PATHOLOGICAL ANATOMY OF ACUTE RADIATION SICKNESS IN AN EXPERIMENT

(GENERAL EXPOSURE TO RAYS GENERATED BY A BETATRON)

I. V. TOROPTSEV and N. V. SOKOLOVA

(Presented by the scientific seminar of the Physico-Technical Faculty)

The material for the study consisted of adult guinea pigs subjected to a single exposure to rays generated by a betatron. The morphology of radiation sickness is fairly fully represented in the literature; however, studies of radiation sickness caused by the action of a betatron are still far from sufficient. Our material makes it possible to characterize the pathoanatomical changes observed in death under the beam (death of animals within the first 12 hours after irradiation) and in acute forms of radiation sickness (death of animals within 10 days after irradiation).

We set ourselves the task of studying in detail the morphology of these forms of radiation sickness and of attempting to clarify the features of manifestation of the disease caused by this type of irradiation.

In cases of death under the beam, macroscopically one can detect only uneven blood filling of the organs. Histological examination documents universal damage to the blood and lymphatic vessels: necrobiotic changes of the endothelium and increased permeability of the vascular walls with phenomena of scanty diapedesis. A disturbance of hemodynamics is clearly expressed: considerable dilation of vessels with redistribution of blood elements, “settling out” of erythrocytes, which become concentrated in individual areas near the vessel walls (Fig. 1). Changes in the tinctorial properties of the blood plasma are very typical. With ordinary eosin–hematoxylin staining it has a bright-yellow color. It must be assumed that the peculiar staining of the plasma is the result of changes in the blood proteins. These phenomena recur with great constancy throughout the entire circulatory system, differing only in the degree of expression of the process. Thus, a feature of our material is the early development of diapedesis, thrombus formation, and distinct changes in the blood plasma.

In the nervous system there are large foci of necrosis with death of ganglion cells of the subcortical nuclei, the spinal-cord trunk, and peripheral ganglia, with preservation of the cerebral cortex (Figs. 2, 3). In the literature available to us, only reversible changes in the nervous system are described, characterizing its reactive state.

Figure 1

Pia mater. The vessel wall is frayed and translucent. The endothelium is partially absent. The phenomenon of “lacing” of erythrocytes.

Figure 2

Spinal cord. Dead ganglion cell—absence of the nucleus.

In the sex glands, phenomena of necrobiosis are observed. In the testes, spermatogonia are in a state of dystrophy; some cells perish. At the same time, mature spermatozoa and Sertoli cells retain their usual structure. In the ovaries, ova and the layers of follicular epithelium adjacent to them perish. Throughout the ovary, preserved ova cannot be detected.

Fig. 3

Solar plexus ganglion. Ganglion cells at different stages of necrobiosis.

In the literature we found no indications of similar changes in sex cells at such early phases of the development of the disease.

In the parenchymatous organs, dystrophy was markedly pronounced, predominantly of a protein character, with an outcome in necrosis. Necrobiotic changes were also developed in all parts of the cortical layer of the adrenal glands. In the pancreas, the changes were expressed in the incretory islets, while the secretory portions had the usual structure. Meanwhile, in the literature there are indications only of dystrophic changes in the secretory elements of the gland.

In the lungs and gastrointestinal tract, the vascular lesions described above, with phenomena of diapedesis, were clearly expressed.

The most typical changes were observed in the lymphoid tissue. Here there was a sharp depletion of the follicles in lymphoid elements and the presence of a large number of large cells containing coarse, uneven basophilic granularity in the cytoplasm (Fig. 4). These cells, having the appearance of granular “spheres,” are evidently macrophages that have phagocytosed products of lymphocyte disintegration. The red pulp of the spleen is depleted of cells. The nuclei of the endothelium of the sinuses are pyknotic; the preserved myeloblastic elements are in a state of necrobiosis. The leukocytes encountered have hypersegmented nuclei. It should be noted that all leukocytes have a similar nuclear structure, both those located in the bloodstream and those that have migrated into the tissues. In the literature there is no description of this peculiar state of macrophages of the lymphoid tissue; meanwhile, in our experiments they are a constant and extremely characteristic-

…a sign of the most acute forms of radiation sickness, namely, cases of death under the beam.

It must be emphasized that the morphological picture described for death under the beam was repeated with photographic accuracy in all the cases studied and, consequently, may be regarded as specific for this type of injury.

Fig. 4

Splenic follicle. The central portion is translucent; its cells are in a state of necrobiosis. Along the periphery there are numerous granular “spheres.”

Acute radiation sickness is characterized macroscopically by the phenomena of a moderately pronounced hemorrhagic diathesis, with predominant localization of the lesions in the lungs and stomach. Histological examination reveals progressive destructive changes in the vessels, parenchymatous organs, lymphoid tissue, bone marrow, and sex glands, with no proliferative reaction.

In the vessels there occurs extensive necrosis of the endothelium, homogenization of the walls as a result of compaction of the protein masses impregnating them, and the process of thrombus formation progresses. The plasma retains the bright-yellow coloration noted in the early stages of the disease. There is perivascular edema. Increased permeability of the vascular walls is very clearly expressed in the lungs (Fig. 5). Analysis of the morphological picture observed in the lungs makes it possible to decipher the sequence of development of the pathology. Apparently, already in the first phases of the disease there is a significant disturbance of vascular-wall permeability—diapedesis occurs. Subsequently plasma is repeatedly exuded, which pushes the erythrocytes away from the vessel walls into the central portions of the alveoli; homogeneous protein masses precipitate from the plasma and, in the form of massive clumps, surround the thickened walls of the alveoli.

In the nervous system, phenomena of necrobiosis are pronounced, with localization of the lesion in the region of the subcortical nuclei, the brain stem, the spinal cord, and the peripheral ganglia. No changes are found in the structure of the cerebral cortex. The glial reaction is absent.

In the sex glands there is a progressive destructive process. In the testes, only in isolated areas can preserved epithelium and a small number of mature dying spermatozoa be found, with peculiar changes in the structure of the head (Fig. 6).

Fig. 5

Pulmonary artery. The perivascular tissue is sharply edematous. Erythrocytes in the alveoli.

Fig. 6

Seminiferous tubule. Dystrophic changes in the spermatozoa: club-shaped swelling of the heads; the chromatin substance is pale and displaced to the periphery.

In the majority of the tubules, phenomena of necrobiosis are pronounced in the epithelium, and Sertoli cells also perish. The lumina of the tubules are filled with a peculiar meshwork which, apparently, is formed from products of cytoplasmic disintegration. In the ovaries, further changes are observed in the dead ova: they decrease in size, and their membrane collapses somewhat. Many follicles are devoid of ova; in their place, fluid poor in protein accumulates. The follicular epithelium is in a state of necrobiosis. Mitotic figures are absent (Fig. 7).

Fig. 7

Ovarian follicle. Dead ovum: absence of the nucleus, vacuolization of the cytoplasm. In the follicular epithelium, phenomena of rhexis.

In the lungs, in addition to the phenomena of diapedesis and plasmorrhagia described above, extensive foci of necrosis were observed. In these areas only “shadows” of the alveolar walls are visible. The lumina of the alveoli are filled with homogeneous, often lumpy masses of coagulated protein; in some areas a fibrin network is visible. Erythrocytes are present in many alveoli. There is no inflammatory reaction around the foci of necrosis. In a number of cases, outside the zone of necrosis, flat, predominantly triangular crystals are found in alveoli containing erythrocytes. The latter have a staining completely analogous to erythrocytes. It is possible to trace the transition from clumps of agglutinated erythrocytes to figures resembling triangles and, finally, to sharply contoured crystals, which arise as a result of peculiar changes in erythrocytes (Fig. 8). In the bronchi there is marked mucous dystrophy of the lining epithelium. The lumina of the bronchi contain blood and desquamated epithelium. Vacuolar dystrophy of the mesothelium of the visceral pleura is very typical and constant (Fig. 9).

In the heart, in addition to vascular changes with phenomena of plasmorrhagia and diapedesis, there are numerous foci of necrosis of the muscle tissue (Fig. 10), death of the cellular elements of the endocardium, areas of protein impregnation and homogenization of the subendocardial layer of the left ventricle. There is no reaction in the interstitial tissue of the heart.

Fig. 8

Lung. In the alveoli there are masses of partially agglutinated erythrocytes and homogeneous figures with the facets of crystals.

Fig. 9

Visceral pleura. Enlarged mesothelial cells, with vacuolated cytoplasm and peripheral arrangement of the nuclei.

In the liver, numerous large and small progressive foci of necrosis are observed. In the zone of necrosis only the “shadows” of disorganized trabeculae and isolated, well-contoured nuclei are visible. The latter belong to Kupffer cells, which retain their structure. In the areas of preserved liver tissue, the leukocytic and proliferative

Fig. 10

Heart muscle. Necrosis of muscle fibers: pallor of staining, increase in volume, absence of nuclei.

reaction is absent. Analysis of individual details of the organ’s structure gives very interesting results. In many areas, along the length of the preserved trabeculae, it is possible to detect individual liver cells in a state of necrobiosis. Alongside dying cells there are unchanged ones (Fig. 11). This regularly recurring combination of dying and preserved hepatic cells documents well the primary character of the necrosis and makes it possible to exclude its occurrence as a result of circulatory disturbances.

In the kidneys there are phenomena of hydropic nephrosis, protein impregnation, and homogenization of the interstitial tissue of the medullary layer (Fig. 12).

In the gastrointestinal tract, phenomena of diapedesis, edema, and focal necrobiosis of the lining and glandular epithelium are pronounced. In some cases, in the gastric glands there is no differentiation of the cells into chief and parietal cells. Areas of protein impregnation and homogenization of the interstitial tissue of the gastric mucosa are constantly encountered. In the intestine, the usual infiltration of the mucosa by pseudoeosinophils is absent. The cellular elements of the intestinal submucosa are represented only by plasma cells and macrophages.

The bone marrow is considerably depleted of cells. The latter are represented by plasma cells arranged in small groups, isolated erythroblasts and megakaryocytes, in which phenomena of necrobiosis are pronounced. Cells of the myeloblastic series are absent. The sinusoids are considerably dilated; in many areas the endothelium is absent, often

Fig. 11

Liver. The dead hepatic cells are large, with dark protoplasm, without nuclei; alongside them are liver cells with preserved structure.

Fig. 12

Kidney. The interstitial tissue of the medullary layer is homogenized; some vessels and tubules are compressed and deformed.

parietal granular thrombi are encountered; there are many hemorrhages. The reticular network is denuded, coarse, and in places breaks down into separate homogeneous clumps.

In the lymphoid tissue there is marked depletion of cells, a change in cellular composition—the predominance of plasma elements—and coarsening of the reticular stroma. These pictures are especially distinct in the spleen. In its follicles, cells are preserved only in the central portions. The bulk of these cells consists of plasma cells; lymphoid elements are almost absent, and isolated erythroblasts are present. The peripheral portions of the follicles are represented by a pale-pink homogeneous mass, in which only here and there the contours of sharply swollen reticular fibers are outlined. In the emptied areas of the follicles, fragments of nuclei and isolated fibrocytes are visible. The red pulp is also poor in cells; among them plasma cells predominate, there are erythroblasts and a few cells of the myeloblastic series. The sinuses are considerably dilated; their endothelium has perished in many areas. In the sinuses there are thrombi without signs of organization. Deposits of hemosiderin, situated predominantly extracellularly, are frequently encountered. The reticular stroma in the region of the red pulp as well is coarse and homogenized, and in many areas breaks down into separate clumps.

Thus, in all cases of acute radiation sickness there is a universal alteration of the structure of the paraplastic substance: protein impregnation and homogenization of the walls of vessels, the interstitial tissue of the kidneys, heart, and stomach; coarsening and clumpy disintegration of the reticular network of lymphoid tissue and bone marrow. At the same time, constancy and uniformity of the tinctorial properties of the altered tissue areas are noted. They are pyroninophilic when stained by Van Gieson’s method, which permits one to think of a significant alteration of protein complexes.

A very typical feature of radiation sickness is the absence of a proliferative reaction. In the course of presenting the material we have repeatedly indicated that phenomena of regeneration and organization are absent. The latter is especially demonstrable in the study of changes in the vessels. We observed a distinct process of thrombus formation, which regularly arose in the early stages of the development of the pathology. There was formation of protein flocculi and precipitation of fibrin, but no proliferative reaction arose in the vascular walls. It should be borne in mind that the absence of an organization process makes the morphological determination of the duration of the disease extremely difficult. In our material, the only reliable criterion was the “spheres” of lymphoid tissue, which accurately documented the death of animals during the first day after irradiation.

An interesting detail of the study is the observation of the relative resistance of macrophages, which preserve their structure even in the region of extensive foci of necrosis. However, during acute radiation sickness their phagocytic function is lost or sharply reduced, which is well documented by the absence of “heart-defect” cells in the lungs, the intactness of the Kupffer cells of the liver, and the extracellular location of hemosiderin in the spleen.

It must also be emphasized that in our material on acute radiation sickness there was no microbial invasion and, consequently, the entire morphological picture of the disease described was determined by the primary pathology.

A substantial distinctive feature of our material on acute radiation sickness consists in the clear documentation of profound disturbances of protein metabolism. This is manifested in the universal alteration of the structure of the paraplastic substance and in dystrophic changes giving a picture of hydropic nephrosis and vacuolar degeneration of the mesothelium.

We studied a number of cases of chronic radiation sickness. This material is insufficient for a complete characterization of the morphological picture of the disease. But it has a certain value, since it makes it possible to clarify the dynamics of the development of the process. In cases of late death of the animals (4–6 months after irradiation), there was progression of necrotic processes, no proliferative reaction, and persistent structural changes in the paraplastic substance remained.

Analysis of the material is also of interest from the standpoint of the degree of sensitivity of individual tissues to irradiation. Our investigations differ considerably from the numerous data in the literature reflecting the well-known law of Bergonié and Tribondeau. Thus, in our experiments there was early and irreversible damage to the nervous system, in which all links suffered except the cerebral cortex. Changes in the liver, about which little is said in the literature, were also constant. And, finally, early-occurring and irreversible restructuring of the paraplastic substances was extremely typical. Consequently, in the material presented, it was not possible to establish the fact of tissue sensitivity to irradiation as a function of the intensity of cellular proliferation. Rather, it was possible to show that tissue death does not depend on the state of its cellular elements and that, under the action of rays generated by the betatron, both cellular and noncellular structures are equally sensitive.

Thus, the peculiarities of the manifestation of radiation sickness caused by the betatron consist in the early occurrence of progressive irreversible destructive changes in the internal organs, in the formation of distinctive structures in lymphoid tissue, and in a profound, morphologically documented disturbance of protein metabolism.