From the Guidelines
For evaluating pulmonary nodules, a non-contrast CT chest is typically recommended as the first-line imaging study. This recommendation is based on the most recent evidence from the Journal of the American College of Radiology 1, which suggests that contrast is generally not necessary for the detection and characterization of lung nodules. The natural contrast between air-filled lungs and solid nodules provides excellent visualization, allowing for accurate measurement of nodule size, density assessment, and evaluation of calcification patterns. These features are important for risk stratification and guiding further management.
Some key points to consider when evaluating pulmonary nodules with CT include:
- Nodule size and morphology: larger nodules and those with irregular morphology are more concerning for malignancy
- Nodule location and multiplicity: nodules in certain locations, such as the upper lobes, and multiple nodules may increase the suspicion for malignancy
- Presence of emphysema or fibrosis: these conditions can increase the risk of malignancy
- Patient risk factors: such as smoking history, family history of lung cancer, and exposure to carcinogens
The use of contrast-enhanced CT may be appropriate in specific situations, such as:
- Concern for mediastinal invasion or hilar involvement
- Suspicion for malignancy with potential vascular invasion
- Assessment of mediastinal lymphadenopathy
However, the routine use of contrast-enhanced CT for evaluating pulmonary nodules is not supported by the current evidence 1. The radiation dose from a non-contrast chest CT is also lower than a contrast-enhanced study, which is an important consideration, especially if serial imaging will be needed for nodule follow-up according to established guidelines based on nodule size, appearance, and patient risk factors.
In terms of specific guidelines, the Fleischner Society and ACCP guidelines recommend follow-up CT at different time intervals, PET/CT, biopsy, or standard staging evaluation depending on nodule size, attenuation, risk factors for lung cancer, surgical risk, and clinical probability of cancer 1. These guidelines emphasize the importance of discussing risks and benefits of management strategies with patients and incorporating their preferences.
Overall, the use of non-contrast CT chest as the first-line imaging study for evaluating pulmonary nodules is supported by the most recent evidence and guidelines, with contrast-enhanced CT reserved for specific situations where it is deemed necessary.
From the Research
Indications for CT Scan of the Chest
The indication for a computed tomography (CT) scan of the chest with or without contrast for detecting pulmonary nodules is to evaluate the presence and characteristics of nodules in the lungs.
- Pulmonary nodules are identified in approximately 1.6 million patients per year in the US and are detected on approximately 30% of computed tomographic (CT) images of the chest 2.
- The probability of malignancy is less than 1% for all nodules smaller than 6 mm and 1% to 2% for nodules 6 mm to 8 mm 2.
- A chest CT is often performed as a combination of a nonenhanced and an enhanced scan to assess solitary pulmonary nodules (SPNs) 3.
- Enhanced CT scans can provide information on the degree and pattern of enhancement, which can help distinguish malignant from benign nodules 3, 4.
Characteristics of Pulmonary Nodules
- Pulmonary nodules are categorized as small solid (<8 mm), larger solid (≥8 mm), and subsolid 2.
- Subsolid nodules are divided into ground-glass nodules (no solid component) and part-solid (both ground-glass and solid components) 2.
- The treatment of an individual with a pulmonary nodule should be guided by the probability that the nodule is malignant, safety of testing, the likelihood that additional testing will be informative, and patient preferences 2.
Diagnostic Accuracy of CT and MRI
- CT is the current gold standard for the detection of pulmonary nodules, but it has a high radiation burden 5.
- MRI has been explored as an alternative to CT, but studies have shown that CT is superior to MRI in sensitivity, specificity, and diagnostic accuracy for detecting pulmonary nodules 5.
- Enhanced CT with iodinated contrast material can help differentiate pulmonary carcinomas from benign pulmonary nodules 4.