Age / Sex : 42 / F

Chief complaint: Left hip pain, known ankylosing spondylitis

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: Seunghun Lee, Hanyang University Hospital

Lipoma arborescens

Discussion

Findings: - Plain radiograph of the pelvis shows cortical irregularity in the both sacroiliac joints and osteoarthritis in the left hip joint

MRI- The T1-weighted MR images show frondlike regions of high signal in the joint space representing lipomatous proliferation of the synovium with bone erosion. Fat-suppressed T2-weighted image shows joint effusion with villous proliferation of low signal in the left hip joint.

Differential Diagnosis: none

Diagnosis: Lipoma arborescens

Discussion:

•       An uncommon intra-articular lesion consisting of villous lipomatous proliferation of the synovium

•       Usually in the knee joint, in the suprapatellar pouch

•       Also, in glenohumeral joint, hip joint and elbow joint

•       Between 9 and 68 years, W=M

•       Sx : chronic painful or painless joint swelling of several years duration

-       cyclical with intermittent exacerbation

-       due to trapping of the lipoma villi in the joint space

•       Pathology

-       A benign lesion arising from the synovium - villous proliferation of fat cells

-       Forming frond-like masses

-       Resembling a tree, thus the name 'arborescens', (the Latin word 'arbor' for tree)

-       The exact cause : not known.

-       By one explanation; associated with trauma, osteoarthritis and rheumatoid arthritis(secondary) but without any underlying cause(primary)

•       Imaging findings

-       Plain Radiography : increased lucency in the joint(fat density)

-       NECT : decreased density synovial masses

-       MRI : the gold standard investigation - pathognomic for LA

1) A synovial mass with a frond like architecture

2) Fat signal intensity on all pulse sequences

3) Suppression of signal with fat-selective presaturation

4) Associated joint effusion

5) Absence of magnetic susceptibility effects from hemosiderin