Is a computed tomography (CT) scan appropriate for diagnosing a shoulder mass?

CT Scan for Shoulder Mass

CT is not typically appropriate as the initial imaging modality for a shoulder mass, but it may serve as a useful adjunct after radiography when assessing mineralization patterns or when MRI is contraindicated. 1

Initial Imaging Approach

Radiographs should be obtained first for any shoulder mass, as they remain the best-suited modality for initial assessment and can identify mineralization, osseous involvement, and mass effect on adjacent structures. 1

When CT May Be Appropriate

CT has specific but limited roles in shoulder mass evaluation:

As a Complementary Study After Radiography

• CT is particularly useful for characterizing mineralization patterns when radiographs show calcification but the pattern is unclear, especially in anatomically complex regions. 1
• CT optimally distinguishes ossification from calcification and can identify the zonal pattern of mineralization essential for diagnosing early myositis ossificans—a pattern that may remain nonspecific on radiography alone. 1
• CT's multiplanar capability excels at depicting the interface between a soft-tissue mass and adjacent bone, allowing assessment of cortical remodeling versus invasion. 1

When MRI Is Not Feasible

• CT may be the study of choice when MRI is contraindicated (pacemakers, certain implants) or not feasible (large body habitus, severe claustrophobia). 1
• In a multi-institutional study of 133 patients with primary soft-tissue malignancies, CT showed no statistically significant difference from MRI in determining tumor involvement of muscle, bone, joint, or neurovascular structures, though it lacks MRI's soft-tissue specificity. 1

Why CT Is Generally Not First-Line

CT has virtually no usefulness in diagnosing common soft-tissue pathology such as rotator cuff tears, muscle tears, or other non-mineralized soft-tissue abnormalities that might present as a "shoulder mass." 1

MRI is the technique of choice for detecting and characterizing soft-tissue masses due to superior soft-tissue contrast, multiple-image plane capabilities, and ability to assess neurovascular involvement without IV contrast. 1

Recommended Imaging Algorithm

1. Start with radiographs (AP, Grashey, and axillary or scapular Y views) to assess for mineralization, osseous involvement, and mass effect. 1, 2

2. Proceed to MRI without contrast as the next study for most soft-tissue masses, as it provides optimal soft-tissue characterization and can correctly diagnose approximately 50% of cases when combined with clinical information. 1

3. Consider CT only if:

   • Radiographs show mineralization requiring further characterization 1
   • MRI is contraindicated or not feasible 1
   • Assessing bone involvement or cortical invasion after initial imaging 1

4. Ultrasound may be considered for superficial masses to differentiate solid from cystic lesions, but diagnostic accuracy drops significantly for deep masses. 1

Critical Pitfalls

• Do not order CT as initial imaging unless there is a specific contraindication to radiography or the clinical scenario strongly suggests a mineralized lesion requiring immediate characterization. 1
• Distinguishing subtle calcification from enhancement may be difficult without precontrast images if IV contrast is administered. 1
• CT provides adequate staging data but lacks the specificity of MRI for determining the nature of the mass (benign versus malignant). 1