A study on intersegmental septa.

Publications dealing with anatomy of the lung describe only briefly the intersegmental septa, usually referring to them as “intersegmental planes.” The existence of such “planes” has been doubted by the authors for years, and an investigation was undertaken by filling cadaver lungs according to the method of Tobin, as follows: 1. In two cases the whole lung was filled with unicolored (white) latex, and 2. In six cases, each segment was filled with a different colored latex. The latex was solidified in 20 per cent formalin. 1. In the unicolored specimens the secondary lobuli were marked on the pleural surface equally by connective tissue both in the intersegmental and the interlobular borders. The segments were not bordered by a thicker connective tissue layer than the lobuli; thus in gross appearance the segmental borders were not recognizable. 2. On the smooth pleural surface of the multicolored specimens the intersegmental borders were marked only by the different colors and zig-zagged according to the angulated lobuli. (Fig. 1. and 2. A.) After these observations the authors separated the different colored segments in the intersegmental septa and found that the intersegmental surfaces are not plane, even or smooth, but uneven and bumpy like basalt rocks; the irregular surfaces of the pentagon-shaped lobuli of the neighbouring segments fit into each other as a cast fits to the pattern. (Fig 1. and 2. B.) Naturally not all of the intersegmental surfaces are equally uneven. Less angulated surfaces were seen between the two lingular segments and between some basal segments. (Fig. 2. B.; surface between the lateral and posterior basal segments.) Utilizing the above observations the authors have created a more lifelike segmental model, in which the intersegmental unevenness caused by protrusion of the angulated lobuli was imitated. (Fig. 3.) The above statements have considerable anatomical significance, but they have also some clinical importance: 1. Surgeons find the intersegmental surfaces fairly smooth and planelike in segmental resections, but this is, as consequence of above statements, because of the collapse of the lobuli. However, a larger lobulus can protrude occasionally into a neighbouring segment (Fig. 2. B.) and create a larger elevation on the surface in spite of its collapse. Overholt and Langer write in their book (The Technique of Pulmonary Resection, 1949) that “With extreme rarity small intersegmental bronchi are encountered.” One may ask (a) whether this impression may be the result of unintentional division through the interlobular septum or lobular bronchus projecting from the segment being removed into the adjacent one (or vice versa) ? and (b) whether such an occurrence might not explain an otherwise unexplained post-operative bronchial fistula?