Radiographic Findings

A frontal chest radiograph (A) shows a smoothly-marginated, well-defined nodule, 1.7 cm in diameter, localized on the lateral film (not shown) in the periphery of the right middle lobe.

Differential diagnosis: Pulmonary lesions, 3 cm or less in diameter, usually termed nodules, have a large number of etiologies, but over 95% are one of the following: primary or metastatic malignant neoplasms, TB or fungal granulomas, or benign tumors, particularly hamartomas [1]. A pulmonary lesion greater than 3 cm in diameter is usually termed a "mass" and is associated with a high rate of malignancy [2], although benign etiologies such as lung abscess, Wegener's granulomatosis, and round atelectasis may present as lung masses.

The most important step in the evaluation of a solitary pulmonary nodule is a careful search for prior chest radiographs. In many instances the prior film may show that the nodule was present, but overlooked because of projection, etc. [3], and stability of a nodule for 2 years is associated strongly with benign etiology. The patient's age (lung cancer is rare in patients less than 30 years of age), smoking history, and history of malignancies that may cause lung metastases are all important considerations in the nodule work-up.

CT at level of nodule: A search of multiple outside institutions revealed no prior chest radiographs, and a CT scan was performed for further evaluation. The CT (B) (lung window) shows a sharply circumscribed nodule in the right middle lobe. Soft-tissue windows (not shown) showed the nodule to be homogeneous with attenuation of approximately muscle density.

CT findings often cannot distinguish benign from malignant disease. However, CT is much more sensitive than plain radiographs for density characteristics. If calcification is seen, the pattern (central-core, diffuse dense, or laminated in granulomas, and "pop-corn" in hamartomas) can be characteristic for benign disease [4], and if fat density is seen, hamartoma is almost certain [5]. CT is also much more sensitive for detecting multiple pulmonary lesions (as in metastatic disease) and can show findings consistent with arteriovenous malformation (feeding artery and draining vein) and round atelectasis (adjacent pleural disease, diminished lung volume, and "comet-tail" of vessels swirling toward the lesion [6]. CT is very sensitive for air-bronchograms, which if seen in a nodule, correlate with a high rate of malignancy [7].

References

1. Armstrong P. Basic patterns in lung disease. In: P Armstrong, A Wilson, P Dee, D Hansell (eds): Imaging of Diseases of the Chest, 2nd ed, St. Louis, Mosby-Year Book, 1996, pp 96-97.

2. Zerhouni E, Stitik F, Siegelman S, et al. CT of the pulmonary nodule--a cooperative study. Radiology 1986; 160:319.

3. Fraser R, Paré J, Fraser R, Paré P. Synopsis of Diseases of the Chest, 2nd ed, Philadelphia, W B Saunders, 1994, p 463.

4. Armstrong P. Basic patterns in lung disease. In: P Armstrong, A Wilson, P Dee, D Hansell (eds): Imaging of Diseases of the Chest, 2nd ed, St. Louis, Mosby-Year Book, 1996, pp 98-99.

5. Siegelman S, Khouri N, Scott W, et al. Pulmonary hamartoma: CT findings. Radiology 1986; 160:313-317.

6. Carvalho P, Carr D. Computed tomography of folded lung. Clin Radiol 1990; 41:86-91.

7. Kuriyama K, Tateishi R, Doi O, et al. Prevalence of air bronchograms in small peripheral carcinomas of the lung on thin-section CT: comparison with benign tumors. AJR 1991; 156:921-924.

Clinical summary Image 1

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