Prevalence of pathologically proven intrapulmonary lymph nodes and their appearance on CT.

OBJECTIVE The objective of this study was to assess the prevalence of pathologically proven intrapulmonary lymph nodes and to evaluate their appearance on CT. MATERIALS AND METHODS Over a 15-year period (1980-1994), 184 patients underwent minithoracotomies for evaluation of CT-detected peripheral pulmonary abnormalities. Of these 184 patients, 96 had well-circumscribed peripheral pulmonary nodules. The size, position, and radiographic features of all pathologically proven intrapulmonary lymph nodes were independently assessed by two experienced radiologists. RESULTS The nodules in 17 (18%) of the 96 patients with well-circumscribed peripheral pulmonary nodules were pathologically proven to be intrapulmonary lymph nodes. Two of the 17 patients had two nodules; the remaining patients had solitary nodules. The maximum diameter of the nodules varied from 7 to 12 mm. All the nodes were located within 20 mm of a visceral pleural surface. Twelve of the nodules were located in the lower lobes, and the remaining nodules were located in the right middle lobe. CONCLUSION Although intrapulmonary lymph nodes are not a well-known entity, our results indicate that they are discovered in a significant number of patients who undergo minithoracotomies for the evaluation of CT-detected pulmonary nodules. Although these lymph nodes do not possess any specific CT appearance, they should be considered in the differential diagnosis of single (or multiple) parenchymal nodules, particularly those found in the lower lobes.