Pigmented Villonodular Synovitis
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Direct answer
Pigmented villonodular synovitis is a benign but locally aggressive proliferation of synovium that deposits haemosiderin and forms villous, nodular masses, most often in the knee. Its signature MRI finding is blooming on gradient-echo sequences, caused by the magnetic susceptibility of haemosiderin. Treatment is synovectomy, and the diffuse intra-articular form recurs more often than the localised one.
What you must remember
- Nature: a benign but locally aggressive proliferative disorder of synovium, not an infection and not an ordinary inflammatory arthritis.
- Histology: haemosiderin-laden macrophages, foamy histiocytes and multinucleated giant cells within a villous synovial stroma.
- Commonest site: the knee, with the hip and ankle involved less often.
- Diffuse form: intra-articular and extensive, able to erode bone and cause recurrent effusions after surgery.
- Localised form: a nodular tenosynovial giant cell tumour, usually extra-articular and most often seen in the fingers.
- MRI blooming: low signal on T1 and T2 with marked blooming on gradient-echo sequences, the key diagnostic clue.
- Treatment: complete synovectomy, arthroscopic or open, with radiotherapy kept for recurrent or unresectable disease.
Diffuse and localised forms compared
Both forms share the same histology, but they behave differently and are managed differently. The table separates them by the features that examiners usually ask about, and the distinction rests on location and extent rather than on the cells seen under the microscope.
| Feature | Diffuse PVNS | Localised form |
|---|---|---|
| Location | Intra-articular, mainly the knee | Extra-articular, usually fingers and hand tendon sheaths |
| Pattern | Diffuse villous synovial infiltration | Discrete, well-circumscribed nodule |
| Joint effect | Effusions, cysts and erosions can develop | Usually no joint destruction |
| Recurrence | Common, often needing repeat synovectomy | Uncommon after complete excision |
A knee effusion with blooming on MRI points to the diffuse form, whereas a painless nodule on a finger suggests the localised one. Early films can look normal in either form, so MRI and histology do most of the work in establishing the diagnosis. In practice, the examiner expects you to link the site, the imaging and the extent of disease before choosing between local excision, synovectomy and adjuvant radiotherapy.
Where the exam tries to catch you
Most PVNS questions turn on the MRI sign and on the choice of treatment, and students lose marks by reaching for the wrong one.
- Trap: reading blooming on MRI as a fresh haemarthrosis. Correct: blooming reflects chronic haemosiderin deposition in proliferating synovium, which is the diagnostic clue for PVNS, not a recent bleed.
- Trap: choosing radiotherapy as first-line for typical knee disease. Correct: complete synovectomy is the mainstay, and radiotherapy is reserved for recurrent or unresectable disease.
- Trap: expecting a plain radiograph to make the diagnosis. Correct: radiographs can be normal early, and MRI with histological confirmation establishes the diagnosis.
Frequently asked questions
Which MRI sign is characteristic of pigmented villonodular synovitis?
Blooming on gradient-echo or susceptibility-weighted sequences is the characteristic MRI sign of pigmented villonodular synovitis. It is produced by haemosiderin deposits, which show low signal on T1 and T2 images. This sign is the single most useful clue when a joint effusion is seen in an otherwise unexplained knee.
Which investigation confirms pigmented villonodular synovitis?
MRI suggests the diagnosis, but histology confirms it. Arthroscopic or open synovial biopsy shows haemosiderin-laden synovium, foamy histiocytes and multinucleated giant cells. The biopsy also excludes infection, synovial sarcoma and other synovial lesions.
Is pigmented villonodular synovitis a malignant tumour?
Pigmented villonodular synovitis is histologically benign, although it behaves in a locally aggressive way. It can erode adjacent bone and recur after surgery. Malignant transformation is considered rare.
Why does diffuse pigmented villonodular synovitis recur after surgery?
Diffuse pigmented villonodular synovitis recurs because the disease spreads through the whole synovial lining of the joint. Small islands of abnormal synovium may be left behind after synovectomy, even when the surgery looks complete. Recurrence is therefore managed with repeat synovectomy and, in selected cases, radiotherapy.