In current practice, solitary pulmonary nodules are defined as those having a diameter of 3 cm or less. Benign nodules are almost always healed granulomas secondary to tuberculosis or fungal infection. In rare instances, a solitary nodule may be a rheumatoid granuloma, healed infarct, paraffinoma, pulmonary arteriovenous aneurysm, or manifestation of Wegener's granulomatosis. In such circumstances, the combination of radiologic and clinical findings may provide important clues to the probable diagnosis. In malignant lesions, the doubling time is between 25 and 450 days in most cases, with a median of 120 days.
Stability is determined by retrospective analysis of one or more chest films.
A doubling time of less than 20 days usually signifies that the nodule represents a nonmalignant, acute inflammatory process. However, even in such cases, prospective monitoring for growth with semiannual chest films for a year or two is prudent. A malignant lesion is more likely when the calcification pattern is speckled or eccentric. Multiple calcific specks may appear in carcinoid tumors, and an eccentrically placed single deposit may result from engulfment of a healed calcified granuloma by an adjacent malignant lesion. Solitary pulmonary nodules are usually visible on standard posteroanterior and lateral chest films.