Mediastinal Masses
| Finding | Recommendation |
|---|---|
| Anterior mediastinal mass <3 cm, smooth, homogeneous (likely thymic cyst or small thymoma) | CT chest with contrast in 3 months, then annually × 2 if stable; surgical referral if >3 cm or heterogeneous |
| Anterior mediastinal mass ≥3 cm or heterogeneous/irregular | CT with contrast; surgical or oncology referral |
| Middle mediastinal mass (lymph node enlargement, bronchogenic cyst) | CT with contrast for characterization; if isolated bronchogenic cyst <3 cm and typical → no follow-up; if atypical or >3 cm → surgical referral |
| Posterior mediastinal mass (neurogenic, vertebral origin) | MRI spine/chest for characterization; surgical referral for most neurogenic tumors |
| Thymic cyst (<3 cm, homogeneous, non-enhancing) | No follow-up |
Mediastinal Lymph Nodes
| Short Axis Size | Recommendation |
|---|---|
| <10 mm | No follow-up (non-enlarged) |
| 10–19 mm, no known malignancy | CT in 3 months; if stable → no further follow-up |
| ≥20 mm, OR enlarging, OR necrotic/calcified | PET-CT or tissue sampling; oncology/pulmonology referral |
| Any size, known malignancy | PET-CT or biopsy as clinically indicated |
Pericardial Findings
| Finding | Recommendation |
|---|---|
| Pericardial cyst (smooth, water-density, no enhancement, ≤3 cm) | No follow-up |
| Pericardial cyst >3 cm or symptomatic | Echocardiography; cardiology referral |
| Pericardial effusion (small, asymptomatic) | Echocardiography for characterization and hemodynamic assessment |
| Pericardial thickening or mass | Cardiac MRI; cardiology referral |
Incidental Lung Parenchymal Findings
| Finding | Recommendation |
|---|---|
| Pulmonary nodule (solid, subsolid, part-solid) | Fleischner Society 2017 guidelines; for patients <35 yr or known malignancy, use clinical judgment |
| Pulmonary cyst (<2 cm, thin wall, no nodule) | No follow-up if <2 cm and no high-risk features (smoking, family history of LAM or BHD); if >2 cm or multiple → CT in 12 months |
| Pure ground-glass opacity (GGO) <6 mm, solitary | No follow-up |
| Pure GGO ≥6 mm | CT at 2 and 4 years (Fleischner subsolid nodule guidelines) |
| Reticular / interstitial opacities (UIP, NSIP pattern) | Pulmonology referral for evaluation of ILD; HRCT if not already performed |
| Incidental bronchiectasis (asymptomatic) | Pulmonology referral; evaluate for underlying cause (NTM, CF, immunodeficiency) |
Pulmonary nodule management follows dedicated Fleischner Society 2017 guidelines stratified by nodule type (solid vs. subsolid), size, and patient risk factors (smoking history). These ACR chest incidental findings guidelines apply to non-nodule parenchymal findings and mediastinal/pleural structures.
Why This Matters
Anterior mediastinal masses are the most clinically impactful incidental finding in this category — the differential includes thymoma, lymphoma, germ cell tumor, and thyroid/parathyroid mass. Size and homogeneity are the primary triage criteria. The key rule: any anterior mediastinal mass ≥3 cm or with heterogeneous/irregular morphology requires tissue evaluation, not just follow-up CT.
References
Munden RF, Carter BW, Chiles C, et al. Managing Incidental Findings on Thoracic CT: Mediastinal and Cardiovascular Findings. A White Paper of the ACR Incidental Findings Committee. J Am Coll Radiol. 2018;15(8):1087–1096.
Munden RF, et al. ACR Incidental Lung Findings Update. J Am Coll Radiol. 2021.