 Figure 7a: Transverse 1-mm CT sections obtained 10 months apart show a highly suspicious pattern of progressive thickening in the wall of a right lower lobe cyst (arrow). Resection revealed invasive adenocarcinoma.  Figure 7b: Transverse 1-mm CT sections obtained 10 months apart show a highly suspicious pattern of progressive thickening in the wall of a right lower lobe cyst (arrow). Resection revealed invasive adenocarcinoma. Measurement of attenuation (in Hounsfield units) in solid nodules can be helpful to determine the presence of calcification or fat, either of which can have major diagnostic implications. It is critical that such measurements be made on images without an edge-enhancing filter, such as the type that is generally used on lung and bone images. Measurements on a sharpened image may give erroneously high attenuation values, and other factors, such as beam hardening, can affect the accuracy of the measurements. All attenuation measurements should be made on the thinnest available nonsharpened (typically soft-tissue window) image series; the radiologist should use a small region of interest (not a point value) and realize that substantial variations occur among different scanners, filters, and body locations, even with regular calibration (27). Recommendation 2: multiple solid noncalcified nodules.—For multiple solid noncalcified nodules smaller than 6 mm in diameter, no routine follow-up is recommended (grade 2B; weak recommendation, moderate-quality evidence). Small nodules in this size range are frequently encountered in routine clinical practice and are usually benign in origin. They most often represent either healed granulomata from a previous infection (especially in regions with endemic fungal infections) or intrapulmonary lymph nodes. In patients at high risk, a 12-month follow-up examination may be considered. Note that this recommendation assumes no known or suspected primary neoplasm that might be a source of metastases. In patients with clinical evidence of infection and in those who are immunocompromised, active infection should be considered, and short-term follow-up may be appropriate. For multiple solid noncalcified nodules with at least one nodule 6 mm or larger in diameter, follow-up is recommended at approximately 3–6 months, followed by an optional second scan at 18–24 months that will depend on estimated risk. (grade 1B; strong recommendation, moderate-quality evidence). If a larger or more suspicious nodule is present, it should be used as a guide to management according to the guidelines for solitary nodules, as stated previously. In such situations, metastases remain a leading consideration, particularly when the distribution of nodules has peripheral and/or lower zone predominance and when the size of the nodules has a wide range (Fig 8) (28 |