Embryology of anorectal malformations
Section snippets
The etiology of anorectal malformations
The etiology of ARMs is still unclear. Most researchers assume that its etiology is multifactorial. However, recently a number of animal models has been deployed to study the background of ARM. In these models genetic as well as environmental factors were identified.
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The SD-mouse model: these mice, first bred by Danforth,8 prominently feature a short tail and therefore also are known as “Danforth's short tail mice.”9
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The pig model: another famous model for abnormal hindgut development is the pig.
Normal embryology of the hindgut
The normal embryology of the hindgut always has been a matter of debate because observations made in normal embryos should not only explain the normal embryology but also its abnormal counterpart. As a result, the explanation of normal embryology was always done with abnormal development in mind. Two major theories exist to explain the differentiation of the hindgut into the urogenital (ventral) and anorectal (dorsal) part:
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The theory of the septation of the cloaca; and
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The theory of the
Nomenclature
It must be kept in mind that the term “cloaca” is used to describe not only a transitional organ system in human embryos but also a congenital anomaly and a normal organ in birds. This can lead to the false conclusion that the morphology of these 3 entities is similar. This is not the case. Despite the same name, embryonic cloacas are completely different morphologically from cloacas in females with ARM and in birds. The main difference is the presence/absence of the area of the future anal
Abnormal cloacal development
Until recently,35 the embryology of abnormal hindgut development was generally a matter of speculation. Progress in this field has been hampered by lack of appropriate animal models that would permit systematic embryological studies in a sufficient series of malformed embryos. In 1940, a mutant of the normal house mouse, the SD-mutant, had been described by Dunn et al.36 These mice, first bred by Danforth,8 prominently feature a short tail and therefore also are known as “Danforth's short tail
Conclusions
Traditionally, the normal differentiation of the cloaca into the dorsal anorectum and the ventral urogenital tract is attributable to the proper process of septation by the so-called urorectal septum.38 However, when we used SEM in our study, we noted that neither lateral ridges nor signs of fusing lateral wall components could be discerned. Therefore, clear proof of this process of septation is still missing. It is more likely that a normal-looking septum is the result of normal cloacal
References (38)
- et al.
The principles of normal and abnormal hindgut development
J Pediatr Surg
(1995) - et al.
The embryology of foregut malformations
J Pediatr Surg
(1987) - et al.
Rotation of the gut: Fact or fantasy?
J Pediatr Surg
(1995) Normal and abnormal development of the anorectum
J Pediatr Surg
(1986)- et al.
A new rodent experimental model of esophageal atresia and tracheoesophageal fistula: Preliminary report
J Pediatr Surg
(1996) - et al.
Mechanisms for the development of esophageal atresia
J Pediatr Surg
(2001) - et al.
Midgut atresias result from abnormal development of the notochord in an Adriamycin rat model
J Pediatr Surg
(2002) - et al.
Development of anorectal malformations using etretinate
J Pediatr Surg
(1998) - et al.
Development of the pelvic floor muscles of murine embryos with anorectal malformations
J Pediatr Surg
(2002) - et al.
Sonic hedgehog and bone morphogenetic protein 4 expressions in the hindgut region of murine embryos with anorectal malformations
J Pediatr Surg
(2004)
Clarification of the processes that lead to anorectal malformations in the ETU-induced rat model of imperforate anus
J Pediatr Surg
Deficient motor innervation of the sphincter mechanism in fetal rats with anorectal malformation: A quantitative study by fluorogold retrograde tracing
J Pediatr Surg
Normal and abnormal embryonic development of the anorectum in rats
J Pediatr Surg
Anorectal malformations caused by defects in sonic hedgehog signaling
Am J Pathol
Developmental Biology
The morphology of the malformations in human and animalsPart 1: General Teratology
The developmental anatomy of congenital diaphragmatic hernia
Pediatr Surg Int
Developmental anomalies in a special strain of mice
Am J Anat
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Bowel Control, Bladder Function, and Quality of Life in Children with Cloacal Malformations
2023, Journal of Pediatric SurgeryCitation Excerpt :The clinical phenotype varies from defects with a short common channel to very complex malformations in which an extended common channel may prevent joining vagina and rectum to the perineum without additional reconstructive procedures. The birth prevalence is approximately 1 of 50,000 live births (1) (2, 3), which corresponds to approximately 5% of all anorectal malformations. Cloacal malformations are often associated with other congenital defects, such as vertebral, cardiac, trachea-esophageal, renal, and limb malformations.
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2022, Seminars in Pediatric SurgeryCitation Excerpt :It is commonly believed that the urorectal septum (URS) divides the embryonic cloaca into a ventral urogenital sinus and separate dorsal hindgut,2-6 and the spectrum of anomalies seen clinically likely results from the timing of some kind of developmental arrest.7 However, the mechanism of cloacal septation has been debated with the emphasis shifting to the cloacal membrane (CM) playing a more important role during development of the anorectum8-10 and the mechanism for changes in embryonic anorectal morphology regarded as being the result of embryonic cell differentiation, cell proliferation, and apoptosis.11,12 The definitive cause of ARMs is unknown, but one third of ARMs are isolated and the remainder associated with other congenital urogenital, cardiovascular, skeletomuscular and gastrointestinal tract anomalies.13,14
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Supported in part by Deutsche Forschungsgemeinschaft, Grant Number KL 596/1, Hamburg Werner-Otto-Stiftung.