Imaging for a Golf Ball-Sized Retrosternal Mass
Order a CT chest with IV contrast as the initial imaging study for a golf ball-sized lump behind the sternum. 1
Why CT with Contrast is the Optimal Choice
A golf ball-sized mass (approximately 4-5 cm) behind the sternum represents a mediastinal mass requiring cross-sectional imaging for definitive characterization. The ACR Appropriateness Criteria explicitly state that CT chest with IV contrast is usually appropriate for initial imaging of clinically suspected mediastinal masses, with this modality rated as equivalent to other CT protocols and MRI options. 1
Key Advantages of Contrast-Enhanced CT
Superior tissue characterization: Contrast administration distinguishes cystic from solid lesions, maps lesion borders precisely, and identifies enhancing cellular components versus necrotic areas. 1
Vascular assessment: IV contrast is essential for evaluating the mass's relationship to major blood vessels (aorta, superior vena cava, pulmonary arteries) and detecting potential vascular invasion, which directly impacts surgical resectability and prognosis. 1
Detection of primary sites: For masses that may represent metastatic disease or lymphoma, contrast helps identify potentially small primary sites in adjacent structures. 1
Compartment localization: Cross-sectional imaging definitively localizes the lesion to a specific mediastinal compartment (anterior, middle, or posterior), which significantly narrows the differential diagnosis. 1
What CT Will Reveal
The contrast-enhanced CT will characterize:
Tissue composition: Calcium, macroscopic fat, water-attenuation fluid, or soft tissue density—allowing noninvasive diagnosis of entities like mature teratomas. 1
Invasion patterns: Whether the mass transgresses tissue planes, invades the chest wall, or involves the diaphragm—critical for surgical planning. 1
Associated findings: Lymphadenopathy, pleural involvement, or lung parenchymal abnormalities that may suggest the underlying diagnosis. 1
When to Avoid Contrast
Contraindications to IV contrast include: 1
- Documented contrast allergy
- Severe renal insufficiency (risk of nephrogenic systemic fibrosis with gadolinium-based agents)
- Prior diagnosis that definitively excludes the need for contrast
If contrast is contraindicated, CT chest without IV contrast remains usually appropriate as an alternative, though it provides less tissue characterization. 1
Why Not Start with Chest X-Ray?
While chest radiography can localize a mass to the mediastinum and show associated findings, it offers limited tissue characterization (only occasionally demonstrating calcium) and cannot adequately assess the mass's relationship to vital structures. 1 Given the substantial size of this mass (golf ball = ~4-5 cm), proceeding directly to CT is justified and avoids delay in diagnosis.
Why Not MRI as First-Line?
MRI chest (with or without contrast) is rated as equivalent to CT by ACR guidelines for initial mediastinal mass imaging. 1 However, CT is more widely available, faster to perform, better tolerated by patients, and provides excellent diagnostic information for most mediastinal masses. 1
Reserve MRI for:
- Indeterminate findings on CT requiring further characterization 1
- Neurogenic tumors where neural/spinal involvement assessment is critical 1
- Distinguishing thymic hyperplasia from thymic tumors 1
- Evaluating tissue plane invasion with superior soft tissue contrast 1
Next Steps After CT
If the CT findings remain indeterminate:
- MRI chest without and with IV contrast is usually appropriate for further characterization. 1
- Image-guided transthoracic needle biopsy may be indicated when imaging cannot establish a definitive diagnosis. 1
For mediastinal lymphoma specifically, FDG-PET/CT becomes the standard for staging and treatment response assessment, but only after tissue diagnosis is established. 1
Critical Pitfall to Avoid
Never order "CT with and without contrast" for this indication—it doubles the radiation dose without added diagnostic benefit for mediastinal mass characterization. 1 A single post-contrast study provides all necessary information.