Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Cloacal Abnormalities
Introduction
Cloaca is derived from the Latin word for sewer or drain. Anatomically, it is used to describe a confluence of the urinary, genital, and gastrointestinal (GI) tracts. While this is the norm in birds, reptiles, and amphibians, most mammals have separate outlets for each system. In humans, there is a wide range of cloacal abnormalities. Mild forms may involve only a persistent urogenital sinus opening in combination with an anteriorly displaced anus. More severe varieties involve all three tracts converging in the pelvis. The most extreme type of cloacal anomaly is termed cloacal exstrophy, and includes a large midline abdominal defect.
Cloacal abnormalities were first described in humans over 300 years ago. Historically, these anomalies were fatal because of GI and/or urinary obstruction. With advancements in neonatal management and surgical intervention, children born with these anomalies are now able to survive, and often thrive.
Disease
Definition
A cloaca is a common chamber into which some or all of the digestive, urinary, and reproductive tracts discharge their contents. Cloacal abnormalities present in a spectrum of mild to severe forms and all share a common etiology (see later section). In humans, the most extreme cloacal abnormality, cloacal exstrophy, is often referred to as the OEIS complex. The OEIS complex includes the midline abdominal defect of omphalocele (O), exstrophy of the bladder (E), imperforate anus (I), and spine (S) abnormalities.
Prevalence and Epidemiology
The prevalence of cloacal exstrophy was initially estimated as 1 : 200,000–1 : 250,000 births and all cloacae as 1 : 50,000 births. More recent studies have found a significantly higher prevalence, ranging from 1 : 9715 births to 1 : 27,174 births. The increased incidence may be caused by more accurate diagnosis and record keeping.
Males seem equally affected compared to females ( Table 19.1 ). Cloacal malformations are nonhereditary, as no familial cases have been described. Large cohort studies have not elicited any epidemiologic trends. In particular, no maternal factors, including maternal age, appear to increase the risk for cloaca. Of note, more cases are seen in twin pregnancies than might be expected.
TABLE 19.1
INCIDENCE OF CLOACAL ABNORMALITIES
| Study | Total With Cloacae ( n ) | Male (%) | Twins (%) | Percent Genetically Normal |
|---|---|---|---|---|
| Evans et al. | 10 | 50 | NA | NA |
| Mathews et al. | 38 | 53 | NA | NA |
| Lund and Hendren | 20 | 65 | NA | NA |
| Ricketts et al. | 12 | 50 | 17 | NA |
| Hendren | 41 | 59 | NA | NA |
| Keppler-Noreuil et al. | 15 | 42 | 20 | 100 |
| Meizner et al. | 6 | 66 | 33 | 100 |
| Total, % (95% CI) | 139 | 55 (47–63) | 21 (11–38) | 100 |
CI, Confidence interval; NA, not available.
Etiology and Pathophysiology
A cloaca exists in all human embryos up to 4–6 weeks, at which time it becomes partitioned into the urogenital sinus and the rectum. Failure of this partitioning is one reason the term “persistent cloaca” is sometimes used for fetuses and newborns. The cloacal membrane is a transitory bilaminar structure composed of endoderm and ectoderm. As the embryo develops, mesodermal in-growth leads to the cloacal membrane receding and the formation of the urorectal septum. The posterior area of the cloaca becomes the anus and the anterior portion becomes the urogenital sinus. When the cloacal membrane does not recede and/or the mesoderm does not invade, or if the cloacal membrane is too large, cloacae form. The exact cause of the interruption in normal development is unknown, but it does not appear to be teratogenic or familial; some evidence suggests disruptions in hormonal signaling as well as with homeobox and sonic hedgehog gene signaling.
As noted in Table 19.1 , a cloaca frequently occurs in one embryo of twin gestations. It has been theorized that a cytoplasmic deficiency associated with asymmetric splitting may place these fetuses at increased risk for midline defects. It has also been suggested that a single embryonic disc may increase the risk of mesodermal insufficiency.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here