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Placental changes after experimental abruptio placentae and fetal vessel ligation of rhesus monkey placenta
Placental changes after experimental abruptio placentae and fetal vessel ligation of rhesus monkey placenta RONALD E. MYERS, M.D. TOSHIO FUJIKURA, M.D. San Juan, Puerto Rico, and Bethesda, Maryland After vascular /igation of fetal vessels using rhesus monkq placentas at 100 to 120 days' gestational age, syncytial trophoblasts and cytotrophoblaJts were found to be still growing 40 to 50 days after treatment. The villi in the treated lesions were few, large, and fibrotic. There were neither intervillous fibrin deposits nor thrombi in the wide intervillous spaces. Because of the sparsity of villi, the syncytial trophoblaJt was seemingly increased in amount. The monkey fe/uses appeared to tolerate the insult of fetal vascular ligation, but experimental abruptio placentae resulting in derangements of the maternal circulation caused fetal death in utero.
A L THO UGH many investigations 2 • 3. 6. 7. 11, 12 on the histopathology of toxemic, diabetic, and postmature placentas have been reported, the significance of degenerative changes and simultaneous growth of trophoblasts is not clearly understood. 11 Two separate vascular systems, the maternal and fetal circulations, exist in this unique organ. Much attention has been focused on maternal ischemia and its importance in the placental pathology of these conditions.!' 6, 9 However, the role of fetal vessel occlusion as a possible pathogenetic factor has not been explored except in a recent investigation by Fox.' The purpose of the present study is to produce and analyze pathologic lesions in the rhesus monkey placenta following experimental abruptio placentae and following closure of the fetal placental circulation. Materials and methods The pregnant monkeys (Macaca mulatta, used in this study were obtained from <& From the Laboratory of Perinatal Physiology, Nationallnstitut, of Nllurological Disllases and Blintinllss, San Juan, and thll Perinatal Research Branch, Nationallnstitutl of Neurological Diseaslls and Blindnllss, National Insei/utlls of Health, Bethlsda.
caged breeding colony at the Laboratory of Perinatal Physiology in San Juan, Puerto Rico. Timed mating and animal care have been described in previous papers. t, 5. 10 In 13 monkeys fetal placental vessel ligation was perfonned. In 6 monkeys experimental abruptio placentae was produced. Both procedures were done at 100 to 120 days' gestational age. Placental outline was detennined by transillumination through the uterine wall or by palpation. The placental edge was approached by incision without rupture of the amniotic sac. Extra-amniotic ligation of fetal vessels coursing the fetal surface of the placenta was perfonned. Arteries and veins running alongside each other were ligated together by silk thread. The vessels ligated were either those near the insertion of the wnbilical cord or those bridging the two placental lobes. Experimental abruptio placentae was accomplished by simple manual separation of the placenta from the uterine wall. Manual separation was restricted to the entire accessory lobe in which there was no insertion of the umbilical cord. The animals were later delivered of their fetuses by cesarean section at 156 to 158 days' gestational age unless the pregnancies had already tenninated by spon-
Volume 100 Number 6
Placental changes after ligation of fetal vessels
taneous vaginal delivery. The placentas were examined grossly and microscopically. Relults
Of 13 monkeys in the ligation group, 8 had live births 40 to 50 days after treatment. Of
the remaining 5, 2 had stillbirths and 3 had fetuses which died shortly after the operation. The following description pertains to the placentas associated with live births of the ligation group. Distal to the point of ligation, the placental parenchyma in devascu-
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847
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~. . .. .,'~ .. ' .. .... ..-:.- , . ..... • .• • ~
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Fig. 1. A, DevaJcularized portion of ligated placenta (No. 846). (x63.) B, Devaacularized portion of ligated placenta (No. 846). (x230.) Fetal vellel ligation wu performed at 120 days' ge.tational age and a live monkey was delivered by cesarean section at 158 days. B, A portion of A at high magnification. The fibrotic villi are scattered in the wide intervillow spaces. Cytotrophobla.ts and .yncytial .prouts are relatively increased in proportion to the number and .ize of the remaining villi. A small amount of calcium deposition is Doted in the villow stroma. There are neither intervilloUi fibrin depotit. nor thrombi in the intervillous Ipacel.
848 Myers and Fujikura
larized areas was thin and atrophic being half to one-third the normal thickness. An estimated 20 to 40 per cent of the entire placental areas were devascularized as a result of the procedure. Distribution and degree of devascularization varied with the place of ligation and the presence of collateral circulation. Devascularization was more pronounced when ligation was performed on the vessels bridging the two lobes but was less constant when performed on the fetal vessels of the main placental lobe. Cross sections did not reveal any critical color differences between the affected and normal portions of the fresh specimens, although small parenchymal cavities were found in the devascularized areas. After 10 per cent formalin fixation, some demarcation was noted between the normal and devascularized zones. A sharp contrast between the two zones was observed upon microscopic examination. In the affected portions, the majority of the remaining villi were large, fibrotic, and avascular (Figs. 1, A and Band 2). Wide intervillous spaces of uneven
Maleh \5, 1968
Am .
J. Obol. I: GyDec.
distribution were present between the few villi. Syncytial trophoblasts including syncytial sprouts9 and knots appeared to be increased in proportion to the number and size of the villi (Figs. 1, B, 2, and 3, A and B). Free and pedunculated syncytial sprouts were conspicuous in the wide intervillous spaces. I n some villi the stroma showed specific degenerative changes, such as calcification and fibrinoid and cystic degeneration. In contrast to the degenerative changes, cytotrophoblasts were also growing in the villous stroma and cytotrophoblastic columns (Fig. 2) . For the most part there was no longer any trace of fetal capillaries or larger vessels in the terminal and stem villi. However, there were still several terminal villi with intact capillaries, and presumably these were collateral vessels. Maternal vessels in the decidua basalis appeared normal and showed no thrombosis. In the abruptio group, all 6 fetuses died in utero shortly after the operation. Four monkeys were delivered spontaneously of stillborn fetuses 48 to 72 hours postoperatively and 2
•
. .•
.....
• ••• ~
Fig. 2. Devascularize"d portion of ligated placenta (No. 846). (x230.) This repl'elenta a different microscopic field of the placenta in Fig. 1. Free and pedunculated syncytial .prouts are noted in the wide intervillous spaces. The villus on the left aide ahOWI cyatic degeneration and calcium deposition of the atroma. On the right aide increased cytotrophobluta are seen in the villul.
Volume 100 Number 6
monkeys had fetal retention for more than 72 hours. The treated placental lobe had a dark brown color and showed areas of blood stagnation on cut section. The other placental lobe was of normal color. Microscopic examination showed extensive necrosis of syncytial
Placental changes after ligation of fetal vessels
849
trophoblasts and cytotrophoblasts (Fig. 4-). The fetal capillari!'!s and larger vessels were degenerated or congested. The maternal vessels in the decidua basalis were extremely congested and often thrombosed. Neutrophilic and lymphocytic infiltration in the
Fi&,. 3. A, Nonnal portion of ligated placenta (No. 846). (x63.) B, Normal portion of ligated placenta (No. 846). (x230.) A and B belong to the normal portion of devucularized placentu FigJ. 1 and 2. The chorionic villi are well developed and villous capillariel are patent with numerous erythrocyte.. Syncytial knots and aprouu are noted in the narrow intervlUous apacel. Cytotrophobluu are pretent but relatively few in the villous atroma.
850
March 1!>, 1968
Myers and Fujikura
Am.
."
. '.. .
tt
'
J. Obst. I: Gynec.
.. .
~
Fig. 4. Experimental abruptio placentae (No. 894). (x230.) Treatment WlU performed at 110 days' gestational age, and a stillborn monkey was spontaneously delivered less than 48 hours postoperatively. There is rapid degeneration of the chorionic villi by coagulation necrosis. The intervillous spaces are widened by marked plUsive congestion.
decidua basalis was minimal. Since pregnancy terminated shortly after the operation the remaining chorionic villi were still moderately immature. Comment
It is interesting to know that syncytial trophoblasts and cytotrophoblasts are found to be still abundant following ligation of placental fetal vessels. A review of the literature on the significance of increased syncytial knots has been given by Fox.? No convincing explanation has been provided for the cause of increased syncytial knots in the human placenta. A major factor in the excessive production of syncytial knots, as Fox indicated, may be a diminution in fetal blood flow in the terminal villi. Obstructive lesions of the fetal vessels are known to occur in the placentas in toxemia and diabetes mellitus, but their significance has not been completely understood. 12 Increased syncytial knots have been described in placentas of toxemic8 , 9, 12 and diabetic2 women, and these may be related pathogenetically to fetal vessel occlusion. Tominage and pageta claimed to have produced syncytial knots in tissue
cultures of term human chorionic villi following hypoxia, the knots reducing in number with resumption of normal oxygen concentration. However, this is not necessarily the case in vivo. Under the present microscopic observation there was no absolute increase in the number of syncytial trophoblasts in the devascularized areas, the increase being only apparent because of the sparseness of villi (Figs. 1, A, 2, and 3, B). Trophoblasts in the early stage of placental development exhibit phagocytic and cytolytic activities. I , U It is possible that even in later developmental stages, trophoblasts, under abnormal conditions, may retain such lytic properties, digesting the degenerating villous stroma and producing the wide intervillous spaces. There were neither intervillous thrombi nor increased fibrin deposits in the areas supplied by the ligated vessels. Therefore, this suggests that intervillous thrombosis and fibrin deposition do not result as long as the maternal circulation is intact. That' fetal vessel ligation caused thinning of the devascularized areas indicates the essential role played by fetal vessels in placental growth. During the neonatal period no neurological nor anatomic
Volume 100 Number 6
abnormalities were demonstrated in these animals. However, birth weight in this group was slightly lower than that of controls of similar gestational age.s It is difficult to analyze the significance of this birth weight difference because of the paucity of cases. Experimental abruptio placentae always resulted in fetal death in utero within a short period after treatment, hence the affected placentas were influenced primarily by maternal circulatory disruption and secondarily by cessation of fetal circulation. The experi-
REFEIlENCES 1. Brewer, J. I .: Am. J. Anat. 61: 429, 1937. 2. Burstein, R., Berns, A. W., Hirata, Y., and Blumenthal, H. T.: AM. J. OBST. & GVNEC. 86: 66, 1963. 3. Carter, J. E., Vellios, F., and Huber, C. P.: Am. J. Clin. Path. 40: 363, 1963. 4. Dawes, G. S., Jacobson, H . N., Mott, J. C., and Shelly, H. J.: J. Physiol. 152: 271, 1960. 5. Fleischman, R. W.: Lab. Animal Care 13: 703, 1963. 6. Fox, H.: J. Ob,t. & Gynaec. Brit. Cornrn. 71: 885, 1964. 7. Fox, H.: J. Obst. & Gynaee. Brit. Cornrn. 72: 347, 1965. 8. Fujikura, T ., and Niemann, W. H.: AM. J. OBST. & GYNEC. 97: 76, 1967.
Placental changes after ligation of fetal vessels 851
ment proves the importance of maintaining the integrity of the maternal circulation, disruption of which results in the clinical picture of abruptio placentae. In the human, abruptio placentae accounts for the single most important entity responsible for fetal death in utero of known causes. 12 It is regrettable that abruptio placentae did not produce placental pathology which was solely the result of maternal circulatory disturbance.
9. Hamilton, W. J., and Boyd, J. D.: Brit. M. J . 1: 1501, 1966. 10. Jacobson, H. N., and Windle, W. F.: BioI. neonat. 3: 105, 1960. 11. Maqueo M., Azuela, J . C., and Dosal de la Vega, M.: Obst. & Gynec. 24: 350, 1964. 12. Nesbitt, R. E. L.: Abnormalities and Diseases of the Placenta and Appendages, in Novak's Gynecologic and Obstetric Pathology, Philadelphia, 1963, W. B. Saunden Company, p. 523. 13. Tominaga, T ., and Page, E. W.: AM. J. OBST. & GVNEC. 94: 679, 1966. 14. Wislocki, G. B., and Bennett, H. S.: Am. J. Anat. 73: 335, 1943.
A L THO UGH many investigations 2 • 3. 6. 7. 11, 12 on the histopathology of toxemic, diabetic, and postmature placentas have been reported, the significance of degenerative changes and simultaneous growth of trophoblasts is not clearly understood. 11 Two separate vascular systems, the maternal and fetal circulations, exist in this unique organ. Much attention has been focused on maternal ischemia and its importance in the placental pathology of these conditions.!' 6, 9 However, the role of fetal vessel occlusion as a possible pathogenetic factor has not been explored except in a recent investigation by Fox.' The purpose of the present study is to produce and analyze pathologic lesions in the rhesus monkey placenta following experimental abruptio placentae and following closure of the fetal placental circulation. Materials and methods The pregnant monkeys (Macaca mulatta, used in this study were obtained from <& From the Laboratory of Perinatal Physiology, Nationallnstitut, of Nllurological Disllases and Blintinllss, San Juan, and thll Perinatal Research Branch, Nationallnstitutl of Neurological Diseaslls and Blindnllss, National Insei/utlls of Health, Bethlsda.
caged breeding colony at the Laboratory of Perinatal Physiology in San Juan, Puerto Rico. Timed mating and animal care have been described in previous papers. t, 5. 10 In 13 monkeys fetal placental vessel ligation was perfonned. In 6 monkeys experimental abruptio placentae was produced. Both procedures were done at 100 to 120 days' gestational age. Placental outline was detennined by transillumination through the uterine wall or by palpation. The placental edge was approached by incision without rupture of the amniotic sac. Extra-amniotic ligation of fetal vessels coursing the fetal surface of the placenta was perfonned. Arteries and veins running alongside each other were ligated together by silk thread. The vessels ligated were either those near the insertion of the wnbilical cord or those bridging the two placental lobes. Experimental abruptio placentae was accomplished by simple manual separation of the placenta from the uterine wall. Manual separation was restricted to the entire accessory lobe in which there was no insertion of the umbilical cord. The animals were later delivered of their fetuses by cesarean section at 156 to 158 days' gestational age unless the pregnancies had already tenninated by spon-
Volume 100 Number 6
Placental changes after ligation of fetal vessels
taneous vaginal delivery. The placentas were examined grossly and microscopically. Relults
Of 13 monkeys in the ligation group, 8 had live births 40 to 50 days after treatment. Of
the remaining 5, 2 had stillbirths and 3 had fetuses which died shortly after the operation. The following description pertains to the placentas associated with live births of the ligation group. Distal to the point of ligation, the placental parenchyma in devascu-
,
•
, ., , ~.
,
I
.. ." ,
~ ~ ,. .
847
..
~.
,
~. . .. .,'~ .. ' .. .... ..-:.- , . ..... • .• • ~
.
,
#~
•\ ;
•'-
Fig. 1. A, DevaJcularized portion of ligated placenta (No. 846). (x63.) B, Devaacularized portion of ligated placenta (No. 846). (x230.) Fetal vellel ligation wu performed at 120 days' ge.tational age and a live monkey was delivered by cesarean section at 158 days. B, A portion of A at high magnification. The fibrotic villi are scattered in the wide intervillow spaces. Cytotrophobla.ts and .yncytial .prouts are relatively increased in proportion to the number and .ize of the remaining villi. A small amount of calcium deposition is Doted in the villow stroma. There are neither intervilloUi fibrin depotit. nor thrombi in the intervillous Ipacel.
848 Myers and Fujikura
larized areas was thin and atrophic being half to one-third the normal thickness. An estimated 20 to 40 per cent of the entire placental areas were devascularized as a result of the procedure. Distribution and degree of devascularization varied with the place of ligation and the presence of collateral circulation. Devascularization was more pronounced when ligation was performed on the vessels bridging the two lobes but was less constant when performed on the fetal vessels of the main placental lobe. Cross sections did not reveal any critical color differences between the affected and normal portions of the fresh specimens, although small parenchymal cavities were found in the devascularized areas. After 10 per cent formalin fixation, some demarcation was noted between the normal and devascularized zones. A sharp contrast between the two zones was observed upon microscopic examination. In the affected portions, the majority of the remaining villi were large, fibrotic, and avascular (Figs. 1, A and Band 2). Wide intervillous spaces of uneven
Maleh \5, 1968
Am .
J. Obol. I: GyDec.
distribution were present between the few villi. Syncytial trophoblasts including syncytial sprouts9 and knots appeared to be increased in proportion to the number and size of the villi (Figs. 1, B, 2, and 3, A and B). Free and pedunculated syncytial sprouts were conspicuous in the wide intervillous spaces. I n some villi the stroma showed specific degenerative changes, such as calcification and fibrinoid and cystic degeneration. In contrast to the degenerative changes, cytotrophoblasts were also growing in the villous stroma and cytotrophoblastic columns (Fig. 2) . For the most part there was no longer any trace of fetal capillaries or larger vessels in the terminal and stem villi. However, there were still several terminal villi with intact capillaries, and presumably these were collateral vessels. Maternal vessels in the decidua basalis appeared normal and showed no thrombosis. In the abruptio group, all 6 fetuses died in utero shortly after the operation. Four monkeys were delivered spontaneously of stillborn fetuses 48 to 72 hours postoperatively and 2
•
. .•
.....
• ••• ~
Fig. 2. Devascularize"d portion of ligated placenta (No. 846). (x230.) This repl'elenta a different microscopic field of the placenta in Fig. 1. Free and pedunculated syncytial .prouts are noted in the wide intervillous spaces. The villus on the left aide ahOWI cyatic degeneration and calcium deposition of the atroma. On the right aide increased cytotrophobluta are seen in the villul.
Volume 100 Number 6
monkeys had fetal retention for more than 72 hours. The treated placental lobe had a dark brown color and showed areas of blood stagnation on cut section. The other placental lobe was of normal color. Microscopic examination showed extensive necrosis of syncytial
Placental changes after ligation of fetal vessels
849
trophoblasts and cytotrophoblasts (Fig. 4-). The fetal capillari!'!s and larger vessels were degenerated or congested. The maternal vessels in the decidua basalis were extremely congested and often thrombosed. Neutrophilic and lymphocytic infiltration in the
Fi&,. 3. A, Nonnal portion of ligated placenta (No. 846). (x63.) B, Normal portion of ligated placenta (No. 846). (x230.) A and B belong to the normal portion of devucularized placentu FigJ. 1 and 2. The chorionic villi are well developed and villous capillariel are patent with numerous erythrocyte.. Syncytial knots and aprouu are noted in the narrow intervlUous apacel. Cytotrophobluu are pretent but relatively few in the villous atroma.
850
March 1!>, 1968
Myers and Fujikura
Am.
."
. '.. .
tt
'
J. Obst. I: Gynec.
.. .
~
Fig. 4. Experimental abruptio placentae (No. 894). (x230.) Treatment WlU performed at 110 days' gestational age, and a stillborn monkey was spontaneously delivered less than 48 hours postoperatively. There is rapid degeneration of the chorionic villi by coagulation necrosis. The intervillous spaces are widened by marked plUsive congestion.
decidua basalis was minimal. Since pregnancy terminated shortly after the operation the remaining chorionic villi were still moderately immature. Comment
It is interesting to know that syncytial trophoblasts and cytotrophoblasts are found to be still abundant following ligation of placental fetal vessels. A review of the literature on the significance of increased syncytial knots has been given by Fox.? No convincing explanation has been provided for the cause of increased syncytial knots in the human placenta. A major factor in the excessive production of syncytial knots, as Fox indicated, may be a diminution in fetal blood flow in the terminal villi. Obstructive lesions of the fetal vessels are known to occur in the placentas in toxemia and diabetes mellitus, but their significance has not been completely understood. 12 Increased syncytial knots have been described in placentas of toxemic8 , 9, 12 and diabetic2 women, and these may be related pathogenetically to fetal vessel occlusion. Tominage and pageta claimed to have produced syncytial knots in tissue
cultures of term human chorionic villi following hypoxia, the knots reducing in number with resumption of normal oxygen concentration. However, this is not necessarily the case in vivo. Under the present microscopic observation there was no absolute increase in the number of syncytial trophoblasts in the devascularized areas, the increase being only apparent because of the sparseness of villi (Figs. 1, A, 2, and 3, B). Trophoblasts in the early stage of placental development exhibit phagocytic and cytolytic activities. I , U It is possible that even in later developmental stages, trophoblasts, under abnormal conditions, may retain such lytic properties, digesting the degenerating villous stroma and producing the wide intervillous spaces. There were neither intervillous thrombi nor increased fibrin deposits in the areas supplied by the ligated vessels. Therefore, this suggests that intervillous thrombosis and fibrin deposition do not result as long as the maternal circulation is intact. That' fetal vessel ligation caused thinning of the devascularized areas indicates the essential role played by fetal vessels in placental growth. During the neonatal period no neurological nor anatomic
Volume 100 Number 6
abnormalities were demonstrated in these animals. However, birth weight in this group was slightly lower than that of controls of similar gestational age.s It is difficult to analyze the significance of this birth weight difference because of the paucity of cases. Experimental abruptio placentae always resulted in fetal death in utero within a short period after treatment, hence the affected placentas were influenced primarily by maternal circulatory disruption and secondarily by cessation of fetal circulation. The experi-
REFEIlENCES 1. Brewer, J. I .: Am. J. Anat. 61: 429, 1937. 2. Burstein, R., Berns, A. W., Hirata, Y., and Blumenthal, H. T.: AM. J. OBST. & GVNEC. 86: 66, 1963. 3. Carter, J. E., Vellios, F., and Huber, C. P.: Am. J. Clin. Path. 40: 363, 1963. 4. Dawes, G. S., Jacobson, H . N., Mott, J. C., and Shelly, H. J.: J. Physiol. 152: 271, 1960. 5. Fleischman, R. W.: Lab. Animal Care 13: 703, 1963. 6. Fox, H.: J. Ob,t. & Gynaec. Brit. Cornrn. 71: 885, 1964. 7. Fox, H.: J. Obst. & Gynaee. Brit. Cornrn. 72: 347, 1965. 8. Fujikura, T ., and Niemann, W. H.: AM. J. OBST. & GYNEC. 97: 76, 1967.
Placental changes after ligation of fetal vessels 851
ment proves the importance of maintaining the integrity of the maternal circulation, disruption of which results in the clinical picture of abruptio placentae. In the human, abruptio placentae accounts for the single most important entity responsible for fetal death in utero of known causes. 12 It is regrettable that abruptio placentae did not produce placental pathology which was solely the result of maternal circulatory disturbance.
9. Hamilton, W. J., and Boyd, J. D.: Brit. M. J . 1: 1501, 1966. 10. Jacobson, H. N., and Windle, W. F.: BioI. neonat. 3: 105, 1960. 11. Maqueo M., Azuela, J . C., and Dosal de la Vega, M.: Obst. & Gynec. 24: 350, 1964. 12. Nesbitt, R. E. L.: Abnormalities and Diseases of the Placenta and Appendages, in Novak's Gynecologic and Obstetric Pathology, Philadelphia, 1963, W. B. Saunden Company, p. 523. 13. Tominaga, T ., and Page, E. W.: AM. J. OBST. & GVNEC. 94: 679, 1966. 14. Wislocki, G. B., and Bennett, H. S.: Am. J. Anat. 73: 335, 1943.