Acute, transient middle lobe disease.

The special significance of atelectasis of the middle lobe was first pointed out in 1946 by Zdansky1 and Brock,2 independently. Zdansky described two cases of middle lobe atelectasis in adults caused by compression of the middle lobe bronchus by a calcified lymph node. He noted that in children enlargement of a lymph node often causes compression of a major bronchus leading to atelectasis of the entire lobe without any predilection for any one bronchus and lobe. In adults, on the other hand, atelectasis of an entire lobe will occur more frequently in the middle lobe. In the other lobes, only the smaller bronchi will be compressed leading to segmental atelectasis. This can be explained by the fact that in children all the major bronchi are narrow and easily compressible, while of the major bronchi in adults only the middle lobe bronchus is narrow and is rendered even more easily compressible by virtue of the acute angle it forms with the main bronchus. He, therefore, called the right middle lobe “locus minoris resisteniae der Lunge.” Zdansky also noted that besides cases of permanent atelectasis of the middle lobe one not uncommonly encounters a patient presenting an acute febrile illness in whom a chest film will reveal atelectasis of the middie lobe, which however, will reexpand after a few days with subsidence of symptoms. Not uncommonly one may find an enlarged lymph node near the origin of the bronchus. It is of interest to note here that Shaw,3 in his excellent presentation of a “new clinical entity” caused by mucoid impaction of bronchi, reported 10 cases of segmental atelectasis, bronchiectasis and fibroid pneumonitis caused by plugs of mucus obstructing a bronchus of a second order in patients with asthma or chronic obstructive bronchitis. In one of these cases the middle lobe was involved. Brewer in his discussion of this paper reported a similar case. Brock in “The Anatomy of the Bronchial Tree” also takes note of the frequency of the middle lobe collapse. He pointh out that the middle lobe bronchus is particularly vulnerable to the effects of glandular enlargement because it lies in the lymphatic pathway from the right lower lobe and is closely surrounded by glands which drain the lower and middle lobes. He mentions, however, that left upper and lower lobe bronchi are also liable to be compressed by the many glands which surround them at their origin. The first one to coin the term “Middle Lobe Syndrome” was E. Graham4 who in 1947 reported 12 cases of nontuberculous adults having compression of the middle lobe bronchus by enlarged lymph nodes. All were characterized clinically by hemoptysis and recurrent episodes of pulmonary infection. Atelectasis, fibrosis and bronchiectasis were the pathologic findings. The enlarged compressing lymph nodes showed changes of a chronic nonspecific lymphadenitis. He stressed the necessity of investigating all the lobes in each patient.