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Pigmented villonodular synovitis

Pigmented villonodular synovitis (PVNS) is a condition affecting synovial membranes (and can thus also include bursae and tendons) resulting from synovial proliferation with villous and nodular projections and haemosiderin deposition. This is best evaluated on MRI. The histology of PVNS can look similar to some aggressive neoplasms (rhabdomyosarcoma, synovial sarcoma, epithelioid sarcoma) and imaging therefore has a crucial role to guide the pathologist.

Epidemiology

PVNS occurs predominantly in early to middle age (2nd to 5th decades)1-2.  In intra-articular disease there is no gender predilection, whereas extra-articular disease has a slight female predominance.

Clinical presentation

Presentation is usually with joint swelling, pain and occasionally joint dysfunction. Usually symptoms have been present for many months before diagnosis is made.

Although unusual in the paediatric population, it is sometimes seen, and is more frequently poly-articular. It has also been described in association with: 2

Pathology

Macroscopically the synovium is diffusely thickened with multiple villous and nodular projections. Theeir colour is typically dark brown and heterogeneous with areas of yellow discolouration (xanthoma cells).

On microscopy mononuclear histiocytes predominate mixed in with variable numbers of multi-nucleated giant cells (absent in 20% of cases). Overall there is a diffuse infiltrative growth pattern 2. It is important to note that histologically the appearance of PVNS may mimic aggressive neoplasms such as rhabdomyosarcoma, synovial sarcoma, or epithelioid sarcoma, and thus the role of imaging in guiding the pathologist is crucial.

Malignant transformation of PVNS is rare, and controversy exists as to histologic criteria for its diagnosis.

Location
  • knee (by far the most frequently affected joint 2): 66-80%
  • hip: 4-16%
  • ankle
  • shoulder
  • elbow
  • spine 6
  • other joints
Classification

All synovial membranes may be affected, and thus bursae and tendon sheaths may also be involved. The condition is then known as pigmented villonodular bursitis (PVNB) and pigmented villonodular tenosynovitis (PVNTS) respectively. The latter is also known as giant cell tumour of the tendon sheath (GCTTS).

PVNS/B/TS is divided into a localised and diffuse form:

  • localised: most common and usually extra-articular (PVNB and PVNTS) 2.
  • diffuse: (i.e. involves all of the contiguous synovium) is the most common form of intra-articular disease, although local intra-articular involvement is also sometimes seen.

Typically PVNS is a monoarticular condition and joints with large synovial surfaces are predictably most frequently affected. The remainder of this article focuses on intra-articular disease (PVNS).

Radiographic features

Plain film

On plain film, features are relatively non-specific with appearances mainly being those of a joint effusion. Bone density and joint space are preserved until late stages. Marginal erosions may be present but it is not possible to distinguish PVNS from synovial chondromatosis (non-ossified synovial osteochondromatosis).

CT

Joint effusions commonly co-exist. The hypertrophic synovium appears as a soft tissue mass, which on account of haemosiderin, may appear slightly hyperdense compared to adjacent muscle. Calcification is very rare in the synovial mass (cf. synovioma where it is common).

Erosions are often well seen on CT.

MRI

MRI typically shows masslike synovial proliferation with lobulated margins. This may be extensive in the diffuse form or limited to a well-defined single nodule in the localised form 9 with low signal intensity due to haemosiderin deposition.

Signal characteristics include:

  • T1: low to intermediate signal
  • T1 C+ (Gd): variable enhancement
  • T2
    • low to intermediate signal
    • some areas of high signal may be present likely due to joint fluid or inflamed synovium
  • STIR: predominantly high signal 2
  • GE (gradient echo): low and may demonstrate blooming

Treatment and prognosis

Treatment is with complete synovectomy, which offers a good prospect of cure, provided all the synovium is excised. This can be difficult and therefore adjuvant treatment is often employed, especially external beam radiotherapy which offers excellent control. Intra-articular injection of Yttrium 90 is an alternative.

Medical therapy is also being investigated in refractory cases including α-TNF (tumour necrosis factor) blockade and infliximab.

Recurrence rates after total synovectomy are reported to be 7-20% 2.

History and etymology

The term PVNS was first proposed by Jaffe at al in 1949 6. The first description of the condition was by Chassaignac in 1852 who had described a nodular lesion of the synovial membrane that affects the flexor tendons of the fingers 2.

Differential diagnosis

On MRI there is little differential in classic examples:

On plain film the differential is wide, and findings are non-specific:

See also

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