A Case of Localized Pigmented Villonodular Synovitis Presenting as Loose Body in the Knee Joint

Submit Manuscript | http://medcraveonline.com episode of instability with occasional episodes of locking. Other joints were normal. On clinical examination there was a mild swelling of the right knee joint, with retro-patellar tenderness. Results of Lachman test, anterior and posterior drawer tests, and varus and valgus stress tests were normal. Radiographic findings suggested a normal report (Figure 1). Sagittal T1, T2, coronal PD fatsat, axial T2 MRI of his right knee showed a well-circumscribed single loose body in the retropatellar fossa measuring 1.5*1.5*0.75 cm (Figure 2 & 3). The differential diagnosis at that time included loose body, synovial hemangioma, hematoma, localized PVNS, fibroxanthoma, and less likely a malignant lesion. The patient was considered for arthroscopic removal of the loose body under spinal anaesthesia. With arthroscope in the anterolateral portal, a Introduction


Introduction
Pigmented Villonodular Synovitis is a rare, uncommon benign condition which is characterized mostly with a hyper plastic synovium, large effusion and bone erosions. On an average it is clinically identified after 4.4 yr of presentation [1]. Its local involvement is very rare and mostly involves the smaller joints and in larger joints commonly the knee joints. The difficulty stems from the insidious onset, progressive nature and the non-specific presentation of the disease along with its subtle radiographic presentation. PVNS is also difficult to differentiate from other inflammatory conditions such as Rheumatoid arthritis, osteoarthritis, and neoplastic process of the synovial lining [2]. It was first defined by chassaignac in 1852 [3]. Simon described the first localized form in knees in 1864 and thereafter named by Jaffe in 1941 [4][5][6][7] who further sub divided it into diffuse and local. The annual incidence of PVNS is 1.8 individuals per million [1]. Most reported localized lesion of the knee are confined to the menisci, posterior cruciate ligament and plica [7,8]. We report a case that is localized to their tropatellar space of the right knee which mimics a loose body clinically and also in magnetic resonance imaging. The localized growth was resected and histopathologically confirmed as a pigmented villonodularsynovitis.

Case Report
A 49 year old man presented with right knee pain since 3 months ,which was insidious in onset , localized and progressive in nature with difficulty in walking and sitting for a long time.
There was no episode of injury or night cries. The patient had one diagnostic scopy of the knee joint was performed in search of the loose body at all corners of the knee joint when a small nodular swelling was seen in the retropatellar space just below the patella ( Figure 4A). The swelling was 1.5 cm in diameter and was probed to found out that it was fixed to the underlying surface. It was then punctured with the help of a needle, a yellowish coloured tissue was removed from the swelling ( Figure 4B) which was sent for histopathology. Postoperative histopathology report suggested villous projection and a nodular proliferation of round to polyhedral cells having eosinophilic cytoplasm with round to oval nuclei, haemosiderin laden macrophages, foam cells and multi nucleated giant cells suggestive of PVNS ( Figure 5). The patient recovered in a routine and un-complicated manner. At his last follow-up examination 6 months postoperatively, the patient was completely asymptomatic and has returned to his day to day activity.

Discussion
Localized PVNS of the knee joint mostly present as knee pain and swelling. In some they present as locking and giving way when they involve the menisci [8]. The localized form is most commonly seen in the small joints, though uncommonly seen in the large joints, it is most commonly involved is the knee joint. The disease is insidious, slowly progressive and patients generally presents later in life with pain [9]. As per Myers et al. [10], estimation of the annual incidence of PVNS is 1.8 patients per million populations with the localized form being less severe than the diffuse form. The localized PVNS undergoing an arthroscopic procedure is estimated with only one case per 2,500 [11]. Localized form of PVNS is commonly seen in the third and fourth decade of life [12]. Radiologically it is difficult to diagnose a localized form of PVNS [13] whereas it is clearly seen in the MRI. [14][15][16]. In our case the PVNS localized form explains the retropatellar tenderness for his age.
MRI showed a characteristic mass with focal hypo intense areas on both T1 and T2 weighted images which resembled like a loose body adding to the suspicion considering the age of the person. The MRI findings of PVNS are generally not specific.

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Histologically, it is characterized by an active proliferation of fibroblastic and histiocytic element showing an evident macrophagic activity with phagocytosis of abundant blood pigment (hemosiderin) and lipids. Arthroscopy is an effective diagnostic tool and can also be used for therapeutic purpose. Previous report of arthroscopic treatment of localized PVNS treatment showed lower recurrence rate [17][18][19]. Review of the literature has made it simpler to consider that this uncommon presentation as a loose body and diffuse retropatellar tenderness is unique in its presentation and at the same time we would like to state that all solitary swelling is not a loose body in 3 rd -4 th decade. Because of the uncommon presentation of the tumor, it is very easy to miss the swelling considering the search for a loose body inside the knee joint.

Conclusion
Localized Pigmented VillonodularSynovitis can present in various ways. A clinician should always rule out PVNS in his differential diagnosis when there is a chronic knee pain in 3 rd -4 th decade of life. Arthroscopic diagnosis and resection is the best method of treatment for PVNS since it gives a better picture of the joint and it is atleast as effective assynovectomy and is less aggressive.