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What is The Most common type of imperforate anus is and explain in detail?
(C) Anorectal agenesis # Imperforate anus> (The term is used as a well-recognised description. Strictly it should be 'agenesis' and 'atresia' of the rectum and anus.)> One infant in 4500 is born with an imperforate anus, or with imperfect fusion of the post-allantoic gut with the proctodaeum.> The condition is divided into two main groups: the high and the low, depending on whether the termination of the bowel is above or below the pelvic floor.> Low varieties are easy to diagnose and relatively simple to treat, and the outlook is good.> High varieties often have a fistula into the urinary tract together with a deficient pelvic floor, and are difficult to treat.# Low abnormalities:> Covered anus. The underlying anal canal is covered by a bar of skin with atrack running forwards to the perineal raphe. The track should be opened with scissors, followed by routine dilatation of the anus.> Ectopic anus. The anus is situated anteriorly and may open in the perineum in boys, or more commonly in the vulva in girls, or rarely into thevagina. A plastic 'cut back' operation isrequired (Pena).> Stenosed anus. The anus is microscopic, but careful examination usually reveals a minute opening which responds to regular dilatation.> Membranous stenosis. Here the anus is normally sited, but is covered with a thin membrane which bulges with retained meconium. It is rare, and an incision will cure the condition.# High abnormalities:> These are often associated with a fistulous connection between the blind rectal stump and the bladder, or other abnormalities of the pelvic structures.> Anorectai agnesis. A blind rectal pouch lies just above the pelvic floor -- its anterior aspect in the male is attached to the bladder and often there is a rectovesical fistula manifested by the passage of gas or meconium in the urine. In the female, the fistula is usually into the posterior fornix.> Rectal atresia. The anal canal is normal but ends blindly at the level of the pelvic floor. The bowel also ends blindly above the pelvic floor without a fistulous opening. This anomaly is rare but must be treated by mobilisation of the rectum and excision of the stricture. After that, end-to-end anastomosis of the anus and rectum must be attempted.> More conservative measures are followed by an intractable stricture.> Cloaca. This occurs only in females and here the bowel, urinary and genital tracts all open into a common wide cavity. Commonly severe malformations of the area are associated with other developmental abnormalities, e.g. tracheobronchial fistula.