Cloaca, the Latin word for sewer, is aptly named as it represents the persistence of a developmental phase (typically in a female fetus) in which the rectum, vagina, and urinary tract share a common channel. In normal human development, there is a stage during which the cloaca forms from the confluence of the allantois and hindgut (Stephens and Smith, 1971). At 4 to 6 weeks of development, the urorectal septum descends, separating the allantois from the hindgut. Failure of this urorectal septum to descend results in persistent cloaca (Figure 85-1). The infant with persistent cloaca usually presents at birth with abdominal distention and an abnormal perineum. Typically, these children have only a single perineal opening without an anus or a vaginal introitus. The genitalia are ambiguous, often with a hooded phalluslike structure suggesting a masculinized gender, yet their chromosomes are consistently 46,XX and they have two normal ovaries. The length of the common channel to the perineum may vary, from 1 to 12 cm (Canning et al., 1998, Pena et al., 2004). In cases with a common channel <3 cm, there is usually a well-developed sacrum and sphincter complex. In contrast, longer common channels are more likely to have an abnormal sacrum and a poor sphincter complex, and these are usually more complex defects. In more than 50% of cases, there is hydrocolpos due to partial obstruction of the entry of the vagina into the common channel. The hydrocolpos can compress the trigone of the bladder, with resulting bladder outlet obstruction and hydroureteronephrosis. The prenatal sonographic detection of hydronephrosis may be the only indication of cloacal malformation. Duplicated vagina and uterus didelphys are commonly seen in persistent cloaca (Figure 85-2).

In 90% of cases of persistent cloaca, there are other associated urogenital anomalies (Rich et al., 1988). There is also a high incidence of nongenitourinary anomalies associated with persistent cloaca, including esophageal atresia, duodenal atresia, diaphragmatic hernia, vertebral anomalies, congenital heart disease (particularly tetralogy of Fallot), spina bifida, and caudal regression syndrome.

Persistent cloaca occurs in approximately 1 in 50,000 livebirths (Gray and Skandalakis, 1972). Because of the rarity of prenatal diagnosis of persistent cloaca, no data are available on its prenatal incidence.

The prenatal sonographic features of persistent cloaca are often secondary effects of the anomaly. A septated or bilateral cystic pelvic mass may be observed. In as many as 50% of cases, hydrocolpos may be present and may be the most striking feature. This may also partially obstruct the trigone of the bladder, with resulting vesicomegaly and hydroureteronephrosis. The distinction between hydrocolpos and a distended bladder may be very difficult to make. We have had one patient who presented with a dilated cystic pelvic mass (Figure 85-3) due to hydrocolpos and vesicomegaly. It was notable that mucus or meconium from the vagina or colon had refluxed into the bladder, forming a sediment in the trigone of the bladder. With passage of urine from the ureters to the bladder, a striking swirling of this sediment could be observed sonographically. We believe this to be a specific sonographic sign of communication between the urinary tract and either the vagina or colon. This can be seen in either persistent cloaca or, perhaps, a persistent urogenital sinus. The presence of calcifications within the lumen of the bowel should raise the possibility of either imperforate anus and rectourethral fistula or a cloaca, as urine mixing with meconium will create luminal calcifications.