A neonate is examined in the nursery and found to have no anal orifice: only a small perineal fistulous opening is visualized. Decision as to the operative approach necessitates determining how high or low the anus has descended. Which of the following statements concerning imperforate anus is true?
|A||Imperforate anus affects males more frequently than females|
|B||In 90% of males, but only 50% of females, the rectum ends below the level of the levator ani complex.|
|C||The rectum usually ends in a blind pouch|
|D||The chance for eventual continence is greater when the rectum has descended to below the levator ani muscles.|
a. Anorectal malformations describe a spectrum of congenital anomalies that include imperforate anus and persistent cloaca.
b. The embryologic basis includes failure of descent of the urorectal septum. The level to which this septum descends determines the type of anomaly that is present, which subsequently influences the surgical approach.
c. Traditionally, anatomic description of imperforate anus has been characterized as either "high" or "low," depending on whether the rectum ends above the levator ani muscle complex or partially descends through this muscle.
d. Based upon this classification system, in male patients with high imperforate anus, the rectum usually ends as a fistula into the membranous urethra.
e. In females, high imperforate anus often occurs in the context of a persistent cloaca.
f. In both males and females, low lesions are associated with a fistula to the perineum. In males, the fistula connects with the median raphe of the scrotum or penis.
g. In females, the fistula may end within the vestibule of the vagina, which is located immediately outside the hymen, or at the perineum
h. In males the fistula may communicate with:
i. The perineum (cutaneous perineal fistula);
ii. The lowest portion of the posterior urethra (rectourethral bulbar fistula);
iii. The upper portion of the posterior urethra (rectourethral prostatic fistula); or
i. The bladder neck (rectovesicular fistula). In females, the urethra may open onto the perineum between the female genitalia and the center of the sphincter (cutaneous perineal fistula), or into the vestibule of the vagina (vestibular fistula). In both sexes, the rectum may end in a completely blind fashion (imperforate anus without fistula).
j. The most frequent defect in males is imperforate anus with rectourethral fistula, followed by rectoperineal fistula, then rectovesical fistula or recto–bladder neck.
k. In females, the most frequent defect is the rectovestibular defect, followed by the cutaneous perineal fistula. The third most common defect in females is the persistent cloaca. This lesion represents a wide spectrum of malformations in which the rectum, vagina, and urinary tract meet and fuse into a single common channel.
l. The surgical management of infants with imperforate anus is determined by the anatomic defect.
m. In general, when a low lesion is present, only a perineal operation is required, without a colostomy.
n. Infants with a high lesion require a colostomy in the newborn period, followed by a pull-through procedure at approximately 2 months of age.
o. If there is any doubt about the type of lesion, it is safer to perform a colostomy rather than jeopardize the infant's long-term chances for continence by performing an injudicious perineal operation.