From the Guidelines
A chest CT without contrast is the recommended initial imaging study for evaluating a pulmonary nodule, as IV contrast is not required to identify or initially characterize pulmonary nodules in clinical practice. According to the American College of Radiology Appropriateness Criteria, CT is widely recognized as the modality of choice to evaluate pulmonary nodules, and guidelines recommend routine use of contiguous thin sections (1.5 mm) and reconstructed multiplanar images to ensure adequate characterization, particularly for nodules with a ground-glass attenuation component 1. The use of IV contrast is not supported by high-quality evidence for the initial evaluation of incidentally detected indeterminate pulmonary nodules, and it may not provide additional benefits in differentiating between benign and malignant nodules 1.
Some key points to consider when evaluating a pulmonary nodule with CT include:
- Nodule size, morphology, location, multiplicity, and the presence of emphysema or fibrosis can increase the risk of malignancy 1
- Certain nodule characteristics, such as diffuse, central, laminated, or popcorn calcifications patterns, are predictors of benign etiology 1
- Low-dose technique is recommended for CTs performed to follow lung nodules, and standardization of acquisition and reconstruction CT protocols can result in more accurate comparisons 1
- The mean attenuation value of indeterminate benign and malignant nodules on unenhanced CT is not significantly different, and therefore not useful in their differentiation 1
In terms of the procedure, patients should be informed about any allergies, especially to iodine or contrast materials, and about kidney problems, as contrast can affect kidney function, although contrast is not typically used for this indication. During the procedure, patients will lie on a table that moves through a donut-shaped scanner, and they'll need to hold their breath briefly during image acquisition for optimal clarity.
From the Research
Indications for Chest Computed Tomography (CT) Scan with Contrast for a Pulmonary Nodule
The following are indications for a chest CT scan with contrast for a pulmonary nodule:
- To characterize the likelihood that a nodule is benign or malignant based on visual or quantitative features on CT 2
- To evaluate the size, margins, calcifications, and fatty component of the nodule, as well as internal features such as cavitations, pseudocavitations, air bronchogram, and halo sign 3
- To assess the growth rate and contrast enhancement of the nodule, which can aid in characterization and management 3, 4
- To identify the enhancing rim sign, a new radiological sign that indicates a solitary pulmonary nodule is benign rather than malignant 5
- To perform dynamic contrast-enhanced CT and MRI techniques, which can improve diagnostic performance for pulmonary nodule assessment 6
Key Features to Evaluate
When evaluating a pulmonary nodule using a chest CT scan with contrast, the following features are important to consider:
- Size and change in size over time
- Attenuation and contrast enhancement
- Edge characteristics and morphology
- Presence and pattern of calcification
- Internal features such as cavitations and air bronchogram
- The enhancing rim sign, which can indicate a benign nodule 5
Clinical Applications
Chest CT scans with contrast can be used in a variety of clinical applications, including:
- Screening for lung cancer in high-risk populations 2
- Evaluating solitary pulmonary nodules detected on chest radiography or low-dose CT scans 3, 4
- Monitoring the growth and characteristics of known pulmonary nodules over time 4
- Guiding biopsy or surgical procedures for nodules with suspicious features 4, 5