CASE 130

By: Dr. Nizar Al-Nakshabandi MD, FRCPC

HISTORY: 27-year-old with swelling of the left knee.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

The lateral radiograph of the left knee [A] demonstrates a large knee joint effusion with some associated fatty lucencies in the soft tissue of the suprapatellar recess in addition some bony erosions in the distal femur.

Ultrasound of the suprapatellar recess [B] demonstrates a large knee joint effusion with echogenic frond-like projections into this effusion.

Axial T1 [C] demonstrate high signal soft tissue masses in the suprapatellar recess.

Coronal fat-sat T2-weighted images [D] demonstrate that these fronds are saturated on fat suppressed sequences.

Sagittal T1 fat-sat with gadolinium enhancement [E] demonstrate avid enhancement of the periphery of these fronds which are also suppressed on the fat-saturated sequence.  Note the enhancement of the synovium.

DIFFERENTIAL DIAGNOSIS:

·        Lipoma arborescens.

·        Synovial osteochondromatosis.

·        Pigmented villonodular synovitis.

·        Synovial hemangioma.

DIAGNOSIS:

Lipoma arborescens.

PEARLS AND DISCUSSION:

Frond like appearance resembles a tree leaf Therefore the term arborescens means tree forming in the Latin language.

This disease usually affects the patients in the 5th to 7th decade, but has been reported in younger populations, such as our patient.

The synovium is replaced by hypertrophied villi from the deposition of mature lipocytes within them. A joint effusion is a common association. Long-term erosive changes in the bone thus from degeneration and synovial cysts can occur.

Imaging features have been discussed above.

Treatment is usually by synovectomy and recurrence is uncommon.

FURTHER READING:

1.      See comment in PubMed Commons belowAl-Nakshabandi NA, Ryan AG, Choudur H, Torreggiani W, Nicoloau S, Munk PL, Al-Ismail K. Pigmented villonodular synovitis. Clin Radiol. 2004 May;59(5):414-20.

2.      Senocak E, Gurel K, Gurel S et-al. Lipoma arborescens of the suprapatellar bursa and extensor digitorum longus tendon sheath: report of 2 cases. J Ultrasound Med. 2007;26 (10): 1427-33. 

3.      Manaster BJ, Disler DG, May DA et-al. Musculoskeletal imaging, the requisites. Mosby Inc. (2002) ISBN:0323011896