An imperforate anus is malformation of the rectal are athat may occur in several forms. The rectum may end in a blind pouch that doesnt connect with the colon. This means that from the outside, what appears to be an anus is evident, but it doesnt go anywhere. Or it may have openings to urethra, bladder, base of the penis or scrotum in boys, or vagina in girls. A condition of narrowing of the anus or absence of the anus may be present.
Typically, there are two types of imperforate anus:
The "high type" means that no opening is presents on the outside of the childs body and the bowel ends above the muscles at the bottom of the pelvis.
The "low type" means that the bowel ends below the muscles of the pelvis and there is an opening present, but it is an abnormal position or is covered by a layer of skin or ather type of membrane.
The malformation are caused by abnormal development of the fetus, and many are associated with other birth defects. Imperforate anus is a relatively common congenital malformation that accors in about one out of 5000 infants. It is not the fault of the mother; the cause is unknown.
Anorectal malformations include wide spectrum of defects in the development of the lowest portion of the intestinal and urogenital tracts. Many children with this malformations are said to have an imperforate anus because they have no opening where the anus should be. Although the term may accurately describe a child's outward appearence, it often belies thr true complexity of the malformation beneath. When malformation of the anus is present, the muscles and nerves associated with the anus often have a similar degree of malformation. The spine and urogenital tract may also involved.
Symptoms may include the absence of anal opening, or one in the wrong area, such as very close to the vaginal opening in females, and no stool within 24 to 48 hours after birth, or stool that comes out of the vagina, the base of the penis , urethra (where you urinate) or scrotum. Parents also may notice a swollen abdomen.
To diagnose this, the doctor may physically examine the child. He or she also may order a lower abdominal X-ray or enema to see whether fluid inserted into the anus is moving up into the small intestine.
The treatment is surgery. The "low type" may involve opening the thin membrane of skin or other tissue in surgery, repeated stretching of the opening, or surgical reconstruction.
The "high type" is treating by creating a temporary colostomy (re-routing the bowel out the abdominal wall). The baby than has bowel movements into a bag. At about six to 12 months, surgical rebuilding of an anal opening is completed, and any posible fistula is closed, The colostomy is removed a few weeks later.
The position and nature of these malformations made repair difficult for early surgeons. The affacted organs are located deep in the pelvis and are not well visualized through abdominal incisions. Traditional surgical dictum did not allow for division of the posterior midline because this division of the muscle was believed, somewhat erroneously, to cause incontinence in the child. Therefore, surgeons approached these malformation using a combine abdominal, sacral and perineal approach, with limited visibility. Such approaches have put continence, and surroundings genitourinary structures, at greater risk than simply cutting sphincter limited incisions. This principle was central to the development of the surgical techniques currently used to repair these malformations.
In 1982, Pena et al reported the results of the use of a posterior sagittal surgical repair approach. Pena et al used the traditional approach with sacral incision and made the incisions progresively larger in an attempt to adequately visualize the anatomy. Eventually, the entire posterior sagittal plene was opened, affording a full view of the complete malformation. This technique, referred to as posterior sagittal anorectoplasty (PSARP) or posterior sagittal anorectovaginourethroplasty (PSARVUP), has led to more complete understanding of the anatomy of these children and of what is required to repair the malformations with optimal results. After reconstructive surgery for the malformation, many children still experience effects in the form of urinary or fecal incontinence. Despite optimal surgical management, no adequate repair for poorly developed muscles or nerves has been developed. Bowel management regiments can provide an excellent quality of life for these children whwn primary continence is not achievable.
The embryogenesis of these malformations remains unclear. The rectum and anus are believed to developed from the dorsal potion of the hindgut or cloacal cavity whwn lateral ingrowth of the mesenchyme forms the urorectal septum in the midline. This septum separates the rectum and anal canal dorsally from the bladder and urethra. The cloacal duct is small communication between the 2 portions of the hindgut. Downgrowth of the urorectal septum is believed to close this duct by 7 weeks gestation. During this time, the ventral urogenital portions acquires an external opening, the dorsal anal membrane opens later. The anus develops by a fusion of the anal tubercles and an external invagination, known as the proctodeum, which deepens toward the rectum but is separated from it by the anal membrane. This separating membrane should disintegrate at 8 weeks gestation.
Interference with anorectal structure development at varying stages leads to various anomalies, ranging from anal stenosis, incomplete rupture of the anal membrane, or anal agenesis to complete failure of the upper portion of the cloaca to descend and failure of the proctodeum to invaginate. Continued communication between the urogenital tract and rectal portions of the cloacal plate causes rectourethral fistulas or rectovestibular fistulas.
The external anal sphincter, derived from exterior mesoderm, is usually present but has varying degrees formation, ranging from robust muscle (perineal or vestibular fistula) to virtually no muscle (complex long-common-channel cloaca, prostatic or bladder -neck fistula).
Anorectal and urogenital malformations are rarely fatal, although some associated anomalies (cardiac, renal) can be life threatening. Intestinal perforationor post operative septic complications in a newborn with imperforate anus can result in mortality or severe morbidity.
Morbidity generally arises from the following 2 sources:
Malformation-related morbidity and surgery-related morbidity
Malformation-related morbidity relates to associated malformations of rectal motility, anorectal innervation, and sphincteric musculature. The most common morbidity in this category is constipation. Most children have mild malformations that commonly result in constipation for reasons that remain unclear, If left untreated, chronic constipation results in rectal dilatation, which worsens the constipation. This become a visious cycle, which, if untreated, results in fecal impactions and overflow pseudoincontinence, also known as encopresis. The most severe forms of malformation-associated morbidity are fecal and urinary incontinence. Higher malformations, such as long-common-channel cloacae and prostatic or bladder-neck fistulas, are associated with poorer nerve and muscle formation, all of which increase the likelihood of fecal or urinary inconteinence. Malformations that directly involve urinary sphicteric mechanisms, and spesifically, any malformation in which the rectum and vagina joins the urinary tract at the bladder neck, often results in either urinary incontinence or inability to complete void.
Surgery-related morbidity can include standard complications such as line infections and pnemonia. Wound infections or anastomic breakdowns can occur in any intestinal surgery. Children with imperforate anus are at greater risk for injury to surrounding pelvic organs because these organs (such as vagina or urethra and seminal vesicles) are located immediately adjacent to the rectum, and may also be involved in the malformation in some unsuspected way. During blind exploration in the pelvis, a dilated ureter can be mistaken for the rectum. Urethras can be opened or transected, and prostates or seminal vesicals can be easily injured. Dissection of these delicate structures can result in ischemia and possible stricture or complete stenosis.
Most children with an anorectal malformation are identified upon routine newborn physical examination. Delayed presentationis often the result of incomplete initial examination. Newborn anorectal and urogenital examination can be technically challenging and makes many practitioners uncomfortable. Subtle malformation, such as those in some children with perineal fistula that may look normal to the casual glance, may present months or years after birth when the child presents to a primary care provider for constipation or urinary tract infection and appears to have a small perineal body upon physical examination. Anorectal malformation in females with a normal-appearing anus who have absent vagina or persistent urogenital sinus may go undiagnosed for years because of examiner reluctance to separate the labia during physical examination, These malformation can be discovered upon evaluation for urinary tract infection or primary ammenorrhea.
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