📌Synovial Chondromatosis of the Subacromial–Subdeltoid Bursa

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Imaging Findings – Radiology-Focused Review

Subacromial–subdeltoid (SASD) osteochondromatosis is an uncommon extra-articular manifestation of synovial chondromatosis arising from the bursal synovium rather than the glenohumeral joint. Recognition of its characteristic imaging features is essential to avoid misclassification as simple bursitis or intra-articular disease.

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1. Radiography

• Multiple round or ovoid calcified nodules clustered in the subacromial–subdeltoid region
• Variable ring-and-arc or stippled calcification patterns
• Non-calcified (early) phase may be radiographically occult

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2. CT

• Superior modality for defining the number, size, and degree of mineralization of loose bodies
• Cartilaginous nodules with or without ossified centers confined to the bursal space
• Useful for demonstrating bursal distension and confirming extra-articular location

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3. MRI (Key Modality)

Bursal Findings

• Marked distension of the subacromial–subdeltoid bursa
• Multiple intra-bursal nodules (loose bodies)

Signal Characteristics

• T1-weighted images
• T2-weighted / Proton Density Fat-Suppressed images
• Gradient-echo / Susceptibility-weighted sequences

Synovium

• Synovial thickening and proliferative changes lining the bursa
• Possible enhancement after contrast administration, if performed

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4. Associated Imaging Findings

• Chronic subacromial–subdeltoid bursitis
• Possible features of subacromial impingement
• Typically no primary glenohumeral joint involvement, a key diagnostic distinction

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5. Key Differential Diagnostic Points

• Versus simple SASD bursitis: presence of multiple nodules or loose bodies
• Versus lipoma arborescens: villous fatty synovial proliferation with fat signal on T1-weighted images and signal suppression on fat-saturated sequences, rather than discrete cartilaginous nodules
• Versus intra-articular synovial chondromatosis: disease confined to the bursa without intra-articular loose bodies

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Example One-Line MRI Impression

Marked subacromial–subdeltoid bursal distension containing multiple cartilaginous to calcified loose bodies with synovial proliferation, compatible with SASD osteochondromatosis (extra-articular synovial chondromatosis).

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