Case of the Week # 510

Case of the Week # 510

Javier Cortejoso
 on 08/14/2023
 on Monday, August 14th, 2023
Classic cloaca is a developmental defect in which the urinary tract, vagina and rectum converge above the level of the perineum, creating a common channel with a single external opening. The spectrum of cloacal malformations is related to timing of developmental arrest and range from (1) urogenital sinus with two perineal openings, (2) persistent cloaca with a single perineal opening, to (3) urorectal septum malformation sequence with no perineal opening.

Persistent cloacal malformation is seen typically in girls, with an incidence of 1 in 40,000 to 50,000 births, and the incidence is increased in twin pregnancies. It may result from failure of the urorectal septum to join the cloacal membrane during the 4th to 6th weeks of embryonic development resulting in bladder obstruction, hydrometrocolpos and colonic dilatation. The typical initial ultrasound finding is a cystic pelvic mass with a fluid-fluid level formed by the confluence of the genital, urinary, and gastrointestinal tracts. A fluid-debris level occurs with mixing of two different substances, such as urine and vaginal secretions and/or meconium in cloacal malformation. There is no fluid-debris level in posterior urethral valves in which the bladder is distended by urine only, and isolated hydrocolpos with vaginal secretions only. Hydrocolpos and hydrometrocolpos may be associated with a number of conditions other than cloacal malformation, such as McKusick-Kaufman, Ellis-van Creveld and Bardet-Biedl syndromes, and the VACTERL association.

Patients with cloacal anomaly may have a duplicated uterus and vagina because the urorectal septum fails to descend. This is observed in approximately 80% of cases in which hydrocolpos is present. There is often a vertical linear septation running anterior to posterior through the cystic mass, which is rarely asymmetric. The common channel is usually patent but with varying degrees of obstruction at the perineum. Urine and meconium accumulate in the vagina as it is the most compliant structure, leading to hydrocolpos. Uterine duplication (bicorporeal uterus class U3) is usually not seen prenatally, since the uterine walls are less distensible. Urologic abnormalities are present in approximately 90% of patients with cloacal anomalies. Bilateral hydronephrosis is the most common, as a result of extrinsic obstruction of the ureters or reflux due to outlet obstruction. The bowel may be normal in caliber, or there may be colonic dilatation due to distal obstruction. The visualization of a hyperintense signal on T1 weighted sequences anterior to the sacrum, identifying a normally filled rectum with meconium, excludes the diagnosis of cloacal malformation. Meconium peritonitis without intestinal perforation is associated with cloacal malformation and may be visible as peritoneal calcifications. It is thought that meconium mixed with urine refluxes into the peritoneal cavity via the fallopian tubes. Flow of urine through the fallopian tubes is also thought to be the cause of ascites. Additionally, a normal anal dimple is not visible by ultrasound if the anus is ectopic or imperforate.

Retrospective analyses suggest that only 6% of persistent cloaca are diagnosed prenatally, with mild phenotypes being the most difficult to detect. The most common findings suspicious of cloacal malformation in order of descending frequency are: abdominal/pelvic cystic mass, bilateral hydronephrosis, oligohydramnios, hydrocolpos, ascites, and distended bowel. Visualization of the bladder with one or two cystic structures posteriorly is suspicious of hydrocolpos due to cloaca. These findings may also be present in cases of urogenital sinus with normal rectum and in cases of imperforate hymen. MR imaging can distinguish these diagnoses with cloacal malformation by visualizing a normal rectum with meconium, and further differentiate between the two by comparing the signal intensity with urine in the bladder: in urogenital sinus, the vagina is filled with a mixture of genital secretions and urine, which have similar signal intensity to the urine in the bladder. In imperforate hymen, the hydrocolpos has a distinct signal intensity compared to the urine in the bladder. Most cases of urogenital sinus occur within the context of a sexual differentiation disorder, of which the most common is congenital adrenal hyperplasia.

The urorectal septum malformation sequence (URSM) is a group of findings that includes the absence of urethral and anal openings in both sexes and no vaginal opening in females. The reported incidence ranges from 1:50,000 to 1:250,000. The external genitalia are often ambiguous, and renal anomalies are common. It is highly lethal, secondary to pulmonary hypoplasia and renal insufficiency. A milder, generally nonlethal, type of the URSM sequence exists and has been termed partial URSM sequence or persistent cloaca, cloacal dysgenesis, and cloacal malformation. This condition is characterized by an imperforate anus and a single perineal opening that drains a common cloaca.

Megaureter is defined as a ureter that exceeds the upper limits of normal size. Any ureter greater than 7mm in diameter is considered a megaureter in fetuses more than 30 weeks gestation and children <12 years. Boys are affected more commonly than girls, and 30-40% of cases are bilateral. Antenatal ultrasonography demonstrates both hydronephrosis and a dilated ureter that may be tortuous.

The differential diagnosis for a female fetus with an abdominal cystic mass should include:
• hydrocolpos (due to persistent cloaca, urogenital sinus or imperforate hymen)
• ovarian cyst
• enteric duplication cyst
• abdominal cystic lymphangioma
• intestinal atresia
• megacystis-microcolon-intestinal hypoperistalsis syndrome
Since ovarian cysts originate from the adnexa, they are usually found laterally with no additional signs of renal or gastrointestinal involvement. Enteric duplication cysts have a thick, multi-layered wall which demonstrates peristaltic movements. Lymphatic malformations may appear as a cyst (often multilocular), with thin, well-defined walls and anechogenic or variably echogenic contents due to bleeding and fibrin deposition.

The finding of a septate structure with a fluid-fluid level located behind the bladder in a female fetus should make us think about a persistent cloacal malformation. This coffee-bean shaped image represents duplicated obstructed vaginas, perhaps accompanied by the distension of two hemiuteri in its upper part (hydrometrocolpos). Fluid-debris levels only occur when there is a mixture of two or more substances of different density, in this case urine, vaginal secretions and meconium. In addition, the existence of a dilation of the urinary tract is evident, which is present in approximately 90% of patients with cloacal anomalies.

Suggested readings:
[1] Bischoff A, Levitt MA, Lim FY, et al. Prenatal diagnosis of cloacal malformations. Pediatr Surg Int. 2010;26(11):1071–1075. doi:10.1007/s00383-010-2685-3
[2] Calvo-Garcia MA, Kline-Fath BM, Levitt MA, et al. Fetal MRI clues to diagnose cloacal malformations. Pediatr Radiol. 2011;41(9):1117–1128. doi:10.1007/s00247-011-2020-8
[3] Capito C, Belarbi N, Paye Jaouen A, et al. Prenatal pelvic MRI: additional clues for assessment of urogenital obstructive anomalies. J Pediatr Urol. 2014;10(1):162–166. doi:10.1016/j.jpurol.2013.07.020
[4] Hayashi S, Sago H, Kashima K, et al. Prenatal diagnosis of fetal hydrometrocolpos secondary to a cloacal anomaly by magnetic resonance imaging. Ultrasound Obstet Gynecol. 2005;26(5):577–579. doi:10.1002/uog.2584
[5] Livingston JC, Elicevik M, Breech L, et al. Persistent cloaca: a 10-year review of prenatal diagnosis. J Ultrasound Med. 2012;31(3):403–407. doi:10.7863/jum.2012.31.3.403
[6] Peiro JL, Scorletti F, Sbragia L. Prenatal diagnosis of cloacal malformation. Semin Pediatr Surg. 2016;25(2):71–75. doi:10.1053/j.sempedsurg.2015.11.004
[7] Subramanian S, Sharma R, Gamanagatti S, et al. Antenatal MR diagnosis of urinary hydrometrocolpos due to urogenital sinus. Pediatr Radiol. 2006;36(10):1086–1089. doi:10.1007/s00247-006-0249-4
[8] Taori K, Krishnan V, Sharbidre KG, et al. Prenatal sonographic diagnosis of fetal persistent urogenital sinus with congenital hydrocolpos. Ultrasound Obstet Gynecol. 2010;36(5):641–643. doi:10.1002/uog.7721
[9] Thomas DF. The embryology of persistent cloaca and urogenital sinus malformations. Asian J Androl. 2020 Mar-Apr; 22(2): 124–128. doi:10.4103/aja.aja_72_19
[10] Williams DH, Fitchev P, Policarpio-Nicolas ML, et al. Urorectal septum malformation sequence. Urology. 2005;66(3):657. doi:10.1016/j.urology.2005.03.003
[11] Winkler NS, Kennedy AM, Woodward PJ. Cloacal malformation: embryology, anatomy, and prenatal imaging features. J Ultrasound Med. 2012;31(11):1843–1855. doi:10.7863/jum.2012.31.11.1843

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