A 51-year-old man presented with a modest intermittent pain in his left shoulder for 4 months. On examination, he had full active range of motion in his shoulder.
The plain radiograph of the shoulder showed no evidence of fracture, dislocation or mass lesion. There were glenohumeral and acromioclavicular degenerative changes.
MRI of the shoulder was performed for further evaluation. There was a distension of subdeltoid-subacromial bursa and subscapular recess. Within the distended bursa, there were multiple villous projections having isointensity with subcutaneous fat on all pulse sequences and were visualized as dark lesions with fat suppression, consistent with lipoma arborescens (LA) (Fig. 1-3). MRI revealed a bursal-sided supraspinatus partial tear associated with small degenerative cysts near the insertion site of supraspinatus tendon onto the greater tuberosity (Fig. 4). Subscapular, supraspinatus, and infraspinatus tendinosis and degenerative changes of glenohumeral and acromioclavicular joints were also noted.
LA is a rare benign intra-articular lesion with an unknown aetiology. It is characterized by lipomatous proliferation of the synovium in which the subsynovial tissue is replaced by mature adipocytes. It most commonly involves the knee joint, but other locations, including the shoulder, elbow, wrist, and hip, have been reported [1]. Multiple affected joints have also been observed [2]. Subdeltoid bursa is a rare location for LA, and only a few cases have been reported in the literature [1, 3].
Clinically it usually presents as joint swelling, pain, limitation in range of motion, and recurrent effusions [4]. LA was frequently a histological diagnosis, but currently MRI alone is often sufficient to make the diagnosis. The MRI appearance of LA corresponds to the fatty proliferation of the synovial lesion, which enables a specific diagnosis to be made. The subsynovial components of the lesion show high signal intensity similar to subcutaneous fat on T1 and T2-weighted images and are of low signal intensity on the fat-suppressed and STIR sequences. The lesion does not enhance following intravenous administration of contrast medium. The differential diagnosis of LA should include other diffuse pathology of the synovium such as villonodular pigmented synovitis, synovial chondromatosis, synovial haemangioma and rheumatoid arthritis. All these lesions might show fatty areas within the lesion but the MRI appearance of fatty synovial proliferation without other signal intensities within the lesion allows a specific preoperative diagnosis by MRI for LA [5].
Kim MH et al. [1] have pointed out that most published cases of the LA in the subdeltoid bursa were associated with rotator cuff tears and that LA in subdeltoid space might create a rotator cuff tear–prone environment. They recommend paying extra attention to the radiologic and arthroscopic characteristics of the LA in the evaluation and treatment of rotator cuff tears.
Treatment of LA is open or arthroscopic synovectomy. Recurrence of the lesions following synovectomy is uncommon [4].
Lipoma arborescens of the subdeltoid bursa, supraspinatus tendon tear
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Based on the provided shoulder MRI images, there is visible localized thickening of soft tissue under the left acromion (subacromial bursa). The lesion exhibits fatty signal characteristics:
Overall, the imaging suggests a fatty proliferative lesion in the subacromial bursa with associated synovial thickening, but no marked bony or tendinous abnormal destruction.
Combining the patient's symptoms (intermittent shoulder pain for 4 months, relatively preserved range of motion) with the MRI findings (fatty components as the primary feature in the synovium or bursa), the following differential diagnoses should be considered:
Considering the patient’s age, clinical presentation (relatively mild pain with no significant functional limitation), and imaging features (predominantly fatty signal proliferation within the subacromial bursa), the most likely diagnosis is
Lipoma Arborescens of the subacromial bursa.
In general, MRI has a high specificity for this condition. If there remains any doubt, further histopathological investigation (biopsy or intraoperative frozen section) may be performed for definitive confirmation.
Given that the shoulder’s range of motion is relatively preserved but potential rotator cuff strain exists, rehabilitation should follow a gradual progression, applying the FITT-VP principle (Frequency, Intensity, Time, Type, Volume/Progression, and Individualization):
In cases where the patient has osteoporosis, compromised cardiopulmonary function, or other comorbidities, training intensity and methods should be adjusted under professional supervision to ensure safety.
This report is based solely on the current clinical and imaging data for reference purposes and cannot replace an in-person consultation or individualized diagnosis by a qualified physician. In case of further questions or changes in condition, the patient should seek prompt consultation with a specialist and undergo any necessary examinations or treatments.
Lipoma arborescens of the subdeltoid bursa, supraspinatus tendon tear
