The Rectourogenital
Connection in Anorectal Malformations Ectopic Anal Canal
By R. Rintala,
H. Lindahl, H. Sariola, J. Rapola, and I. Louhimo Helsinki,
0 Histological
investigation
rectourogenitel formed
or
of the rectal blind pouch and
rectoperineal
in 10 patients
connection
was
with high or intermediate
per-
anorectal
malformations. Nine of the patients underwent postoperative menometric evaluation. In nine of the 10 patients, transitional
epithelium
typical
could be found in the distal fistulous
connection.
was aganglionic linesterase
normal
anal canal
or rectal
end of the
The zone of transitional
and showed
reaction.
of the
rectum
abnormally
A positive
was found manometrically
inhibitory
The
structed canal.
slow
wave activity
pressure
anal canal was
The
manometric
there is a functional
charecteristic evidence
internal
malformations.
that in anorectal
malformations
WORDS:
recon-
suggests
anal that
in high and interme-
The present
study shows
the distal rectal pouch with
is actually an ectopic anal canal.
@ 1999 by W.B. Saunders
INDEX
of the anal
of the
of a normal
strongly
sphincter
diate anorectal
the fistulous connection
reflex
in all cases in which the distal
rectal pouch was utilized in the reconstruction canal.
epithelium
strong acetylcho-
rectoenal
Anorectal
Company.
malformations:
anorectal
me-
nometry.
D
URING THE LAST decades, the cornerstone in the operative treatment of anorectal malformations has been preservation of the voluntary muscles of fecal continence. This concept has been based on the classifications of anorectal anomalies in common use,l’* where the anal canal in high and intermediate anomalies has been considered to be agenetic. The term “fistula” has been used for the rectourogenital or rectoperineal connection. The internal sphincter has been considered to be hypoplastic or missing in intermediate and high anomalies. In operations for high and intermediate anorectal malformations, little attention has been paid to the preservation of the terminal rectum and the fistulous connection.3 Only a few authors have advocated the importance of these structures in the reconstruction of the anal canal. These pediatric surgeons have found histologica14,5 or manometri&’ evidence of the existence of normal anal canal structures like the transitional epithelium and internal sphincter in the rectal termination and fistula. In this paper we report the histological and manometric results of 10 patients with a preserved rectal terminal pouch. The results show that the rectourogenital or rectoperineal communication is in fact an ectopic anal canal. Journal
of Pediatric
Surgery,
is an
Vol 25, No 6 (June), 1990: up 665-666
Finland MATERIALS
AND
METHODS
Tissue specimens from the rectourogenital fistulous connection and the rectal blind pouch were taken during the reconstruction of the anorectum in 10 patients with intermediate or high anorectal malformations. The samples for histology and histochemistry were prepared from a longitudinal strip of tissue from the rectal end of the fistula and bowel wall, harvested in the tapering procedure of the distal rectal blind pouch. The tissue strips were sectioned longitudinally into two pieces and fixed in formaldehyde for histological staining, or frozen in liquid nitrogen for histochemistry. The histological preparations were stained using the routine hematoxylin & eosin method. The frozen specimens were stained for the assessment of acetycholinesterase (AChE) activity according to Karnovsky and Roots.* The histopathologic evaluation of the preparations was carried out independently by two pathologists (J.R. and H.S.). The operative procedure for all patients was posterior sagittal anorectoplasty, as described by de Vries and Pena.’ The original technique was modified by preserving the rectal end of the fistulous connection. The blind pouch was always tapered, but the length of the specimen for histological examination varied according to the operative situation. In one case the blood supply to the blind pouch was compromised and it could not be used in the reconstruction. In one male infant no evident connection to the urethra was present but the histological examination showed a microscopic channel, probably representing the remnant of a fistula. Nine of the patients underwent postoperative manometric evaluation. One patient who had a tetralogy of Fallot died of bacterial meningitis 3 months after surgery. The manometric evaluation was performed using a perfused open-tip catheter. The details of the manometric technique have been published elsewhere.“’ One purpose of the manometry was to find evidence of internal sphincter function in the reconstructed anal canal. The criteria for functional internal sphincter were positive rectoanal inhibitory reflex (RAIR) and anal-type slow pressure wave activity (SPWA). RESULTS Transitional stratified epithelium and glands typical of the anal canal were found in nine of the 10 specimens (Fig 1). The epithelium oral to the transitional zone was normal rectal mucosa. Marked fibrosis of the submucosa and muscular layer was found in all cases. The amount of subepithelial fibrosis decreased cranially. In the case in which no transitional epithelium was found, there was no subepithelial fibrosis, which suggests that the histological samples were not
From the Children’s Hospital. University of Helsinki, Helsinki, Finland. Date accepted: June 14,1989 Address reprint requests to R. Rintala. MD, Children’s Hospital, University of Helsinki, Stenbackinkatu I I, SF-00290 Helsinki, Finland. 0 1990 by W.B. Saunders Company. 0022-3468/90/2506-0020$03.00/O 665
RINTALA ET AL
Fig 1. (A) Micrograph of a rectal pouch. An anal-type mucosa covers a thick fibrotic subepithelial layer. The transitional zone between the rectal and anal-type mucosa is indiated by an arrow. (6) Higher magnffication of the arrowed area of A shows how the rectal mucosa with glands (on the left) transforms into transitional mucosa with anal glands (on the right). (C) In the ectopic anal canal, transitional epithelium is noted in large folded glands. (D) Acetylcholinesterase reaction in the ectopic anal canal shows an increased number of nerve fibers (arrow) in the subepithelial area (left. with hematoxylin counter stain: right, without countsr stain).
taken from the region of rectourethral connection. A thickening of the muscular layer was found in the zone of transitional epithelium. The muscular layer was approximately three times thicker than in the rectal zone. Although histologically and histochemically looked for, no ganglion cells were found in the transitional zone of the rectal blind pouch in any case. In the glandular rectal zone the distribution of the ganglion cells was normal. Sections from the transitional zone stained for AChE activity from the transitional zone were available in four cases. In all cases there was increased AChE activity in the mucosal lamina propria (Fig 1D). The zone with increased AChE activity was
always limited to the region of transitional epithelium. More cranial samples from the rectal zone could be evaluated in eight cases. AChE activity was normal in all of these specimens. Postoperatively, manometric evaluation showed that the RAIR was present in all but one patient. In this case, the distal blind pouch was not used in the reconstruction. SPWA was characteristic of the normal anal canal in all cases with a positive RAIR.” The mean activity was 13.4 cycles per minute. In the reconstructed rectal ampulla the mean SPWA was 22.2 cycles per minute, which compares with normal rectocolonic SPWA. The mean pressure in the rectal neoampulla was 7.4 cm HzO. There was a distinct
667
ECTOPIC ANAL CANAL IN ANORECTAL ANOMALIES
Table 1. The Histological
Characteristics
Blind Pouch in Anorectal
Table 2. Manometric
of the Distal Rectal
Malformations
Reconstructed
and Normal
Characteristics
of the Anal Canal
From the Distal Rectal Blind Pouch and Fistula
(10 Cases) and Normal Anal Canals (15 Cases)
Distal Anal Canal BlindPouch
Reconstructed
Nomlal
Transitional epithelium
+
+
Rectoanal inhibitory reflex
Hypoganglionosis or aganglionosis
+
+
Mean slow pressure wave activity
9110
Increased AChE activity
+
Subepithelial fibrosis
+
kycles/min) Maximal anal canal pressure (mean cm H,O)
Normal 15115
13
12
35
47
Abbreviations: +, present; -, absent; AChE, acetylcholinesterase.
high-pressure zone (mean pressure, 35.8 cm H,O) in all patients with positive RAIR. The high-pressure zone was situated in the distal anal canal. The histological features of the distal rectal blind pouch in anorectal malformations are compared with those of a normal anal canal in Table 1. The manometric characteristics of the anal canal reconstructed from the rectal blind pouch and rectourogenital connection in this series (10 cases) are related with those of the anal canal in 15 healthy children (Table 2). DISCUSSION
The surgical treatment of high and intermediate anorectal malformations has centered on preserving the puborectalis muscle’ and more recently on utilizing the whole voluntary sphincter complex, as described by deVries and PenaS However, as early as 1963, Gans et al4 stressed the importance of preserving the recta1 blind pouch in the reconstruction of anorectal anomalies based on their findings on the histology of the termination of this structure. The findings of Gans et al and those in the present series are equivalent. In a recent report by Lamprecht and Lierse,‘* a similar anatomical correlation was found in neonatal pigs with anorectal malformations. Internal sphincter function has been manometrically confirmed preoperatively and postoperatively in a large number of patients with preserved rectourogenital or rectoperineal opening, as recently reported by Penninckx and Kerremans.’ Their conclusion is that the rectourogenital communication is in fact an ectopic anal canal, not a fistula. Our results are in agreement with their conclusions. The histology of the “ectopic anal canal” was quite uniform in the present series. No ganglion cells were found in this zone. This is in accordance with the findings of Lamprecht and Lierse in their animal
model.‘* The increased AChE activity in the mucosal lamina propria suggests that there is true aganglionosis rather than physiological hypoganglionosis of the distal anal cana1.i3 This is in contradiction to the presence of rectoanal inhibitory reflex in the present patients and in those of Penninckx and Kerremans.’ This discrepancy may be explained by the fact that the aganglionotic zone in the ectopic anal canal is limited to a very short segment of the distal bowel termination. A part of the internal sphincter may be situated crania1 to the transitional zone and may have normal innervation. The marked subepithelial fibrosis in the zone of transitional epithelium is probably secondary in nature. Fecal stasis and, in male patients, the reflux of urine from the urethra to the blind pouch may be the underlying causes of the fibrotic changes. The presence of a functional internal sphincter in the distal blindly terminating bowel in anorectal malformations calls for reevaluation of the standard operative strategies. The internal anal sphincter is an important barrier against the fecal flow and should be preserved. In our experience, the identification and preservation of the distal bowel and the rectourogenital or rectoperineal connection is accomplished most effectively using the posterior sagittal approach.t4 In the classification of anorectal malformations there should be a reappraisal of the concepts of Bill and Johnson” and Gans et a1.4 The abnormal connection between the rectum and perineum or urogenital tract currently classified as fistula is histologically and functionally an ectopic anal canal. There is no real agenesis of bowel except in some very rare cases, such as cloaca1 exstrophy. One of these cases demonstrates that even when the rectum ends without any connection to the urogenital tract or perineum, there is transitional epithelium and functional internal sphincter in the bowel termination.
REFERENCES 1. Stephens FD, Smith ED: Proposed international classification, in Ano-Rectal Malformations in Children, appendix C. Chicago, IL, Year Book, 1971, pp 1-8 2. Stephens FD, Smith ED: Classification, assessment of surgical treatment of anorectal Surg Int 1:200-205,1986
identification, and anomalies. Pediatr
3. Stephens dren. Chicago,
FD, Smith ED: Arm-Rectal Malformations IL, Year Buck, 1971, pp 224-257
in Chil-
4. Gans SL, Friedman NB, David JS: Congenital anorectal anomalies: Changing concepts in management. Clin Pediatr 2:605613,1963 5. Yokoyama
J, Hayashi
A, lkawa
H, et al: Abdomino-extended
RINTALA ET AL
sacroperineal approach in high-type anorectal malformation and a new operative method. Z Kinderchir 40:151-157, 1985 6. Frenckner B: Use of the recta-urethral fistula for reconstruction of the anal canal in high anal at&a. Z Kinderchir 40:312-314, 1985 7. Penninckx FMA, Kerremans RPJ: Internal sphincter saving in imperforate anus with or without fistula. Int J Colorect Dis 1:28-32, 1986 8. Karnovsky MS, Roots L: A direct-colouring thiocholine method for cholinesterases. J Histochem Cytochem 12:219-22 1,1964 9. deVries P, Pena A: Posterior sagittal anorectoplasty. J Pediatr Surg 17:638-643, 1982 10. Rintala R, Lindahl H, Louhimo I: Biofeedback conditioning for fecal incontinence in anorectal malformations. Pcdiatr Surg Int 3:418-421,1988
11. Holschneider AM: Elektromanometrie des Enddams (2 Auflage). Munich, West Germany, Urban & Schwarzenberg, 1983, pp 57-60 12. Lambrecht W, Lierse W: The internal sphincter in anorectal malformations: Morphologic investigations in neonatal pigs. J PediatrSurg 22:1160-l 168,1987 13. Meier-Ruge W: Morphological diagnosis of Hirschsprung’s disease, in Holschneider AM (ed): Hirschsprung’s Disease. New York, NY, Thieme, 1982, pp 62-71 14. deVries P, Pena A: Posterior sagittal anorectoplasty: Important technical considerations and new applications. J Pediatr Surg 17:796-811, 1982 15. Bill AH, Johnson RJ: Failure of migration of the rectal opening as a cause for most cases of imperforate anus. Surg Gynecol Obstet 106:643&S 1, 1958
Connection in Anorectal Malformations Ectopic Anal Canal
By R. Rintala,
H. Lindahl, H. Sariola, J. Rapola, and I. Louhimo Helsinki,
0 Histological
investigation
rectourogenitel formed
or
of the rectal blind pouch and
rectoperineal
in 10 patients
connection
was
with high or intermediate
per-
anorectal
malformations. Nine of the patients underwent postoperative menometric evaluation. In nine of the 10 patients, transitional
epithelium
typical
could be found in the distal fistulous
connection.
was aganglionic linesterase
normal
anal canal
or rectal
end of the
The zone of transitional
and showed
reaction.
of the
rectum
abnormally
A positive
was found manometrically
inhibitory
The
structed canal.
slow
wave activity
pressure
anal canal was
The
manometric
there is a functional
charecteristic evidence
internal
malformations.
that in anorectal
malformations
WORDS:
recon-
suggests
anal that
in high and interme-
The present
study shows
the distal rectal pouch with
is actually an ectopic anal canal.
@ 1999 by W.B. Saunders
INDEX
of the anal
of the
of a normal
strongly
sphincter
diate anorectal
the fistulous connection
reflex
in all cases in which the distal
rectal pouch was utilized in the reconstruction canal.
epithelium
strong acetylcho-
rectoenal
Anorectal
Company.
malformations:
anorectal
me-
nometry.
D
URING THE LAST decades, the cornerstone in the operative treatment of anorectal malformations has been preservation of the voluntary muscles of fecal continence. This concept has been based on the classifications of anorectal anomalies in common use,l’* where the anal canal in high and intermediate anomalies has been considered to be agenetic. The term “fistula” has been used for the rectourogenital or rectoperineal connection. The internal sphincter has been considered to be hypoplastic or missing in intermediate and high anomalies. In operations for high and intermediate anorectal malformations, little attention has been paid to the preservation of the terminal rectum and the fistulous connection.3 Only a few authors have advocated the importance of these structures in the reconstruction of the anal canal. These pediatric surgeons have found histologica14,5 or manometri&’ evidence of the existence of normal anal canal structures like the transitional epithelium and internal sphincter in the rectal termination and fistula. In this paper we report the histological and manometric results of 10 patients with a preserved rectal terminal pouch. The results show that the rectourogenital or rectoperineal communication is in fact an ectopic anal canal. Journal
of Pediatric
Surgery,
is an
Vol 25, No 6 (June), 1990: up 665-666
Finland MATERIALS
AND
METHODS
Tissue specimens from the rectourogenital fistulous connection and the rectal blind pouch were taken during the reconstruction of the anorectum in 10 patients with intermediate or high anorectal malformations. The samples for histology and histochemistry were prepared from a longitudinal strip of tissue from the rectal end of the fistula and bowel wall, harvested in the tapering procedure of the distal rectal blind pouch. The tissue strips were sectioned longitudinally into two pieces and fixed in formaldehyde for histological staining, or frozen in liquid nitrogen for histochemistry. The histological preparations were stained using the routine hematoxylin & eosin method. The frozen specimens were stained for the assessment of acetycholinesterase (AChE) activity according to Karnovsky and Roots.* The histopathologic evaluation of the preparations was carried out independently by two pathologists (J.R. and H.S.). The operative procedure for all patients was posterior sagittal anorectoplasty, as described by de Vries and Pena.’ The original technique was modified by preserving the rectal end of the fistulous connection. The blind pouch was always tapered, but the length of the specimen for histological examination varied according to the operative situation. In one case the blood supply to the blind pouch was compromised and it could not be used in the reconstruction. In one male infant no evident connection to the urethra was present but the histological examination showed a microscopic channel, probably representing the remnant of a fistula. Nine of the patients underwent postoperative manometric evaluation. One patient who had a tetralogy of Fallot died of bacterial meningitis 3 months after surgery. The manometric evaluation was performed using a perfused open-tip catheter. The details of the manometric technique have been published elsewhere.“’ One purpose of the manometry was to find evidence of internal sphincter function in the reconstructed anal canal. The criteria for functional internal sphincter were positive rectoanal inhibitory reflex (RAIR) and anal-type slow pressure wave activity (SPWA). RESULTS Transitional stratified epithelium and glands typical of the anal canal were found in nine of the 10 specimens (Fig 1). The epithelium oral to the transitional zone was normal rectal mucosa. Marked fibrosis of the submucosa and muscular layer was found in all cases. The amount of subepithelial fibrosis decreased cranially. In the case in which no transitional epithelium was found, there was no subepithelial fibrosis, which suggests that the histological samples were not
From the Children’s Hospital. University of Helsinki, Helsinki, Finland. Date accepted: June 14,1989 Address reprint requests to R. Rintala. MD, Children’s Hospital, University of Helsinki, Stenbackinkatu I I, SF-00290 Helsinki, Finland. 0 1990 by W.B. Saunders Company. 0022-3468/90/2506-0020$03.00/O 665
RINTALA ET AL
Fig 1. (A) Micrograph of a rectal pouch. An anal-type mucosa covers a thick fibrotic subepithelial layer. The transitional zone between the rectal and anal-type mucosa is indiated by an arrow. (6) Higher magnffication of the arrowed area of A shows how the rectal mucosa with glands (on the left) transforms into transitional mucosa with anal glands (on the right). (C) In the ectopic anal canal, transitional epithelium is noted in large folded glands. (D) Acetylcholinesterase reaction in the ectopic anal canal shows an increased number of nerve fibers (arrow) in the subepithelial area (left. with hematoxylin counter stain: right, without countsr stain).
taken from the region of rectourethral connection. A thickening of the muscular layer was found in the zone of transitional epithelium. The muscular layer was approximately three times thicker than in the rectal zone. Although histologically and histochemically looked for, no ganglion cells were found in the transitional zone of the rectal blind pouch in any case. In the glandular rectal zone the distribution of the ganglion cells was normal. Sections from the transitional zone stained for AChE activity from the transitional zone were available in four cases. In all cases there was increased AChE activity in the mucosal lamina propria (Fig 1D). The zone with increased AChE activity was
always limited to the region of transitional epithelium. More cranial samples from the rectal zone could be evaluated in eight cases. AChE activity was normal in all of these specimens. Postoperatively, manometric evaluation showed that the RAIR was present in all but one patient. In this case, the distal blind pouch was not used in the reconstruction. SPWA was characteristic of the normal anal canal in all cases with a positive RAIR.” The mean activity was 13.4 cycles per minute. In the reconstructed rectal ampulla the mean SPWA was 22.2 cycles per minute, which compares with normal rectocolonic SPWA. The mean pressure in the rectal neoampulla was 7.4 cm HzO. There was a distinct
667
ECTOPIC ANAL CANAL IN ANORECTAL ANOMALIES
Table 1. The Histological
Characteristics
Blind Pouch in Anorectal
Table 2. Manometric
of the Distal Rectal
Malformations
Reconstructed
and Normal
Characteristics
of the Anal Canal
From the Distal Rectal Blind Pouch and Fistula
(10 Cases) and Normal Anal Canals (15 Cases)
Distal Anal Canal BlindPouch
Reconstructed
Nomlal
Transitional epithelium
+
+
Rectoanal inhibitory reflex
Hypoganglionosis or aganglionosis
+
+
Mean slow pressure wave activity
9110
Increased AChE activity
+
Subepithelial fibrosis
+
kycles/min) Maximal anal canal pressure (mean cm H,O)
Normal 15115
13
12
35
47
Abbreviations: +, present; -, absent; AChE, acetylcholinesterase.
high-pressure zone (mean pressure, 35.8 cm H,O) in all patients with positive RAIR. The high-pressure zone was situated in the distal anal canal. The histological features of the distal rectal blind pouch in anorectal malformations are compared with those of a normal anal canal in Table 1. The manometric characteristics of the anal canal reconstructed from the rectal blind pouch and rectourogenital connection in this series (10 cases) are related with those of the anal canal in 15 healthy children (Table 2). DISCUSSION
The surgical treatment of high and intermediate anorectal malformations has centered on preserving the puborectalis muscle’ and more recently on utilizing the whole voluntary sphincter complex, as described by deVries and PenaS However, as early as 1963, Gans et al4 stressed the importance of preserving the recta1 blind pouch in the reconstruction of anorectal anomalies based on their findings on the histology of the termination of this structure. The findings of Gans et al and those in the present series are equivalent. In a recent report by Lamprecht and Lierse,‘* a similar anatomical correlation was found in neonatal pigs with anorectal malformations. Internal sphincter function has been manometrically confirmed preoperatively and postoperatively in a large number of patients with preserved rectourogenital or rectoperineal opening, as recently reported by Penninckx and Kerremans.’ Their conclusion is that the rectourogenital communication is in fact an ectopic anal canal, not a fistula. Our results are in agreement with their conclusions. The histology of the “ectopic anal canal” was quite uniform in the present series. No ganglion cells were found in this zone. This is in accordance with the findings of Lamprecht and Lierse in their animal
model.‘* The increased AChE activity in the mucosal lamina propria suggests that there is true aganglionosis rather than physiological hypoganglionosis of the distal anal cana1.i3 This is in contradiction to the presence of rectoanal inhibitory reflex in the present patients and in those of Penninckx and Kerremans.’ This discrepancy may be explained by the fact that the aganglionotic zone in the ectopic anal canal is limited to a very short segment of the distal bowel termination. A part of the internal sphincter may be situated crania1 to the transitional zone and may have normal innervation. The marked subepithelial fibrosis in the zone of transitional epithelium is probably secondary in nature. Fecal stasis and, in male patients, the reflux of urine from the urethra to the blind pouch may be the underlying causes of the fibrotic changes. The presence of a functional internal sphincter in the distal blindly terminating bowel in anorectal malformations calls for reevaluation of the standard operative strategies. The internal anal sphincter is an important barrier against the fecal flow and should be preserved. In our experience, the identification and preservation of the distal bowel and the rectourogenital or rectoperineal connection is accomplished most effectively using the posterior sagittal approach.t4 In the classification of anorectal malformations there should be a reappraisal of the concepts of Bill and Johnson” and Gans et a1.4 The abnormal connection between the rectum and perineum or urogenital tract currently classified as fistula is histologically and functionally an ectopic anal canal. There is no real agenesis of bowel except in some very rare cases, such as cloaca1 exstrophy. One of these cases demonstrates that even when the rectum ends without any connection to the urogenital tract or perineum, there is transitional epithelium and functional internal sphincter in the bowel termination.
REFERENCES 1. Stephens FD, Smith ED: Proposed international classification, in Ano-Rectal Malformations in Children, appendix C. Chicago, IL, Year Book, 1971, pp 1-8 2. Stephens FD, Smith ED: Classification, assessment of surgical treatment of anorectal Surg Int 1:200-205,1986
identification, and anomalies. Pediatr
3. Stephens dren. Chicago,
FD, Smith ED: Arm-Rectal Malformations IL, Year Buck, 1971, pp 224-257
in Chil-
4. Gans SL, Friedman NB, David JS: Congenital anorectal anomalies: Changing concepts in management. Clin Pediatr 2:605613,1963 5. Yokoyama
J, Hayashi
A, lkawa
H, et al: Abdomino-extended
RINTALA ET AL
sacroperineal approach in high-type anorectal malformation and a new operative method. Z Kinderchir 40:151-157, 1985 6. Frenckner B: Use of the recta-urethral fistula for reconstruction of the anal canal in high anal at&a. Z Kinderchir 40:312-314, 1985 7. Penninckx FMA, Kerremans RPJ: Internal sphincter saving in imperforate anus with or without fistula. Int J Colorect Dis 1:28-32, 1986 8. Karnovsky MS, Roots L: A direct-colouring thiocholine method for cholinesterases. J Histochem Cytochem 12:219-22 1,1964 9. deVries P, Pena A: Posterior sagittal anorectoplasty. J Pediatr Surg 17:638-643, 1982 10. Rintala R, Lindahl H, Louhimo I: Biofeedback conditioning for fecal incontinence in anorectal malformations. Pcdiatr Surg Int 3:418-421,1988
11. Holschneider AM: Elektromanometrie des Enddams (2 Auflage). Munich, West Germany, Urban & Schwarzenberg, 1983, pp 57-60 12. Lambrecht W, Lierse W: The internal sphincter in anorectal malformations: Morphologic investigations in neonatal pigs. J PediatrSurg 22:1160-l 168,1987 13. Meier-Ruge W: Morphological diagnosis of Hirschsprung’s disease, in Holschneider AM (ed): Hirschsprung’s Disease. New York, NY, Thieme, 1982, pp 62-71 14. deVries P, Pena A: Posterior sagittal anorectoplasty: Important technical considerations and new applications. J Pediatr Surg 17:796-811, 1982 15. Bill AH, Johnson RJ: Failure of migration of the rectal opening as a cause for most cases of imperforate anus. Surg Gynecol Obstet 106:643&S 1, 1958
