[size=20px]Which of the following is most accurate regarding the embryology of anorectal malformations (ARM)?

 

A Most ARM are a result of failure of the rectum to continue caudal migration down to the perineum.

 

B Most ARM are a result of failure of fusion of lateral cloacal folds.

 

C A cloaca is the result of a persistence of the embryological cloaca.

 

D Most ARM are a result of early embryonic perturbation of the cloacal membrane.

 

E Most ARM are a result of prenatal exposure to teratogens.[/size]

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b

think again my dear

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d

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d

correct answer

D Most ARM are a result of early embryonic perturbation of the cloacal membrane.

 

The two historical prevailing theories to explain anorectal malformations (ARM) have been that

• the rectum fails in caudal migration or
  
• there is a failure of cloacal lateral ridges to fuse and segregate the ventral urogenital structures from the dorsal rectum.
  

However, in studies using rodent models and human specimens, investigators have found that the cloacal membrane, the structure which separates the amniotic cavity from the embryologic cloaca, is critical to the formation of ARM. The observations are that the urorectal septum descends, dividing the cloaca, and fuses with the cloacal membrane which then degenerates via apoptosis and allows the urogenital septum to fuse with the perineum creating the perineal body. The aberrant maturation, including the most dorsal degeneration of the cloacal membrane, results in abnormal fusion with the urorectal septum explaining the typical spectrum of ARM. These experiments also report that the embryonic cloaca is morphologically completely different from cloacas in female infants making the argument that “persistent cloaca” is a misnomer.