Anorectal malformations

Associated genitourinary defects

Important associated anomalies include genitourinary defects, which occur in approximately 50% of all patients with anorectal malformations. All patients must be evaluated at birth to rule out one of these defects, and the most valuable screening test is an abdominal and pelvic ultrasound. Urologic evaluation prior to colostomy provides the surgeon the necessary information needed to address the urologic problem at the time of the colostomy. The surgeon must be prepared to perform a urologic diversion if necessary.

Unfortunately, a common error in diagnosis occurs during the perineal inspection, when a female is thought to have "imperforate anus with rectovaginal fistula" when in actuality, all three structures, the urinary tract, vagina, and rectum all meet in a common channel and the baby has a cloaca [8–10] (Figure 1). The presence of a single perineal orifice is clinical evidence of a patient with persistent cloaca. Patients with these anomalies also have small genitalia. In patients with cloaca, examination of the abdomen may reveal an abdominal mass which likely represents a distended vagina (hydrocolpos), (Figure 2) present in 50% of patients with cloaca. An abdominal ultrasound determines the presence of an obstructive uropathy as well as the presence of a hydrocolpos. This misconception has important therapeutic implications that will be discussed below. It is vital to make the correct determination of cloaca because 90% of babies have an associated urologic problem, and 50% have hydrocolpos. Both the urinary tract and the distended vagina may need to be dealt with in the newborn period to avoid serious complications. Missing the diagnosis of cloaca frequently means that an obstructive uropathy is overlooked. The patient may then receive only a colostomy and subsequently may suffer from sepsis, acidosis, and sometimes death. The other implication of missing the diagnosis of cloaca involves repairing only the rectal component of the anomaly, leaving the patient with a persistent urogenital sinus.

Associated spinal anomalies

The sacrum is the most frequently affected bony structure. Traditionally, to evaluate the degree of sacral deficiency, the number of sacral vertebral bodies were counted. A more objective assessment of the sacrum can be obtained by calculating a sacral ratio. The sacrum is measured and its length is compared with bony parameters of the pelvis. The lateral film is more accurate than the anterior posterior view because its calculation is not affected by the tilt of the pelvis. A hemisacrum is always associated with a presacral mass, which is commonly formed of dermoids, teratomas, or anterior meningoceles. Hemivertebrae may also affect the lumbar and thoracic spine, leading to scoliosis.

Spinal anomalies including a tethered spinal cord can occur [11, 12]. This anomaly, which refers to the intravertebral fixation of the phylum terminale is known to occur in approximately 25% of patients. The prevalence of tethered spinal cord rises with increasing height and complexity of the anorectal anomaly. In addition, patients with a hypodeveloped sacrum and with associated urologic problems have a higher likelihood of having tethered cord. Motor and sensory disturbances of the lower extremities may result. Concerning bowel and urinary function, patients with anorectal malformations and tethered cord have a worse functional prognosis but they also have higher anorectal defects, less developed sacrums, associated spinal problems, and less developed perineal musculature. So, the actual impact of tethered cord itself on their functional prognosis is unclear. Untethering of the cord is indicated in the neurosurgical literature to avoid motor and sensory problems. There does not appear to be evidence that this operation will impact on the functional prognosis of a patient with anorectal malformation. Spinal ultrasound in the first 3 months of life and magnetic resonance imaging thereafter are useful radiologic modalities to establish the diagnosis. Furthermore, patients may have other spinal anomalies besides tethered cord such as syringomyelia and myelomeningocele.

Perineal fistula

Perineal fistulas in both male and female have traditionally been called "low" defects. In these cases the rectum opens in a small orifice, usually stenotic and located anterior to the center of the sphincter (Figure 3). Most of these patients have excellent sphincter mechanisms and a normal sacrum. In males, the perineum may exhibit other features that help in recognition of this defect, such as a prominent midline skin bridge (known as 'bucket handle') or a subepithelial midline raphe fistula that looks like a black ribbon because it is full of meconium. These features are externally visible and help diagnose a perineal fistula. A simple anoplasty enlarges the stenotic orifice and relocates the rectal orifice posteriorly within the limits of the sphincter complex. The operation is called a "minimal posterior sagittal anoplasty". It is performed with the patient positioned prone with the pelvis elevated; multiple fine silk sutures are places at the mucocutaneous junction of the bowel orifice for traction. A short (1–2 cm) midsagittal incision is made posterior to the fistula site, dividing the entire external sphincter complex. The fistula and lower part of the rectum are carefully dissected to permit mobilization of the rectum for backward placement within the limits of the sphincter complex. The perineal body, that area where the fistula was located, is repaired with a few long-term absorbable sutures [7].

Decision-making for male newborns

Male newborns with recto-perineal fistula do not need a colostomy. They can undergo a posterior sagital anoplasty whereas male babies with evidence of a recto-urinary tract communication should undergo fecal diversion with a colostomy.

In 80–90% of male newborns, clinical evaluation and urinalysis will provide enough information for the surgeon to decide whether the baby requires a colostomy. If none of the clinical signs to determine the location of the anorectal anomaly becomes evident by 24 hours, a cross-table lateral film with the baby in prone position, with the pelvis elevated, and with a radioopaque marker placed on the perineum is performed (Figure 4). This x-ray on rare occasion may show the column of air in the distal rectum to be within 1 cm of the perineum, and if this is the case, the baby can be treated like those with a recto-perineal fistula, and a newborn perineal operation can be performed. If the air column is greater than 1 cm from the perineum, a colostomy is indicated.

A definitive repair in the newborn period avoids a colostomy but there is considerable risk to the urinary tract with this practice because the surgeon does not know the precise anorectal defect. The only way to definitively determine the patient's anorectal defect is to perform a distal colostogram, which of course requires the presence of a colostomy. Without this information an operation in the newborn period is essentially a blind perineal exploration. The surgeon may not be able to find the rectum and may find and damage other, unexpected, structures, such as the posterior urethra, seminal vesicles, vas deferens, and ectopic ureters during the search for the rectum. Finally, without fecal diversion, there is the risk of dehiscence and infection. These complications may compromise the ultimate functional prognosis.

Decision-making for female newborns

The decisions involved in managing the female newborn are less complicated. In 90% of patients, a meticulous perineal inspection will demonstrate the anorectal defect. Waiting 16–24 hours for enough abdominal distension to demonstrate the presence of a rectoperineal fistula or rectovestibular fistula applies to females as well.

The most common anomaly in females is a rectovestibular fistula (Figure 5). Perineal inspection shows a normal urethra, normal vagina, and another orifice, which is the rectal fistula in the vestibule. The safest option for a surgeon without extensive experience in anorectal anomalies when faced with a baby with clinical evidence of a rectovestibular fistula is to perform a diverting colostomy. Colostomy prior to the main repair avoids the complications of infection and dehiscence. Definitive repair of this anomaly in the newborn period should be reserved for surgeons with significant experience repairing these defects. This anomaly has an excellent prognosis and therefore complications that could affect future continence must be avoided.

Unfortunately, the most common referral for redo operations to tertiary centers that care for anorectal anomalies are for patients with rectovestibular fistulas who underwent a failed primary repair in the newborn period.

Occasionally, the fistulas are big enough to decompress the gastrointestinal tract, and may be dilated to facilitate fecal drainage until the baby is older and a definitive repair is performed. Definitive repair involves a posterior sagittal approach. The most delicate part of this operation is the separation of the rectum and vagina, which share a common wall. Females like males can have a rectoperineal fistula and for them an anoplasty in the newborn period should be performed. Like in males, less than 5% of female babies have no clinical evidence of the location of the rectum after 24 hours. They may have imperforate anus with no fistula. A cross-table lateral x-ray should be performed, and will help determine the need for a colostomy.

Surgery

As discussed previously, the surgeon must decide in the newborn period whether the child requires fecal diversion with a colostomy, or can undergo a primary repair procedure.

• Posterior sagittal approach

◦ Anorectal repair

The repair of an anorectal malformation requires a meticulous and delicate technique and a surgeon with experience in the management of these defects. The posterior sagittal approach is an ideal method of defining and repairing anorectal anomalies. If the baby growing well, the repair can be performed at 1–2 months of age. Detailed surgical procedure can be found in the following references: [1, 2, 5, 6].

Ninety percent of male patients can be approached with a posterior sagittal approach alone, while 10% require an abdominal component (with laparotomy or laparoscopically) to mobilize a very high rectum. All female malformations, with the exception of about 30% of cloacas can be repaired with this approach. In 30% of cloacas, the rectum or vagina is so high as to require an abdominal approach as well [20].

◦ Rectobladder neck fistula

In the rare case of a true supralevator malformation (rectobladder neck fistula), the operation involves both a posterior sagittal incision and an abdominal component, which can be done with laparoscopy or laparotomy (Figure 6).

◦ Imperforate anus without fistula

In patients with imperforate anus without fistula, the same meticulous dissection is required to separate the distal rectum from the urinary tract as in patient with rectourinary fistulae because the rectum and urethra still share a common wall.

◦ Rectovestibular fistula

In cases of rectovestibular fistula, the posterior sagittal incision can be shorter than in male patients with rectourethral fistulae. Often the entire levator mechanism needs not be divided and only the external sphincter, muscle complex, and part of the lower portion of the levator mechanism need to be divided. The rectum and posterior vagina share a common wall, and it is this separation that is the most difficult part of the operation. Once the rectum is completely mobilized, a perineal body is constructed, and the rectum is placed within the limits of the sphincter mechanism [21].

◦ Rectal atresia

A very rare malformation, rectal atresia, occurs in 1% of cases. The anal canal is normal and externally the anus appear normal. However, there is a blockage 1–2 cm from the anal skin, usually found when the nurse tries to pass a thermometer. These babies should undergo colostomy at birth, and then their definitive repair involves a posterior sagittal approach and an end-to-end anastomosis between the upper rectal pouch and the anal canal.

◦ Persistent cloacas

The repair of persistent cloacas represents a serious technical challenge that should be performed in specialized centers by pediatric surgeons dedicated to the care of these complicated patients [22]. This malformation represents a wide spectrum of defects by itself. The defect involves fusion of the rectum, vagina, and urethra together to form a common channel (Figure 7). The length of this common channel can range from 1 to 10 cm. The rectum and vagina share a common wall and the vagina and urinary tract likewise have a common wall. The goals of surgical treatment are to achieve bowel control, urinary control, and normal sexual function. Sometimes all three goals are achieved, sometimes only two, often only one, and occasionally none [23].

Prognostic factors include the quality of the sacrum, the quality of the muscles, and the length of the common channel. We have arbitrarily defined two groups of patients. The repair of patients with a common channel less than three cm is reproducible and is feasible for most pediatric surgeons. For patients with a common channel greater than three cm, the repair should be performed at a specialized center by a surgeon with experience managing the urologic anomalies and able to performing complex vaginal reconstructions. If the common channel is less than 3 cm, the posterior sagittal approach without an abdominal approach can be used to repair the defect.

For patients with a common channel greater than three cm, a laparotomy is usually required. Often the vagina and urinary tract must be separated trying to gain length, and the urethra must then be reconstructed. The surgeon must be prepared to open the bladder and to reimplant the ureters if necessary. Complex vaginal mobilizations are often required and frequenly a vaginal replacement with small intestine or colon is necessary. The pullthrough of the rectum is similar to other anorectal malformations. It is the repair of the vagina, the urethra, and the associated urologic defects that represents the main surgical challenge. A large vagina can be an advantage during the definitive repair because the surgeon can more easily mobilize it and has more alternatives for the vaginal repair. About 50% of patients have various degrees of vaginal or uterine septation. These can be totally or partially repaired during the main operation. The precise gynecologic anatomy must be ascertained either during the main repair or during colostomy closure (if a laparotomy was not required during the main repair). We have learned that approximately one third of our patients have obstructed Mullerian structures which can lead to severe problems resulting from retrograde menstruation. Predictions of future problems such as amenorrhea in cases of atretic uteri, or hydrometrocolpos and retrograde menses can be made in the newborn period. Presentations of pelvic pain or amenorrhea as teenagers should prompt the assumption of anomalous gynecologic structures.

Post-operative management

Voluntary muscle structures

In the normal patient, the voluntary muscle structures are represented by the levators, muscle complex, and external sphincter. Normally, they are used only for brief periods, when the rectal fecal mass reaches the anorectal area, pushed by the involuntary peristaltic contraction of the rectosigmoid motility. This voluntary contraction occurs only in the minutes prior to defecation, and these muscles are used only occasionally during the rest of the day and night.

Patients with anorectal malformations have abnormal voluntary striated muscles with different degrees of hypodevelopment. Voluntary muscles can be used only when the patient has the sensation that it is necessary to use them. To appreciate that sensation, the patient needs information that can only be derived from an intact anal sensory mechanism, a mechanism that many patients with anorectal malformations lack.

Anal canal

Exquisite sensation in normal individuals resides in the anal canal. Except for patients with rectal atresia, most patients with anorectal malformations are born without an anal canal; therefore, sensation does not exist or is rudimentary.

It seems that patients can perceive distention of the rectum but this requires a rectum that has been properly located within the muscle structures. This sensation seems to be a consequence of stretching of the voluntary muscle (proprioception). The most important clinical implication of this is that liquid stool or soft fecal material may not be felt by the patient as it does not distend the rectum. Thus, to achieve some degree of sensation and bowel control, the patient must have the capacity to form solid stool.

Bowel motility

Perhaps the most important factor in fecal continence is bowel motility; however, the impact of motility has been largely underestimated. In a normal individual, the rectosigmoid remains quiet for variable periods of time (one to several days), depending on specific defecation habits. During that time, sensation and voluntary muscle structures are almost not necessary because the stool, if it is solid, remains inside the colon. The patient feels the peristaltic contraction of the rectosigmoid that occurs prior to defecation. Voluntarily, the normal individual can relax the striated muscles which allow the rectal contents to migrate down into the highly sensitive area of the anal canal. There, accurate information is provided by the anal canal concerning the consistency and quality of the stool. The voluntary muscles are used to push the rectal contents back up into the rectosigmoid and to hold them if desired, until the appropriate time for evacuation. At the time of defecation, the voluntary muscle structures relax.

The main factor that provokes the emptying of the rectosigmoid is a massive involuntary peristaltic contraction helped sometimes by a Valsalva maneuver. Most patients with an anorectal malformation suffer from a disturbance of this sophisticated bowel motility mechanism. Patients who have undergone a posterior sagittal anorectoplasty or any other type of sacroperineal approach, in which the most distal part of the bowel was preserved, show evidence of an over-efficient bowel reservoir (megarectum). The main clinical manifestation of this is constipation, which seems to be more severe in patients with lower defects.

Constipation that is not aggressively treated, in combination with an ectatic distended colon, eventually leads to severe constipation, and a vicious cycle ensues, with worsening constipation leading to more rectosigmoid dilation, leading to worse constipation. The enormously dilated rectosigmoid, with normal ganglion cells, behaves like a myopathic type of hypomotile colon.

Those patients with anorectal malformation treated with techniques in which the most distal part of the bowel was resected behave clinically as individuals without a rectal reservoir. This is a situation equivalent to a perineal colostomy. Depending on the amount of colon resected, the patient may have loose stools. In these cases, medical management consisting of enemas plus a constipating diet, and medications to slow down the colonic motility is indicated.

True fecal incontinence

For patients with true fecal incontinence, the ideal approach is a bowel management program consisting of teaching the patient and his/her parents how to clean the colon once daily so as to stay completely clean for twenty-four hours. This is achieved by keeping the colon quiet in between enemas. These patients cannot have voluntary bowel movements and require an artificial mechanism to empty their colon, a daily enema. The program, although simplistic, is implemented by trial and error over a period of one week. The patient is seen each day and an x-ray film of the abdomen is taken so that they can be monitored on a daily basis for the amount and location of any stool left in the colon, as well as the presence of stool in the underwear. The decision as to whether the type and/or quality of the enemas should be modified as well as changes in their diet and/or medication can be made daily [34].

Approximately 75% of all patients with anorectal malformations have voluntary bowel movements [35]. About 50% of them have voluntary bowel movements, but soil their underwear occasionally. Episodes of soiling are usually related to constipation, and when constipation is treated properly, the soiling frequently disappears. Approximately 40% of the group have voluntary bowel movements and never soil, thus making them totally continent. 25% of patients suffer from fecal incontinence and must receive a bowel management regimen to artificially keep them clean.

Once the diagnosis of the specific defect is established, the functional prognosis can be rapidly predicted, which is vital in order to avoid raising false expectations in the parents. Factors such as the status of the spine, sacrum, and perineal musculature affect the counseling of the parents. Patients with a hypodeveloped sacrum are much more likely to be incontinent and a hypodeveloped sacrum is also a good predictor of associated spinal problems such as tethered cord. If the patient's defect is of the type pointing to a good prognosis such as vestibular fistula, perineal fistula, rectal atresia, rectourethral bulbar fistula, or imperforate anus without fistula, one should expect that that child will have voluntary bowel movements by the age of 3. Such children need supervision to avoid fecal impaction, constipation, and soiling. If a patient's defect points to a poor prognosis, such as a high cloaca (common channel greater than 3 cm) or a recto-bladder neck fistula, the parents should be informed of the likelihood that that child will need a bowel management program to remain clean, which should be implemented at the age of 3 or 4. Patients with rectoprostatic fistulas have almost equal chance of having voluntary bowel movements or being incontinent. Toilet training should be attempted at age 3, and if unsuccessful, a bowel management program should be initiated. Each year, during summer vacation, an attempt should be made to try to achieve bowel control, and if unsuccessful, the bowel management should be restarted. As the child grows older and more cooperative, the likelihood of achieving bowel control will improve.