malformation, as much as 1 in 100, compared with the incidence of about 1 in 5000 in the general population. Since that time there have been reports of families with 2 or more affected members and associations of ARMs with multisystem syndromes. In particular, mutations in specific genes encoding transcription factors have been described in patients having Townes-Broks syndrome, Currarino's syndrome, and Pallister-Hall syndrome, each of which have autosomal dominant modes of inheritance. In addition, it has been found that there is not only an increased incidence of ARM in patient with trisomy 21 (Down's syndrome), but that 95% of patients with trisomy 21 and ARM have imperforate anus without fistula, compared with only 5% of all patients with ARM. Based on this evidence, it is likely that the mutation of a variety of different genes can result in ARM, or that the etiology of ARM is multigenic .
The radiologic evaluation of a newborn with imperforate anus includes an abdominal ultrasound to evaluate for urologic anomalies. In the case of persistent cloaca, a distended vagina (hydrocolpos) can be identified. Plain radiographs of the spine can show spinal anomalies such as spina bifida and spinal hemivertebrae. Plain radiographs of the sacrum in the anterior-posterior and lateral projections can demonstrate sacral anomalies such as a hemisacrum and sacral hemivertebrae. Also, the degree of sacral hypodevelopment can be assessed, and a sacral ratio can be calculated measuring the distances between key bony structures. A spinal ultrasound in the newborn period and up to age 3 months (at which time the sacrum becomes ossified) can look for evidence of a tethered spinal cord and other spinal anomalies. A crosstable lateral radiograph can help show the air column in the distal rectum in the small percentage of patients for whom clinical evidence does not delineate in 16–24 hours the likely anorectal anomaly.
After the newborn period, on an outpatient basis after the colostomy (see colostomy) has been created, high pressure distal colostography is performed. Hydrosoluble contrast material is injected into the distal stoma to demonstrate the precise location of the distal rectum and its likely urinary communication. Hydrostatic pressure under fluoroscopic control is required. A foley catheter is placed in the mucous fistula and the 3 cc balloon is inflated and pulled back to occlude the stoma during contrast injection. The hydrostatic pressure must be high enough (manual syringe injection) to overcome the muscle tone of the striated muscle mechanism that surrounds the rectum and keeps it collapsed. This is the best way to demonstrate a recto-urinary communication, and to determine the real height of the rectum. The contrast material usually fills the proximal urethra and bladder through the fistula. The injection is continued until the child voids, and pictures are taken during micturition in order to show, in a single picture, the sacrum, height of the rectum, perineum, fistula location, bladder, vesicoureteral reflux if present, and urethra.
This study is vital in determining the anatomy so the definitive repair can be planned. In 10% of patients, the fistula is at the level of the bladder neck. In this case, during the main repair, the surgeon knows that the rectum will be found only through the abdomen, and a combined posterior sagittal and abdominal or laparoscopic approach is employed. The anorectal defect of imperforate anus without fistula may also be demonstrated with this radiologic evaluation. This defect occurs in approximately 5% of patients, has a good functional prognosis, and is common in patients with Down's syndrome. Except for cloacas, in most cases of female malformations, distal colostography is not necessary because the fistula is evident clinically. If the spine was not evaluated in the newborn period with ultrasound, magnetic resonance imaging is necessary after age 3 months to rule out the presence of tethered cord and other spinal anomalies.
A. Early decision-making
The early management of a newborn infa