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Studies of the pathophysiology of gastroschisis in fetal sheep
Studies of the Pathophysiology of Gastroschisis in Fetal Sheep By J. Alex Hailer, Jr., Beat H. Kehrer, lssam J. Shaker, Dennis W. Shermeta, and Robert G. Wyllie
T
HE COMPLICATED EMBRYOGENESIS of gastroschisis has been proposed and discussed by several authors.‘-4 The pathologic physiology, however, of the exposed bowel in infants with gastroschisis has not been carefully studied nor are there data to explain the dysfunction in peristalsis and the digestive malabsorption which are typical of this condition. Since living human tissue from this anomaly is rarely available for sequential study, an animal model of gastroschisis was designed and then used for studies to clarify the pathogenesis and pathophysiology of gastroschisis. The purposes of this paper are: (1) to describe a technique for the intrauterine creation of gastroschisis in the fetal lamb and (2) to record studies of the gross anatomic and histologic alterations in the exposed, eviscerated bowel. CREATION
OF ANIMAL
MODEL
OF GASTROSCHISIS
Intrauterine operative procedures were completed in 39 pregnant ewes using techniques which have been described from our laboratories.5-7 Fetal lambs from timed pregnancies were chosen at a gestational age of 80-100 days (term = 145 days) for the creation of abdominal wall defects and to allow for periods of lo-30 days during which the eviscerated bowel was exposed to amniotic fluid. The caudal half of the experimental fetus was delivered through a uterotomy incision and a full-thickness disc of abdominal wall was excised lateral to the umbilical cord. This disc varied in diameter from 0.5 cm to 5.0 cm. Several loops of intestine were allowed to eviscerate through this defect (Fig. l), and the animal was then returned to the uterus and all incisions were carefully closed. Twenty animals aborted spontaneously at various times after this procedure and they could not be used for tissue studies. Nineteen fetuses survived and were sequentially sacrificed by Cesarean section lo-30 days after the initial procedure. Intestinal tissues from seven sham-operated normal control lambs were studied in an age range from 70-120 gestational days. In addition, each experimental animal served as a comparison control because its unexposed intestine, which remained in the abdomen, was compared with the eviscerated intestine. The protocol was designed to evaluate the influence of amniotic fluid on the eviscerated bowel over varying periods of exposure. In all surviving experimental animals the eviscerated bowel loops were
From the Division of Pediatric Surgery and the Department of Pathology, The Johns Hopkins University School of Medicine. Baltimore, Md. 21205. Presented before the American Pediatric Surgical Association. New Orleans, La., April 4-6. 1974. Addressfor reprint requests: J. Alex Haller, Jr., M.D., Division of Pediatric Surgery, The Johns Hopkins University School of Medicine, Baltimore, Md. 21205. 0 I974 by Grune & Stratton. Inc. Journal of Pediatric Surgery, Vol. 9, No. 5 (October), 1974
627
HALLER
ET AL.
matted together and covered with a partially translucent membrane of varying thickness (Fig. 2). These gross changes closely mimic those found in the exposed bowel of babies with gastroschisis. MICROSCOPIC
STUDIES
OF INTESTINE
Fresh-frozen tissue from control and experimental animals were sectioned on a cryostat and representative enzymes and metabolites of essential tissue functions were demonstrated by accepted histochemical methods. Control tissues were from sham-operated animals, some were from unexposed, intraperitoneal bowel in animals with gastroschisis. NORMAL
BOWEL
STUDIES
(1) In the longitudinal and circular smooth muscle adenosine triphosphatase (ATPase), an enzyme essential for normal energy transfer processes in smooth and skeletal muscle, increased in amount with age and gradually assumed a pattern of distribution recognizable as mature in type. Similar changes in ATPase were found in the smooth muscle and vascular endothelium of the arteries. (The function of ATPase of the vascular endothelium is not known but it is widely believed to be essential for normal function and is probably related to vital membrane functions.) (2) The morphologic organization of cells lining the crypts and covering the villi increased toward the mature form. Acetylesterase was found to be a convenient marker for these cells, although similar reactions were observed in epithelial cells of ATPase and alkaline phosphatase (APase). Prior to 105 days the enzyme was present in small amounts and distributed evenly within and
PATHOPHYSIOLOGY
629
OF GASTROSCHISIS
without the crypts. Thereafter the esterase increased in amount and was confined to villous epithelial cells beyond the crypts which is the mature pattern. (3) The occurrence of mitotic figures in cells in the base of the crypts averaged one mitotic figure in every third crypt and did not change throughout the period of observation. (4) Submucosal fibroblasts were numerous and unchanged throughout the period. (5) Ganglion cells in the myenteric plexus increasingly resembled mature ganglia morphologically and showed increasing amounts of acetylesterase. (This enzyme probably lies along the path of acetylcholine synthesis-in this experiment it behaved as if this was the case, and since it can be demonstrated more conspicuously than acetylcholinesterase, it was used as a functional marker). The distribution within and between ganglion cells was even. EXPOSED
Group 1.
BOWEL
STUDIES
120 Days’ Gestation and Gastroschisis for 12 Days or Less
(1) Longitudinal and circular smooth muscle ATPase was reduced in amount and uneven in distribution. The changes were mild but readily recognized. Arterial smooth muscle and vascular endothehal ATPase was unchanged. (2) The morphology and acetylesterase content of the lumen epithelial cells was unchanged. (3) The mitotic rate of crypt cells was slightly reduced-one crypt in four or five showed mitotic figures. (4) Submucosal fibroblasts were substantially reduced in number. (5) Cells of the myenteric ganglia morphologically were within normal limits but showed a slight reduction in amount and distribution of acetylesterase and acetylcholinesterase. Group 2.
120 Days’ Gestation with Gastroschisis of12-18
Days
(1) Longitudinal and circular muscle ATPase was now reduced considerably and its distribution from one part to another of a single transverse cut and from one site to another was very irregular, an occasional part showed trace amounts only of ATPase. A similar reduction occurred in arterial wall smooth muscle. Vascular endothelial ATPase was normal. (2) Morphologically villous epithelial cells showed arrested development. The localization of acetylesterase lacked the even distribution of the normal pattern and now extended beyond the villi into the base of the crypts resembling the distribution in 70 days’ gestation control animals. (3) The mitotic rate in the crypt cells was markedly reduced. Mitotic figures were found in fewer than one crypt in eight. (4) The reduction in the number of submucosal fibroblasts was maintained. (5) The changes in myenteric ganglion cells were now gross. Acetylesterase and acetylcholinesterase were markedly reduced in amount and the amount present varied widely from cell to cell within a single ganglion and between different ganglia.
HALLER ET AL.
630
(6) The hypertrophic of collagen. Group 3.
visceral peritoneum
was increased in width and content
I20 Days’ Gestation With Gastroschisis of 20-30 Days
Essentially the same changes were found as in the previous group, but all changes were much more striking, indicating a continuing cumulative noxious influence. (1) Longitudinal and circular smooth muscle ATPase was reduced still more and the inequality of its distribution was more widely spread. Arterial wall smooth muscle ATPase was similarly affected, vascular endothelial cell ATPase was normal. (2) The morphologic immaturity and irregularities in distribution of acetylesterase in lumen epithelial cells had extended. Crypt cells were still positive for acetylesterase. (3) The retardation in mitotic rate was maintained. (4) The reduction in submucosal fibroblasts was unchanged. (5) Changes in ganglion cells had increased. Many ganglion cells appeared atrophic, all had decreased amounts of acetylesterase and acetylcholinesterase. The unevenness of the distribution of these enzymes in and between ganglia had increased further. (6) The thickness and content of collagen in the hypertrophic visceral peritoneum was increased also. DISCUSSION
The mortality of infants with gastroschisis is usually due to one or more potentially lethal complications. There is a significant incidence of associated serious abnormalities, such as respiratory distress syndrome, immaturity,8 intestinal atresia, and midgut volvulu~.*~~A second major complication may be sepsis due to exposure of the eviscerated bowel and abdominal cavity to bacterial contamination.’ The third potentially lethal complication is small-bowel injury with paralytic ileus, persistent malabsorption, and occasionally, necrosis with perforation.2*‘0-‘2 Increasingly improved management of sick newborn infants in regional neonatal intensive care centers has decreased mortality from the first group of potential complications, although associated anomalies may always constitute a limit to this salvage. The second complication, sepsis, has responded dramatically to immediate coverage’3*‘4 with plastic material and the use of potent specific antibiotics. Some improvement may still be forthcoming with further modifications in this area of surgical management. The third potential complication is now managed by total parenteral alimentation.” The pathogenesis of the bowel abnormality is unknown and was the primary target of these experimental studies. Since very few studies of the pathogenesis of the bowel injury are likely to be forthcoming from human studies,” an animal model seemed to be a first step in elucidating the pathophysiology of bowel dysfunction in gastroschisis. Sherman et aLI used a rabbit fetal preparation for acute observation of exposed intestine, but their studies did not focus on the pathogenesis of more chronic changes in the bowel.
PATHOPHYSIOLOGY
OF GASTROSCHISIS
631
The gross pathologic findings, as noted in the description of the experimental technique, are similar to those found in a human infant with gastroschisis (Fig. 2). These findings are characterized by matting together of the exposed loops of small intestine, marked edema and swelling of the exposed bowel wall, frequent association of an opalescent pseudomembrane which encompasses the bowel, and thickening and shortening of the mesentery. Only two explanations seem logical for the marked derangements present in the eviscerated bowel. The edema and thickening can result from lymphatic and venous obstruction in the exposed bowel, secondary to a type of incarceration through a small defect in the abdominal wall. The eviscerated bowel is then damaged by exposure to an abnormal environment of amniotic fluid. To exclude the possibility of lymphatic and venous obstruction due to incarceration, a very large abdominal wall defect, constituting practically half of the abdominal wall, was produced in several fetal lambs. The same abnormalities in the exposed bowel were noted. As noted, the microscopic pathology involves all components of the bowel wall. The tissues are unselectively filled with edema fluid with a notable absence of inflammatory cells and macrophages. Whether the absence of inflammatory cells which were observed by Sherman et a1.16in acute preparations indicates a subsequent disappearance of this inflammatory response or a different pattern of response in the fetal lamb model remains to be clarified. Our findings appear to be more characteristic of passive transfer of fluid rather than a reactive inflammatory process. The marked distortion of tissues in the wall of the exposed bowel is most striking when it is compared with the normal appearance of other parts of the same intestine which is contained within the abdominal cavity, and thus, is not exposed to the same concentration of amniotic fluid. The findings suggest a specific loss of those vital enzymes required for the propagation of motor nerve impulses. Reduction in the mitotic index of crypt cells and the retarded development of villi and submucosa represent additional functional deficits. In essence, these and the other changes observed are atrophic in nature and may be consequent to the constraints imposed upon normal motility by the thickened visceral peritoneum. The general distortion of all tissue planes of the bowel wall was accompanied by what appeared to be a specific lesion of the myenteric ganglion cells in the eviscerated bowel. The exact mechanism of this ganglionic injury is not known. We believe that the disordered peristalsis in the eviscerated bowel of gastroschisis results from potentially reversible damage to myenteric ganglion cells. The digestive dysfunction may be related to alterations in the specific enzyme systems in the mucosal cells of this exposed bowel. SUMMARY
An experimental model of gastroschisis has been developed in fetal lambs which grossly and microscopically resembles this anomaly in human infants. Histologic studies of the exposed eviscerated intestine demonstrate interstitial edema without cellular infiltration which appear to result from contact with amniotic fluid. The specific damage to the myenteric ganglion cells and a progressive disappearance of ATPase in the muscle of exposed bowel strongly
HALLER
632
ET Al.
suggest an alteration in neural conduction and a decrease in contractile potential. Preliminary enzyme studies show concomitant abnormalities in intracellular enzymes within the mucosa of the exposed bowel. REFERENCES 1. Duhamel B: Embryology of exomphalos and allied malformations. Arch Dis Child 38: 142, 1963 2. Rickham PP: Rupture of exomphalos and gastroschisis. Arch Dis Child 38: 138, 1963 3. Hutchin P: Somatic anomalies of the umbilicus and anterior abdominal wall. Surg Gynecol Obstet 120:1075, 1965 4. Izant R, Brown F, Rothmann BF: Current embryology and treatment of gastroschisis and omphalocele. Arch Surg 93:49, 1966 5. Hailer JA, Shaker IJ, Gingell R, et al: Intrauterine production of coarctation of the aorta. J Thorac Cardiovasc Surg 66:343, 1973 6. Hailer JA Jr, Morgan WW Jr, Rodgers BM, et al: Chronic hemodynamic effects of occluding the fetal ductus arteriosus. J Thorac Cardiovasc Surg 54: 770, 1967 7. Andrews HG, Shermeta DW, White JJ, et al: Hepatic artery interruption in fetal and neonatal swine. Surg Forum 21:384, 1970 8. Moore TC: Gastroschisis with antenatal evisceration of intestines and urinary bladder. Ann Surg 168:263, 1963
9. Hutchin P, Goldenberg IS: Surgical treatment of omphalocele and gastroschisis. Arch Surg 90:22, 1965 IO. Forshall I: Prognosis for children undergoing operation during the first few weeks of life. Proc R Sot Med 53:954, 1960 I I. Touloukian RJ, Spackman TJ: Gastroschisis function and radiographic appearance following gastroschisis repair. J Pediatr Surg 61427, 1971 12. Raffensperger JG, Jona JZ: Gastroschisis. Surg Gynecol Obstet 138:230, 1974 13. Shuster SR: A new method for the staged repair of large omphaloceles. Surg Gynecol Obstet 125:837, 1967 14. Allen RG, Wrenn EL: Silon as a sac in the treatment of omphaloceles and gastroschisis. J Pediatr Surg 4:3, 1969 15. Filler RM, Eraklis AJ, Das JB, et al: Total intravenous nutrition: An adjunct to the management of infants with ruptured omphalocele. Am J Surg 121:454, 1971 16. Sherman NJ, Asch MJ, Isaacs H Jr., et al: Experimental gastroschisis in the fetal rabbit. J Pediatr Surg 8: 165, 1973
Discussion Dr. A. Shaw (Charlortesville): In these cases when atresia, stenosis, or perforation was present, the gross findings were those typical of gastroschisis. Microscopically, the serosal surface was covered by a thick layer of organized collagenous tissue. There was extensive transmural edema causing varying degrees of disorganization in the cellular architecture. The muscularis external was markedly attenuated, and ganglion cells were reduced in number or absent. Dr. J. Rufensperger (Chicago); The ganglion cells in three or four children in whom we have resected intestine for atresia in gastroschisis were perfectly normal. The serosal reaction always seems to extend only to the serosa in these children and the muscle seems to be normal. The mortality rate really shouldn’t be any higher than that in appendicitis or other ordinary diseases, provided you take a very simple approach to this lesion. I don’t think you can equate gastroschisis with an omphalocele because the liver isn’t herniated, if you simply irrigate out the meconium and stretch the abdominal wall and then undermine the skin very slightly. You can close the skin with subcuticular sutures and steri strips. There is no gastrostomy, no arterial lines, and no source of sepsis. Every time you put another tube into these babies, whether it is a gastrostomy, or an arterial line, or what have you, you introduce another source of sepsis to complicate hyperalimentation. Dr. A. Huller (Baltimore): Constriction doesn’t seem to cause all the typical features of gastroschisis. Incarceration may cause more difficulty. There must be a great variation in the ganglion cells in these patients; however, Dr. Shaw’s observations in patients coincide with ours.
T
HE COMPLICATED EMBRYOGENESIS of gastroschisis has been proposed and discussed by several authors.‘-4 The pathologic physiology, however, of the exposed bowel in infants with gastroschisis has not been carefully studied nor are there data to explain the dysfunction in peristalsis and the digestive malabsorption which are typical of this condition. Since living human tissue from this anomaly is rarely available for sequential study, an animal model of gastroschisis was designed and then used for studies to clarify the pathogenesis and pathophysiology of gastroschisis. The purposes of this paper are: (1) to describe a technique for the intrauterine creation of gastroschisis in the fetal lamb and (2) to record studies of the gross anatomic and histologic alterations in the exposed, eviscerated bowel. CREATION
OF ANIMAL
MODEL
OF GASTROSCHISIS
Intrauterine operative procedures were completed in 39 pregnant ewes using techniques which have been described from our laboratories.5-7 Fetal lambs from timed pregnancies were chosen at a gestational age of 80-100 days (term = 145 days) for the creation of abdominal wall defects and to allow for periods of lo-30 days during which the eviscerated bowel was exposed to amniotic fluid. The caudal half of the experimental fetus was delivered through a uterotomy incision and a full-thickness disc of abdominal wall was excised lateral to the umbilical cord. This disc varied in diameter from 0.5 cm to 5.0 cm. Several loops of intestine were allowed to eviscerate through this defect (Fig. l), and the animal was then returned to the uterus and all incisions were carefully closed. Twenty animals aborted spontaneously at various times after this procedure and they could not be used for tissue studies. Nineteen fetuses survived and were sequentially sacrificed by Cesarean section lo-30 days after the initial procedure. Intestinal tissues from seven sham-operated normal control lambs were studied in an age range from 70-120 gestational days. In addition, each experimental animal served as a comparison control because its unexposed intestine, which remained in the abdomen, was compared with the eviscerated intestine. The protocol was designed to evaluate the influence of amniotic fluid on the eviscerated bowel over varying periods of exposure. In all surviving experimental animals the eviscerated bowel loops were
From the Division of Pediatric Surgery and the Department of Pathology, The Johns Hopkins University School of Medicine. Baltimore, Md. 21205. Presented before the American Pediatric Surgical Association. New Orleans, La., April 4-6. 1974. Addressfor reprint requests: J. Alex Haller, Jr., M.D., Division of Pediatric Surgery, The Johns Hopkins University School of Medicine, Baltimore, Md. 21205. 0 I974 by Grune & Stratton. Inc. Journal of Pediatric Surgery, Vol. 9, No. 5 (October), 1974
627
HALLER
ET AL.
matted together and covered with a partially translucent membrane of varying thickness (Fig. 2). These gross changes closely mimic those found in the exposed bowel of babies with gastroschisis. MICROSCOPIC
STUDIES
OF INTESTINE
Fresh-frozen tissue from control and experimental animals were sectioned on a cryostat and representative enzymes and metabolites of essential tissue functions were demonstrated by accepted histochemical methods. Control tissues were from sham-operated animals, some were from unexposed, intraperitoneal bowel in animals with gastroschisis. NORMAL
BOWEL
STUDIES
(1) In the longitudinal and circular smooth muscle adenosine triphosphatase (ATPase), an enzyme essential for normal energy transfer processes in smooth and skeletal muscle, increased in amount with age and gradually assumed a pattern of distribution recognizable as mature in type. Similar changes in ATPase were found in the smooth muscle and vascular endothelium of the arteries. (The function of ATPase of the vascular endothelium is not known but it is widely believed to be essential for normal function and is probably related to vital membrane functions.) (2) The morphologic organization of cells lining the crypts and covering the villi increased toward the mature form. Acetylesterase was found to be a convenient marker for these cells, although similar reactions were observed in epithelial cells of ATPase and alkaline phosphatase (APase). Prior to 105 days the enzyme was present in small amounts and distributed evenly within and
PATHOPHYSIOLOGY
629
OF GASTROSCHISIS
without the crypts. Thereafter the esterase increased in amount and was confined to villous epithelial cells beyond the crypts which is the mature pattern. (3) The occurrence of mitotic figures in cells in the base of the crypts averaged one mitotic figure in every third crypt and did not change throughout the period of observation. (4) Submucosal fibroblasts were numerous and unchanged throughout the period. (5) Ganglion cells in the myenteric plexus increasingly resembled mature ganglia morphologically and showed increasing amounts of acetylesterase. (This enzyme probably lies along the path of acetylcholine synthesis-in this experiment it behaved as if this was the case, and since it can be demonstrated more conspicuously than acetylcholinesterase, it was used as a functional marker). The distribution within and between ganglion cells was even. EXPOSED
Group 1.
BOWEL
STUDIES
120 Days’ Gestation and Gastroschisis for 12 Days or Less
(1) Longitudinal and circular smooth muscle ATPase was reduced in amount and uneven in distribution. The changes were mild but readily recognized. Arterial smooth muscle and vascular endothehal ATPase was unchanged. (2) The morphology and acetylesterase content of the lumen epithelial cells was unchanged. (3) The mitotic rate of crypt cells was slightly reduced-one crypt in four or five showed mitotic figures. (4) Submucosal fibroblasts were substantially reduced in number. (5) Cells of the myenteric ganglia morphologically were within normal limits but showed a slight reduction in amount and distribution of acetylesterase and acetylcholinesterase. Group 2.
120 Days’ Gestation with Gastroschisis of12-18
Days
(1) Longitudinal and circular muscle ATPase was now reduced considerably and its distribution from one part to another of a single transverse cut and from one site to another was very irregular, an occasional part showed trace amounts only of ATPase. A similar reduction occurred in arterial wall smooth muscle. Vascular endothelial ATPase was normal. (2) Morphologically villous epithelial cells showed arrested development. The localization of acetylesterase lacked the even distribution of the normal pattern and now extended beyond the villi into the base of the crypts resembling the distribution in 70 days’ gestation control animals. (3) The mitotic rate in the crypt cells was markedly reduced. Mitotic figures were found in fewer than one crypt in eight. (4) The reduction in the number of submucosal fibroblasts was maintained. (5) The changes in myenteric ganglion cells were now gross. Acetylesterase and acetylcholinesterase were markedly reduced in amount and the amount present varied widely from cell to cell within a single ganglion and between different ganglia.
HALLER ET AL.
630
(6) The hypertrophic of collagen. Group 3.
visceral peritoneum
was increased in width and content
I20 Days’ Gestation With Gastroschisis of 20-30 Days
Essentially the same changes were found as in the previous group, but all changes were much more striking, indicating a continuing cumulative noxious influence. (1) Longitudinal and circular smooth muscle ATPase was reduced still more and the inequality of its distribution was more widely spread. Arterial wall smooth muscle ATPase was similarly affected, vascular endothelial cell ATPase was normal. (2) The morphologic immaturity and irregularities in distribution of acetylesterase in lumen epithelial cells had extended. Crypt cells were still positive for acetylesterase. (3) The retardation in mitotic rate was maintained. (4) The reduction in submucosal fibroblasts was unchanged. (5) Changes in ganglion cells had increased. Many ganglion cells appeared atrophic, all had decreased amounts of acetylesterase and acetylcholinesterase. The unevenness of the distribution of these enzymes in and between ganglia had increased further. (6) The thickness and content of collagen in the hypertrophic visceral peritoneum was increased also. DISCUSSION
The mortality of infants with gastroschisis is usually due to one or more potentially lethal complications. There is a significant incidence of associated serious abnormalities, such as respiratory distress syndrome, immaturity,8 intestinal atresia, and midgut volvulu~.*~~A second major complication may be sepsis due to exposure of the eviscerated bowel and abdominal cavity to bacterial contamination.’ The third potentially lethal complication is small-bowel injury with paralytic ileus, persistent malabsorption, and occasionally, necrosis with perforation.2*‘0-‘2 Increasingly improved management of sick newborn infants in regional neonatal intensive care centers has decreased mortality from the first group of potential complications, although associated anomalies may always constitute a limit to this salvage. The second complication, sepsis, has responded dramatically to immediate coverage’3*‘4 with plastic material and the use of potent specific antibiotics. Some improvement may still be forthcoming with further modifications in this area of surgical management. The third potential complication is now managed by total parenteral alimentation.” The pathogenesis of the bowel abnormality is unknown and was the primary target of these experimental studies. Since very few studies of the pathogenesis of the bowel injury are likely to be forthcoming from human studies,” an animal model seemed to be a first step in elucidating the pathophysiology of bowel dysfunction in gastroschisis. Sherman et aLI used a rabbit fetal preparation for acute observation of exposed intestine, but their studies did not focus on the pathogenesis of more chronic changes in the bowel.
PATHOPHYSIOLOGY
OF GASTROSCHISIS
631
The gross pathologic findings, as noted in the description of the experimental technique, are similar to those found in a human infant with gastroschisis (Fig. 2). These findings are characterized by matting together of the exposed loops of small intestine, marked edema and swelling of the exposed bowel wall, frequent association of an opalescent pseudomembrane which encompasses the bowel, and thickening and shortening of the mesentery. Only two explanations seem logical for the marked derangements present in the eviscerated bowel. The edema and thickening can result from lymphatic and venous obstruction in the exposed bowel, secondary to a type of incarceration through a small defect in the abdominal wall. The eviscerated bowel is then damaged by exposure to an abnormal environment of amniotic fluid. To exclude the possibility of lymphatic and venous obstruction due to incarceration, a very large abdominal wall defect, constituting practically half of the abdominal wall, was produced in several fetal lambs. The same abnormalities in the exposed bowel were noted. As noted, the microscopic pathology involves all components of the bowel wall. The tissues are unselectively filled with edema fluid with a notable absence of inflammatory cells and macrophages. Whether the absence of inflammatory cells which were observed by Sherman et a1.16in acute preparations indicates a subsequent disappearance of this inflammatory response or a different pattern of response in the fetal lamb model remains to be clarified. Our findings appear to be more characteristic of passive transfer of fluid rather than a reactive inflammatory process. The marked distortion of tissues in the wall of the exposed bowel is most striking when it is compared with the normal appearance of other parts of the same intestine which is contained within the abdominal cavity, and thus, is not exposed to the same concentration of amniotic fluid. The findings suggest a specific loss of those vital enzymes required for the propagation of motor nerve impulses. Reduction in the mitotic index of crypt cells and the retarded development of villi and submucosa represent additional functional deficits. In essence, these and the other changes observed are atrophic in nature and may be consequent to the constraints imposed upon normal motility by the thickened visceral peritoneum. The general distortion of all tissue planes of the bowel wall was accompanied by what appeared to be a specific lesion of the myenteric ganglion cells in the eviscerated bowel. The exact mechanism of this ganglionic injury is not known. We believe that the disordered peristalsis in the eviscerated bowel of gastroschisis results from potentially reversible damage to myenteric ganglion cells. The digestive dysfunction may be related to alterations in the specific enzyme systems in the mucosal cells of this exposed bowel. SUMMARY
An experimental model of gastroschisis has been developed in fetal lambs which grossly and microscopically resembles this anomaly in human infants. Histologic studies of the exposed eviscerated intestine demonstrate interstitial edema without cellular infiltration which appear to result from contact with amniotic fluid. The specific damage to the myenteric ganglion cells and a progressive disappearance of ATPase in the muscle of exposed bowel strongly
HALLER
632
ET Al.
suggest an alteration in neural conduction and a decrease in contractile potential. Preliminary enzyme studies show concomitant abnormalities in intracellular enzymes within the mucosa of the exposed bowel. REFERENCES 1. Duhamel B: Embryology of exomphalos and allied malformations. Arch Dis Child 38: 142, 1963 2. Rickham PP: Rupture of exomphalos and gastroschisis. Arch Dis Child 38: 138, 1963 3. Hutchin P: Somatic anomalies of the umbilicus and anterior abdominal wall. Surg Gynecol Obstet 120:1075, 1965 4. Izant R, Brown F, Rothmann BF: Current embryology and treatment of gastroschisis and omphalocele. Arch Surg 93:49, 1966 5. Hailer JA, Shaker IJ, Gingell R, et al: Intrauterine production of coarctation of the aorta. J Thorac Cardiovasc Surg 66:343, 1973 6. Hailer JA Jr, Morgan WW Jr, Rodgers BM, et al: Chronic hemodynamic effects of occluding the fetal ductus arteriosus. J Thorac Cardiovasc Surg 54: 770, 1967 7. Andrews HG, Shermeta DW, White JJ, et al: Hepatic artery interruption in fetal and neonatal swine. Surg Forum 21:384, 1970 8. Moore TC: Gastroschisis with antenatal evisceration of intestines and urinary bladder. Ann Surg 168:263, 1963
9. Hutchin P, Goldenberg IS: Surgical treatment of omphalocele and gastroschisis. Arch Surg 90:22, 1965 IO. Forshall I: Prognosis for children undergoing operation during the first few weeks of life. Proc R Sot Med 53:954, 1960 I I. Touloukian RJ, Spackman TJ: Gastroschisis function and radiographic appearance following gastroschisis repair. J Pediatr Surg 61427, 1971 12. Raffensperger JG, Jona JZ: Gastroschisis. Surg Gynecol Obstet 138:230, 1974 13. Shuster SR: A new method for the staged repair of large omphaloceles. Surg Gynecol Obstet 125:837, 1967 14. Allen RG, Wrenn EL: Silon as a sac in the treatment of omphaloceles and gastroschisis. J Pediatr Surg 4:3, 1969 15. Filler RM, Eraklis AJ, Das JB, et al: Total intravenous nutrition: An adjunct to the management of infants with ruptured omphalocele. Am J Surg 121:454, 1971 16. Sherman NJ, Asch MJ, Isaacs H Jr., et al: Experimental gastroschisis in the fetal rabbit. J Pediatr Surg 8: 165, 1973
Discussion Dr. A. Shaw (Charlortesville): In these cases when atresia, stenosis, or perforation was present, the gross findings were those typical of gastroschisis. Microscopically, the serosal surface was covered by a thick layer of organized collagenous tissue. There was extensive transmural edema causing varying degrees of disorganization in the cellular architecture. The muscularis external was markedly attenuated, and ganglion cells were reduced in number or absent. Dr. J. Rufensperger (Chicago); The ganglion cells in three or four children in whom we have resected intestine for atresia in gastroschisis were perfectly normal. The serosal reaction always seems to extend only to the serosa in these children and the muscle seems to be normal. The mortality rate really shouldn’t be any higher than that in appendicitis or other ordinary diseases, provided you take a very simple approach to this lesion. I don’t think you can equate gastroschisis with an omphalocele because the liver isn’t herniated, if you simply irrigate out the meconium and stretch the abdominal wall and then undermine the skin very slightly. You can close the skin with subcuticular sutures and steri strips. There is no gastrostomy, no arterial lines, and no source of sepsis. Every time you put another tube into these babies, whether it is a gastrostomy, or an arterial line, or what have you, you introduce another source of sepsis to complicate hyperalimentation. Dr. A. Huller (Baltimore): Constriction doesn’t seem to cause all the typical features of gastroschisis. Incarceration may cause more difficulty. There must be a great variation in the ganglion cells in these patients; however, Dr. Shaw’s observations in patients coincide with ours.