Experimental abruptio placentae in the rabbit

Experimental abruptio placentae in the rabbit DOUGLAS M. HAYNES. M.D Loui.sville, Kentucky

S I N c E the observation, by Howard and Goodson/ that compression of the inferior vena cava of the pregnant dog near term regularly results in separation of the placenta, a method has been available for the experimental production of abruptio placentae. Before this observation, only isolated instances of abruptio-like states had been reported in experimental animals in the absence of direct trauma. Morse/ in 1918, isolated and ligated the ovarian, mesometric, and uterovaginal veins to one horn of the uterus of a pregnant rabbit, with the production of generalized uterine cyanosis, partial placental separation, and small myometrial hemorrhages. Barcroft, Herkel, and Hill, 3 in 1933, while studying the blood flow of the pregnant rabbit uterus, noted that moderate pressure on the uterine vein resulted in intrauterine hemorrhage; regrettably, they undertook no follow-up studies to clarify the mechanism of this bleeding. In 1939, McKelvey 4 advanced the hypothesis that the retroplacental hemorrhage of abruptio originates in the vessels of the decidua basalis. McKelvey's study of the histologic features of the decidual vessels in the nearterm human placenta suggested that decidual arteriolar rupture may be preceded by

deposition of fibrinoid material in the vessel walls; focal weakening in the walls may then result in pseudoaneurysmal dilatation and ultimate hemorrhage per rhexis. These changes take place normally as term is approached; but exceptionally the hemorrhage is sufficient to produce clinical signs of abruptio. McKelvey concluded that the tissue changes involved in premature separation of the placenta may be present in most, or all, human placentas, so that to some extent abruptio placentae may be regarded as a pathologic exaggeration of a normal process. These findings tend to throw doubt on the hypothesis that abruptio placentae associated with specific toxemia of pregnancy results from local tissue changes of toxic origin. In 1953, Mengert, Goodson, Campbell, and Haynes 5 experimentally produced separation of the human placenta at term by compressing the inferior vena cava for 5 minutes at cesarean section in 2 women who demonstrated the supine hypotensive syndrome of late pregnancy. From this observation they concluded that inferior vena cava compression constitutes a valid experimental method of producing abruptio placentae in the human. These workers did not claim that the usual clinical forms of abruptio are so produced; they considered caval compression to be merely one possible mechanism of accidental hemorrhage. Further support of this hypothesis >vas provided by Nesbitt, Powers, Boba, and Stein, 6 who produced abruptio placentae in dogs by ligation of the inferior vena cava below the renal and above the right ovarian vein. Unfortunately, their histologic studies were limited to the observation of hemorrhagic

From the Department of Obstetrics and Gynecology of Louisville General Hospital and the University of Louisville School of Medicine. Supported by a grant from the Heart Association of Louisville and Jefferson County. Presented by invitation at the Seventythird Annual Meeting of the American Association of Obstetricians and Gynecologists, Hot Springs, Virginia, Sept. 6-8, 1962.

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necrosis of the decidual plate and hemorrhage into the muscle wall with dissection of blood between the membranes and the uterus; minute vascular changes were not described by them. From these various reported findings, it appeared reasonable to undertake a systematic serial investigation of the histogenesis of abruptio placentae in an appropriate laboratory animal. The rabbit was chosen for the present study because rabbit does ovulate on demand and develops a hemochorial placenta. It was realized that species differences would restrict possible analogies with findings in human material; nevertheless, it was thought that the study might produce data of intrinsic interest. The present study was designed, first, to describe histologic changes in decidual vessels of the rabbit on various known days of gestation 24 and 48 hours after temporary occlusion of the inferior vena cava; and, second, to compare these changes quantitatively and qualitatively with normal findings. The experimental procedure was carried out as follows: On alternate days of gestation beginning with the twentieth, gravid rabbits were subjected to celiotomy under ether anesthesia. The inferior vena cava was identified, and a braided silk ligature was so placed as to encircle the vessel. The ligature was then tightened with a hemostat so as to occlude the vena cava for 5 timed minutes, after which the ligature was released and the abdomen closed. Twenty-four hours later, each animal in the series was reanesthetized, the peritoneal cavity was reopened, the pelvic genitals were excised en masse by clamping the mesometrium, and the animal was sacrificed. The complete uterus with its contained fetuses was then fixed in 10 per cent formalin solution after an initial injection of approximately 10 c.c. of formalin into each fetal sac. Tissue sections were cut from each uteroplacental junction after fixation for at least 24 hours, and many representative areas of each tissue block were studied histologically. A second series was then studied in which the animals were sacrificed 48 hours after operation, all

the other variables in the experiment being the same as in the original series. A series of control animals subjected to celiotomy without inferior vena cava ligation was similarly studied at 24 hours and 48 hours following operation on days of gestation corresponding with those of the experimental animals. From this control material it was established that the celiotomy itself did not produce any significant variations from the nonoperated controls. Early in the study, permanent ligation of the vena cava was done in several instances, but this procedure was soon abandoned because the placentas were so extensively disrupted that fine histologic details were obliterated by the resulting diffuse hemorrhagic infarction. The latter was invariably associated with death of all fetuses of the litter involved. Satisfactory experimental and control material was ultimately obtained for days 20, 22, 24, 26, and 28 of rabbit gestation. Placentas of less than 20 days' gestation were not included because of their immature morphology. Although the length of rabbit gestation is usually stated to be 30 days, it was never possible to obtain a 30 day specimen, as all the animals operated upon at this time exhibited spontaneous labor before the end of the 24 hour postoperative period. Results

Histologic features of the normal rabbit placenta. By the twentieth day of gestation, all essential features of the organization of the rabbit placenta are present. The following distinct layers can easily be identified, proceeding inward toward the amniotic sac from the uterine wall near the mesometric attachment: (1) serosa, (2) outer (longitudinal) myometrium, ( 3) inner (circular) myometrium, (4) decidual layer, ( 5) "junctional area" (between decidua and villous tufts), (6) cotyledons, ( 7) amniotic sac. The inner, circular muscle layer contains a few venous channels with investing syncytial masses which have penetrated the musculature for a short distance. The decidual layer is prominent: it is at least as thick

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as the entire muscular layer, and in some areas it may be twice as thick. Vascular channels are scattered throughout the decidual layer; they are relatively small and inconspicuous in the 20 day placenta, but they increase markedly in prominence thereafter. Morphologic distinctions between arterioles and venules may be made on the basis of the amount of smooth muscle present in the walls of the vessels; however, Mossman 7 has pointed out that such differentiation does not correspond to the physiologic function of the vessels in question. Gross changes produced by temporary occlusion of the inferior vena cava. The 5 minute occlusion of the inferior vena cava regularly, though not invariably, produced grossly observable areas of hemorrhage, usually located close to the margin of each placenta. Occasionally, there was gross bleeding into the amniotic sac, but this finding was quite inconstant. Complete gross separation was not seen in any of the placentas from animals whose venae cavae had been temporarily occluded, although it regularly followed permanent occlusion in the few animals in whom this procedure was done early in the study. Microscopic observations. Since the experimentally induced changes can be interpreted only by comparison with normal findings for any given day of gestation, the histologic illustrations which follow will include appropriate sections from the control specimens. Study of the extensive control material of this series was minutely confirmatory of Mossman's 7 definitive descriptions of rabbit placentation, and added nothing to his original findings. The significant observations of the present study consist chiefly of microscopic changes in vascular structures of the decidual layer following the experimental procedures described. They will be summarized by means of representative photomicrographs. The 20 day placenta. On the twentieth day of gestation, the decidual layer of the rabbit placenta at the uterodeciduai junction (Fig. 11 contains numerous vascular channels of a peculiar morphology. These "arterioles"

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are lined by a trophoblastic plasmodium which forms a sheath around the vessd and extends into the lumen. Some of the \'Cssels are so encroached upon by the plasmodium that the lumen of the blood vessel is narrowed to a slit. In hematoxylin-eosin preparations, the decidua itself superficially resembles adipose tissue; the cytoplasm is abundant and clear, and the nuclei are haphazardly distributed. The wall of a typical decidual vascular channel (Fig. 2) shows focal areas of acellular fibrinoid change. Similar fibrinoid deposition was observed in human material by McKelvey. 4 The material in the present series gave a slightly positive periodic add-Schiff reaction, and thus fulfilled Montgomery and Muirhead's" histochemical criteria for the differentiation between vascular fibrinoid and vascular hyaline tissue reaction. Note the binucleate cdl at one end; it is probably the remnant of a trophoblastic lining celL The plasmodium acts as an endothelium, and no separate endothelial lining layer is present. At this stage, the decidual vessels rarely shmv any focal weakening of their walls with compensatory dilatation. Fig. 3 shows a fnrther example of the trophoblastic plasmodium lining a decidual arteriole. The granula1 change in the cytoplasm represents the earliest form of the already mentioned fibrinoid change; this feature becomes much more prominent later. Some of the vessels mntain thickly clumped collars of trophoblastic cells (Fig. 4). The vessel lumens often contain clumped cellular material made up of leukocytes or, as here, of poorly identifiable reticuloendothelial cells. Fig. 5 shows a high-power view of a small decidual vessel in an animal in the 24 hour series. Here, the fibrinoid deposition is marked and resembles that seen in the control material after the twenty-sixth day. Clumping of erythrocytes in the vessel lumen is evidence of early focal thrombosis, a phenomenon which was often encountered in rabbits sacrificed 48 hours after operation. There is still no weakening of the wall or focal dilatation. In Fig. 6, however, beginning pseudoaneurysmal dilatation is seen.

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Fig. 1. Deciduomyometrial junction of normal rabbit on the twentieth day of gestation, showing typical appearance of the de cidua and two characteristic vessels lined by trophoblastic plasmodium. (x400.)

Fig. 2. Decidual "arteriole" of normal rabbit on the twentieth day of gestation. The vessel wall shows focal deposition of fibrinoid material. (x300.)

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Fig. 3. D ecidual "arteriole" of normal rabbit on the twentieth day of gestation , showing th•.: early granular cytoplasmic change which pren'des the deposition of fibrinoid. ! <400. \

rig. 4. Decidual vessel of normal rabbit on twentieth day of gestation, showing prominent :rophoblastic lining and clumped intravascular cellular material. ( ><400.)

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Fig. 5. High-power view of small decidual vessel of rabbit sacrificed 24 hours after temporary occlusion of the inferior vena cava on the twentieth day of gestation. Note marked fibrinoid deposition in wall and beginning thrombosis. (x740.)

Fig. 6. Vascular sinus in junctional zone of the 20 day rabbit placenta 24 hours after temporary occlusion of the inferior vena cava. Note beginning focal pseudoaneurysmal dilatation and marked fibrinoid change. (x300.)

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Fig. 7. D eciduomyometrial junction of rabbit ut erus 48 hours following temporary occlusion of th e inferior vena cava on the twentieth day of gestatio n, showing focal myometria l hemo rrhage not involving decidua or placenta. (x l 40.)

Fig. 8. Cotyledon of normal 22 day rabbit placenta. Note uniform distribution of blood in the na rrow sinusoids. (x140.)

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The figure illustrates a segment of the wall of a large sinusoid located in the junctional zone between the decidua basalis and the villous tufts of the cotyledons. Here, the trophoblastic plasmodium is markedly thickened and infiltrates the underlying decidual layer. This section is representative of many studied in the experimental series which indicate that the fibrinoid material is either deposited in the cytoplasm of the trophoblastic plasmodium or else it represents a metamorphosis of that cytoplasm. Fig. 7 shows a myometrial hemorrhagic focus close to the deciduomyometrial junction in an experimental animal of the 48 hour series. A focal hemorrhage is seen separating the myometrial fibrils, but the bleeding involves neither the decidua nor the placenta, which is adjacent to the area pictured but not connected with it. Such focal hemorrhagic areas in the myometrium were noted by Morse 2 in his early studies of the changes following partial ligation of the uterine blood supply of the pregnant rabbit. Evidence from the present material shows that this frequently encountered finding is anatomically unrelated to abruptio placentae. It may be a nonspecific manifestation of hypoxic damage; in any event, it was observed sufficiently often to rule out mere artifactive dismption as its origin. The 22 day placenta. Fig. 8 is a section through the cotyledonal tissue of the normal rabbit placenta on the twenty-second day of gestation. A part of the intercotyledonary groove separating the two principal villous tufts is clearly seen at the edge. The longitudinal sinuses lined by a low cuboidal endothelium are also clearly seen. Their contained red blood cells are uniformly distributed throughout. This is the normally expected degree of vascularity seen in the villous tufts on the twenty-second day. In marked contrast is the appearance of the same anatomic region 24 hours after temporary occlusion of the inferior vena cava (Fig. 9). Here, the cotyledonary tissue shows the typical changes of subacute passive hyperemia, with focal areas of necrosis resulting in skeletonization of the sinusoidal

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structure. This is a nonspecific change of a different character from that seen in the decidual vessels, but it may well result from the same hypoxic stimulus. The focal avascularity of the area of maximum ischemic necrosis is characteristic of the kind of pathologic change that can be denoted as an ischemic or anemic infarct. Somewhat similar areas were noted in the control placentas at tenn, but not with a regularity that might suggest any analogy with the white infarcts of human placentas at term. Fig. 10 shows a high-power view of a small decidual vessel from an animal in the 48 hour series. The lumen of this vessel is completely obliterated by a plug of fibrin. This type of vascular thrombosis was frequently encountered in the experimental tissues and appeared to be a common precursor of ischemic changes in the surrounding decidua proper. The thromboses were by no means ubiquitous, and when present they involved mainly the smaller vessels. The finding is significant, however, since it indicates that the intravascular thrombosis observed in connection with clinical abruptio may be explainable by nothing more esoteric than some form of passive hyperemia. The 26 day placenta. By the twenty-sixth day, little decidual tissue remains in the region of the uterine sinuses, most of which are normally completely plugged with fibrin. Some remnants of the endometrial glands are still occasionally seen, usually near the edge of the placental implantation. Fig. ll illustrates this circumstance. Here, there is focal hemorrhage at the edge of the implantation site resulting from vena cava occlusion 24 hours earlier. This may extend to the margin of the placenta itself. Large areas of disruption such as that pictured are often encountered, but the placentas themselves remain firmly adherent to the uterine wall over most of their attachment area. This is as close to actual abruptio as the rabbit ever comes in the absence of direct separatory trauma. This degree and kind of separation is in marked contrast with human abruptio, with its well-defined retroplacental separation.

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Fig. 9. Cotyl edon of 22 day rabbit placen ta 24 hours aft('r trm porary occlusion of the inferior vPna cava. showing subacute passivf' hyperemia and focal necrosis. {:<140.)

Fig. 10. Small decidual vessel of the 22 day rabbit uterus 48 hours after temporary compression of the inferior vena cava. Note intact decidua and complete obliteration of the vessel by a fib rin plug. (x640.)

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Fig. 11. Twenty-six day rabbit uterus near placental margin showing endometrial gland remnants and disruption of the decidua 24 hours following temporary occlusion of the inferior vena cava. (x 130.)

Fig. 12. Junctional zone of the 26 day rabbit placenta 48 hours following temporary occlusion of the inferior vena cava. Note marked destruction of the degenerating decidual stroma and relative preserva tion of the vessel walls. ( x l30.)

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Fig. 13. Junctional zone of the 26 day rabbit placen ta 48 hours following tempora ry occl usion of the inferior vena cava. showing focal vacuolizatio n of the trophoblas tic plasmodium li ni ng th e vessel walls. (x ! 30.)

Fig. 14. Deciduomyometrial junction of the 26 day rabbit uterus 48 hours following tempora ry occlusion of the inferior vena cava, showing focal hemorrhagic disruption of the decidua bas alis. (x! 30.)

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Fig. 15. Cotyledon of normal 28 day rabbit placenta. Note relative avascularity and atrophy of sinusoidal endothelium. (x140.)

Fig. 16. Cotyledon of 28 day rabbit placenta 48 hours after temporary occlusion of the inferior vena cava, showing extensive areas of hemorrhage and widespread karyolysis and karyorrhexis. ( x 130.)

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Fig. 17. Myometrium of rabbit 48 hours after temporary occlusion of the inferior vena cava on the twenty-eighth day of gestation. Note ex tensive edema separating the muscle bundles. (x l30.)

More extensive changes appear in the junctional zone of the 48 hour specimen, as shown in Fig. 12. There is widespread destruction of the decidua, which is now less prominent. Pyknotic and karyorrhectic nuclear debris are scattered throughout the extensively altered ground substance but, despite widespread changes in the surrounding tissues, it will be noted that the vessel walls themselves are relatively uninvolved. Another section from the same placenta is seen in Fig. 13. Here, the trophoblastic plasmodium lining the vessel walls shows a peculiar type of focal vacuolization which was not encountered in any of the control animals. These vacuoles stained with Sudan III and appeared to be variants of the foam cells described in early atherosis of human decidual spiral arterioles by Marais. 9 The previously noted stromal necrosis is intensified around the edges of the vessel. The fibrinoid transformation seen in other experimental tissues is rarely present when this vacuolar change occurs : these seem to be mutually exclusive phenomena. This ob-

servation strikingly corroborates Marais' findings in decidual material from hypertensive women. Fig. 14 shows one of the few examples of hemorrhage into the decidua itself in the 48 hour experimental series. The cellular infiltration about the edges of the hemorrhagic focus is also typical of the findings at 48 hours after vena cava occlusion. The location of these hemorrhages was usually far from the placental site and is therefore quite different from the hemorrhage of true abruptio. These hemorrhages into the placenta arc unassociated with the infarction-like changes seen in other parts of the tissue, and the two lesions must be considered to be distinct from one another. The 28 day placenta. On the twentyeighth day, there is no significant histologic change from the twenty-sixth day. The venous sinuses are characteristically filled with fibrin plugs. The changes in the vessel walls already described are prominent in both 24 and 48 hour experimental tissues. In the normal placenta at this time (Fig. 15 ).

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the sinusoidal lining endothelium of the cotyledonal units is flattened and inconspicuous, and the sinusoids themselves are avascular. In the 48 hour experimental tissue (Fig. 16), there is loss of cellular integrity, and the microscopic fields are peppered with karyorrhectic nuclear fragments. The infarction-like change regularly seen in the cotyledonal units in earlier specimens after inferior vena cava compression is absent at this stage of gestation, presumably because of the marked reduction in vascularity. Typical areas of ischemic necrosis are, however, still present. Finally, Fig. 17 illustrates myometrial changes in the 28 day rabbit uterus 48 hours after vena cava occlusion. Here, extensive edema separates the muscle bundles, accounting for the gross finding of virtual transparency of the uterine wall. Although some similarly distributed edema is noted in the control specimens, it is much less marked than in the experimental tissues. Comment

The present experimental study has confirmed prior observations that an abruptiolike state can be produced by compression of the inferior vena cava. Although the gross and histologic uterine and placental changes which follow the performance of such a procedure in the rabbit differ significantly from the corresponding changes in the dog and the human, certain interesting similarities have been observed between the two. The specific lesions involve principally the vascular channels of the decidual layer of the rabbit placenta and, to a lesser extent, the myometrium and villous tufts. The main lesions noted consist of: ( 1) deposition of fibrinoid material in the vessel walls; (2) focal weakening and pseudoaneurysmal dilatation of the vessels; (3) thrombosis; (4) vacuolar degeneration of vascular walls; (5) focal hemorrhage at the placental edges into the decidua; (6) coagulative necrosis of the villous tufts; (7) myometrial hemorrhage and edema. The histologic features of the vascular lesions correspond closely to those described by McKelvey in the arteri-

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oles of the upper part of the decidua basalis in normal human pregnancy and in material from minimal cases of clinical abruptio placentae. Since the experimental procedure of the present study could produce only acute passive hyperemia, it is clear that the vascular lesions described are of hypoxic origin. It is unnecessary to postulate that the underlying hypoxia is the result of a circulating toxin, or indeed of any other specific circumstance; it may be of any origin at all. Thus, the present study throws no new light on the relationship between toxemia of pregnancy and abruptio placentae except to describe changes due to nonspecific hypoxia which bear some resemblance to those seen in toxemia. The fibrinoid transformation and vacuolar degeneration of the blood vessel walls of the rabbit decidua may represent an early acute form of atherosis; certainly, the appearance and location of these changes are similar to those observed by Marais 9 in human decidual arterioles, and regarded by him as basically normal, although subject to accentuation in toxemia. The present study has demonstrated that these early atherosclerotic lesions are greatly accelerated and accentuated by the experimental production of the acute passive hyperemia of short duration which follows mechanical compression of the inferior vena cava. From the present study, it would appear justifiable to state that gross abruptio placentae does not occur in the rabbit placenta in the same way as in the dog or in man. However, the effect of compression of the inferior vena cava in late pregnancy does produce histologic changes which suggest that vascular lesions similar to those of abruptio in other animals may be the result of hypoxia secondary to passive hyperemia alone. The progressive decidual changes observed in the experimentally treated rabbits have been systematically studied and described, and appear to be exaggerations of the normal process of placental degeneration which precedes the physiologic termination of pregnancy in this animal.

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Certain interesting differences between placental attachment in the rabbit and in other animals have been demonstrated for the first time, notably the extreme resistance of the rabbit placenta to retroplacental hematoma formation and gross separation from the uterine wall. This finding, now documented, refutes the contrary implications of other workers. 2 • 3 Direct systematic investigation of the pathogenesis of abruptio placentae in man is obviously impractical, and the analogies with human material of such findings as those reported here must be interpreted with caution, especially when they are so striking as to be interesting. If the associated cumbersome practical problems could be solved, it would be interesting to perform a parallel series of experiments in the monkey, whose placental anatomy bears a closer relationship to the human than does that of the rabbit.

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1. An abruptio-like state was produced in pregnant rabbits by temporary occlusion of

the inferior vena cava at varying intervals between the twentieth and twenty-eighth days of gestation. 2. Histologic studies were made of the uteri and placentas from the experimental animals after postocclusion recovery intervals of 24 and 48 hours. 3. The principal microscopic lesions observed under these conditions were ( I ) fibrinoid deposition and focal pseudoancurysmal dilatation, thrombosis, and vacuolar degeneration of decidual vessels; (2~; coagulative necrosis of villous tufts; and (3) myometrial hemorrhage and edema. 4. These changes, which strikingly resemble previously described findings in human decidual arterioles in abruptio and toxemia, appear to be exaggerations of the normal process of placental degeneration. 5. Differences between placental attachment in the rabbit and other species have been demonstrated, notably the t'xtreme resistance of the rabbit placenta to retroplacental hematoma fonnation and to gross separation from the uterine wall.

REFERENCES 1. Howard, B. K., and Goodson, J. H.: Obst. & Gynec. 2: 442, 1953. 2. Morse, A. H.: 8urg. Gynec. & Obst. 26: 133, 1918. 3. Barcroft, J., Herkel, W., and Hill, 8.: J. Physiol. 77: 194, 1933. 4. McKelvey, J. L.: AM. J. 0BST. & GvNEC. 38: 815, 1939. 5. Mengert, W. F., Goodson, J. H., Campbell,

R. G., and Haynes, D. M.: AM. J. OssT. & GYNEC. 66: 1104, 1953. Nesbitt, R. E. L., Jr., Powers, 8. R., Jr., Boba, A., and Stein, A.: Obst. & Gynec. 12: 359, 1958. Mossman, H. W.: Am. J. Anat. 37: 433, 1926. Montgomery, P. O'B., and Muirhead, E. E.: Am. J. Path. 33: 285, 1957. Marais, W. D.: J. Obst. & Gynaec. Comm. 69: 234, 1962.

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Discussion F. MENGERT, Chicago, Illinois. Because of time limitation, Dr. Haynes omitted most of the background material and correctly confined himself to a description of the experimental results. Therefore, I will supply this background material, although much of it is familiar to you. In September, 1950, a young multigravida at term, lying supine on the examining table in a district prenatal clinic complained of acute, severe, right lower quadrant pain, became pale, DR. WILLIAM

sweated profusely, and exhibited mild muscular twitching. The blood pressure was insufficient to be recorded on the sphygmomanometer but the pulse rate was 160 per minute. We suspected placental abruption or ruptured uterus and upon arrival at the hospital promptly opened the abdomen, to find only a normal pregnancy. Nothing was available at that time in clinical writings regarding this phenomenon which, we subsequently discovered, occurs in about I in 10 pregnant women at term. Every obstetrician

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knows that no woman in late pregnancy will remain voluntarily on the back for any considerable period of time. By means of polyethylene catheters indwelling in the femoral vein, we learned that every woman in late pregnan<:y lying supine quickly develops an elevated venous pressure two to three times greater than that when she assumes any other position, including standing, sitting, or lateral prone. Despite the universality of elevation of femoral venous pressure in the supine position, only 1 woman in 10 develops the signs and symptoms of clinical shock. From studies on pregnant dogs it was learned in the laboratory that occlusion of the vena cava, and nothing else, reproduced this phenomenon. Moreover, it could not be produced in nonpregnant dogs or those in early pregnancy. As an unexpected result of these experiments, it was noted that abruption of a portion of the placenta often followed temporary caval occlusion. We gave some thought to extending this observation to the human, but for obvious rf'asons refrained. In April, 1953, a made-to-order clinical situation fortuitously appeared. A multigravida with 8 living children entered the hospital 24 hours after onset of labor with obvious obstruction because of a large fetus. At cesarean section the vena cava was occluded for 5 minutes by digital pressure. About seven-eighths of the placenta abrupted and several hundred cubic centimeters of dark blood was found retroplacentally. The child survived and weighed 5,000 grams. Subsequently we did this in another multigravida with abruption of about one-half of the placenta and the birth of a living child. Dr. Haynes decided that with a method at hand to produce abruption at will, it would be interesting to study the resulting histologic rhanges. He chose the rabbit probably because of its ready availability and because Morse and Barcroft each noted phenomena similar to abruption in this animal many years before. Neither investigator pursued his observation or studied the histologic changes. Although Dr. Haynes did not find gross placental abruption in the rabbit and, therefore, did not have opportunity to study specific early histologic changes, he has developed knowledge and skills. Knowledge of the etiology of this relatively common obstetric accident is so important, I hope Dr. Haynes will have opportunity to pursue these studies in the monkey

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or perhaps even in the dog. Not only does he possess the obstetric knowledge and essential training in general pathology, but also specific ability to work on this problem. Finally, he must be the world's leading expert in the histopathology of the rabbit placenta. DR. E. D. CoLVIN, Atlanta, Georgia. The work of Dr. Haynes has demonstrated that temporary occlusion of the venous drainage of the uterus in the pregnant rabbit consistently produces grossly observable areas of hemorrhage at the margin of each placenta. In all instances the central portion of the placenta failed to separate. Furthermore, he reports that the path of the hemorrhage was into the adjacent decidua with a spread outward between the membranes and uterine wall. Time does not permit a review of the controversial ideas advanced in regard to the path of the maternal intervillous circulation. Obstetricians increasingly recognize rupture of the marginal sinus as a clinical entity and in our experience it is the most frequent cause of hemorrhage throughout pregnancy. It is readily conceivable that obstruction to venous drainage in the presence of unaltered arterial inflow would lead to forceful rupture of the channel at its most vulnerable area --the marginal sinus. In my opinion, Dr. Haynes' production of hemorrhage at the edge of the placenta represents a forced break of the marginal barrier of the placenta rathrr that the production of true abruptio placentae. It is very significant that the central portion of the placenta did not separate. Basal spiral arterioles, weakened by degenerative changes in their walls, showed no tendency to rupture and create hemorrhage sufficient to detach the placenta, as is the case in true abruptio placenta<'. It is important that rupture of the marginal sinus be recognized as an entity and not be confused with abruptio placentae. One sees this confusion far too often in obstetric literature. There must be some explanation offered for the high incidence of tox<>mia and coagulation defects often associated with abruptio placentae, but conspicuously absent in hemorrhage due to rupture of the marginal sinus. The hallmark of true abruptio placentae is the finding of a black or brown area of acute or subacute infarction overlying a firm clot. indenting the placenta in this area. The placenta must have been fixed in 10 per cent formalin

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Fig. 1. (Reprinted from Bartholomew, R. A.: AM. 0BST. & GYNEC. 82: 277, 1961.)

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4 or :l weeks. Microscopically, the villi are enlarged, the intravillous space almost obliterated, the chorionic epithelium necrosed, and, particularly noticeable, there is a marked distention of the villous capillaries (AM. J. 0BsT. & GYNEC. 82: 277, 1961, Fig. JC). The condition of the capill aries, enlarged and crowded with the blood cells in infarcted areas, poses a question: Why are they distended with erythrocytes while in adjacent normal tissue the capillaries are small and the erythrocyte content far less conspicuous (idem, Fig. !B)? Bartholomew, in the aforementioned article, expressed the view tha t Fig. I possibly offers an explanation. Along the course of fetal veins on the surface of the placenta there are occasional indentations, some of which mark the site of the sphincters. This illustration (idem, Fig. 4) shows a cross section of the circular smooth muscle fibers of a sphincter. The congestion in the capillaries must be due to placental vein sphincter spasm obstructing afferent blood flow to the fetus, causing rapid aecrosis of chorionic tissue, and output of thromboplastin, foll owed by generalized intravascular fibrination. This characteristic placental pathology is apparently not to be found in pseudo-abruptio placentae. In Dr. Haynes' rabbits the intervillous maternal blood is blocked, whereas in true abruptio placentae the afferent fetal intravillous blood is blocked. The consistent presence of these ac ute infarcts in the formalinfixed placenta of toxic pregnancies causes me to agree with Bartholomew, and believe that abruptio placentae and acute toxemia have a common background in infarction of the placenta produced by interference with fetal, rather than

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maternal, circulation. Hence, ou r views as to the etiology of abruptio placentae conflict with those of Dr. Haynes. It is doubtful if any situation could ari,; ,~ in pregnancy, comparab le in its effect s, tn manual occlusion of the vena cava. It is possible that partial degrees of occlusion such as I ying- too long in the su pine position might be a factor in producing rupture of the marginal sinus. Discomfort in this position usually causes the patient to lie on her side for relief. I have enjoyed the privilege of studying Dr. Haynes' paper and, although I differ with him regard ing the etio logy of abruptio placf'ntae, 1 believe that his investigation will result in further stimulating our thinking in regard to the pathologic background of this seyere n>mplication of pregnancy. In closing, I wish that I could persuade Dr. Haynes to block a fetal vein of the intact placenta of the ape or human. In the early 1930's, Dr. Bartholomew and I unsuccessfully attempted such an experiment in the rabbit. Consistently, the rabbits delivert'd. It seems possible 1hat an illumination equipped instrument with ,\ clipbearing tip, similar to the resectoscope of the urologist, could be passed through the nterin<' wall into the amn iotic sac and a vein he identifi ed and occluded . J firmly believe that 'uch a procedure would produce a localized infarction and that an intNesting placenta would ''""Ir. DR. CoNRAD G. CoLLINS, ~<; w Orleans, Louisiana. Separation of the placenta has been produced in dogs by compression or ligation of the inferior vena cava (Howard, B. K., and Goodson, J. H.: Obst. & Gynec. 2: '142, I 953). Now Dr. Haynes has produced similar re~ults by ligation of the vC'na cava in th e rabbit. To compare these results with what happens when the wna cava is ligated in the hunnn is not wholly justified in that the placenta in rhc dog, rabbit, and man differ. True, all thn-c have deciduate placentas but all deciduate placentas are not of the same type by morphology or histology. In the dog the placenta differs from that in man both in morphology and histology, the dog placenta being categorized as zonary (labyrinthine) and endochorial. In man the placenta is discoid (villous) and hemorhorial. In the rabbit though the placenta is drsroid it is not villous, but labyrinthine, and though Witschi (Deve lopment of V ertebrates, 1956, W. B. Saunders Company) classifies it as hemochorial

Volume 85 Number 5

Arey (Developmental Anatomy, 1956, W. B. Saunders Company) classifies it as hemoendothelial. Also, when one considers the amount of decidua that the uterine mucosa contributes to the placenta, or the loss of maternal tissue at birth, dogs and rabbits fall in the classification of moderate deciduates and man as an extensive deciduate. Certainly these factors must be considered in the determination of the ease or difficulty one encounters in separating placenta from uterus by raising venous pressure distal to a suddenly occluded site in the vena cava. Furthermore when one ligates a major vessel all the vessels distal to the point of ligation go into spasm. We believe this is one of the reasons Nesbit, Powers, Boba, and Stein (Obst. & Gynec. 12: 359, 1958) demonstrated a reduced incidence of placental separation as well as degree of separation and retroplacental bleeding in pregnant dogs subjected to ganglion blockade at the time of vena cava ligation as compared to those in whom ganglion blockade was not utilized. Vasospasm in the artery and arterioles of the maternal portion of the placenta leading to increased capillary permeability or rupture has not been mentioned as a possibility in any of these experiments, yet these factors are recognized as being most important in theories explaining bleeding from estrogenic or progestational endometria. It would therefore certainly appear that factors other than increased venous pressure play a part in the form of experimental placental separation. Also to be considered are the routes of collateral venous circulation available. In the human following ligation of the inferior vena cava most of the venous blood returns through the vertebral and lumbar veins. This has been demonstrated in our laboratories (Robinson, L. S.: Surgery 25: 329, 19•1:9). I do not know anything about the collateral flow in dogs or rabbits. Our experiences at Tulane with ligation of the vena cava in the human have been reported. The series now numbers well over 150 cases. Immediate and long-term follow-up as regards survival, control of sepsis, vascular studies, and pregnancy following this procedure have been studied in detail and recorded. However, all these cases represented those in which the procedure had been utilized in postpartal or postabortal women. What then happens in women who are pregnant and in whom the vena cava is ligated? Does premature separation of the placenta occur? Are there any other untoward

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results? Do humans react in the same manner as dogs and rabbits? The evidence derived from 4 known cases in which the vena cava was ligated during pregnancy iri the human is that there is a vast difference between the results found in the human and those in the dog and rabbit. Of 4 cases referred to are 2 to be found in the literature and 2 that have occurred in New Orleans but previously unreported. Case 1 (Young, R. L., and Derbyshire, R. C.: Ann. Surg. 131: 252, 1950). Inferior vena cava ligation at 9 weeks' gestation for left common and external iliac vein thrombosis following appendectomy. Spontaneous labor during the thirty-ninth week of gestation. Normal delivery with episiotomy and low forceps following uneventful 8 hour labor. Placenta removed manually 15 minutes later because of only partial separation. Estimated total blood loss 125 c.c. Examination 12 months later showed the patient to be normal. Case 2 (Rubin, N. W.: AM. J. OnsT. & GYNEC. 80: 542, 1960). Ligation of inferior vena cava at 14 weeks of pregnancy for pulmonary infarction and ileofemoral thrombosis failing to respond to anticoagulant therapy. Subsequent prenatal course was uneventful. Spontaneous labor at tenn of 9;h hours resulted in birth of normal 6 pound, 14 ounce female. There were no complications. At the last examination 2 years later the patient was entirely normal. Case 3 (Tulane Unit, Charity Hospital: Not reported previously; G. J. T59-320991). I! eofemoral thrombophlebitis, left leg, at 16 weeks' gestation, admitted by general surgery service. Anticoagulant therapy prescribed with good symptomatic improvement. One month later readmitted with recurrence and pulmonary infarct. Ligation of inferior vena cava and ovarian vessels performed (patient 20 weeks pregnant). No further antenatal complications. Spontaneous labor and delivery at 36 weeks of 4 pound, 1 ounce premature infant. No complications in labor or puerperium. Case 4 (Dr. 0. R. Depp: Not reported previously; Mrs. S. J.). Admitted to Baptist Hospital for progressive ileofemoral thrombophlebitis following Pott's fracture. Patient at tenn; cervix 4 em. dilated. Ligation of inferior vena cava performed. As no color changes or contractions were noted in the uterus for a period of 15 minutes following ligation the abdomen was closed. Spontaneous labor 60 hours later with normal delivery and no complications, or evidence of premature separation at any time. Patient has remained well since that time. We wish to reiterate that ligation of the inferior vena cava in the human during pregnancy in these cases failed to produce any evidence of premature separation of the placenta or any untoward results. This differs from the

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experience of those who have ligated the inferior vena cava in carnivores or higher rodents. We sugge$t that their future animal experiments bf' performed on primates.

DR. WILI~ARD ALLEN, St. Louis, Missouri. Having been a rabbit expert myself some years ago, I would like to bring to your attention some rxperiences which George Heckel and I had and which were reported at that time. These concerned the administration of a single dose of ('Strogen to pregnant rabbits which killed the fetuses. This was extraordinary because not much estrogen was required and the fetuses were not killed immediately. These rabbits were near term aud the fetuses died 17 to 18 hours after injection. One of the most remarkable aspects of the situation was this: When the abdomen of 'uch a rabbit was explored just prior to fetal dPath, thf' pelvic veinR were extraordinarily dilated. Ht're one would have the impression that venous stagnation induced by the administration of estrogen caused so much anoxia that the fetuses died. In those days we were not as fancy about the details of placental separation and pathology, but I am sure what we saw \\'aS precisely the same as what has been describPd so well this morning. DR. R. A. BARTHOLOMEw,* Atlanta, Georgia. Dr. Haynes' conclusions indicate that his experiment did not produce true abruptio, but did produre hemorrhages around the margin of the placenta. There was no separation of the placenta and no accumulation of clots beneath it. I believe the experiments were of value in that they showed the site of greatest vulnerability to be along the course of the marginal sinus. This is understandable, since the outer wall of the sinus h membranous and therefore very fragile. Any considerable increase in pressure in this circulation would first affect the sinus. Dr. Colvin's illustrations show the consistent appearance which we have found to be specific for true placental abruptio, and the mechanism hy which it develops. In contrast to the effects of ligation of the vena cava, which blocks exit of maternal hlood from the placenta and causes rupturf~ of the marginal sinus, true abruptio placentae apparently results from blockage of fetal arterial blood in the placental veins I>\ plarental sphinctt>r .~pasm. This causr.s markerl 7

Bv ittdtatinn.

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March l , I!lb:> & Gyn
J Obst.

dilatation of the villus capillaries and, secondarily, expansion of the villi. The intervillous spaces are narrowed or occluded, thereby causing anoxir necrosis of the cytotrophoblast. Release of throrn~ boplastin takes place, setting up intra\'asculat fibrination (See Fig. 5A, AM. J. 0BST. & UY"'Ec. 82: 277, 1961). Vara, a Finnish investigator, verified the normal increase in fibrinogen late in pregnancy, enhanced during nnd after delivery for a short time before returning to normal (Geburtsh. ll. Frau· enh. 18: 432, 1958). Pre-eclampsia caused a decrease in fibrinogen preceding labor, followed by a considerable decrease during and just after delivery thereafter retuming to normal. Abruptio placentae was associated with the greatest de· crease, often causing afibrinogenemia and loss of dotting power. We do not believe that partial or complete occlusion of the vena cava, whether experi· mental or clinical, produces the gross and microscopic appearance which is shown in the'>l~ slides and which is consistently specific in •:ases of true abruptio. In case that Dr. Haynes finds it possible to use apes experimentally, it >vould he of great interest to note the behavior of fibrin· ogen before, during, and after partial or complete occlusion of the VPna cava. It is our opinion that these variations in fibrinogen, charactt>ristic of toxemia, would not occur in ligation of the vena c:ava. DR. HAYNEs (Closing). The interesting possibility that the lesions seen in the experimental tissues might have resulted from some form of rupture of the marginal sinus was raised in Dr. Colvin's discussion. I did not mention this possibility in discussing the experimental material since my primary concern was the objective presentation of the histologic findings. Then, too, the rabbit placenta does not have a dearly demonstrable structure corresponding to the marginal sinus in the human, and any analogy along these lines seemed unjustifiable from the anatomic viewpoint. Dr. Colvin's suggestion that the rabbit lesion described by me be termed "pseudoabruption" rather than "abruption" is an excellent one. Dr. Collins' follow-up observations on patients with antecedent ligation of the inferior \'ena cava did not startle me unduly. Our investigations of the supine hypotensive syndrome have never led us to maintain that the etiology of human abruptio placentae is often, m necessarily ever,

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Numbe-r 5

compression of the inferior vena cava. In the course of the experimental investigation of the hypotensive syndrome, we fortuitously discovered that abruptio placentae resulted in the pregnant dog from inferior vena cava compression, and later we produced abruption-like changes in the human placenta by the same means. After doing this rather extensive study in the rabbit, I was disappointed to find that in this animal caval compression did not produce gross separation of the placenta. As a consequence, direct analogies between the rabbit and the human could not be

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drawn. Nevertheless, it seemed to me that the changes which were observed in the rabbit material did present several intriguing points of similarity with previously described human material, and deserved being placed on record. Dr. Allen has encouragingly supported my underlying thesis by his suggestion that estrogeninduced passive hyperemia might well haYe the same effect as hyperemia resulting from mrchanical blockage of venous outflow. Such a hypothesis seems to me to be entirely logical.