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Localized Villonodular Synovitis of the Knee

Laurent Hermann Marion Ondima*, Badr Slioui, Fitzgerald Sylvestre Ondongo, Nabil Hammoune, Abdelilah Mouhsine
Medical Imaging Department, Avicenne Military Hospital, Marrakech, Morocco.

Corresponding author: Laurent Hermann Marion Ondima Medical Imaging Department, Avicenne Military Hospital, Marrakech, Morocco. E-mail: [email protected]

Received Date: 18 January, 2023 Accepted Date: 26 January, 2023 ; Published Date: 30 January, 2023

Localized villonodular synovitis is a benign proliferative tumour of the synovium that rarely occurs in large joints such as the knee. The etiology is uncertain and debated. It is rarely mentioned in the first instance. Although the clinical manifestations are aspecific, MRI allows a diagnostic approach, even if it can pose differential diagnostic problems in case of atypia or with synovial sarcoma. Treatment consists of complete removal of the lesion to avoid recurrence. We report this case in order to make clinicians and radiologists aware of the imaging features of this rare pathology in adults.

Keywords: Villonodular synovitis; Localized form; Knee; Imaging


Villonodular synovitis is a benign proliferative process of the synovium [1]. It usually occurs in adults in their third or fourth decade of life with an estimated incidence of 1.8 cases per million population [1,2].  The localised form predominates in the fingers and wrists; it is mainly located in the synovial sheath or interphalangeal joints.  Involvement of large joints such as the knee is rare [3]. 

The clinical presentation is not very specific and the imaging results may pose problems of differential diagnosis with other lesions: synovial sarcoma [2]. This condition is often unrecognised and therefore not evoked as a first-line diagnosis. This report aims to increase awareness among clinicians and radiologists of the imaging features of this rare condition in adults.


Case Report

A 45-year-old man with no previous history was referred for left knee pain that had been present for two years. He presented with mechanical pain and swelling of the knee, with no other joint complaints. On physical examination, the knee was normo-axed, swollen, with obvious tenderness on the medial surface, and no obvious mass was palpable. The skin colour of the knee was normal. Standard radiographs were unremarkable. Magnetic resonance imaging (MRI) revealed a well-limited, oval-shaped lesion in the anteromedial compartment of the knee, measuring 28 mm in long axis, presenting as a Dp FS hypersignal with areas of T2 EG asignal and strong enhancement after gadolinium injection. This lesion displaces the anterior cruciate ligament (ACL) outward, Hoffa's fat forward and protrudes into the intercondylar groove (Figs. 1, 2 and 3). MRI also revealed a complex fissure of the posterior horn of the medial meniscus (classified as Stoller type 3); a bipartite patella with fluid signal abnormalities on its lateral border; and femorotibial osteoarthritis with joint pinch and cartilage signal abnormalities opposite. The rest of the examination was normal. The diagnosis of localized villonodular synovitis was made and confirmed by histology. Treatment consisted of subtotal synovectomy.



Villonodular synovitis was first described by Chassaignac in 1852 and then by Jaff in 1941, who gave the current description [1,2]. It is a rare benign tumour causing hyperplasia of the synovial villi, which may coalesce into a nodule. Lesions may involve the articular synovium, bursa and/or tendon sheath [1,4]. 

The etiopathogenesis is still uncertain and controversial today [5]. However, several hypotheses have been proposed, such as the occurrence of inflammatory synovial hyperplasia, benign neoplasia of unknown etiology, abnormal local lipid metabolism, repeated trauma and intra-articular haemorrhage [1,4,5]. Cytogenetic abnormalities such as monoclonality and chromosomal abnormalities (Trisomy 5 and 7) have also been reported [4,5].

Villonodular synovitis can affect any joint in the body. Two types are described: the localised and the diffuse form [6]. The diffuse type mainly affects large joints such as the knee and hip while the localised type predominates in the fingers and ankles [3,7]. Although the knee is often affected in the diffuse type, localized knee involvement was less common.

Villonodular synovitis remains silent for a long time and often has a chronic onset with almost no acute symptoms [1]. The clinical manifestations of localised forms are aspecific.  The most frequently reported clinical signs are the presence of a soft tissue mass and pain that may be related to joint dysfunction [1,2,6]. Murphy et al. reported different aspects of clinical presentation depending on the location, whether intra- or extra-articular. The extra-articular localised form often presents with a soft tissue mass and pain, whereas the intra-articular localised form is associated with pain, swelling and sometimes a soft tissue mass [1].  Joint dysfunction is less common in the intra-articular localised form and unusual in the extra-articular localised form [1].


Imaging plays an important role in the accurate diagnosis, treatment and monitoring of localised villous synovitis. Standard radiography is the basic examination. It is usually normal, especially in the early stages of the disease. Bone abnormalities such as erosion and subchondral cysts may be seen in advanced stages, but erosions of the knee are rare due to the superior ability of the joint to stretch and decompress normal tissues in the various bursae in contrast to the so-called tight joints [1,6,8]. Opaque areas of soft tissue may be seen replacing the normal fatty tissue areas of Hoffa's fat pad [8].

Ultrasound may reveal a complex heterogeneous echogenic mass, synovial thickening or possibly intra-articular effusion. It may also allow visualisation of extra-articular lesions in the bursa or tendon. However, the diagnostic value of ultrasound is still low [8].

On CT, focal villonodular synovitis appears as a well-defined, non-specific soft tissue mass with a density similar to that of the adjacent muscle. A feature probably reflecting the more variable amount of haemosiderin in these lesions compared to diffuse villonodular synovitis [1,9]. Slightly increased densities are rare [1]. CT also shows subchondral cyst formation and extrinsic bone erosion on both sides of the joint [1]. 

MRI is the gold standard in the diagnosis of villonodular synovitis. It allows precise localisation of the lesion, knowledge of its morphology and signal properties (haemosiderin, lipids and inflammatory fibrosis) which reflect its histological composition [9]. Specificity is due to haemosiderin because of its magnetic susceptibility properties, which manifest as low-signal 'blooming' artefacts more commonly seen in gradient echo sequences [9]. Localized villonodular synovitis presents as an ovoid lesion or multilobed soft tissue mass, heterogeneous with an isointense signal to the muscle in the T1 sequence and variable in the T2 sequence. Its borders are well delineated by capsules of low signal intensity due to fibrosis or haemosiderin. This intensity varies according to the amount of haemosiderin and the degree of fibrosis [9,10]. Localized nodular synovitis also tends to grow outwards and become pedunculated [10]. Huang et al. observed in 7 lesions in their series, the presence of a high signal intensity or linear region of the lesion on T2-weighted sequences. This novel finding may be related to tissue necrosis [10].

Histological examination confirms the diagnosis. Macroscopically, it is a well-defined lesion, whether pedunculated or not, containing septa and surrounded by a brown collagen capsule [2,11]. Microscopically, villonodular synovitis is described as proliferation of synovium within villi or nodules without evidence of malignancy, with brown haemosiderin deposits in fibroblasts, histiocytes, macrophages and giant cells [2,11,12].

The therapeutic management of focal villonodular synovitis is surgical. It usually consists of complete removal of the lesion by arthroscopy or open arthrotomy. The procedure depends mainly on the location and size of the lesion [10,12]. Recurrence is rare, except in cases of incomplete resection of lesions [2,6,10].



Localized villonodular synovitis of the knee is a rare benign tumour in adults. This report highlights the importance of imaging, in particular MRI, in the preoperative diagnosis, which is essential for surgical interventions to minimise the risk of recurrence due to the latter. Confirmation of the diagnosis is based on histopathology.


Conflicts of interest : The authors declare no conflicts.

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Citation: Ondima LHM, Slioui B, Ondongo FS, Hammoune N, Mouhsine A (2023) Localized Villonodular Synovitis of the Knee. Open J Case Rep 4: 169