Lipoma arborescens of the shoulder

Clinical History

Our patient, a 77-year-old woman complained of pain of the right shoulder for 6 months. At physical examination, she had slightly diminished external rotation motion and a positive Jobe´s test.

Imaging Findings

Plain radiograph of the shoulder:
- glenohumeral and acromioclavicular joint degenerative changes;
- signs of enthesopathy: tuberosity irregularities, a cyst and sclerosis;
- linear calcification near the supraspinatus insertion;
- absence of calcified intra-articular loose bodies;

MRI:
- Distension of the subacromial/subdeltoid bursa, subscapularis recess, subcoracoid bursa and biceps sheath by effusion and multiple frond-like synovial projections. These projections had signal intensity similar to the subcutaneous fat in all sequences: high signal intensity in T1, PD and T2 sequences; low signal intensity in T2* and T2FS sequences. Absence of intra-articular loose bodies or magnetic susceptibility artefact.
- Other findings: articular-sided supraspinatus partial tear (3mm thick high T2 signal intensity involving the insertional fibres of the supraspinatus); supraspinatus and subscapularis tendinosis (diffuse intermediate intra-substance signal intensity on T1- and T2-weighted images); greater tuberosity cysts; degenerative glenohumeral and acromiclavicular changes; os acromiale (Type A).

Discussion

BACKGROUND
Lipoma arborescens is a rare benign intra-articular lesion. It is characterized by diffuse replacement of the subsynovial tissue into mature fat cells, producing villous transformation of the synovium [1, 2, 3]. The macroscopic appearance of the villi resemble a tree, thus the name "arborescens", from the Latin word "arbor" for tree [4].
Its aetiology is not completely understood, but it has been considered a nonspecific reactive change of the synovial membrane to joint trauma, chronic synovitis or arthritis [3, 4].

CLINICAL PERSPECTIVE
Lipoma arborescens is usually monoarticular and most frequently affects the knee, especially the suprapatellar pouch. However, it can also occur in the wrist, elbow, hip and shoulder.
Only six cases have previously been described in the shoulder [1]. In this location, lipoma arborescens has been associated with rotator cuff tears and affects frequently the subacromial/subdeltoid bursa [1, 2].
This condition usually occurs after the fifth decade of life. Patients present with joint swelling, pain and motion limitation [2]. Pain is usually associated to the underlying articular disease, but it can also result from compression and impingement of villous projections during motion [4]. Recurrent effusion is a common finding.

IMAGING PERSPECTIVE
Plain films:
- soft tissue swelling/joint effusion;
- signs of osteoarthritis or entesopathy.
CT:
- intra-articular fatty infiltration;
- signs of osteoarthritis or entesopathy;
- absence of intra-articular calcified loose bodies.
MRI:
- joint effusion with villous and frond-like synovial projections that have signal intensity similar to subcutaneous fat on all sequences: high signal intensity on T1 and T2-weighted images and low signal intensity on fat-suppressed images;
- absence of magnetic susceptibility artefact in the synovial projections [3];
- synovial projections do not enhance after gadolinium injection [2];
- rotator cuff tears are commonly associated with lipoma arborescens of the shoulder [1, 2];
- in this case, the os acromiale might also contribute to the degenerative/inflammatory changes.

OUTCOME
Treatment of lipoma arborescens is synovectomy. Recurrence of the lesions following synovectomy can occur but is uncommon [2]. However, in many cases, because of the age of the patient and the benignity of the lesion, only conservative treatment is performed [2].

MRI TEACHING POINTS
- Solid synovial frond-like synovial projections with: fat signal intensity on all pulse sequences and suppression of signal with fat-selective pre saturation; absence of magnetic susceptibility artefact.
- Joint effusion.

Differential Diagnosis List

Final Diagnosis

Lipoma Arborescens of the Shoulder

URL:	https://www.eurorad.org/case/11370
DOI:	10.1594/EURORAD/CASE.11370
ISSN:	1563-4086