Recognition and Incidence of Intrapulmonary Lymph Nodes

Lymph nodes are normally found in man in the mediastinum and around the main bronchi at the hilum of the lung. A few such nodes, which have confusingly been called intrapulmonary (Pidry and Jacques, 1906; Johnston, Davies, and Davies, 1958), may also be present alongside lobar bronchi as far into the lung as the third or fourth branching of the bronchi. Aggregations of lymphocytes are common at the bifurcations of bronchi and beneath the pleura, as Miller (1911) clearly showed. However, definite nodes with a capsule and lymphoid follicles may be found in some individuals far out in the lung and even close to the pleura. These are truly intrapulmonary and must be distinguished from those near the hilum of the lung or in the mediastinum, which may conveniently be grouped together as tracheo-bronchial lymph nodes. According to Heller (1895), the first to describe subpleural lymph nodes was Meinel (1869), whose work was soon followed by that of Sanderson (1869) and Is (1876). Arnold (1880) showed the truly lymphoid character of these nodules and that they occurred in normal lungs. Later, Luders (1892), Heller (1895), and Bossuet (1905) confirmed the work of the earlier authors. They showed that subpleural nodes were visible macroscopically, varying in size up to that of a lentil, being abundant in some cases and rare or absent in others. Miller (1911, 1947) investigated the lungs of dogs and other animals as well as those of man, and failed to show definite lymph nodes in normal lungs but found in each instance small masses of lymphoid tissue. Elsewhere in his 1911 paper he said he had found definite intrapulmonary and subpleural lymph nodes: he suggested that these occurred only in abnormal lungs and that the nodes must have developed from normal masses of lymphoid tissue. However, no evidence was given to support this. Later, in 1924 and 1947, he suggested that there was a definite increase in the