Age / Sex : 53 / M

Chief complaint: Intermittent
left knee pain (onset: 2 years ago)

What is your impression? 

Two weeks later, you can see the final diagnosis with a brief discussion of this case. (Please submit only one answer)

Courtesy: Sang Min Lee, Bundang Medical Center, CHA University

Synovial lipoma arborescence

Discussion

Findings:

- Diffuse
hypertrophy of the synovium is seen in the joint space with diffuse contrast
enhancement.

- Fatty
villous proliferation of the synovium is also seen in the suprapatellar recess
and infrapatellar recess. And multifocal small fatty signals are seen in the
hypertrophied synovium.

- Multiple
marginal erosions are also noted on the medial and lateral femoral condyles,
and medial and lateral tibial plateau and erosions are also seen in the
intercondylar fossa of femur.

- Peripheral
fatty signal of a few erosions is also seen.

- Small amount
of subsemimembranous–subgastrocnemius bursal effusion with synovial hypertrophy
is also seen.

Differential Diagnosis:

- Synovial proliferative disease (e.g., Rheumatoid
arthritis, synovial osteochondromatosis, pigmented villonodular synovitis) combined
with synovial lipoma arborescence

Diagnosis:
Synovial lipoma arborescence with diffuse synovitis and multifocal bony
erosions

Discussion:

1. Synovial lipoma arborescence

1) Rare benign
intra-articular mass

- Characterized by
“tree-like” (arbo = tree in Latin) fatty proliferation

- Involving
connective tissue of synovial membrane

- Mostly affects
suprapatellar bursa in patients in fifth to seventh decades

- Usually
unilateral

2) Etiology is unknown

- Reactive changes
of synovium due to trauma or inflammation

- Commonly
associated with degenerative arthritis or rheumatoid arthritis

- Secondary type
is more common in adult population, while primary type is predominantly seen in
younger population

3) Clinically, patients present with
painless joint swelling and effusions

4) Laboratory
findings, including joint fluid analysis for crystals and culture, and
generally unremarkable

5) Definitive
treatment is synovectomy

2. Characteristic MR Imaging Finding

1) Frond-like
synovial proliferation with fat signal intensity on all sequences

- Best seen on
T1-WIs or fat-suppressed T2-WIs

- Typically a
diffuse synovial process (diffuse synovial lipoma), but may present as a focal
synovial-based lipomatous mass

- Associated
findings:

•       
Joint effusion: very common

•       
Degenerative changes: common

•       
Meniscal tears: common

•       
Synovial cysts : uncommon

•       
Bone erosions : uncommon

•       
Chondromatosis: uncommon to rare

•       
Patellar subluxation: rare

•       
Discoid meniscus: rare