Interstitial Suppurative Pneumonia
A second type of suppurative pneumonia is characterized by acute inflammation of interstitial tissue between the secondary lobules of the lung and by acute lymphangitis; suppuration involves the interstitial septa and the walls of the lymphatics. The lesion is designated by Kaufmann,[[82]] Beitzke[[83]] and others acute interstitial pneumonia. Pneumonia dissecans in which solution of interstitial tissue isolates sections of lung tissue is said to be a consequence of the lesion. Many text books of pathology, overlooking the occurrence of this lesion, limit the consideration of interstitial pneumonia to chronic processes in which the interlobular and interalveolar fibrous tissue is increased.
Acute inflammation and edema of the interlobular septa of the lung with no suppuration is often found with both lobar and bronchopneumonia and is occasionally so far advanced that it can be recognized on gross examination of the lungs. In a small area interlobular septa are conspicuous as yellowish lines of edematous appearance which may be 1 to 1.5 mm. in thickness and sometimes form a network with rectangular or polygonal meshes. The gelatinous appearance of the edematous fibrous tissue does not suggest suppuration. Microscopic examination shows that the tissue is distended by edema and contains fibrin and polynuclear leucocytes; the lymphatics are distended and contain a network of fibrin within which leucocytes are numerous. Inflammatory edema of the interstitial tissue has been recognized at autopsy four times in association with bronchopneumonia (Autopsy 253 with Pneumococcus II; Autopsy 335, with Pneumococcus IV and S. viridans; Autopsy 477 with S. hemolyticus and Autopsy 498 with S. viridans); twice with lobar pneumonia (Autopsy 343 with Pneumococcus IV and Autopsy 353 with atypical Pneumococcus II); twice with combined lobar and broncopneumonia (Autopsy 273 with S. hemolyticus and Pneumococcus IV and Autopsy 357 with Pneumococcus IV). Edema of interstitial septa was recognized at autopsy in the immediate neighborhood of an abscess three times (Autopsies 277 and 278 with hemolytic streptococci and Autopsy 282 with hemolytic streptococci and Pneumococcus II). In these instances of inflammation and edema the lymphatics are found distended by fibrinous thrombi, and it is probable that occlusion of lymphatics determines the occurrence of inflammatory edema within the surrounding tissue. Inflammation has not proceeded to suppuration.
With interstitial suppurative pneumonia, interlobular connective tissue is marked by conspicuous yellow lines, 1 to 3 or even 5 mm. in thickness, forming a network with polygonal meshes which represent secondary lobules (Figs. 10 and 11). The distended septa not infrequently have bead-like enlargements at intervals and from the cut surface it is often possible to scrape away creamy yellow pus. These lines of suppuration invariably extend up to the pleura and are often broadest immediately below it. Adjacent septa which have not undergone suppuration are much thickened and have the yellowish gray appearance produced by edema.
Fig. 10.—Interstitial suppurative pneumonia; interstitial septa are the site of suppuration and lymphatics are distended with purulent fluid; empyema. Autopsy 474, left lung. (See right lung) Fig. 9.
Fig 11.—Suppurative interstitial pneumonia; the left lower lobe is the site of almost uniform consolidation and here interstitial septa and their lymphatics are distended with pus. There is more extensive interstitial suppuration in the upper lobe where consolidation is absent. The cloudy appearance of the consolidated lung is well shown. Autopsy 452.
Suppurative interstitial pneumonia frequently occurs in association with bronchopneumonic consolidation which may be peribronchiolar, hemorrhagic or lobular, but there is in addition consolidation of the pulmonary tissue between the inflamed septa which may affect part of a lobe, an entire lobe, or parts of several lobes; it does not exhibit the characters of confluent lobular pneumonia.
In approximately half of the cases consolidation, associated with interstitial suppuration, has been lobar in distribution (Fig. 11). The tissue is laxly consolidated, finely granular, and has a cloudy red or gray appearance. The coarsely granular surface of lobar pneumonia is absent. The affected lung may weigh 1,500 or 1,650 grams. Occasionally, interstitial septa of air containing lung tissue is the site of suppurative inflammation or edema. In Autopsy 452 the lower lobe, save a small part at the base, is laxly consolidated; interstitial septa in the consolidated area are yellow, 1.5 to 2 mm. in thickness, beaded and exude purulent fluid on pressure. In the adjacent part of the upper lobe there is a patch of consolidation, and a network of yellow thickened septa extends from it far into the surrounding air containing tissue. The weight of the right lung is 635 grams; of the left, 1,650 grams.