Localize / Describe

Report these CT features

• Mediastinal compartment: prevascular/anterior, visceral/middle, or paravertebral/posterior.
• Texture: cystic versus solid, fat, calcification, heterogeneity, or fluid attenuation.
• Edge contour: well-circumscribed versus infiltrative or invasive.
• Relationship to adjacent structures: airway, vessels, pericardium, pleura, chest wall, or spine.
• Clinical context: myasthenia gravis, prior chemo/radiation, systemic symptoms, malignancy history.

Compartment differential

• Prevascular/anterior: thymic cyst, thymic epithelial tumor, thymic hyperplasia, germ cell tumor, lymphoma, ectopic thyroid/parathyroid.
• Visceral/middle: lymphadenopathy, bronchogenic cyst, foregut duplication cyst, esophageal lesion, vascular lesion.
• Paravertebral/posterior: neurogenic tumor, meningocele, extramedullary hematopoiesis, paraspinal abscess, spine-related lesion.

Cystic / Benign

Benign cyst features

• Well-circumscribed margins.
• Simple fluid attenuation or homogeneous fluid signal on MRI.
• No enhancing solid component.
• No invasive features or suspicious lymphadenopathy.
• Typical thymic, pericardial, bronchogenic, or duplication cyst appearance.

When MRI helps

• CT density is higher than simple fluid and cyst versus solid lesion is uncertain.
• Internal complexity, proteinaceous/hemorrhagic content, or thymic cyst is suspected.
• Posterior compartment mass is present; MRI is generally preferred for follow-up/characterization.
• Anterior lesion is indeterminate and thymic cyst versus thymic epithelial lesion is the key question.

Escalation

Worrisome features

• Infiltrative or irregular margins.
• Enhancing solid component in a cystic lesion.
• Rapid growth or large invasive mass.
• Invasion of vessels, pericardium, pleura, chest wall, airway, or spine.
• Associated bulky lymphadenopathy, pleural nodules, or pleural effusion.
• Fat plus calcification in an anterior mass, suggesting germ cell tumor/teratoma.
• Symptoms or myasthenia gravis, suggesting clinically significant thymic disease.

Next steps

• Anterior or middle compartment cystic lesion: no further work-up if confidently benign; MRI if CT is indeterminate.
• Anterior or middle compartment noncystic lesion: MRI or PET/CT depending on suspected etiology and malignancy potential.
• Posterior compartment lesion: MRI for characterization and follow-up.
• Suspicious mediastinal mass: urgent thoracic surgery/oncology evaluation and tissue diagnosis as clinically appropriate.

Sources

• ACR incidental thoracic CT guidance for mediastinal findings.
• ITMIG CT-based mediastinal compartment system.
• Anterior mediastinal lesion literature supports MRI characterization and patient-tailored follow-up for small nonaggressive lesions.