Chapter 42 Imperforate Anus
PATHOPHYSIOLOGY
The congenital malformation known as imperforate anus (anorectal agenesis) involves the anus, the rectum, or the junction between the two. There are two classifications of imperforate anus, related to the placement of the distal end of the colon (the rectum). In high lesions, the rectum ends above the puborectalis sling, the main muscle complex responsible for sphincter control and fecal continence. In low lesions, the rectum has traversed the puborectalis sling, with an abnormal location in the perineum. Affected infants can be expected to have rectal continence after repair.
Along with the imperforate anus, the following may also occur:
1. In girls, a fistula may be present between the rectum and the vagina.
2. In boys, a fistula may be present between the rectum and the urinary tract at the scrotum.
The appearance of the defect varies, depending on its severity. A less-involved imperforate anus appears as a deep anal dimple and exhibits strong muscular reaction to pinprick, which indicates innervation of that area. More severe involvement is initially seen as a flat perineum with no dimple and poor muscular response to pinprick, a result of defective perineal innervation and muscle formation. A highly involved defect includes other anomalies as well (Table 42-1). The infant may initially be seen with poorly developed labia, undescended testicles, or ambiguous genitalia. Outcomes are favorable after definitive surgery is performed.
| Type | Incidence (%)* |
|---|---|
| Esophageal atresia | 10–13 |
| Intestinal atresia | 4 |
| Intestinal malrotation | 4 |
| Cardiovascular defects | 12–22 |
| Skeletal deformities (spina bifida, agenesis of sacrum) | 6 |
| Genitourinary anomalies (renal agenesis, hypospadias, epispadias) | 20–54 |
INCIDENCE
1. Congenital anomalies of the anus and rectum are relatively common. Minor anomalies occur in approximately 1 per 500 live births; major anomalies occur in 1 per 5000 live births.
2. Most studies report a male preponderance of 55% to 65%. High anomalies occur more often in males, whereas low lesions occur more often in females.
3. Of affected infants, 20% to 75% have an associated anomaly, with genitourinary (GU) tract malformations found most frequently (20% to 54%), tracheoesophageal fistula occurring in 10% of infants, and cardiovascular malformations in 12% to 22%.
4. The associated anomalies are usually the cause of death.
5. There are no reported racial differences in disease incidence or severity of disease.
CLINICAL MANIFESTATIONS
1. Physical examination showing absent external anal opening, flat perineum with a short sacrum
2. Failure to pass meconium within first 24 hours after birth
3. Caregiver inability to locate anus to take infant’s rectal temperature
4. Passage of meconium through fistula or misplaced anus
5. Gradual distention and signs of bowel obstruction if no fistula present
COMPLICATIONS
1. Renal and GU: hyperchloremic acidosis, continuing urinary tract infection, urethral damage (result of surgical procedure), problems or delays associated with toilet training
2. Gastrointestinal: constipation, eversion of anal mucosa, stenosis (result of contraction of scar from anastomosis), impactions and constipation (result of sigmoid dilation), problems or delays associated with toilet training, incontinence (result of anal stenosis or impaction), prolapse of anorectal mucosa (results in persistent seepage and incontinence), recurrent fistulas (result of tension in surgical site and infection)
LABORATORY AND DIAGNOSTIC TESTS
1. Visual and digital rectal examination is generally diagnostic.
2. If a fistula is present, urine may be examined for meconium epithelial cells.
3. Radiographic study after infant kept in knee-chest position for approximately 30 minutes. May demonstrate air collected in the blind-ending rectum at or near the perineum; may be misleading if the rectum is filled with meconium, which prevents air from reaching the end of the rectal pouch.
4. Ultrasonography may be helpful in locating the rectal pouch.
5. Cloacal anomalies deserve special attention. Hydrocolpos and bladder outlet obstructions can confound conventional radiographic evaluation. For these patients, voiding cystourethrography and vaginography are necessary to define the malformation.
6. A distal colostogram accurately defines the type of lesion and the usual rectal fistula.
SURGICAL MANAGEMENT
Surgical therapy in the newborn varies with the severity of the defect. The higher the lesion, the more complicated the corrective surgical procedure. The decision to perform an anoplasty in the newborn period or to delay the repair and perform a colostomy is based on the infant’s physical examination findings, the appearance of the perineum, and any changes that occur over the first 24 hours of life. Operating early and in a single stage is potentially beneficial for the infant. However, a more conservative approach is warranted in low birth weight babies and those with associated cardiac or respiratory conditions. Anoplasty is recommended for both males and females with rectoperineal fistulas. Imperforate anus without fistula, rectal atresia, rectovesical fistula, and rectovaginal fistula requires a colostomy. A colostomy is performed a few days after birth. The definitive surgery, a perineal anoplasty (an abdominal-perineal pull-through procedure), is generally delayed 3 to 12 months. This delay allows the pelvis to enlarge and the musculature to develop. It also enables the infant to gain weight and attain satisfactory nutritional status. Low lesions are corrected by pulling the rectal pouch through the sphincter to the opening on the anal skin. Fistulas, if present, are closed. Membranous defects require only minimal surgical treatment. The membrane is punctured with a hemostat or scalpel.
In most instances, correction of the imperforate anus requires a two-stage surgical approach. For mild to moderate defects, the prognosis is favorable. The defect can be repaired, and normal peristalsis and continence can be obtained. More serious defects are usually associated with other anomalies, which complicate the surgical outcomes.
NURSING INTERVENTIONS
Postoperative Care
1. Monitor infant’s response to surgery.
2. Monitor for signs and symptoms of complications.
3. Promote and maintain fluid and electrolyte balance.
4. Provide dressing care; maintain integrity of surgical site (depends on type of surgery).
5. Promote adequate nutritional intake.
6. Protect infant from infection.
Discharge Planning and Home Care
1. Encourage parents to express concerns about outcomes of surgery.
2. Refer to specific institutional procedures for information distributed to parents about home care.
3. Instruct parents on signs of intestinal obstruction, poor tolerance of feedings, and impaired healing processes.
4. Instruct parents about follow-up techniques to promote optimal surgical outcomes.
5. Instruct parents that, as children age, psychologic counseling should be part of follow-up care. Twenty nine percent of affected children experience some behavioral problems.
Beals DA. Imperforate anus. (website) www.emedicine.com, March 24, 2006. Accessed March 24, 2006
Funakosi S, et al. Psychosocial liaison-consultation for the children who have undergone repair of imperforate anus and Hirschsprung disease. J Pediatr Surg. 2005;40(7):1156.
Levitt MA, Pena A. Outcomes from the correction of anorectal malformations. Clin Opin Pediatr. 2005;17(3):394.
Magnuson DK, Parry RL, Chwals WJ. Selected Abdominal Gastrointestinal Anomalies. Martin RJ, Fanaroff AA, Walsh MC. Neonatal-perinatal medicine, ed 8, St. Louis: Mosby, 2006.
Pena A, Levitt MA. Imperforate anus and cloacal malformations. Ashcraft KW, Holcomb GW, Murphy JP. Pediatric surgery, ed 4, Philadelphia: WB Saunders, 2005.
Zderic SA. Developmental abnormalities of the genitourinary system. Taeusch HW, Ballard RA, Gleason CA. Avery’s diseases of the newborn, ed 8, Philadelphia: WB Saunders, 2005.
