Diffuse Intraarticular PVNS 23%

= DIFFUSE-TYPE GIANT CELL TUMOR

= benign locally destructive proliferation of mononuclear cells that resemble those in the synovium, admixed with multinuclear giant cells and inflammatory cells

Incidence: 1.8÷1,000,000 population per year; 0.9% of all benign soft-tissue masses

Path: infiltrative mass involving synovium of entire joint with thickening + irregular papillary / villous projections + larger nodular / villonodular protrusions

Histo: diffuse villonodular infiltrative sheetlike growth of synovial membrane with hyperplasia of undifferentiated connective tissue + multinucleated large cells ingesting hemosiderin / lipoid (foam / giant cells) ± fibrosis

Age: mainly 3^rd–4^th decade (range, 12–68 years); 50% <40 years; M÷F=1÷1

• history of antecedent trauma (44–53%)
• mean duration of symptoms: 15 (range 1–120) months
• hemorrhagic “chocolate” / serosanguinous / xanthochromic joint effusion without trauma
• insidious onset (93%) with intermittent fluctuating symptoms + slow progression:
  • pain (79–90%), swelling (72–79%)
  • soft-tissue mass (6–19%)
  • joint dysfunction (26–28%):
    • stiffness with decreased range of motion, joint locking

Location: knee (66–80%), hip (4–16%) >ankle >shoulder >elbow >tarsal + carpal joints; predominantly monoarticular

Radiography:

• normal (in up to 21%)
• soft-tissue swelling ← effusion + synovial proliferation:
  • dense soft tissues ← hemosiderin deposits
• joint effusion in knee, but not relevant in other joints
• extrinsic pressure erosion with rim of sclerosis involving both sides of joint: hip (93%), shoulder (75%), elbow (63%), ankle (56%), knee (30%)
• multiple sites of irregular cystlike subchondral radiolucent defects ← invasion of bone by synovium
• normal bone mineralization, preservation of joint space, NO calcifications until late in the disease:
  • joint space narrowing (7%)
  • degenerative disease (4%)
  • intraarticular osteochondral bodies (7%)
  • osteopenia (7%)

US:

• joint effusion
• complex heterogeneous echogenic masses
• markedly thickened hypoechoic synovium ± nodular / villous projections with increased blood flow

CT:

• joint effusion of low-attenuation
• diffuse synovial thickening
• hyperattenuating to muscle (29%) ← hemosiderin
• small radiographically invisible extrinsic erosions
• subchondral cyst formation
• juxtaarticular soft-tissue mass ← involvement of synovium in joint recesses + bursae

MR (optimal modality):

• heterogeneous diffuse plaquelike synovial thickening ± nodularity of intermediate to low SI on T1WI + T2WI
• lobulated intraarticular masses of synovial tissue with joint effusion
• nearly PATHOGNOMONIC “blooming” artifact of low SI on gradient-echo pulse sequences ← magnetic susceptibility artifact of hemosiderin
• high-SI areas ← fat, effusion, edema, inflammation
• bone erosion / subchondral cyst (62%), septations (67%)
• edema in adjacent bone / soft tissue (23%)
• articular cartilaginous defects (31%)
• scalloping / truncation of prefemoral fat pad

NUC:

• diffusely increased radionuclide activity on blood flow and blood pool >delayed images

PET:

• hypermetabolic activity with maximum SUV values of up to 11.3

Arthrography:

• bloody (23%) / yellow (70%) / brownish (9%) effusion
• extensive synovial thickening with villous / nodular projections extending into joint

Angiography:

• prominent neovascularity with tumor blush
• mild arteriovenous shunting

Rx: synovectomy (50% recurrence rate), arthrodesis, arthroplasty, radiation

DDx:

1. Degenerative / traumatic arthritis
2. Synovial sarcoma (solitary calcified mass outside joint)
3. Sclerosing hemangioma
4. Benign xanthoma
5. Xanthogranuloma