Is a non-contrast computed tomography (CT) scan sufficient to recheck mild mediastinal lymphadenopathy, likely a reactive finding on a CT scan of the abdomen?

Non-Contrast CT is Appropriate for Rechecking Mild Mediastinal Lymphadenopathy

A non-contrast CT scan is appropriate and sufficient for rechecking mild mediastinal lymphadenopathy that was likely a reactive finding on a previous CT abdomen. 1

Rationale for Non-Contrast CT

• CT scanning is the most widely available and commonly used non-invasive modality for evaluation of the mediastinum, providing superior anatomic detail compared to chest radiography 1
• For follow-up of known mild mediastinal lymphadenopathy that was previously characterized as likely reactive, non-contrast CT is adequate as the primary goal is to assess for changes in size rather than to newly characterize the lesions 1
• While contrast-enhanced CT can improve visualization of the mediastinum, it is "unlikely that clinically significant mediastinal lymphadenopathy would be overlooked on a noncontrast scan" 1
• Non-contrast CT with thin sections (≤5 mm) has been shown to be an appropriate scanning technique for evaluation of mediastinal lymphadenopathy 2

Considerations for Lymph Node Assessment

• The widely accepted definition of normal-sized mediastinal lymph nodes is a short-axis diameter of <1 cm on a transverse CT scan image 1
• CT scanning has limited ability to either rule in or exclude mediastinal metastasis, with reported median sensitivity and specificity of 55% and 81%, respectively 1
• When assessing lymph nodes, CT can both overstage and understage mediastinal nodes, as there is no node size that can reliably determine malignancy 1
• For reactive lymphadenopathy, the primary goal is to monitor for changes in size over time, which can be adequately accomplished with non-contrast CT 1, 3

When Contrast May Be Beneficial

• Contrast administration would be more important in the following scenarios:
  • Initial characterization of unknown mediastinal masses 1
  • Suspected invasion of adjacent structures 1
  • Need to distinguish vascular structures from lymph nodes in complex anatomical areas 1
  • Evaluation for enhancing, cellular components of lesions 1
• For simple follow-up of already characterized mild reactive lymphadenopathy, these benefits are less critical 1

Alternative Imaging Considerations

• If there is concern for malignancy rather than reactive lymphadenopathy, FDG-PET/CT would be more appropriate for metabolic assessment 1
• MRI could provide superior tissue characterization if there is uncertainty about the nature of the mediastinal finding, but is not necessary for routine follow-up of mild reactive lymphadenopathy 1

Common Pitfalls to Avoid

• Do not rely solely on size criteria for determining the nature of lymphadenopathy, as both small malignant nodes and large benign nodes can occur 1
• Avoid unnecessary contrast administration when following known benign or reactive findings, as it adds risk without significant diagnostic benefit 1
• Remember that 5-15% of patients with clinical stage IA tumors may have positive lymph node involvement despite normal-appearing nodes on CT 1

Non-contrast CT provides adequate visualization for follow-up assessment of mild mediastinal lymphadenopathy while avoiding the risks associated with intravenous contrast administration.