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The pathology of influenza

Chapter 28: Summary.
By M. C. Winternitz
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The authors present a systematic pathological study of cases from the 1918 influenza epidemic, based on eighty-two autopsies, detailing gross and microscopic findings. They describe necrotizing hemorrhagic lesions of the trachea and bronchi and several pulmonary patterns including acute diffuse fulminant hemorrhagic pneumonia, localized necrotizing pneumonias, and organizing bronchiolar/alveolar exudates. The work documents extrarespiratory effects on lymphoid tissues, spleen, bone marrow, blood vessels, the alimentary and urinary tracts, central nervous system structures, and changes observed in pregnancy. A comparative analysis contrasts these lesions with those produced by inhaled poisonous gases and emphasizes peculiar histologic features such as hemorrhagic and hyaline necrosis and patterns of organization. Bacteriological findings and their relation to pleural involvement and pneumonic types conclude the study.

C. MISCELLANEOUS LESIONS

In this series of cases lesions elsewhere in the body are not sufficiently constant or important to merit emphasis.[13] Hemorrhages have been found occasionally in other structures, especially the testes. The usual cloudy swelling of the parenchymatous organs is, of course, marked, and in many cases has been associated with actual cellular necrosis both in the liver and the kidney. Such necroses are usually focal, and occasionally mitotic figures in the cells of the renal convoluted tubules or in the liver may be a similar expression of previous damage. Acute nephritis was not found in our series.[14] The swollen liver cells often show the bile canaliculi clearly, and this appearance may be associated with a variable degree of jaundice which has been found frequently, although the explanation of the jaundice is, in all probability, an hemolysis of the red cells caused by the infecting microorganisms. The only other lesion encountered and of sufficient importance to mention, has been the congestion of the membranes of the brain and a swelling of the cerebral substance, in all probability dependent upon edema. One example of purulent meningitis was encountered.[15] The dilatation of the right side of the heart with a greater or lesser degree of splanchnic engorgement is such a common feature in acute pulmonary diseases that it is hardly worthy of detailed discussion.

FIG. XXXVI. AUTOPSY NO. 133. A SMALL ABSCESS IN AN EDEMATOUS BAND OF INTERLOBULAR CONNECTIVE TISSUE.

FIG. XXXVII. AUTOPSY NO. 114. ILLUSTRATES AN UNUSUAL ANATOMICAL PICTURE IN INFLUENZA—AN EXTENSIVE FIBRINOPURULENT PLEURISY. THE BRONCHIAL LYMPH GLANDS ARE PROMINENT ON ACCOUNT OF THE HEMORRHAGIC INFLAMMATORY PROCESS WHICH HAS INVOLVED THEM.

A striking feature of influenza is the occurrence of abortion in cases complicated by pregnancy. Of the ninety-five cases included in this report, twenty-seven were women of whom three died undelivered (three months, six months, term), three had suffered complete abortion (one, three months, and two, six months), and one (six months) was in process of abortion. It is not our purpose to discuss the relation between pregnancy and this complication. Here it is desirable simply to point out that, although in the non-complicated cases of influenza, pregnancy does not influence the course of the disease, if pneumonia supervenes, the mortality for the mother, as well as for the child, is definitely increased (57, 148, 164).

A specific placental lesion would be difficult, indeed, to establish since hemorrhage is a part of the normal process of placental separation. However, the hemorrhagic lesion of influenza seems a plausible explanation for the frequency of abortions in this disease.

Summary.

The most important extrapulmonary lesions in influenza are those of the hematopoietic and the vascular systems. The first are typical of a general non-suppurative, inflammatory process, and are characterized in the majority of cases by a picture not unlike that encountered in typhoid fever, although the hyperplasia of the lymphadenoid tissues, as seen in the latter disease, is not present. The more important lesions are associated with the vascular system; phlebitis and arteritis occur, but are not so frequent as hemorrhages in the skeletal system, in the parenchymatous organs, and in the mucous membranes of the hollow viscera. These hemorrhagic necroses may be etiologically associated with capillary bacterial thrombi.