Anorectal malformations.

Anorectal malformations (ARMs) are among the more frequent congenital anomalies encountered in paediatric surgery, with an estimated incidence ranging between 1 in 2000 and 1 in 5000 live births. Antenatal diagnosis of an isolated ARM is rare. Most cases are diagnosed in the early neonatal period. There is a wide spectrum of presentation ranging from low anomalies with perineal fistula having simple management to high anomalies with complex management. Advances in the imaging techniques with improvement in knowledge of the embryology, anatomy and physiology of ARM cases have refined diagnosis and initial management. There has been marked improvement in survival of such patient over the last century. The management of ARM has moved forward from classical procedures to PSARP to minimal invasive procedures. But still the fecal and urinary incontinence can occur even with an excellent anatomic repair, mainly due to associated problems. There has been a paradigm shift in approach to these patients which involves holistic approach to the syndrome of Anorectal malformations with a long term goal of achievement of complete fecal and urinary continence with excellent quality of life.

INTRODUCTION

Anorectal malformations (ARMs) are among the more frequent congenital anomalies encountered in pediatric surgery, with an estimated incidence ranging between 1 in 2000 and 1 in 5000 live births.[1] Antenatal diagnosis of an isolated ARM is rare. Most cases are diagnosed in the early neonatal period. There is a wide spectrum of presentation ranging from low anomalies with perineal fistula having simple management to high anomalies with complex management.

ETIOLOGY

The etiology of such malformations remains unclear and is likely multifactorial. There appears to be a low rate of association in families, but some appear to have an autosomal dominant inheritance pattern with a high incidence, as much as 1 in 100. Chromosome 7q39 has three important loci, which are implicated for development of ARM, these include genes: SHH, EN2, and HLXB9. Some studies demonstrated several mutations of HLXB9 associated with ARM.[2] Few syndromes with autosomal dominant mode of inheritance such as Townes-Broks syndrome, Currarino's syndrome, and Pallister-Hall syndrome are associated with ARM.[3]

CLASSIFICATION

There has always been a need for classifying these anomalies in order to decide the management and predict the final outcome. The earliest classification of ARM was based on the position of the terminal bowel in relation to the levator ani or pelvic floor.[4] Wingspread classification was established according to the level of the arrest of rectal descent and patient's sex [Table 1].[5] This classification was widely accepted and was used for many years. After the advent of posterior sagittal approach by Peña et al., it was realized that the site of fistula has an important bearing on the long-term outcome of these patients.[6] Peña proposed a classification in 1995 based on the presence and position of the fistula as a result of his experience with the posterior sagittal anorectoplasty (PSARP) [Table 2].[78] The position of the fistula was used to determine operative management. Although PSARP soon became the operation of choice, the results of the studies comparing the long-term outcome between PSARP and other classical operations were highly variable.[9] This was supposed to be due to the variation in the follow-up criteria used in different studies. To standardize the methodology for evaluation of outcome of patients with ARM Krickenbeck group came with their classification.[10] The Krickenbeck classification system incorporated criteria from the Wingspread and Peña's classification. It comprised of three distinct elements: A diagnostic category, a surgical procedure category, and a category documenting functional outcome criteria [Tables 3a-c]. The Krickenbeck classification also gave equal emphasis to both constipation and soiling compared with previous scoring systems which hardly took constipation into account.

Table 1

The Wing spread conference classification (1984)

Table 2

Pena classification (1995)

Table 3a

Krickenbeck classification for ARMs (2005)

ASSOCIATED ANOMALIES

Approximately, half of children with ARM have associated anomalies.[11] The incidence of reported anomalies is variable, but most groups agree the genitourinary anomalies (40-50%) are most common followed by cardiovascular (30-35%), spinal cord tethering (25-30%), gastrointestinal anomalies (5-10%), and VACTERL (4-9%) anomalies.[12] The higher the rectal pouch ends, the higher are its chances to be associated with anomalies. Hence, the anomalies are most frequently associated with rectovesical fistula, but the major spinal anomalies are seen in all groups including those with perineal fistula.[12]

CLINICAL PRESENTATION

At birth, a general examination in any newborn should include the perineum. The absence or abnormal location of the anus is generally apparent. In the male, besides the absent anus, a note must be made of the anal pit. The fistula may be of small caliber; hence, it may take up to 24 h for it to be apparent. The reason for this is that it takes this long for ingested gas to travel down the gut to the blind rectum. In the female child, the diagnosis rests on the appearance of the perineum. Normally, there are three visible openings — the most anterior being the urethra, followed by the vagina, both of these being within the vestibule. Behind the perineal body is the anus. The presence of three openings, with the anus not being at its normal site is indicative of either a perineal fistula, formerly called the anterior perineal anus. If the third opening is seen within the vestibule, it is a vestibular fistula. Two openings only, indicate two extremely rare clinical entities, namely a recto vaginal fistula, or a blind ending rectum with no fistula. A single opening indicates the persistent cloaca.

INVESTIGATIONS

Invertogram

Wangensteen and Rice first described the use of inversion radiography in 1930 to indicate the distance between the gas bubble within the terminal colon and the perineal skin. Direct measurement between the gas-filled gut and the skin of the anus by placing a radiopaque marker on the skin is made. Subsequently, the P–C line and the I line are determined by invertography. If the rectum ends below the P–C line, but not below the I line, it is “intermediate”. When a rectal pouch that is clearly below the I line, it may be referred to as “low,” whereas when pouch ends above the P–C line is called as high type.

Prone cross-table lateral view

The babies are kept in the genupectoral position for 3 min by holding their facedown with hips flexed. Prone lateral radiographs is obtained, which is centered over the greater trochanters like in the invertogram. The prone cross-lateral view’ has few advantages like the baby is comfortable, whereas in invertogram requires splints and adhesive tapes and the baby keeps crying due to which puborectalis sling contracts and hence there is deceptive obliteration of the lower rectum.

Ultrasonic examination

Ultrasonographic examination has been used to know the pouch perineal distance. It can be performed through a transperineal or infracoccygeal route. Infracoccygeal route can directly demonstrate the puborectalis as a hypoechoic U-shaped band. The noninvasive nature and no radiation exposure are the main advantages, but it is highly observer dependent.

Computer tomography and magnetic resonance imaging

Computer tomography (CT) and magnetic resonance imaging (MRI) of pelvis have been utilized for the direct visualization of the sphincteric muscles. These have been used for the structural evaluation of pelvic floor muscle and relation to the pouch, for both the pre- and post-operative evaluation. The exact location of fistula and relation to the pelvic floor muscle provides crucial information regarding the approach, whether a sagittal approach or an approach through abdominal route is required. MRI and CT scans are also utilized for the assessment of structural development following different procedures for ARM and can help in comparison of outcome between different procedures. MRI is considered superior to CT scan because of excellent soft tissue characterization, multiplanar imaging, and lack of ionizing radiation.[1314]

SURGICAL MANAGEMENT

Initial evaluation and decision-making

The early management of a newborn with an anorectal anomaly is crucial. In developing countries, presentation can be delayed. This is with associated abdominal distension, dehydration and sepsis. Initial resuscitation with intravenous fluid and broad spectrum antibiotics holds the key for the final outcome in such cases. After assessment of associated anomalies the child can be taken for a protective colostomy, followed by delayed repair later or a single staged definitive procedure can also be performed in selected cases. Management of male and females cases differ.

Male newborn

Male newborns with rectoperineal fistula do not need a colostomy. They can undergo a posterior sagittal anoplasty or limited PSARP. The male babies with evidence of a recto-urinary tract communication should undergo fecal diversion with a colostomy. Patients with rectobulbar, rectoprostatic fistula can be managed by primary PSARP. Abdominal approach is required to get access to fistula in cases with recto-bladder neck fistula. Pouch colon also requires abdominal approach. In cases with sepsis, perforation a protective colostomy is performed in the neonatal period followed by a definitive pull-through procedure at 3-6 months of age. Before the definitive operation, a pressured distal colonogram and voiding cystourethrogram should be performed to reveal the site of rectourethral fistulas.

Female newborn

General condition, duration of presentation and number of openings in the vestibule decide the management. Gross abdominal distension, sepsis, or single opening (persistent cloaca) warrants a diversion colostomy. The most common anomaly in females is a rectovestibular and shows a normal urethra, normal vagina, and another orifice, which is the rectal fistula in the vestibule. Such cases can be managed by a diversion colostomy and delayed definitive repair by PSARP. In selected cases, a primary PSARP or a primary anterior sagittal anorectoplasty can also be performed. Definitive repair of persistent cloaca is performed through PSARP. In cases with common channels longer than 3 cm, it is difficult to mobilize the vagina through PSARP, and an abdominoperineal approach is required. In cases with a common channel of <3 cm, total urogenital mobilization is possible, in which both the vagina and urethra are mobilized as a unit, without separation. If the distance from the vagina to the perineum is long, a bowel segment can be used to bridge the gap, preferably a segment of the colon or a vaginal switch procedure can be done in cases with bicornuate uterus.

Single stage versus staged procedure

There has been debate over single stage versus staged repair of ARM. Single stage procedure has less morbidity, mortality at low cost. The better continence may be attributed to the better development of cerebral fibers. These cerebral cortical fibers develop in the 1st year of life and sensations of rectal fullness are essential for these fibers to develop fully so that continence can be achieved to its maximal potential. The other advantages of single stage repair are easier dissection in the neonatal period due to virgin tissue planes with no fibrosis due to pouchitis, no need of bowel preparation and colostomy is not usually accepted in our society. Physical and psychological stress to the parents, child and surgeon are less. Absolute contraindication for single stage repair is severe life-threatening other congenital malformations, sepsis or necrotizing enterocolitis with pneumoperitoneum, extreme prematurity and common cloacae.

The single staged repair carries a 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 ureter 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.

Newer imaging modalities and advances in radiological technique have made it possible to exactly delineate the site of rectourethral fistula. This has tilted the balance in favor of single stage repair of appropriately selected cases, as most feared complication of single staged repair like trauma to urinary tract can be avoided.

Surgical procedure

Understanding of anatomy and thus the principal of surgical repair of ARM has evolved continuously over the past century. Prof. Douglas Stephens puborectalis concept introduced in 1953 remained the basis of all surgical procedures for intermediate and high ARM.[15] Classically abdominoperineal pull-through approach is used for high-or intermediate-type ARMs. A combination of perineal and abdominal approach was done by Rhoads et al., and a pull-through route was made blindly with the fingers.[16] There was fear of damage to pelvis innervations with this approach. So Rehbein performed endorectal pull-through to avoid any damage to the pelvic innervations.[17] A modified abdominoperineal pull-through procedure was proposed by Iwai et al. in which the rectum was dissected carefully along the rectal wall to avoid damage to the pelvic nerves, using an electric stimulator.[18] Stephens's procedure involved the identification of the proximal portion of the levator ani through a posterior approach through the sacrococcygeal junction. In cases with rectal pouch distal to the pubococcygeal line, it was possible to divide the fistula and mobilize the rectum via the sacrococcygeal route alone without abdominal exploration.[19] Stephens's sacral dissection with Rehbein's endorectal dissection was combined by Kiesewetter to developed a sacroabdominoperineal pull-through approach that preserved the puborectalis muscle.[10] In spite of the vast number of procedure and their modification, the postoperative outcome of ARM remained dismal and variable throughout the world. Peña introduced the posterior sagittal approach (PSARP).[620] Soon after its introduction, PSARP became the gold standard procedure worldwide. This approach allowed surgeons to view the anatomy of these defects clearly, to repair them under direct vision, and to learn about the complex anatomic arrangement of the junction of the rectum and genitourinary tract.[21] It has become the predominant surgical method for anorectal anomalies. In cases, when the rectum is very high an abdominal approach is needed Abdomino-PSARP. Posterior sagittal anorectoplasty has become the standard of care for dealing with ARM. Despite the excellent exposure of anatomy and exact placement of the distal rectum within the muscle complex, the technique is not perfect, especially in patients with “high” ARM defects. Georgeson et al. described a new laparoscopically assisted anorectal pull-through (LAARP) for the repair of high-type ARMs, which utilizes a laparoscopic vantage point to reduce the amount of posterior dissection required for accurate placement of the bowel into the muscle complex.[22] Sharp dissection and cautery are used laparoscopically to expose the rectal pouch down to the urethral or vaginal fistula. LAARP is not recommended for intermediate-type ARMs, because this method requires wide dissection of the rectum and may cause damage to the rectal nerves and pelvic plexus, resulting in poor bowel function. Bischoff et al. suggested that laparoscopy for the ARM is a less invasive procedure when compared with those operations that would have previously required a laparotomy such as a rectobladder neck fistula and rectoprostatic fistula.[23]

Congenital pouch colon

Congenital pouch colon (CPC) is a congenital anomaly in which whole or part of the colon is replaced by a pouch-like dilatation that communicates distally with the urogenital tract by means of fistula and is uniformly associated with ARMs. The incidence of CPC among all cases of ARM has been reported to occur from 2% to 18% with a high incidence (30-40%) reported from Indian sub-continent. Various classifications have been proposed for CPC, but classification proposed by Rao et al. is most acceptable classification.[24] The standard procedure for the management of the CPC cases is a three-staged procedure. In cases with complete pouch colon (types I and II), as adequate length of the normal colon is absent, construction of distal colon by tabularizing (coloplasty) of the remaining colon has been proposed. Single staged management of pouch colon has also shown good results, though few authors have found increased mortality with this approach.

Spinal cord tethering

Intravertebral fixation of the filum terminale results in the tethering of the spinal cord In recent years, high resolution diagnostic equipment such as spinal MRI and three-dimensional CT have demonstrated a higher frequency of tethered cord in the setting of ARM than previously estimated. The prevalence in the literature is variable (10-52%). A conservative approach has been advocated for ARM patients with asymptomatic tethered cord. Prophylactic surgery appears to have a minimal benefits and release of tethered cord should be done in symptomatic cases only.[25]

Secondary reconstruction/redo posterior sagittal anorectoplasty

Secondary reconstructions to improve fecal continence have been used extensively in patients with ARMs. In most reports, the long-term functional outcome is not better in patients who had secondary surgery and may be worse than in those with only primary repair. However, Peña et al. produced good results with secondary penicillin-resistant streptococcus pneumonia. Rerouting of the pulled-through bowel has been advocated for patients who have a misplaced anal canal following primary operation. The bowel may traverse the levator and not lay anterior to it.[26]

Long-term results

The main objective of any surgery for ARMs is to achieve a good quality of life in adults patients with ARMs.

Bowel function

Most patients who undergo repair of an ARM suffer from variable degrees of fecal incontinence, depending upon the type of anomaly, associated anomalies and the effectiveness of corrective procedure. The functional results after surgical correction of ARMs are often assessed by a manometric study, neural electrophysiological studies, magnetic spinal stimulation, and fecoflowmetry. Most cases with low ARM have good bowel function and enjoy social activities. One-third of patients with high- or intermediate-type anomalies occasionally complained of fecal soiling. Bowel management is an artificial way to keep patients who have fecal incontinence clean. It consists of enemas, colonic irrigation, or daily suppositories to keep the rectum vacant. Biofeedback therapy was reported to be a simple and safe method for treating children. In resistant cases, The Malone antigrade continence enema procedure using an Appendicectomy represents a useful alternative. Secondary reconstructions to improve fecal continence have been used extensively in patients with ARM. Historically, a gracilis muscle or gluteus maximus muscle transplant to strengthen the striated anal sphincter has been used.[27]

Urinary function

The patients with ARM are frequently complicated with urinary tract anomalies or sacral anomalies. One-third of patients with traditional abdominoperineal methods, have urinary complaints compared to about 10% of those who underwent PSARP.[28]

Sexual function

In male patients with urinary tract or sacral anomalies, erection and ejaculation problems are often seen. Sexual problems of pubescent males with high- and intermediate-type ARM such as erectile and ejaculatory dysfunction is about 40%. Adolescent females with low ARM are limited in terms of sociosexual activities. Other common problems in females are vaginal and uterine septation anomalies and vaginal agenesis. In sexually active females, these anomalies often cause infertility and sexual problems.[29]

Long-term growth and development

Very few long-term prospective studies have been performed to know the overall growth and development of ARM patients. Newborns with severe anatomical malformations with associated anomalies, long duration hospital stay and multiple surgical interventions may negatively influence growth and development within the first 2 years of life. Children with an ARM are at risk for gross motor function problems so the nutritional status and bowel management should be optimized individually to prevent stunting and comprehensive physical and mental development.[30]

Table 3b

Krickenbeck classification of surgical procedures

Table 3c

Krickenbeck classification for postoperative results (Age >3 years, no therapy)