Case of the Week # 492

Case of the Week # 492

Javier Cortejoso
 on 01/15/2023
 on Sunday, January 15th, 2023
Ultrasonographic, T2 and T1-weighted magnetic resonance images show a cystic image located in the pelvis behind the bladder and in front of the rectum. This cystic image seems to be divided in half by an anteroposterior vertical septum and presents in its upper zone two other cystic images of smaller size. This creates a four-chamber type appearance. The conical-shaped cyst descends very low in the perineum thus, the anal dimple that identifies the opening of the anus in normal conditions is not visualized. Image 2 demonstrates a single umbilical artery. Both kidneys are of normal size, presenting only a slight dilation of the excretory pathway. This appears to be a female fetus based on the findings in images 3 and 4.

Classic cloaca represents a developmental defect in which the urinary tract, the vagina and the rectum converge above the level of the perineum, creating a common channel with a single external opening. The complete spectrum of cloacal malformations is related to timing of developmental arrest and range from urogenital sinus with two perineal openings, to cloacal dysgenesis in which there is no perineal opening.

Cloacal malformation is typically seen in females with an incidence of 1 in 40,000 to 50,000 births. It occurs more frequently in twin pregnancies than might be expected. Cloacal malformations are thought to result from failure of the urorectal septum to join the cloacal membrane during the 4th to 6th weeks of embryonic development. It can lead to bladder obstruction, hydrometrocolpos and colonic dilatation.

Patients are often referred due to a pelvic mass which is formed by the confluence of the genital, urinary, and gastrointestinal tracts. While there is a broad range of anatomic connections described in the surgical literature, the prenatal imaging findings of cloacal malformations are consistent: a cystic pelvic mass with a fluid-fluid level or fluid-debris level. This fluid-debris level occurs with mixing of two substances, such as urine and vaginal secretions with or without meconium. There is no fluid-debris level in posterior urethral valves (bladder distended by urine only) or in isolated hydrocolpos (vaginal secretions only).

Patients with cloacal anomaly may have a duplicated uterus and vagina as 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 may be asymmetric. The common channel is usually patent but with varying degrees of obstruction at the perineum. Thus, urine and meconium accumulate in the most compliant structure, the vagina, causing hydrocolpos. Uterine duplication (bicorporeal uterus class U3) often is 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 and results from 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 the typical hypersignal on T1W sequences anterior to the sacrum identifies a normally filled rectum with meconium and excludes the diagnosis of cloacal malformation. Meconium peritonitis without intestinal perforation is associated with cloacal malformation and may be visible sonographically as peritoneal calcifications. It is thought that meconium mixed with urine refluxes into the peritoneal cavity via the fallopian tubes. Decompression of urine through the fallopian tubes is also thought to be the cause of ascites. A normal anal dimple is not seen if the anus is ectopic or imperforate.

On prenatal ultrasound, the findings most suspicious of cloacal malformation in order of frequency include abdominal/pelvic cystic mass, bilateral hydronephrosis, oligohydramnios, hydrocolpos, ascites, and distended bowel. However, retrospective analyses suggest that among patients with a diagnosis of cloaca at birth, as few as 6% are suspected prenatally. Mild forms of cloaca may be difficult to diagnose prenatally.

Complete cloacal dysgenesis is associated with severe oligohydramnios due to complete urinary obstruction. Affected fetuses may also have pulmonary hypoplasia. Other findings include ambiguous genitalia, a 2-vessel cord, abnormalities of the spine, and a tethered cord. Many of these fetuses may present with associated malformations and syndromes, such as cloacal dysgenesis sequence, VACTERL association, McKusick-Kaufman, Ellis-van Creveld or Bardet-Biedl syndromes.

The visualization of the bladder with one or two posterior cystic structures is highly suspicious of hydrocolpos due to cloaca. However, these findings can also be present in imperforate hymen and urogenital sinus with a normal rectum. MRI can assist in distinguishing between the two diagnoses. In both cases, there is meconium in the rectum that can be seen on MRI. However, in isolated genital obstruction, there is a different signal between the bladder and the hydrocolpos, while in urogenital sinus, the MRI signal of the vagina is similar to the bladder since the vagina is filled with a mixture of genital secretions and urine.

Megaureter is defined as a ureter that exceeds the upper limits of normal size, which is >7mm in fetuses greater than 30 weeks gestation and in children <12 years of age. Boys are affected more commonly than girls, and bilateral involvement ranges between 30 to 40%. Antenatal ultrasonography demonstrates both hydronephrosis and a dilated ureter that can be tortuous.

The differential diagnosis for a female fetus with an abdominal cystic mass includes ovarian cysts, enteric duplication cysts, abdominal cystic lymphangioma, intestinal atresia, hydrocolpos due to imperforate hymen or urogenital sinus, and megacystis microcolon intestinal hypoperistalsis syndrome. As ovarian cysts originate from the adnexa, they are located laterally rather than in the midline, and do not present with renal or gastrointestinal involvement, which is often the case in cloacal malformations. The main characteristic of an enteric duplication cyst a thick, multilayer wall with peristaltic movements. Lymphatic malformations appear as a thin-walled, often multilocular cyst, with either anechogenic content or with variable echogenicity due to bleeding and fibrin deposit.

Suggested readings

[1] Bischoff A, Levitt MA, Lim FY, et al. Prenatal diagnosis of cloacal malformations. Pediatr Surg Int 2010; 26: 1071-1075.
[2] Calvo-Garcia MA, Kline-Fath BM, Levitt MA, et al. Fetal MRI clues to diagnose cloacal malformations. Pediatr Radiol 2011; 41: 1117-1128.
[3] Capito C, Belarbi N, Jaouen AP, et al. Prenatal pelvic MRI: Additional clues for assessment of urogenital obstructive anomalies. J Pediatr Urol 2014; 10: 162-166.
[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: 577-579.
[5] Livingston JC, Elicevik M, Breech L, et al. Persistent cloaca. A 10-year review of prenatal diagnosis. J Ultrasound Med 2012; 31: 403-407.
[6] Peiro JL, Scorletti F, Sbragia L. Prenatal diagnosis of cloacal malformation. Semin Pediatr Surg 2016; 25: 71-75.
[7] Taori K, Krishnan V, Sharbidre KG, et al. Prenatal sonographic diagnosis of fetal persistent urogenital sinus with congenital hydrocolpos. Ultrasound Obstet Gynecol 2010; 36: 641-643.
[8] Winkler NS, Kennedy AM, and Woodward PJ. Cloacal malformation. Embryology, anatomy, and prenatal imaging features. J Ultrasound Med 2012; 31: 1843-1855.

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