A 30-year-old female presents to your office with a chief complaint of episodic right knee pain, swelling, and stiffness. She reports that over the past 6 months, she has been walking 3 miles per day as part of a new exercise program but does not report any history of acute trauma to the knee. Over the past 3 months, she has woken up to a swollen, stiff knee several times. She has had her knee aspirated twice during these episodes, and the aspirated fluid has been bloody in both cases. Other times, the process has self-resolved over about 5 days. She has never had issues with her knees before, denies fever and chills, and denies swelling or pain in any other joints. She has no family history of autoimmune or rheumatologic disease.

What is the most likely diagnosis?

1. Pigmented villonodular synovitis

2. Septic arthritis

3. Gout

4. Rheumatoid arthritis

Discussion

The correct answer is (A). PVNS is a proliferative synovial process that most commonly affects patients 30 to 50 years old. It presents clinically as recurrent atraumatic episodes of swelling, pain, and stiffness accompanied by hemarthrosis. Eighty percent of cases occur in the knee and usually it is monoarticular. The bloody aspirations, monoarticular presentation, and lack of family history of rheumatologic disease are support in favor of PVNS over rheumatoid arthritis in this patient.

What would you expect this patient’s x-rays to reveal?

1. Chondrocalcinosis with a relatively preserved joint space

2. Well-defined erosions on both sides of the joint causing joint space collapse

3. A hypoplastic lateral femoral condyle and evidence of medial joint space narrowing

4. A well-aligned knee with preservation of joint space, no osteophytes, possible effusion

Discussion

The correct answer is (D). Early in the course of PVNS, x-rays are generally normal. After a long period of any untreated synovitis, erosions on both the femoral and tibial side can be seen; this signifies advanced, diffuse disease. Since this patient has only been having symptoms for 3 months, you would expect x-rays to be normal. MRI is the more sensitive test of choice for this lesion.

The patient brings an MRI to the office for your review. There is a focal nodule within the posterior aspect of the joint with low signal intensity on T1- and T2-weighted images. What does this low signal intensity represent?

1. Calcium urate deposition

2. Areas of fat within the lesion

3. Hemosiderin deposition

4. Blood vessels within the synovial fluid

Discussion

The correct answer is (C). PVNS is characterized on MRI as either focal or diffuse areas of low-signal on both T1- and T2-weighted images, due to hemosiderin deposits. There may also be fat present within the area, which is bright on T1 and T2.

Objectives: Did you learn...?

Clinical and radiographic features of PVNS?