INTRODUCTION

Anorectal malformations (ARMs) are a complex set of anomalies involving the development of the anorectal region. They manifest themselves along a spectrum from the simple membrane covering a well-formed anorectal canal to the cloaca and other complex defects that present a considerable challenge for reconstruction. The etiology of ARMs is unknown. The reported incidence is about 1 in 5000 live births, with a slight male preponderance.¹ Associated anomalies are common, occurring in about 50% or 60% of the patients.² They include cardiovascular, genitourinary, gastrointestinal, gynecologic, spinal, and vertebral anomalies. They have been associated with other syndromes and have been described to occur in families.^3,4

CLASSIFICATION

There are multiple historical classification schemes but the most widely used system is currently that proposed by Peña^5,6 (Table 81-1). The scheme is based on a description of the anatomy and the presence or absence of a fistula from the rectum to the urinary system. It is different for males and females and has prognostic and therapeutic implications. Most defects with a perineal fistula are considered “low” and are usually amenable to primary repair in the newborn period if the baby is stable and has no other underlying major issues. If no perineal fistula is detected, it usually indicates a “high” defect that is best managed with a colostomy first followed by repair.

Table 81-1 Classification of Anorectal Malformations

CLINICAL PRESENTATION AND PREOPERATIVE PREPARATION

Some ARMs are suspected prenatally because of the presence of polyhydramnios and dilated echogenic intestinal loops on a fetal ultrasound. The majority are detected at birth. A careful physical examination including the anorectal and genitourinary systems is essential to classify the defect and guide the next step in management. Perineal fistulas are sometimes subepithelial in the midline raphe of the scrotum or perineal body and not always evident initially. In addition, because meconium is viscous, it takes a significant pressure within the rectum to force the meconium through the small diameter of the fistula.⁷ That pressure usually builds up in the first 24 hours after birth. Therefore, unless the newborn is massively distended and at risk for perforation, there should be a systematic search for the fistula in the first 24 hours after birth. A small gauze should be placed at the tip of the urethra to collect any meconium in the urine. The perineal body should be inspected again a few hours after birth to detect any subepithelial accumulation of meconium. Concurrently, a search for associated anomalies should be undertaken with an echocardiogram to rule out cardiac defects, a renal ultrasound to rule out hydronephrosis, vertebral radiographs to detect spinal defects, and a spinal ultrasound to rule out a tethered cord. In addition, esophageal atresia should be ruled out. Just like with any other intestinal obstruction, intravenous hydration and nasogastric decompression should be initiated. Antibiotics are necessary to prevent contamination of the urinary tract by a rectourinary fistula.

INDICATIONS

The mere presence of an ARM is an indication to repair it.

CHOICE OF OPERATION

The three operations available to the surgeon in the newborn period are (1) a primary anoplasty, also called a limited posterior sagittal anorectoplasty; (2) a definitive repair of the ARM with a pull through of the rectum, called posterior sagittal anorectoplasty (PSARP); and (3) a protective colostomy. The decision of which operation to perform depends on the sex of the patient and the complexity of the defect.⁷ Laparoscopic techniques have been reported in the management of high ARMs.^8–10 The principles are the same as for PSARP with laparoscopic mobilization of the rectum and division of the fistula. The short-term results seem to be equivalent to those of PSARP, but long-term results are not yet mature enough to allow an evidence-based comparison with PSARP.^11,12

Male Patients

A male newborn with a perineal fistula and no other serious anomalies and no prematurity is a good candidate to have a primary anoplasty without a protective colostomy (Fig. 81-1). If a perineal fistula is not detected, a cross-table lateral radiograph with the patient in the prone position is obtained to determine the level of the rectum. If the rectum is above the coccyx, it is best to perform a protective colostomy followed by an elective repair. If the rectum ends below the coccyx, a primary PSARP could be contemplated if the patient is stable without any other associated problems and if the surgeon is experienced. Otherwise, it is always safest to perform a colostomy in the newborn period, then do the definitive PSARP later. The repair of high ARMs in the newborn period without a protective colostomy has been reported but should be limited to surgeons with extensive experience.¹³

Figure 81-1 A male newborn with a perineal fistula behind a “bucket-handle” skin deformity.

(Courtesy of Dr. Richard Ricketts, Emory University, Atlanta.)

Female Patients

Just like for males, a female newborn with a perineal fistula and no other issues is a good candidate for a primary anoplasty. If a vestibular fistula is present, a colostomy followed by definitive repair is recommended even though there is a recent trend of performing primary PSARP in these situations, depending on the surgeon’s experience level (Fig. 81-2). If the baby has only one perineal opening visible and no separate opening for the vagina and urethra, that patient has a cloaca and a colostomy should be performed (Fig. 81-3). A detailed evaluation of the urinary and gynecologic systems should be performed to rule out severe hydronephrosis and hydrometrocolpos caused by obstruction secondary to the small size of the common channel. If the baby has separate openings for the urethra and vagina and no perineal fistula, a cross-table lateral radiograph with the patient in the prone position is obtained to determine the level of the rectum. The same algorithm as in males, as discussed earlier, would apply.

Figure 81-2 A female newborn with a rectovestibular fistula. The clamp is in the fistula.

(Courtesy of Dr. Richard Ricketts, Emory University, Atlanta.)

Figure 81-3 A female newborn with a cloaca. Note the small external genitalia.

(Courtesy of Dr. Richard Ricketts, Emory University, Atlanta.)

OPERATIONS

Because of the wide spectrum of ARMs, the actual operation has to be tailored to the specific defect and associated anomalies. Therefore, we discuss only the pitfalls of the three most common operations performed for ARMs.