Posterior Sagittal Anorectoplasty (PSARP) for Imperforate Anus

Abstract

Imperforate anus is a birth defect in which the anal opening is absent. This condition develops during the fifth to seventh weeks of pregnancy and the cause is unknown. It affects about one in every 5,000 newborns and is noted to be more common among boys than girls. Imperforate anus is usually present with other birth defects such as vertebral defects, cardiac problems, tracheoesophageal fistula, renal anomalies, and limb abnormalities, collectively known as the VACTERL association. These are classified as low or high type. In the low type, in which the rectum remains close to the skin, there may be associated stenosis of the anus, or the anus may be missing altogether, with the rectum ending in a blind pouch. In the high type, in which the rectum is higher up in the pelvis, there may be a fistula connecting the rectum and the bladder, urethra, or the vagina. The diagnosis is made by performing a physical exam after birth. An x-ray of the abdomen and abdominal ultrasound can help reveal the extent of the abnormalities. Treatment is surgical creation of an opening or new anus to allow stool to pass. The type of surgery differs and depends on whether the anus ends high or low in the pelvis. In the case of a low type, an anal opening is made in a single operation, and the rectum is pulled down to the anus. For high type, surgical correction is performed in three stages. The first procedure is bringing the intestine out of the abdomen creating a stoma; the second procedure is pulling the rectum down to the anus where a new anal opening is created; and the third procedure is closure of the intestinal stoma. Here, we present a case of a 9-month-old male who was born with a high-type imperforate anus. A posterior sagittal anorectoplasty (PSARP) was done as the second of three stages of treatment. The first was an emergency sigmoid colostomy, and the third will be to close the colostomy in about 6 to 8 weeks following the PSARP.

Keywords 

Anorectal malformation; posterior sagittal-anorectoplasty; VACTERL; pediatric; general surgery 

Case Overview

Background

Anorectal malformations (ARM) are a group of congenital anal anomalies that encompass a wide variety of structural defects from simple membranous coverings to complete cloacal disfiguration.¹ These defects occur in between 1:1500 and 1:5000 births, making them the most commonly seen anomaly in the neonatal period.      

Although traditional classification defines ARM as either “high”, “intermediate”, or “low”, depending on the distance of the rectal pouch to the perineum, it is also appropriate to classify according to common diagnostic, therapeutic, and prognostic features. These criteria largely depend on the type of fistula, which is an abnormal connection between two body regions, present in the setting of an imperforate anus. There are several types of fistulous formations observed depending on the regions of the body connected. In males, these connections can be recto-urethral-bulbar, recto-urethral-prostatic, or recto-bladderneck. In females, recto-vestibular fistulas can be seen, as well as formation of a cloaca with either a short (<3cm) or long channel (>3cm). Levitt and Pena note that rectovaginal fistulas in females are exceedingly rare, and that most females with suspected rectovaginal fistulas are more likely to have a cloaca, or a single opening encompassing the urinary tract, vagina, and rectum.¹⁶

Prenatal diagnosis of the anomaly is rare, even with recommended prenatal screening. In cases where prenatal diagnosis does occur, it is usually because of large bowel dilatation or possibly calcified intraluminal meconium visualized on ultrasound.² Most diagnoses are conferred in the early prenatal period and adhere to the Wingspread classification, which classifies malformations as either low-, medium-, or high-type, depending on the distance of the rectum to the perineal musculature, otherwise known as the pouch-perineum distance.³ Since the advent of the posterior sagittal anorectoplasty (PSARP), newer classification systems have been incorporated such as the Pena classification (1995) and the Krickenbeck classification (2005), which incorporate the presence, type, and location of a fistula, which helps guide surgical management.⁴      

Low-type ARM are commonly managed with immediate one-step transperineal anoplasty following birth. However, intermediate to high ARM require diverting colostomy followed by further surgical intervention such as PSARP.⁵

The etiology of ARM remains uncertain; however, most studies agree that it is both multifactorial and has a genetic component.^{1,4, 6} Autosomal dominant inheritance has been implicated in some cases, and certain genetic conditions such as Currarino syndrome, Townes-Brock syndrome, Pallistar-Hall syndrome, and Down’s syndrome have also been observed.¹ However, most notable is the association with vertebral, anorectal, cardiac, tracheoesophageal, renal, and limb defects (VACTERL) defects, as noted above. In fact, a study by Brantberg et al. noted that in 69 cases of children with imperforate anus, only 14.5% were without coexisting malformations. The remaining 85.5% of affected individuals suffered from other anomalies, the most common being urogenital (62.7%), followed by cardiac (40.7%) and craniofacial (39.0%) malformations.²    

The diagnostic evaluation of a child with suspected imperforate anus begins with an abdominal ultrasound which can evaluate for urologic malformations. Assessment of spinal abnormalities such as tethered chord syndrome can be accomplished using spinal ultrasound within the first 3 months of life. Plain radiographic films of the spine can also show vertebral anomalies such as spina bifida and spinal hemivertebrae. If the diagnosis cannot be made within the first day of life through clinical exam, lateral crosstable radiographs can be used to visualize a distant air bubble in the rectum to an absent anal opening, but this is generally not required.¹⁶ 

Focused History of the Patient 

The patient in this video is a 9-month-old male diagnosed with high-type imperforate anus. Initially, this patient underwent a diversion colostomy, and the PSARP marks the completion of the second of three surgeries. The final surgery, closure of the colostomy, will occur 6–8 weeks after appropriate weight gain, anal dilation, and healing have occurred. Unfortunately, the patient was delayed in having the operation, likely due to financial constraints.  

Physical Exam 

Physical exam findings in similar patients include obstructive symptoms such as abdominal distension and failure to pass meconium via the anus.¹ It must be noted that passing meconium does not eliminate the possibility of having an ARM, as it may be the result of pressure building inside the rectum and forcing meconium through a patent fistula.⁷ Other findings on physical exam are related to associated anomalies and include intolerance to feeding (tracheoesophageal fistula), cardiac murmur, and a sacral dimple from vertebral anomalies such as tethered cord syndrome.¹ Meconium found in the urine due to a rectovestibular fistula or meconium in the vagina via a rectovestibular fistula can also be seen in males and females, respectively. An anal pit can also sometimes be appreciated. Additionally, flattened perineum and absent horizontal gluteal crease can be seen due to underdeveloped perineal musculature.⁴

Imaging 

Due to the high degree of association with other congenital anomalies, 60% as noted by Smith et al., multiple modalities of imaging must be employed.⁶ Imperforate anus can be initially diagnosed clinically when the infant fails to pass meconium through the anus or inadvertently through a fistula within 24 hours of birth.⁵ Imaging at this point should consist of radiography and ultrasound. An invertogram, or an x-ray of the abdomen after the infant has been held upside down, was previously used to estimate the distance between the distal gas bubble in the colon and the perineum.⁴ However, infants do not generally tolerate this position well, and incessant crying can cause contraction of the puborectalis muscle leading to difficulty visualizing the distal rectal gas bubble and inaccurate pouch-perineum estimates.⁶ A superior alternative is a lateral film radiograph after the infant has been in the prone position with their hips flexed, which allows the gas bubble to travel similarly to an invertogram. A bubble-perineum distance of less than 1 cm generally indicates a low defect, whereas a distance greater than 1 cm indicates a high defect.¹ However, Wood and Levitt posit that the surgical procedure employed depends on the likelihood of reaching the rectum with a posterior incision.³ However, the only way to definitively determine the patient’s ARM is through a colostogram, which necessitates a colostomy in order to be performed.⁴

Ultrasound can also play a role in estimating bubble-perineum distance. Perineal ultrasound is useful for classifying the type of fistula present, whereas the infracoccygeal approach can visualize the puborectalis muscle directly. Hosokawa et al. report that it may be optimal to perform ultrasound 24 hours after birth as this allows fecal matter to travel to the distal rectum, providing superior visualization.⁵

Additionally, physicians must evaluate for the presence of other congenital malformations. An echocardiogram is useful to evaluate for heart defects, followed by cardiac CT or MRI.⁸ The most common defects being tetralogy of Fallot (ToF), atrial septal defects (ASD), and ventricular septal defects (VSD).⁹ Placement of a nasogastric tube followed by abdominal or chest x-ray is indicated to evaluate for a tracheoesophageal fistula.⁶ Radiographs, ultrasound, and MRI of the spine can be used, bearing in mind MRI is necessary for showing soft tissue anomalies like tethered cord syndrome. Renal ultrasound and radiographs of the extremities can also be used.⁸ However, the only way to definitively determine the patient’s ARM is through a colostogram. In order to perform a colostogram though, a patient must first have a colostomy, necessitating a three-stage procedure over the single-stage.⁴

Natural History 

All cases of ARM require treatment, either through PSARP, colostomy, or another kind of anorectal procedure. However, surgical intervention can be delayed in certain cases of difficult anatomy to allow for the growth of the child which can make the operation easier. These include males with perineal fistulas and females with rectovestibular fistulas. Instead of operating immediately, a Hegar dilator can be used to increase the diameter of the fistula which allows for adequate stool evacuation during the waiting period. However, the fistulous tract must be large in enough to perform dilations, and ultimate surgical intervention should occur at 3 months before the transition to solid food.⁶ Without treatment, the patient could develop colonic obstruction, fecal impaction, profuse vomiting, dehydration, toxic megacolon, sepsis, and death.¹

Options for Treatment 

There are two widely accepted treatment options that can be used for those with an ARM. The gold-standard procedure remains the PSARP, but laparoscopically-assisted anorectal pull-through (LAARP) also has utility in treating high malformations.^1,4,10 In regard to the PSARP procedure, single-stage procedure (without a colostomy) is preferred over a staged procedure (with a colostomy). Gangopadhyay and Pandey note that this is due to better procedural outcomes while incurring less cost.⁴ Additionally, single-stage procedures optimize fecal continence later in life, by limiting interference with delicate cerebral fibers in the first year of life necessary for sensation of rectal fullness. Other advantages of performing a single-stage include easier dissection and less psychological stress on the patient.⁴

As noted above, the decision to use either the PSARP procedure or laparoscopic intervention is centered around the distance of the rectum from the perineal skin, or pouch-perineum distance. If the rectum is within reach via posterior incision, then a single-stage PSARP can be used. However, if the rectum is high, a divided colostomy will be required followed by either a PSARP, laparoscopic-assisted PSARP, or laparotomy with PSARP. As an alternative to these treatment options, the LAARP procedure can be utilized. A systematic review by Han et al. found that LAARP may be superior to PSARP in terms of safety, feasibility, and overall effectiveness in treating intermediate/high ARM in pediatric patients. However, more research is necessary due to low-moderate quality of evidence. 

Rationale for Treatment 

The goal of treatment is to establish a patent connection between the rectum and the anus to allow for adequate fecal continence later in life. 

Special Considerations 

Relative contraindications, such as prematurity and congenital heart disease, may delay surgical intervention. However, no absolute contraindications exist for either single-stage or staged procedures.¹⁸

Discussion 

In this case, a successful PSARP procedure was performed on a 9-month-old child who was diagnosed with imperforate anus. This procedure was the second of three procedures total; the first operation was a diverted sigmoid colostomy, and the last will be the closure of the colostomy. PSARP remains the gold-standard procedure for ARM; however, it is sometimes necessary to use laparoscopy in order to assist in the treatment of high ARM defects.⁴

The advent of the procedure can be traced back to 1963 when Professor Douglas Stephens introduced the “puborectalis concept”. The notion was that the puborectalis was considered to be the most important structure for determining continence later in life.^{10, 11} Stephens approach involved using a sacral dissection in order to hopefully identify this muscle and preserve it. However, this approach was optimal only for low defects, whereas intermediate and high defects required a different approach. This gap was filled by Rhoads et al., by using an abdominoperineal pull-through approach followed by a blind pull-through of the rectum with the fingers. However, fear of causing damage to delicate nerves through blind dissection in the pelvic region led to a similar yet modified procedure proposed by Iwai et al.. They found that performing a careful dissection of the rectal wall using an electric stimulator instead of just a blind pull-through was effective in preserving delicate neurovascular tissue in the rectum. Ultimately, both the sacral dissection by Stephens combined with the abdominopull-through devised by Rehbein were combined by Kiesewetter to form a surgical technique that would not only allow for adequate access, but also preservation of the puborectalis muscle. However, despite these advancements, postoperative outcomes remained poor. Consequently, a new technique was invented by Dr. Alberto Pena, who was the first to describe the PSARP, which has become the gold standard for the management of ARM.⁴ 

The treatment algorithm for ARM mainly depends on the accessibility of the distal rectal pouch through a posterior approach, and the type, presence, and number of fistulas. One method of measurement involves calculating the distance between the distal colonic gas bubble and the skin of the anatomical anus, marked by a radiopaque marker. Two lines are marked; the pubococcygeal line  (P-C line) and the ischial line (I line). A rectum that forms a pouch above the P-C line would be considered high, whereas a pouch formed below the I line would be low, and in between the two would be intermediate.⁴

In female infants, it is important to identify the number of the orifices present (either one, two, or three). In the case of one opening, the defect is identified as a cloaca and an ultrasound is required to identify whether a hydrocolpos is present, which will require a colostomy and vaginostomy as opposed to just a colostomy. However, in the case of three openings (vagina, anus, fistula), then a PSARP is appropriate, regardless of the type of fistula. If only two openings are presents, it is important to determine what type of fistula is present if any, because recto-vaginal fistulas and vaginal atresia require colostomy, whereas those without a fistula may also be managed with a single-stage PSARP, depending on the pouch-perineum distance.  

In males, the treatment differs slightly. If meconium is found on the perineum, this indicates a perineal fistula which can be easily repaired with a single-stage PSARP. However, if meconium is found in the urine, this indicates a rectourethral fistula. Any male with a rectourethral fistula requires a diverting descending sigmoid colostomy in order to allow for stool evacuation and also for the child to grow before definitive surgical intervention.^6,7 Additionally, a colostogram (which necessitates the presence of a colostomy), allows surgeons to precisely determine where the rectum will be located, which makes the operation much safer.³ Furthermore the colostomy should be diverting, which provides the mucous tract necessary for the colostogram but also bowel decompression.³ Following the colostomy, a PSARP should be performed, with or without laparoscopic assistance, depending on the pouch-perineum distance. Finally, the absence of meconium in the urine or on the perineum indicates the absence of a fistula. These patients can be evaluated with a cross table lateral radiograph to determine the pouch-perineum distance and management as previously described.³ Male infants who do require colostomy will be prepared for PSARP in 4–8 weeks, after proper nutrition and absence of infection. 

There are some other important considerations that must be noted about the procedure. First, one of the most common causes of PSARP failures is undue tension placed on the anoplasty. This can occur when the rectum is not adequately separated from surrounding structures (bladder, urethra, vagina), and thus, when joined to the perineal skin, the rectum becomes stretched and ruptures. By placing silk sutures in the rectum, uniform traction can be applied to safely separate the rectum from surrounding viscera. Furthermore, it is essential that a urinary catheter be placed in the bladder, especially during male PSARP procedures, as this helps the surgeon to correctly identify it via the inflated balloon.³

The operating time of the procedure is usually between 45–60 minutes, although the presence of fistulas can extend this time. The typical length of stay for the procedure is 4–5 days, and blood loss is minimal.

Most patients who undergo PSARP can be discharged 2 days after their procedure or 1-3 days longer if they require an additional laparoscopic procedure.⁷ The foley catheter usually remains in place for 5-7 days after the procedure, however, can remain in place for up to 28 days postoperatively after cloaca repair with total urogenital mobilization.^7,16 The incision made during PSARP is relatively painless and anal dilatations can start 2 weeks after the procedure occurring twice daily. Once adequate dilation according to the child’s age has occurred, the colostomy can be closed and dilations can cease over the following 3 to 4 months.⁷ One important complication to consider during this time is the development of megacolon due to anal stenosis, which is usually a complication of poor anal dilations.¹⁷ Thus, it is important for the clinician to monitor for adequate bowel movements, which is ideally 1-3 well-formed bowel movements daily, while maintaining continence during the interim.⁷ Perineal skin irritation and subsequent excoriation can also develop from perineal skin exposure to stool.¹⁶ Other early complications such as peritonitis, wound dehiscence, and development of recurrent fistula have also been reported, but it is noteworthy that severe post-operative complications are significantly less common in PSARP (2%) as compared to other similar operations, including abdominoperineal and sacroabdominoperineal pull-through operations (10%-30%).¹⁷ 

Postoperative complications of PSARP specifically include recurrent fistula formation, stricture formation in surrounding structures, anal stenosis resulting in obstruction, and rectal prolapse.¹ In general, the lower the defect is, the better chance for developing full continence as an adult.¹ In fact, Wood and Levitt have determined that three main factors combine to determine fecal continence: voluntary muscle structures, anorectal sensation, and bowel motility. Depending on the experience of the surgeon and stage of development of the patient, the perineal tissues and muscle could be placed under considerable stress. Furthermore, the development of the PSARP has granted better visualization and thus protection to the pelvic nerves; however, it is still noteworthy that damage to these nerves can impact sensation of stool in the rectum and thus continence. Finally, any surgical procedure involving the rectal tissues and muscles will necessarily disrupt the overall strength and integrity of the muscle, which will have an impact on bowel motility.⁷

One of the most important outcome measures of the procedure is fecal continence rate. Ghorbanpoor et al. found in their single-center study that over 85% of patients were able to maintain fecal continence after several years. Although not a significant difference, patients with high ARMs had less continence compared with those with low ARMs, a trend that Smith et al. also noted.^6,12 Some studies, however, have reported a fecal incontinence rate of between 30–60%.^13,14 There is some evidence to suggest that this may have to do with the level of the ARM (low, intermediate, or high); however, this difference has not been statistically significant. It is possible, as postulated by Ghorbanpoor et al., that the large amount of variation is due to the various fecal continence scoring systems that are used. Also, it is possible that fecal continence after surgery changes with age, but this too has not been proven. Overall, however, multiple studies have found fecal incontinence to be well above 50%, sometimes exceeding 80%.^12,14,15 Further research should be directed at determining the optimal age to undergo PSARP. 

In the case of this patient, a staged PSARP was used, in which an intermediate colostomy was placed. It is important to note that colostomy placement has been shown to reduce surgical site infection leading to less morbidity and mortality overall. Colostomy procedures also help prevent wound dehiscence. However, they also carry disadvantages, such as increased cost for multiple procedures and non-compliance by patients to return within the recommended 6–8 weeks. Careful selection of patients for single-stage PSARP is thus important. Other complications like stenosis of the neoanus and urinary incontinence have been reported to occur less than 15% of the time.¹⁵

Equipment 

In addition to standard equipment used, an electric stimulator was also used. This device allows for the surgeon to map the location of the muscle tissue, allowing for him to reconstruct the new anus within its boundaries to ensure adequate sphincter control. 

Disclosures 

Nothing to disclose. 

Statement of Consent

The patient referred to in this video has given their informed consent to be filmed and is aware that information and images will be published online.