Nodule Growth

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Evaluation of growth is performed by reviewing preexisting chest radiographs or CTs. The majority of malignant nodules double in volume between 30 and 400 days [34]. Nodular opacities that double in volume more rapidly than 30 days are usually infectious or inflammatory in origin (Fig. 18), whereas those that double in volume more slowly than 400 days are usually benign pul-

Figure 15 Squamous-cell lung cancer. Computed tomography shows thick-walled cavitary nodule in left upper lobe. Thick walls and eccentric cavitation are suggestive, but not diagnostic, of malignancy.

Figure 16 Nontuberculous mycobacterium infection (Mycobacterium avium intracellulars). Computed tomography shows well-circumscribed, cavitary nodule (arrowheads) with thick walls in right upper lobe. Note bronchiectasis and scattered branching tubular opacities, findings often associated with M. avium intracellulars infection.

Figure 16 Nontuberculous mycobacterium infection (Mycobacterium avium intracellulars). Computed tomography shows well-circumscribed, cavitary nodule (arrowheads) with thick walls in right upper lobe. Note bronchiectasis and scattered branching tubular opacities, findings often associated with M. avium intracellulars infection.

Figure 17 Squamous-cell lung cancer. Computed tomography shows thin-walled cavitary nodule in right upper lobe (arrows). Soft tissue within nodule is due to necrotic lung. Extensive necrosis can occasionally result in thin walls and erroneously suggest a benign etiology.

monary neoplasms or sequelae of prior pulmonary infections. An absence of visible growth over a 2-year period is generally reliable in determining benignity [1,35,36]. Recently, the use of these criteria to infer benignity has been questioned [37]. These concerns are particularly important when the accuracy of growth assessment in small nodules is considered. To detect growth on a radiograph requires a nodule to change in diameter by 3 to 5 mm [37,38]. The small change in diameter (approximately 25%) that occurs when a small nodule doubles in volume makes it difficult to assess interval growth in these nodules. For example, a 4-mm nodule will increase to only 5 mm in diameter after doubling in volume and, consequently, will appear stable on the chest radiograph. Although this change in diameter can theoretically be detected by CT, slight differences in the level at which the image is obtained occurs commonly from study to study and makes the confident detection of a small diameter change difficult. The use of CT does, however, in most cases allow an accurate assessment of growth and it has been recently reported that growth can be detected in lung cancers as small as 5 mm when CT imaging is repeated within 30 days [39]. Furthermore, the measurement of serial volumes, rather than diameters, of small nodules has been suggested to be an accurate and potentially useful method to assess growth [40]. Presently, however, there is no consensus as to what parameters should be measured, when the first and subsequent serial CTs should be performed, or the

Figure 18 Nocardia infection in heart transplant recipient. (A) Computed tomography shows small, well-circumscribed right upper lobe nodule (arrow). (B) Computed tomography 1 week later shows marked increase in size of right upper lobe nodule and interval development of smaller right upper lobe pulmonary nodules. Transthoracic needle aspiration biopsy confirmed diagnosis of Nocardia infection. Rapid growth is indicative of a benign, in this case infectious, etiology.

Figure 18 Nocardia infection in heart transplant recipient. (A) Computed tomography shows small, well-circumscribed right upper lobe nodule (arrow). (B) Computed tomography 1 week later shows marked increase in size of right upper lobe nodule and interval development of smaller right upper lobe pulmonary nodules. Transthoracic needle aspiration biopsy confirmed diagnosis of Nocardia infection. Rapid growth is indicative of a benign, in this case infectious, etiology.

period of time required to ascertain that a small nodule is benign based on absence of growth.

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