Anorectal Malformations

Anorectal Malformations Anorectal malformations (ARMs) are congenital malformations, in which the terminal part of the hindgut is abnormally placed and lies outside (partially or completely) the sphincter mechanism. Incidence § The average incidence worldwide is 1 in 5000 live births, § A male preponderance (55% to 65% of cases) is seen. Two thirds of the males had high abnormalities and two thirds of the females had low abnormalities. § The most common defect in females is rectovestibular fistula, whereas the most common defect in males is rectourethral fistula. § Imperforate anus without fistula occurs in 5% of patients, and interestingly, patients with Down syndrome and anorectal malformations have this type of defect 95% of the time. Embryology The cloaca in the embryo is a U-shaped cavity into which open hindgut; tail gut, allantois and later the mesonephric ducts. The cloaca is first formed at around 21 day’s gestation. § A septum in the middle (urorectal septum) grows downward, fusing with lateral folds (Rathke’s plicae) until it joins the cloacal membrane creating two cavities; a urogenital cavity anteriorly and an anorectal cavity posteriorly. This process is completed at 6th week’s gestation. § Rapid growth of the genital tubercle changes the shape of the cloaca and the orientation of the cloacal membrane, which is displaced posteriorly. § The cloacal membrane breaks down at 7 weeks gestation, thereby creating two opening; the urogenital and the anal ones § Old theory explains how defective formation of the urorectal septum accounts for wide variety of defects in both males and females. By contrast, the newer theory suggests that defects in the shape of the dorsal cloaca and an absence of the dorsal cloacal membrane results in anorectal malformations. Classification § The Peňa classification system shown in Table 1 is anatomically descriptive with therapeutic and prognostic implications Male Female § Perineal fistula § Perineal fistula § Recto-urethral fistula: § Vestibular fistula - Bulbar § Persistent cloaca: - Prostatic - <3 cm common channel § Rectobladder neck fistula - >3 cm common channel § Imperforate anus without fistula § Imperforate anus without fistula § Rectal atresia § Rectal atresia § Complex defects § Complex defects Associated malformations § The incidence of such defects varies from 50% to 60%. The higher abnormalities have more associated malformations. § Cardiac anomalies: Present in approximately one third of patients. The most common lesions are atrial septal defect and patent ductus arteriosus. § GIT anomalies: Tracheoesophageal abnormalities occur in about 10% of cases and duodenal atresia in 1% to 2%. § Vertebral anomalies: Lumbosacral anomalies such as hemivertebrae, scoliosis, butterfly vertebrae, and hemisacrum are common. A sacral defect, particularly hemisacrum, in association with imperforate anus and a presacral mass is known as the Currarino triad. § Genitourinary anomalies: The incidence ranges from one third to half of patients. Vesicoureteric reflux is the most common anomaly found, and renal agenesis and dysplasia are the next most frequent findings. Cryptorchidism is reported in up to 20% of males with imperforate anus, and hypospadias occurs in approximately 5%. § Gynecologic anomalies: Hydrocolpos can lead to urinary obstruction or can cause pyocolpos. Uterine malformations (predominantly bicornuate uterus and uterus didelphys), vaginal abnormalities (particularly a vaginal septum), and Clinical findings and management in a male baby First the clinician must perform a thorough perineal inspection, which usually provides the most important clues about the type of malformation that the patient has. § It is important not to make a decision about a colostomy or a primary operation before 20 to 24 hours of age. The reason for waiting is that significant intraluminal pressure is required for meconium to be forced through a fistula, which is the most valuable sign of the location of distal rectum in these babies. § Similarly, radiologic evaluations do not show the real anatomy before 24 hours because the rectum is collapsed by the muscle tone of the sphincters that surround its lower part. Therefore, radiologic evaluations done too early (before 24 hours) will likely reveal a “very high rectum” and therefore yield a false diagnosis. § During this first 24 hours, the newborn should receive intravenous fluids, antibiotics, and nasogastric decompression to prevent aspiration. The clinician should use these hours to evaluate for the presence of associated defect eg. echocardiography, US kidney and spine. § If meconium is visualized on the perineum, it is evidence of a rectoperineal fistula. An anoplasty can be performed without a protective colostomy in the newborn period. § After 24 hours, if no meconium is seen on the perineum or in the urine, a cross- table lateral x-ray film with the baby in prone position should be obtained. If the gas in the rectum is located below the coccyx and the baby is in good condition with no significant associated defects, a posterior sagittal operation without a protective colostomy can be considered. A more conservative alternative would be to perform a colostomy, with the definitive repair planned for a second stage. § If rectal gas is seen above the coccyx or the patient has meconium in the urine, significant associated defects, and/or an abnormal sacrum or a flat bottom, a colostomy is recommended. § The descending or upper sigmoid colostomy is done rather than a right or transverse colostomy in order to have a relatively short segment of defunctionalized distal colon. Clinical findings and management in a female baby In females, and as in males, the most important step in diagnosis and decision making is the perineal inspection. The first 24 hours should also be used to rule out serious associated defects. § Perineal inspection may disclose the presence of a solitary perineal orifice (cloaca). It is important to rule out any urologic or gynecologic disorders. Such a baby requires a colostomy and drainage of the hydrocolopos if present. § Perineal inspection may show the presence of a perineal fistula, and an anoplasty can be performed without a colostomy. § Vestibular fistula may be repaired during the neonatal period without a protective colostomy; however, colostomy is still the most effective way to protect these patients from a perineal wound infection or dehiscence. The decision to repair this malformation primarily or to open a colostomy should be based on the experience of the surgeon. § Occasionally (<10% of cases), no fistula is visible and there is no meconium apparent even after 24 hours of observation. This small group of patients requires a cross-table lateral radiograph. If the radiograph shows gas in the rectum located near the skin, the patient probably has imperforate anus with no fistula. If the patient is in good condition, one can perform a primary operation without a colostomy. Newborn male—anorectal malformation Perineal inspection Cardiac echo/Kidney US 20-24 hours Spinal US/Rule out EA Re-evaluation and cross-table lateral film No Rectal gas above coccyx Perineal Rectal gas below Associated defects fistula coccyx Abnormal sacrum No associated defects Flat bottom Meconium per urethra Consider Anoplasty PSARP Colostomy with or without colostomy . Algorithm for the of a male newborn with an anorectal malformation. treatment Newborn female—anorectal malformation Cardiac echo/Kidney US 20-24 hours Spinal US/Rule out EA Perineal inspection Single perineal Perineal Vestibular No visible opening fistula fistula Fistula (<10%) Cloaca Urologic evaluation 24 hrs Rule out hydrocolpos Colostomy Anoplasty Colostomy Drain Cross-table or primary hydrocolpos lateral film repair* Urinary diversion (if necessary) Rectum below High rectum coccyx Colostomy *Depending on the experience of the surgeon and general condition of the patient . Algorithm for the treatment of a female newborn with an anorectal malformation. Definitive repair § Before proceeding with definitive reconstruction, the anatomy of the anorectal malformation is delineated by high-pressure distal colostography. It helps to visualize the true extent of the rectum and the presence of a rectourinary fistula § All defects can be repaired using a posterior sagittal approach. Approximately 10% of male patients (those with a rectobladder neck fistula) and about 40% of female patients with a cloaca may, in addition, require an abdominal approach for mobilization of a high rectum or vagina. § In males: o In rectoprostatic and bulbar fistulae, through a midline posterior sagittal approach, progressive division of soft tissue is done, strictly in the midline. Next, posterior wall of the rectum is opened to visualize the fistula and the rectum is separated from the urinary tract. Finally, reconstruction of the muscle complex around mobilized rectum and anocutaneous anastomosis are done In rectobladder neck fistula, a laparotomy or laparoscopy is done initially to separate the rectum from the bladder and continue as a small perineal incision to deliver and anastomose the new anus § In females: o A rectovestibular fistula is also repaired with a posterior sagittal operation. Special emphasis is placed in the separation of the rectum from the vagina, because they have a common wall without a plane of separation. o In cloaca, the goal of this procedure is to separate the rectum from the vagina and the urinary tract. The length of the common channel should be assessed by endoscopy. Those patients with a common channel length of < 3 cm can be managed by posterior sagittal approach as described above, whilst patients with a common channel length of > 3 cm require more extensive procedure including a laparotomy and often vaginal replacement with a segment of bowel. Outcomes § The higher the ARM anomaly, the lower the achieved continence. § Sacral anomaly leads to decreased achieved continence. § Lower malformations tend to suffer more from constipation .

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