Solitary Pulmonary Nodule: How and How Much to Investigate?

A solitary pulmonary nodule (SPN) is radiologically defined as an intraparenchymal lung lesion that is < 3 cm in diameter and is not associated with atelectasis or adenopathy. Lung lesions > 3 cm in size are defined as lung masses. A solitary pulmonary nodule is noted on 0.09 to 0.20 per cent of all chest radiographs. An estimated 150,000 such nodules are identified each year. Ninety per cent of these are incidental radiologic findings, found unexpectedly in radiographs obtained for unrelated diagnostic workups. Although the causes may include many benign conditions, bronchogenic carcinoma as a cause of solitary nodules has been increasing, especially in the elderly. However, in developing countries, tuberculosis and fungal infections are important clinical entities in the differential diagnosis of an SPN, especially in young age, non-smokers, and immunocompromised individuals. Table 1 lists the various causes of a solitary pulmonary nodule. In patients with resected malignant nodules, survival may be as high as 80 per cent at five years; in contrast, survival rates at five years among those with advanced malignant disease remain below 5 per cent. Ideally, diagnostic approaches to pulmonary nodules would permit definitive resection when possible and avoid resection in patients with benign disease. Recent developments in the approach to pulmonary nodules include improvements in radiographic imaging, techniques to distinguish benign from malignant nodules without surgery, lung-cancer screening, and minimally invasive surgical approaches. Early detection of small nodules may potentially reduce lung cancer–specific mortality.