KEY POINTS
- 1.
Congenital anorectal malformations and Hirschsprung disease present in neonates with symptoms of distal intestinal obstruction and distal gastrointestinal tract dysmotility.
- 2.
Anorectal malformations are a congenital group of disorders that occur when the hindgut fails to develop in the appropriate anatomic position and with appropriate caliber. These malformations are associated with problems of fecal incontinence.
- 3.
Hirschsprung disease is a congenital disorder of the enteric nervous system characterized by the absence of ganglion nerve cells, resulting in the inability of stool to pass through the colon and rectum.
- 4.
Patients with anorectal malformations and Hirschsprung disease benefit from early diagnosis and generally require surgical intervention.
- 5.
Long-term outcomes and quality of life are optimized through adequate follow-up, dietary adjustments, and an effective bowel management program.
Introduction
Congenital anorectal malformations (ARMs) and Hirschsprung disease (HSCR) are disorders that present in neonates with symptoms of intestinal obstruction and distal gastrointestinal tract dysmotility. ARMs compose a spectrum of congenital malformations that result in mechanical bowel obstruction, whereas HSCR is a disorder of the enteric nervous system that results in varying degrees of functional obstruction. Both ARMs and HSCR disorders are frequently associated with a variety of other disorders and syndromes. Patients with either an ARM or HSCR benefit from early diagnosis and require surgical intervention, which generally provides improvement in bowel function and quality of life.
Anorectal Malformations
Pathophysiology of Anorectal Malformations
ARMs are a congenital group of disorders that occur when the hindgut fails to develop in the appropriate anatomic position and with appropriate caliber. One out of every 4000 to 5000 newborns is born with a congenital ARM. The incidence is slightly higher in males. Prenatal diagnosis is generally uncommon. A minority of cases present after the neonatal age, with the majority of patients developing symptoms in the first weeks of life. Prompt, early diagnosis allows for appropriate counseling, operative planning, and overall management in the neonatal period. The goal of surgery is to restore normal anatomy and in so doing allow for normal function and motility with minimal long-term morbidity.
Normal Continence
The three primary components that maintain bowel continence are voluntary muscle constriction, anal canal sensation, and bowel motility. Voluntary muscle structures include the levator muscles, the striated muscle complex, and the external sphincter. Neonates with ARMs will have varying degrees of hypodevelopment of these voluntary muscles. For these voluntary muscles to contract appropriately, sensation of the anal canal must be intact. In general, patients with ARMs are born without an anal canal or with a malformed anal canal, thus severely impairing sensation and inhibiting voluntary muscle contracture. Lastly, peristaltic contraction of the distal large bowel, the rectosigmoid, is usually felt prior to defecation. This leads to relaxation of the voluntary rectal muscles, which allows the contents within the rectum to be interrogated by the sensate anal canal. These voluntary muscles can either then push the rectal contents back into the sigmoid until the appropriate time for evacuation or, together with a Valsalva maneuver, evacuate the contents. Rectosigmoid motility is disrupted in ARMs, contributing to an inability to achieve appropriate continence.
Clinical Features of Anorectal Malformations
As mentioned, ARMs compose a spectrum of disorders. Some disorders such as rectoperineal fistulas occur in both males and females, whereas other disorders are unique to each sex. Risk factors for the development of congenital ARMs include prematurity, being small for gestational age, and possibly maternal obesity and smoking.
In general, ARMs can be classified according to whether the fistula or hindgut opening is “high” or “low.” Patients with “low” fistulas have anterior fistulas that open onto the perineal surface and are best treated with early surgical corrections. Repairs of low fistulas usually do not require diversion and can be repaired in a single-stage procedure.
In some patients, the fistula cannot be clearly visualized and the anatomy is not clearly delineated. This is because the fistula location is “high,” occurring at the bladder or urethra (rectobladder neck or rectourethral) in males or at the posterior fourchette or within the introitus (rectovestibular fistula) in females. The most severe form, seen in females, is a cloaca in which the neonate has a single perineal orifice, with the rectum and genitourinary tract sharing a common channel. In other cases still, there may be normally developed anus and sphincter muscles without a fistula, yet the rectum is strictured or atretic. In general, high fistulas are repaired in multiple stages to minimize risk of injury to neighboring structures and to allow for the delineation of the variant anatomy prior to definitive repair.
Types of Anorectal Malformations
There are several types of ARMs, as described in Table 85.1 . A rectoperineal fistula is an ARM that can occur in both males and females. In this defect the rectum is located close to the sphincter mechanism. With rectoperineal fistulas, only the most distal aspect of the rectum is positioned anteriorly. Otherwise, most of the rectum appropriately lies within the muscle complex. These defects tend to have appropriate muscle quality and sacral development. Imperforate anus without fistula occurs when the anal opening is either absent or located in the wrong position. There is an increased incidence of this malformation with Down syndrome. Rectal stenosis or atresia is where the caliber of the rectum is too narrow to allow stool to pass.
| Males | Females |
|---|---|
| Rectoperineal fistula | Rectoperineal fistula |
| Imperforate anus without fistula | Imperforate anus without fistula |
| Rectal atresia/rectal stenosis | Rectal atresia/rectal stenosis |
| Rectourethral bulbar fistula | Rectovestibular fistula |
| Rectourethral prostatic fistula | Rectovaginal fistula |
| Rectobladder neck fistula | Cloaca |
Although several ARMs are shared by both males and females, such as rectoperineal fistulas, each sex has specific defects unique to it. Male neonates can be born with rectourethral fistulas, where the rectum connects directly to the urethra, causing the two structures to share a common wall. Rectourethral bulbar fistulas are the most common ARMs in males. With this defect, the rectum abnormally communicates with the lowest portion of the posterior urethra. In rectourethral prostatic fistulas, the fistula occurs at the more proximal prostatic urethra. In general, lower fistulas are associated with better sphincter muscle quality, a more fully developed sacrum, and a prominent midline groove. Classically, neonates with these defects will pass meconium through the urethra. Another defect seen exclusively in males is the rectobladder neck fistula. In this malformation, the rectum directly opens into the neck of the bladder. In general, these fistulas confer a poor prognosis for bowel control because they are associated with poorly developed levator muscles, a striated muscle complex, and an external sphincter. Further, neonates with this fistula tend to have poorly developed sacrums and flat perineums, further prohibiting adequate bowel continence.
Rectovestibular fistulas are the most common defects in females and occur when the rectum is displaced anteriorly, leading to a fistula between the rectum and the vulva vestibule. This causes an ectopic anus to open into the labia minora. These fistulas are associated with an overall excellent functional prognosis. A rectovaginal fistula occurs when the rectovestibular fistula occurs within the hymen and is a much rarer congenital defect. A persistent cloaca, in which the distal vagina, rectum, and urinary tract all combine to form a single perineal channel, is another defect exclusive to females. The length of this common channel is variable, ranging from 1 to 7 cm. Shorter channels, usually less than 3 cm, can be repaired with posterior sagittal anorectoplasty (PSARP) and confer a better prognosis than do longer channel defects. This is due to the difficulty in mobilizing the vagina with longer defects, which may ultimately lead to the need for vaginal replacement or a transabdominal approach due to the location of the rectal opening high in the vagina.
Fecal Control
As previously discussed, normal fecal continence relies on appropriate voluntary muscle constriction, anal canal sensation, and bowel motility. Factors are impacted by a multitude of issues including the type of ARM, type of operation, operative complications, quality of perineal muscles, sacral deformities, and spinal abnormalities. Rectal atresia or stenosis, a short cloaca less than 3 cm, and imperforate anus without fistula are defects that are associated with a good prognosis. Additional favorable prognostic factors include a normal sacrum, no presacral masses, a good buttock crease, and a good anal dimple. Long cloacal channels greater than 3 cm, higher fistulas such as rectoprostatic and rectobladder neck fistulas, the presence of myelomeningoceles, and sacral or spinal abnormalities are associated with poorer outcomes.
Evaluation of Anorectal Malformations
ARMs may be suspected prenatally if the presence of sacral, renal, or genitourinary anomalies is identified. However, the majority of ARMs are first detected on the initial neonatal examination. If meconium is present, it should be thoroughly cleaned away to enable complete examination of the perineum. Delayed diagnosis of ARMs, which occurs in up to 50% of cases, is associated with significant morbidity and mortality. Of note, patients with rectal stenosis may have an unremarkable physical exam. If stenosis is suspected, a rectal catheter can be passed to evaluate luminal patency, and anal calibration with dilators can be useful in excluding stenosis. The presence of meconium in urine after 24 to 48 hours of life is indicative of a fistula with the urinary tract. Clinical exam is generally sufficient for discriminating between low and high fistulas. To further delineate the anatomy, contrasted prone images can be taken after 24 hours of life once gas has had time to reach the distal bowel.
Defects Associated With Anorectal Malformations
ARMs are frequently associated with VACTERL (vertebral, anorectal, cardiac, tracheoesophageal, renal, and limb) defects. In general, the higher the defect, the more likely that an associated VACTERL defect is present. , All patients with a confirmed or suspected ARM should undergo an investigation for VACTERL abnormalities.
Vertebral defects include sacral hypoplasia and a tethered cord. Sacral deformities are the most common defects associated with ARMs and are directly associated with the ability to achieve continence with either medical or surgical repair. For all patients with an ARM, plain radiographs should be obtained in the neonatal period. Having more than two absent sacral vertebrae is a poor prognostic sign for bowel continence. The sacral ratio, which is the ratio of the distance between the tip of the coccyx to the inferior point of the sacroiliac joint divided by the distance between the iliac crest to the inferior point of the sacroiliac joint, has been shown to be correlated with bowel function and fecal continence in patients with ARMs ( Fig. 85.1 ). A sacral ratio less than 0.7 is associated with poor bowel function, whereas a ratio less than 0.3 is associated with no chance for bowel control. A ratio greater than 0.7 is associated with good bowel control.
An association exists between rectal stenosis, sacral abnormalities, and presacral masses. Thus magnetic resonance imaging for presacral masses in patients with rectal stenosis should be considered. , ,
A tethered cord is associated with higher defects that generally have a poorer prognosis. All patients with an ARM should have a spinal cord ultrasound within the first month of life, because it becomes difficult to visualize the spinal cord thereafter. , Releasing the tethered cord may improve urinary function, although there is no clear evidence that it improves bowel function.
A cardiac echocardiogram is recommended to evaluate structural cardiac anomalies, and any cardiac anomaly identified other than a patent ductus arteriosus or patent foramen ovale should be referred to a pediatric cardiac surgeon. , There is no association between cardiac defects and the ARM subtype.
Patients with an ARM are also at increased risk of esophageal atresia or tracheoesophageal fistulas. If a nasogastric tube can be passed into the stomach and the neonate is feeding normally, esophageal atresia can be excluded and the chances of a tracheoesophageal fistula are minimal. If an H-type tracheoesophageal fistula (4%–5% of all tracheoesophageal fistulas) is suspected, an appropriate esophagogram and surgical referral should ensue. ,
Renal and genitourinary defects are associated with the presence of ARMs, and anomalies of the upper urinary tract system are the most common defects present with VACTERL syndromes (>90%). , Vesicoureteral reflux is common, and there is evidence that prophylactic antibiotics should be administered until a urologic assessment including a renal ultrasound and a voiding cystourethrography is complete. Generally, higher malformations have more frequent urologic abnormalities. Patients with low defects have a 10% chance of a genitourinary defect, whereas lower defects such as cloaca and rectobladder neck defects have a 90% chance of a genitourinary defect. , Early identification is essential for optimal treatment and long-term management.
Limb defects including polydactyly, syndactyly, hypoplastic thumbs, and radial aplasia are also more common in patients with ARMs, although these are less common than in HSCR. If such defects are identified, referral should be made to a pediatric plastic or orthopedic surgeon. Additionally, nonfistula types of ARMs are strongly associated with Down syndrome.
Management of Anorectal Malformations
Once the infant’s ARM anatomy has been identified and the infant has been resuscitated and evaluated for associated anomalies, surgical planning should commence as appropriate. As mentioned, patients with low fistulas may be candidates for single-stage repair, whereas those with high fistulas are usually first managed with a diverting colostomy. For those with high fistulas who undergo a two-stage repair, contrast should be injected into the mucous fistula to appropriately distend the rectum, delineating the anatomy prior to definitive surgery. This assists with surgical planning by allowing for an understanding of the fistula position in relation to the urethra and the sacrum.
Generally, midline approaches to repairing high ARMs reduce the chance of injury to surrounding nerves or muscle. PSARP is the standard of care for high fistulas, including rectourethral fistulas and rectoprostatic fistulas. The goal of repairing the ARM with this approach is to carefully dissect the fistula from the urethra and place it within the sphincter while minimizing damage to the surrounding structures and muscles. Because the fistula is often fused or intimately related to the rectum, often there is no clear surgical plane. This underscores the necessity of meticulous surgical dissection required for this crucial step. Laparoscopy may be useful for the dissection, particularly for higher defects. Once dissection is complete, the hindgut must be carefully and accurately placed within the sphincter mechanism. This can be aided by the use of a muscle stimulator.
The goal of PSARP when repairing cloacae, in which the rectum, vagina, and/or urinary tract fuse to form a common channel, is to safely separate the urogenital structures from the gastrointestinal tract. This may be best achieved through a multidisciplinary approach consisting of pediatric surgery, urology, and gynecology. Postoperative care after PSARP entails daily dilatations after 3 to 4 weeks to prevent stricturing and stenosis.
Long-Term Outcomes of Anorectal Malformations
A mechanism for long-term follow-up of patients undergoing surgical repair for ARMs is essential. Acquiring a good functional outcome is paramount, and this consists of allowing the child to begin school and live a normal social life with minimal difficulty. Problems with incontinence or constipation are relatively common and can be a source of major distress for the patients and their families; however, the majority of these symptoms can be controlled with adequate follow-up, dietary adjustments, and a good bowel management program. These patients typically follow up routinely with a surgeon to tailor the bowel regimen according to the needs of the individual patient. Daily enemas are often part of the regimen in patients who are unable to achieve continence and therefore rely on mechanical evacuation of stool on a daily basis. Osmotic laxatives such as polyglycol have been shown to exacerbate fecal incontinence in these patients, whereas stimulant laxatives in combination with a high-fiber diet are more efficacious. Patients who are dependent on daily enemas may benefit from an antegrade enema procedure such as the antegrade continence enema. In an institutional study examining intermediate and long-term outcomes of a bowel management program for children with severe constipation of incontinence, more than one-third of postoperative patients had antegrade continence enema management, which was associated with successful treatment of their symptoms. Additionally, evidence suggests that the outcomes among patients with nonfistula types of ARMs are similar to those of patients with fistula types of ARMs.
Hirschprung Disease
Pathophysiology of Hirschsprung Disease
Hirschsprung disease (also known as HSCR, congenital megacolon, or colonic aganglionosis) is a congenital disorder of the enteric nervous system characterized by failed neural crest migration and subsequent absence of myenteric and submucosal ganglion nerve cells (Auerbach and Meissner plexuses) in a segment of distal bowel. This failed migration occurs during weeks 4 through 12 of gestation and results in spastic, uncoordinated muscle movement, preventing the ability of stool to pass through the colon and rectum. This ineffective peristalsis leads to constipation and functional obstruction, putting the patient at risk for bowel perforation, enterocolitis, and serious bacterial infections, among other complications. Distally, the aganglionic bowel segment usually starts at the anus and extends most commonly to the rectosigmoid; however, long-segment disease has been reported, extending throughout the colon and sometimes into the small bowel. , Other variants include ultrashort disease and the controversial skipped-lesion pathology. , ,
HSCR is multifactorial and can be either familial or spontaneous. Roughly 20% of all patients with HSCR have other neurologic, cardiovascular, urologic, or gastrointestinal abnormalities. It is believed that isolated HSCR occurs due to mutations in two major groups of genes, the RET and EDNRB genes. Short-segment HSCR is associated with a RET proto-oncogene abnormality located on chromosome 10q11.2. HSCR can also occur in the setting of chromosomal abnormalities or genetic syndromes. Down syndrome is the most common chromosomal abnormality associated with HSCR, present in roughly 10% of all patients. Additional disorders associated with HSCR that are potentially linked to failed neural crest migration include congenital deafness, hydrocephalus, bladder diverticulum, Meckel diverticulum, imperforate anus, ventricular septal defects, renal agenesis, cryptorchidism, Waardenburg syndrome, Mowat-Wilson syndrome, Fryns syndrome, neonatal central hypoventilation syndrome, neuroblastoma, pheochromocytoma, multiple endocrine neoplasia type 2a, and familial medullary thyroid carcinoma. , , Retrospective and prospective genetic analyses have demonstrated a potential benefit to systematic RET mutation screening in HSCR patients to identify preclinical medullary thyroid carcinoma. Furthermore, in patients with multiple endocrine neoplasia type 2a who exhibit gastrointestinal symptoms, the threshold for investigation for HSCR should be very low.
Clinical Features of Hirschsprung Disease
HSCR occurs in approximately 1 in 5000 infants and is three to four times more common in males than females. It is less common in premature infants compared with term infants. It most commonly presents shortly after birth in the neonatal period, although it may present in older childhood or even in adulthood. In the majority (80%) of patients with HSCR, the colon or rectum is affected. Infants with an absence of ganglion cells in the rectum and sigmoid colon are said to have short-segment disease. Roughly 12% of infants have ganglion cells missing from the majority of the large intestine and have what is referred to as long-segment disease. Approximately 6% to 8% of infants will have ganglion cells missing throughout the entire colon and possibly part of the small intestine, referred to as total colonic HSCR. If there is an absence of ganglion cells throughout the entire small bowel and large bowel, this is referred to as total intestinal aganglionosis.
Enterocolitis and colonic perforation are the most serious complications associated with HSCR and the most common causes of HSCR-related mortality. Enterocolitis is the result of functional intestinal obstruction due to the absence of ganglion cells in the distal bowel. Early symptoms of enterocolitis include abdominal distention, foul-smelling watery diarrhea, poor feeding, and lethargy. Late symptoms include emesis, hematochezia, shock, and multiorgan failure. Once enterocolitis is suspected, prompt treatment should begin, which entails thorough rectal irrigation several times a day along with antibiotics. Oral Flagyl may be adequate for mild disease, whereas intravenous broad-spectrum antibiotics should be used for more severe disease. Rectal irrigation consists of repeatedly irrigating with 10 to 15 cc/kg warm normal saline through a large-caliber catheter as it is advanced proximally.
Evaluation of Hirschsprung Disease
The majority of patients with HSCR are diagnosed in infancy. Prompt diagnosis is essential to avoid potentially devastating complications including toxic megacolon and enterocolitis. Integral to an accurate diagnosis is a complete patient and family history, a thorough physical examination, appropriate imaging, and a sufficient biopsy. HSCR should be suspected in any infant who fails to pass meconium within the first 24 to 48 hours of life, a finding present in 90% of all patients with HSCR. Associated additional signs and symptoms in the neonate include abdominal distention and pain, bilious emesis, jaundice, difficulty stooling, poor feeding, and a tight anal sphincter with an empty rectum or explosive diarrhea upon digital interrogation. The differential diagnosis for HSCR should include ileal atresia, colonic atresia, malrotation with volvulus, meconium plug syndrome, meconium ileus, necrotizing enterocolitis, toxic megacolon, and sepsis.
The initial recommended workup should include an abdominal x-ray, which may reveal a nonspecific bowel gas pattern or dilated proximal loops of bowel suggestive of obstruction. Anorectal manometry, which is used to test the rectoanal inhibitory reflex, has a negative predictive value up to 100% and may be employed as a screening test to reduce the number of negative biopsies , ( Fig. 85.2 ). In patients with suspected HSCR, a Gastrografin contrast enema is recommended, with images taken immediately after contrast instillation and then 24 hours after the enema. A pathognomonic finding on contrast enema for HSCR is the presence of a transition zone, where a marked change in caliber occurs with a dilated normal colon above and a narrowed aganglionic colon below. Additional features include a delay in contrast evacuation after 24 hours, a rectosigmoid index (the maximum width of the rectum divided by the maximum width of the sigmoid) less than 1, and irregularity or jejunization of the mucosa. The 24-hour delayed film after the contrast enema has a high negative predictive value (>85%) and can be useful in ruling out disease if there is an absence of contrast in the colon. The level of radiologic transition zone on the enema can also be useful for assessing the extent of disease involvement and can assist with operative planning. , A contrast enema should not be performed in patients with suspected enterocolitis due to the risk of perforation.
