Morphologic imaging findings suggestive of a benign solitary pulmonary nodule
Small size and smooth, well-defined margins suggest a benign SPN, although 15% and 40% of malignant nodules are less than 1 cm and 2 cm in diameter, respectively, and 20% of malignant nodules have well-defined margins. Intranodular fat is a reliable indicator of a hamartoma, which is a benign lesion ( Figure 17-1 ). Central, diffusely solid, laminated, and “popcorn-like” patterns of nodule calcification are indicative of benignancy, with the first three typically seen in calcified granulomas and the last in a pulmonary hamartoma ( Figure 17-2 ). Indeterminate patterns of calcification exist, and 15% of lung cancers may contain amorphous, stippled, or punctate and eccentric patterns of calcification. Avidly enhancing serpentine or tubular feeding arteries and a dilated draining vein associated with an enhancing nodular lung opacity are pathognomonic of an arteriovenous malformation ( Figure 17-3 ). Small satellite nodules adjacent to a smooth dominant nodule strongly suggest a granulomatous infection. Ground glass opacity surrounding a nodule (“CT halo” sign) may be seen with angioinvasive opportunistic infection, such as by aspergillosis, particularly in the setting of neutropenia ( Figure 17-4 ). Similarly, gas in a crescentic shape along the margin of a nodule (the “air crescent” sign) can be seen in the setting of an angioinvasive fungal infection. A three-dimensional ratio of the nodule’s largest axial diameter to the largest craniocaudal diameter greater than 1.78 : 1 (i.e., a flattened configuration) is highly suggestive of benignancy. A peripheral rim of enhancement or the “enhancing rim” sign of a nodule may also suggest a benign SPN.
