Clinical History: A 39 year-old female presents with right knee pain and swelling. (1a) Proton density weighted axial and (1b) gradient-echo weighted sagittal images are provided. What are the findings? What is the diagnosis?
Pigmented villonodular synovitis
Pigmented villonodular synovitis (PVNS) is a benign proliferative synovial lesion of uncertain etiology.1 PVNS is typically mono-articular, and the knee is the most commonly affected joint.2 Affected patients may be of any age, though the process is most often seen in the 3rd and 4th decades. Patients initially present with painless swelling that may mimic a joint effusion. Over time, pain develops, but is mild relative to the degree of swelling within the joint. Limitation of motion and hemorrhagic joint effusions may also be present, particularly at the knee.
On plain radiographs, bone density and the joint space are usually well preserved. X-rays may be normal or may simply reveal peri-articular soft-tissue swelling. Calcification is extremely rare. Bone erosions may be present, particularly in joints with a tight capsule such as the hip, ankle, or elbow.
On MR images, PVNS is identified by multiple, lobulated intraarticular soft tissue masses. The lesions generally have intermediate to low signal intensity on both T1 and T2 weighted images. PVNS lesions tend to bleed, resulting in characteristic deposition of very low-signal intensity hemosiderin. Hemosiderin is best displayed at high magnetic field strength and with gradient-echo techniques, which accentuate the magnetic susceptibility effects of hemosiderin.3 When present, erosion into bone or adjacent soft-tissue structures such as the patellar tendon is well demonstrated with MR (3a,3b).
PVNS is considered a diffuse process. When it takes a localized form, it is referred to as localized nodular synovitis.4 The infrapatellar fat pad is the most common location for localized nodular synovitis. Although histologically the two entities are quite similar, the MR appearance and clinical course of PVNS versus localized nodular synovitis are distinctly different. PVNS is more likely to have a frond-like appearance, and hemosiderin deposition is usually more abundant than with localized nodular synovitis. The lesions of localized nodular synovitis are usually better circumscribed and are smaller (4a,5a). Whereas PVNS tends to fill the joint and therefore restrict motion, localized nodular synovitis commonly grows outward in a pedunculated fashion.
When localized nodular synovitis arises in association with a tendon sheath, the process may be designated a “giant cell tumor of the tendon sheath”. The giant cell tumor of the tendon sheath is unrelated to giant cell tumor of bone. Although they may be identified at the knee (6a,6b), giant cell tumors of the tendon sheath are most common in the hand, and indeed are the most common soft-tissue mass encountered at the hand.
The only curative treatment for PVNS or localized nodular synovitis (including giant cell tumor of the tendon sheath) is surgical excision. Because PVNS is a diffuse process, total synovectomy is typically required. Despite total synovectomy, however, recurrence in patients with PVNS is common. In contrast, patients with localized nodular synovitis are able to undergo local excision, and recurrence in this patient population is rare.
Patients with pigmented villonodular synovitis often present with pain and swelling that is difficult to distinguish clinically from internal derangement. MR provides accurate diagnosis of the process in affected patients. The ability of MRI to delineate the extent of disease and to differentiate PVNS from its related, localized forms, is important, as the entities differ considerably in terms of treatment approach and their typical response to surgical excision.
1 Llauger J, Palmer J, Ros?n N, Cremades R, Bagu” S. Pigmented villonodular synovitis and giant cell tumors of the tendon sheath. Am J Roentgenol 1999; 172:1087-1091.
2 Sheldon PJ, Forrester DM, Learch TJ. Imaging of intraarticular masses. Radiographics 2005: 25:105-119.
3 Narvaez JA, Narvaez J, Ortega R, et al. Hypointense synovial lesions on T2-weighted images: differential diagnosis with pathologic correlation. Am J Roentgenol 2003; 181:761-769.
4 Huang G, Lee C, Chan WP, Chen CY, Yu JS, Resnick D. Localized nodular synovitis of the knee: MR imaging appearance and clinical correlates in 21 patients. Am J Roentgenol 2003; 181:539-543.