The term imperforate anus is a misnomer; it is commonly used to refer to a spectrum of anorectal malformations, ranging from a benign defect that requires a minor operation and results in an excellent prognosis to complex malformations with a high incidence of associated defects requiring sophisticated and specialized surgical procedures with less than optimal functional results. Most cases are not actually “imperforate,” but rather have the rectum ending in a structure such as in the urinary or gynecologic tract. Since the mid-1980s, significant advances have been achieved in pediatric surgery that allow for a better anatomic reconstruction of these defects, preserving other important pelvic structures. Yet, at least 30% of all patients born with these defects still have fecal incontinence, even after a technically correct surgical repair, and another 30% have other functional defecation problems, mainly constipation and varying degrees of soiling. We have made great strides in anatomic reconstruction, but are still challenged in consistently obtaining an excellent functional result. These malformations occur in about 1 : 4000 to 1 : 5000 newborns. In general, the chance of having a second child affected by this type of defect is about 1%. This number may change if one considers each type of anorectal malformation separately.
Classification and Description of Defects
A classification presented here ( Table 55-1 ) is based on therapeutic and prognostic factors as well as the frequency of associated defects. It was designed to help the clinician increase the index of suspicion and to establish therapeutic priorities.
| Males | Females |
|---|---|
| Perineal fistula | Perineal fistula |
| Rectourethral fistula | Vestibular fistula |
| Bulbar | Imperforate anus without fistula |
| Prostatic | Rectal atresia |
| Rectobladderneck fistula | Cloaca |
| Imperforate anus without fistula | Complex malformations |
Anorectal Malformation in Male Patients
Perineal Fistula
In perineal fistula, the rectum opens into the perineum anterior to the center of the sphincter, into a usually stenotic orifice. In male patients, the perineum may exhibit other features that help in recognition of this defect, such as a prominent midline skin bridge (known as a “bucket-handle” malformation) or a subepithelial midline raphe fistula that looks like a black or white ribbon because it is full of meconium or mucus ( Figure 55-1 ). These features are externally visible and help in the diagnosis of a perineal fistula. This is the most benign of anorectal defects. Less than 10% of these children have an associated urologic defect, and 100% of them achieve bowel control after proper treatment, if they have a normal sacrum and no tethered cord.
Of interest, this group of patients has the highest incidence of constipation, a disorder that should not be underestimated, as discussed later in this chapter. The operation to repair these malformations is a relatively simple anoplasty; it usually is performed during the neonatal period without a protective colostomy. Even when this is considered a relatively easy procedure, there is a risk of provoking an urethral injury in male patients. Therefore, this operation should always be performed with a urethral catheter in place.
Rectourethral Fistula
The rectourethral fistula is by far the most common defect in male patients. The rectum communicates with the posterior urethra through a narrow orifice (fistula). This fistula may be located in the lower posterior urethra (bulbar fistula) ( Figure 55-2 ) or in the upper posterior urethra (prostatic fistula) ( Figure 55-3 ). Eighty-five percent of patients with rectourethral bulbar fistula achieve voluntary bowel movements after the main repair, but only 60% of those with rectoprostatic fistula do so. About 30% of patients with bulbar urethral fistula and 60% of patients with rectoprostatic fistula have associated urologic defects. The quality of the sacrum usually is good in the former case but frequently is abnormal in the latter. Most of these patients must receive a colostomy at birth, with definitive repair done at 2 to 3 months of life.
Rectobladderneck Fistula
The rectobladderneck fistula is the malformation with the highest location in the the rectum of male patients. The rectum opens into the bladder neck ( Figure 55-4 ). Ninety percent of these patients have significant associated urologic defects. Only 15% achieve bowel control after the main repair. The sacrum usually has poor quality. In these patients, the repair includes a posterior-sagittal approach plus a laparotomy or a laparoscopy to reach a rectum that is located high in the pelvis. The perineum in these patients is usually flat, meaning that they do not have the normal midline groove and one cannot see an anal dimple ( Figure 55-5 ).
Imperforate Anus Without Fistula
In imperforate anus without fistula, the rectum ends blindly, without a fistula, approximately 1 to 2 cm above the perineum, usually at the level of the bulbar urethra. The sacrum and sphincter mechanism are usually good, and about 80% of these patients achieve bowel control after the main repair. Approximately 50% of patients with this defect have Down syndrome. Conversely, 95% of patients with Down syndrome who have anorectal malformations have this specific type. With or without Down syndrome, children with this defect have a good functional prognosis. This malformation can be repaired primarily at birth, without a colostomy, provided the surgeon has enough experience and the baby is in good condition. Although not connected to the distal rectum, the urinary tract is intimately attached to the urethra, and great care must be taken not to injure the urethra.
Rectal Atresia/Stenosis
In this rare defect, the patient is born with a normal-looking anus externally, but an attempt to take the rectal temperature discloses an obstruction located 1 to 2 cm above the mucocutaneous junction of the anus. The sphincter mechanism in these patients is normal, as is the anal canal. Associated defects are almost nonexistent except for presacral mass, which must be screened for. The prognosis is excellent, when there is no presacral mass, and 100% of these patients achieve bowel control. The repair involves an operation called a posterior-sagittal anorectoplasty (PSARP), with a diverting colostomy, initially done at birth.
Anorectal Malformation in Female Patients
Perineal Fistula
In the perineal fistula in female patients, the rectum opens into the perineum anterior to the center of the sphincter, into a usually stenotic orifice. This is the most benign of anorectal defects. Less than 10% of these children have an associated urologic defect, and gynecologic anomalies are rare. One hundred percent of patients with these defects achieve bowel control after proper treatment, provided they have a normal sacrum and no tethered cord.
During surgical repair, it is important to be aware of the proximity between the rectum and vagina. After repair, patients should be screened and followed because of a high incidence of constipation.
Vestibular Fistula
The vestibular fistula is the most common defect in female patients. The rectum opens into the vestibule of the female genitalia, which is the mucosa-lined area outside the hymen ( Figure 55-6 ). The rectum and vagina share a very thin common wall. The sacrum and sphincters are usually of good quality. Approximately 95% of these patients achieve bowel control after surgery, and 30% of them have associated urologic defects.
This malformation can be repaired primarily, without a colostomy, provided the patient is in good health and the surgeon has experience in the management of newborns with these defects. Approximately 5% have an associated gynecologic anomaly, either a vaginal septum or absence of the vagina, and a vaginoscopy is performed at the time of the planned reconstruction to assess this.
Cloaca
This is by far the most complex problem seen in female patients ( Figure 55-7 ). This defect is defined as a malformation in which rectum, vagina, and urethra are fused together into a single common channel that opens into a single orifice in the perineum (see Figures 55-7 and 55-8 ). The prognosis varies depending on the quality of the sacrum and spine and the length of the common channel. Most patients with a common channel longer than 3 cm require intermittent catheterization after the main repair in order to empty the bladder. About 50% of these patients have voluntary bowel movements. On the other hand, if the common channel is shorter than 3 cm, 20% of the patients require intermittent catheterization to empty the bladder and about 70% have voluntary bowel movements.
Ninety percent of patients with cloaca have an associated urologic problem. This may represent a serious urologic emergency that the clinician should recognize early in life, in order to detect and treat an obstructive uropathy.
Thirty percent of cloacas also have hydrocolpos, which is a very distended, tense, giant vagina that may compress the opening of the ureters at the trigone, provoking bilateral megaureters. A significant number of these patients also have vesicoureteral reflux. At birth, these patients require the opening of a colostomy and drainage of the hydrocolpos when present. Rarely, some sort of urinary diversion is needed to address the obstructive uropathy. After 2 to 4 months of life, they undergo a complex operation during which the three main structures (the rectum, vagina, and urethra) are separated and placed in their normal location. Patients with cloacas with a common channel shorter than 3 cm, require an operation done posterior-sagittally, and it is not usually necessary to open the abdomen. In doing this procedure, a maneuver called total urogenital mobilization is performed ( Figure 55-9 ), which facilitates the procedure. On the other hand, a cloaca with a common channel longer than 3 cm requires not only the posterior-sagittal approach but also a laparotomy and a series of decision-making steps that require a significant amount of experience. These malformations should be repaired at specialized centers.
Associated Defects
The most common defects associated with anorectal malformations are urologic. The frequency of these associations varies with each defect, as has already been described. The next most common associated defects are those of the spine and sacrum. The quality of the spine and sacrum has a direct impact on the prognosis for bowel and urinary control. A very hypoplastic sacrum, absent sacrum, or associated spinal problem, such as tethered cord or myelomeningocele, correlate directly with poor fecal and urinary continence.
Another subgroup of patients has gastrointestinal defects, including esophageal atresia, duodenal atresia, or other kinds of atresia in the intestinal tract. Approximately 30% of all patients have some sort of cardiovascular defect, but only 10% require surgery. The other 20% usually represent patent ductus arteriosus, atrial or ventricular septal defects, or defects with no hemodynamic implications.
Early Management and Diagnosis
When a child is born with an anorectal malformation, two main questions must be answered within the first 24 hours of life:
- 1.
Does the infant have an associated defect (most likely urologic or cardiac) that endangers his or her life and requires immediate treatment?
- 2.
Does the infant need a colostomy, or can the malformation be repaired in a primary way without a colostomy?
These two questions must be answered in this order. The higher in the pelvis, the location of the rectum and more complex the anorectal defect, the greater the chance of a dangerous associated defect. Figures 55-10 and 55-11 show decision-making algorithms used in the early management of these newborns.
