What does the presence of calcification and fat in a pulmonary nodule typically indicate?

The presence of calcification and fat in a pulmonary nodule is typically indicative of a benign lesion. This is because benign nodules often exhibit specific patterns that differentiate them from malignant ones. For example, certain types of benign lesions, such as hamartomas, are known to contain fat and can show calcification. The calcification in benign nodules often demonstrates a specific pattern, such as "popcorn" calcification, which is not usually seen in malignant lesions.

In contrast, malignant nodules typically lack these characteristics. They may present as solid masses without fat or with irregular calcification patterns. Thus, the presence of calcification and fat helps clinicians assess the likelihood of a nodule being benign, leading to the conclusion that it is less likely to be associated with malignancy or infectious processes.