The etiology of multiple pulmonary nodules can usually be determined with the help of a thorough history and physical examination. However, further testing is sometimes required for diagnosis, which may include imaging tests and/or a biopsy. The differential diagnosis and diagnostic evaluation of multiple pulmonary nodules are reviewed here. The approach to a solitary pulmonary nodule is discussed separately. (See "Diagnostic evaluation and management of the solitary pulmonary nodule".)
Malignant versus benign — Multiple pulmonary nodules may be caused by malignant or benign diseases.
In patients without a known primary malignant tumor, the following characteristics help differentiate multiple malignant nodules from multiple benign nodules:
- Multiple pulmonary nodules that are ≥1 cm in diameter or detected by conventional chest radiography are most likely due to metastatic disease from a malignant solid organ primary tumor [1,2].
- Multiple pulmonary nodules that are <5 mm in diameter, juxtaposed to either the visceral pleura or an interlobar fissure, and detected incidentally, are more likely to be benign lesions, such as granulomata, scars, or intraparenchymal lymph nodes [1-3].
In contrast, in patients with a known malignant primary tumor, multiple pulmonary nodules exceeding 5 mm in diameter are more likely to be malignant than benign .