 2 weeks, 1, 3, 6 months and 1 year. Pain and swelling had completely subsided at 1 month and 1300 knee range of movement was regained at 3 months (Figure 4,5). There were no signs of recurrence of symptoms/lesion. Child was able to perform pain free routine activities and returned to school at 1 month.DiscussionSynovial Hemangioma is a rare tumor arising from the synovial membrane. It is benign vascular tumor accounting for less than 1% of all Hemangioma3. Knee is the frequently affected joint followed by elbow. It is commonly seen in adolescents and young adults presenting with chronic pain and swelling4.The location of pain, presence of swelling, and restricted movements are so non-specific that it is challenging to make an early diagnosis as was seen in our case. The child had the symptoms for 1 year and was undiagnosed due to this non-specificity.The differential diagnosis is very extensive in adolescents and includes PFPS, Osgood Schattler disease, Plica Syndrome, Patellar tendinitis, Osteochondritis dessicans, quadriceps tendinopathy, stress fractures, bursitis amongst commoner causes. Tumors of the synovium are very rare and include Pigmented Villo Nodular Synovitis, Giant cell tumor, lipoma arborescence, synovial chondromatosis and Synovial Hemangioma. Most synovial tumors result in pain due to inflammation. However, hemangioma usually results in mechanical pain5.Plain radiographs may not yield anything substantial especially in the initial stage. At a later stage, soft tissue shadow, phleboliths, joint erosions and arthritis changes may be visible. The diagnosis requires imaging studies like Ultrasonography and MRI. Ultrasound may show a homogenous hypoechoic lesion with internal vascularity6. However, USG is usually non diagnostic. The lesion was not clearly defined in our case due to its location in the infra patellar compartmental behind the patellar tendon.The gold standard for the diagnosis of synovial hemangioma is an MRI7. The lesion appears as an intra‐articular lobulated mass with a hypo or isointense signal on T1‐weighted images, hyperintensity on T2‐weighted images. The MRI defines various aspects of tumor like the size, its location and its extension to soft tissue. More importantly it helps to rule out other differential diagnoses8.MRI usually provides a clarity in diagnosis and hence a treatment plan can be made based on its features. In cases where radiological investigations are either not clear or is not possible (claustrophobia/younger child requiring anesthesia etc), Arthroscopy is definitely helpful as it not only aids in diagnosis but also provides an added advantage of therapeutic excision and ablation in the same setting. The lesions appear as bunch of grapes which bleeds on incision as was seen in our case.Histopathology is the ultimate confirmation for any biopsy lesion and so is true for synovial hemangioma. The lesions are usually small and hence therapeutic excision is performed without prior biopsy. Biopsy may still be indicated in extensive lesions posing diagnostic dilemma.There are several treatment options for Synovial Hemangioma. These include Sclerotherapy, Selective embolization, Laser ablation, Arthroscopic excision/ablation and Open excision9. We performed Arthroscopic excision and ablation. It has been reported that patients are rid of symptoms after any of the surgical procedures mentioned above. The child in our case was also pain free and resumed schooling and routine activities after 1 post operative month.Long term complications of synovial hemangioma are rare. Joint erosions, chronic arthritis and hemarthrosis are possible. Recurrence is rare after surgery, possibly seen in cases with large lesions with soft tissue extensions. To keep a check on this, long follow-up is required.ConclusionThe vast differential diagnosis of knee pain does not usually alert the possibility of rare Synovial Hemangioma. However, in cases presenting with chronic knee pain and swelling, especially in children and adolescents, the diagnosis of Synovial Hemangioma should be considered and MRI should be done to confirm and/or rule out differentials. Early diagnosis and treatment are required as the lesion has the potential to cause significant morbidity.MRI, Excision of the tumor and long-term follow-up are key features highlighted in this report on management of Synovial Hemangioma.References:Sala D, Silvestre A, Gomar-Sancho F. Intraosseous hyperpressure of the patella as a cause of anterior knee pain. Medscape Orth Sports Med. 1999;3:1–8.Houghton KM. 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