Imaging in Cloacal Malformations: A Comprehensive Update with Insights into Management and Surgical Considerations

Abstract

Cloacal malformations are a rare and complex group of anomalies resulting from faulty or incomplete separation of female genitourinary and anorectal systems. These encompass a wide spectrum of anomalies with varied clinical features, radiological imaging findings, and surgical management. They are frequently associated with spinal, cardiac, and respiratory tract abnormalities. Multidisciplinary teamwork is essential for achieving the best possible outcome in these patients. This article aims to provide a comprehensive analysis of cloacal malformations with review of current literature and discussion of relevant embryology, highlighting various classification systems and describing the role of imaging in diagnosis and preoperative planning, along with insights into management and surgical options.

Keywords

cloaca - common channel - MRI - fluoroscopy - PSARP

Introduction

Cloacal malformations are a rare, complex spectrum of abnormalities involving the female genitourinary and anorectal tracts with an estimated incidence of 1:40,000 to 50,000.[1] These result from an incomplete division and separation of these tracts during intrauterine development, culminating in a variety of anomalies of the pelvic organs and abnormal number or position of perineal orifices. The underlying etiology is thought to be multifactorial, ranging from spontaneous to genetic and environmental causes.[2] Deficiencies in homeobox gene, sonic hedgehog, and bone morphogenetic protein signal pathways have been attributed as putative underlying genetic factors.[3] [4] [5] [6]

The cloacal malformations are exclusive to the female phenotype. The perineum typically has a single orifice that functions as the common conduit for urine, genital secretions, and feces. The male counterpart of this malformation is the high anorectal malformation with rectal atresia and rectourethral fistula. The cloacal malformations are distinct from cloacal exstrophy/OEIS (omphalocele, exstrophy of the cloaca, imperforate anus and spinal defects), with the latter having a different etiopathogenesis, affecting both the sexes and associated with lower abdominal wall defects.[7]

Association of cloacal malformations with numerous anomalies has been described. These include VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities), spinal anomalies (tethered cord, caudal regression, meningomyelocele, vertebral fusion-segmentation anomalies), genital anomalies (ambiguous genitalia), accessory urethra, bladder diverticula, pubic diastasis, ectopic drainage of ureters (into bladder, vagina, or cloaca), and müllerian duplication with or without dilatation among others.[8]

There has been a remarkable improvement in the prognosis of patients with cloacal malformations owing to the development of meticulous techniques of surgical repair. Appropriate surgical planning is contingent upon accurate delineation of the anatomy using preoperative imaging. Imaging also plays a vital role in the detection of concomitant systemic anomalies, which can potentially impact management.

Embryology

During the fifth week of intrauterine life, the cloaca develops at the terminal hindgut and functions as the common channel into which the genitourinary and anorectal tract coalesce. Between the sixth and seventh week, the urorectal septum grows in a caudal direction and compartmentalizes the cloaca into two separate channels (urogenital sinus and rectum). The urorectal septum, upon coming in contact with the cloacal membrane, causes the latter to rupture resulting in the formation of two orifices. The urogenital sinus further differentiates and gives rise to the urinary bladder and urethra, along with a part of the vagina in females. Cloacal malformation, also termed as urorectal septum malformation sequence, results when the urorectal septum does not join the cloacal membrane.[9] As a consequence, a common channel representing the confluence of the lower urinary tract, the female reproductive tract, and the rectum ensues, which communicates externally through a single perineal opening. In urogenital sinus, the urogenital and anorectal tracts separate, leading to a common urogenital channel of variable length, which opens through a single perineal orifice, separate from the anal opening.[6]

Classification

Although cloacal malformations are considered a subset of anorectal malformations, it is prudent to separate the discourse on cloacal malformations from other anorectal malformations. The wide array and complexity of anomalies in cloacal malformations ([Figs. 1] and [2]) needs a classification system of its own, due to unique clinical features and varied prognostic implications of these.[10]

• Cloacal dysgenesis: This entity results when there is a confluence of the urinary bladder, vagina, and rectum into a common channel that fails to open externally. This anomaly lies at the most severe end of the spectrum of cloacal malformations. No perineal orifice is seen on clinical examination.

• Persistent/classic cloaca: Urinary bladder, vagina, and rectum show confluence into a single channel, which opens into the perineum at the location of the urethra. It is the most common type in the entire spectrum of cloacal malformations. Clinical examination reveals a single perineal orifice.

• Posterior cloaca: The cloaca or common channel opens into the perineum posteriorly at the expected location of the anus, instead of the urethral location as seen in the classic cloaca. Here also, only a single perineal orifice is visualized on clinical examination.

Fig. 1 Schematic illustration showing the spectrum of cloacal malformations encompassing (A) cloacal dysgenesis with absent perineal opening, (B) persistent/classic cloaca with single perineal opening at the site of the urethra, (C) posterior cloaca with single perineal opening at the site of the anus, (D) urogenital sinus with two perineal openings, (E) cloaca variant with anteriorly positioned anal orifice, and (F) posterior cloaca variant with posteriorly positioned urogenital orifice. Normal expected location of anal opening is marked by asterisks.

Fig. 2 Flowchart depicting various clinicopathologic features of the cloacal malformation spectrum.

The above three anomalies represent the more severe end of the cloacal malformation spectrum, and result from the failure of the development of both urorectal septum and urogenital septum.

• Urogenital sinus: The common urogenital channel opens into the perineum at the expected location of the urethra. The anal orifice is sited at its normal location. Thus, the perineum has two orifices.

• Cloaca variant: The opening of the urogenital confluence is located at the expected location of the urethra; however, the anal opening is situated anterior to its normal location. The perineum presents with two orifices.

• Posterior cloaca variant: Here the opening of the urogenital confluence is abnormally located posterior to the expected location of the urethra; however, the anal opening is situated at the normal location. Two perineal orifices are present.

The last three anomalies represent the milder end of the spectrum and have separation of the anorectal tract from the urogenital tract, resulting from the normal development of the urorectal septum but failure of the development of the urogenital septum.

To avoid potential confusion in terminology, the cloaca variant may be labeled as the urogenital sinus with the anterior rectum and the posterior cloaca variant can be called the posterior urogenital sinus.[7]

The length of the common channel, that is, the site of urogenital confluence is an important determinant of surgical management. A length of 3 cm is used as a cutoff to distinguish between long and short common channels. The length of the common channel ranges from 1 to 10 cm with an average length of 3 cm; the common channel length is less than 3 cm in over 50% of cases.[11] [12]

Apart from the length of the common channel, the urethral length is also an important factor when deciding the surgical approach. An adequate urethral length is a necessity for undertaking total urogenital sinus mobilization repair. This has led to further modifications in the classification of cloacal malformations.[13] [14] [15] These are summarized below:

• Type 1 cloaca: Common channel length less than 1 cm.

• Type 2 cloaca: Common channel length less than 3 cm and urethral length at least 1.5 cm.

• Type 3 cloaca: Common channel length greater than 3 cm or urethral length less than 1.5 cm.

Management

At first, physical examination of the perineum is done to identify the position and number of orifices and assess the development of external genitalia. The cloaca normally presents with a single perineal opening. Hypertrophic skin folds adjacent to the single perineal orifice may give a misleading impression of a phallus and the patients may be mislabeled as suffering from disorders of sexual development.[12] It is important to look for and identify accessory perineal openings, if any. An accessory urethra (phallic urethra) may show an opening at the clitoral base or tip. It is the female counterpart of urethral duplication seen in males and similar to it in that the dorsal (upper) urethra is rudimentary and the ventral (lower) urethra is more developed and functional.[16]

Genitoscopy can visualize the internal anatomy, the length of the common channel, and the orifices opening into the common channel; however, it provides limited information about the anatomical relationships of these structures with pelvic organs.

Neonates with cloacal malformations are at risk of other complications during the postnatal period, such as hydronephrosis, impairment of renal function, metabolic acidosis, ascites, bowel adhesions, and pyometrocolpos, necessitating individual measures to deal with them. For this reason, before definitive surgical repair, neonates with cloacal malformations undergo a primary stoma creation for rectal decompression and stool diversion. Intermittent catheterization of urine-filled vagina (resulting in bladder obstruction) may be required if the patient is not voiding regularly. Urinary diversion/tube vaginostomy may be required in the presence of bladder compression and hydronephrosis, most commonly by a hydrocolpos, to prevent it from complicating into pyocolpos.[17]

Management under a dedicated multidisciplinary team is essential and collaboration of a group of specialists from neonatology, pediatric surgery, obstetrics and gynecology, and urology in association with radiology is crucial to achieve the best postnatal outcomes.

Surgical Insights

Definitive surgical repair aims to separate the urinary tract, vagina, and rectum and position them normally in the perineum.

The anorectal component of the cloacal malformation is repaired by posterior sagittal anorectoplasty (PSARP) procedure and is relatively uncomplicated. In this procedure, the rectum is separated from the vagina and a pull-through of the rectum through the sphincter mechanism is done. From the surgeon's point of view, the degree of rectal descent dictates the surgical approach. The adjacent sacral vertebrae can be used as a landmark to indicate the level of rectal descent.[18] If the rectum is above the level of the third sacral vertebral body, mobilization during surgery may require an abdominal approach.[19] The pubococcygeal (PC) line can also serve as a reference in deciding whether the rectum is amenable to mobilization by a posterior sagittal approach or if it requires the transabdominal approach. If the rectum extends below the PC line, the posterior sagittal approach suffices. On the contrary, a transabdominal approach (laparoscopy or laparotomy) is required if the rectum terminates above the PC line. Even so, detection of abnormal rectal position in the pelvis with respect to the vagina (anterior to the vagina or off-midline toward one side) is important.[14]

However, unlike the relatively simpler PSARP procedure, the challenge lies in the separation of the vagina from the urogenital sinus.[20] This is because of close adherence of the vagina with the urethra and inconstant submucosal vascularity.[12] [18] [21] To overcome this challenge, the urogenital sinus mobilization technique is used, wherein after separation of the rectum from the vagina, both the urethra and the vagina are mobilized together as a single unit. This technique reduces the operative time and prevents blood loss, but it cannot be performed in all situations.[13] [22] [23]

To summarize, surgical management varies with the type of cloacal malformation.[14] [15] These are as follows:

• Type 1 cloaca (common channel length <1 cm, low urogenital confluence): The urethra is left as it is; introitoplasty and PSARP is performed through the perineal approach.

• Type 2 cloaca (common channel length <3 cm and urethral length at least 1.5 cm, intermediate urogenital confluence): Total urogenital mobilization is performed along with PSARP via deep perineal dissection (abdominal approach is used for high rectal termination).

• Type 3 cloaca (common channel length >3 cm or urethral length <1.5 cm, high urogenital confluence): Urogenital separation and PSARP is performed via the abdominal approach with the common channel retained as the urethra.

Whatever the procedure being employed, the eventual aim of surgery is to achieve long-term bladder and bowel continence, adequate sexual function and obstetric capability, and restoration of optimal cosmetic appearance.

Role of Imaging

Imaging forms the bedrock of diagnosis and classification of cloacal malformations, starting from the antenatal and postnatal period through preoperative evaluation to postoperative follow-up.[24] The goals of imaging are the following:

• Initially, provide an outline of the anatomical environment and necessary information regarding the urgency of immediate surgery (e.g., presence of pyonephrosis or hydrometrocolpos).

• Subsequently, elicit detailed information about the anatomy of the urinary, genital, and anorectal structures; understand the complexity of malformation; and plan for surgical intervention accordingly.

• Finally, search for and identify associated abnormalities that may impact clinical decision-making or require additional management.

Prenatal Diagnosis

It is now possible to pick up these anomalies prenatally, most commonly in the late second trimester or third trimester using ultrasound.[25] [26] [27] Fetal magnetic resonance imaging (MRI) also serves as an excellent complementary tool to confirm or refute the diagnosis and for detailed evaluation of the pelvic structures. It is important to diagnose this malformation accurately and expeditiously and look for other systemic associations so that the parents can be counseled and referral to appropriate center is done, if required.

Antenatal ultrasound: Sonography may reveal a midline, elongated, pear-shaped retrovesical abdominopelvic cystic mass representing hydrocolpos. This occurs due to impeded drainage of the urinary and genital secretions. It may be associated with müllerian duplication with two hemiuteri and hemivaginas. Mass effect from the hydrocolpos may result in displacement of the urinary bladder and bilateral hydroureteronephrosis. Fetal urinary ascites may occur due to escape of urine into the peritoneal cavity via the fallopian tubes. Associated spinal anomalies, if present, can also be evaluated. An interesting association of cloacal malformation with perineal cyst has also been described, which represents the dilated distal part of the cloacal channel due to obstructed external orifice.[28]

Fetal MRI: It can show a variable degree of colonic dilatation depending upon the specific type of cloacal malformation. There may be a decrease in T1 hyperintense signal of the meconium within the rectum and increased T2 signal of rectal contents due to an admixture of the meconium and urine. For the same reason, the bladder may show increased T1 signal and decreased T2 signal. There can be associated duplication of müllerian structures with or without dilatation. Bilateral hydroureteronephrosis and fetal ascites may be present. Spinal anomalies are also well visualized on MRI.

In cloacal dysgenesis, persistent/classic cloaca, and posterior cloaca, the colon is expected to terminate at a higher level; therefore, the meconium in the colon/rectum does not reach the perineum. On the contrary, in the urogenital sinus, cloaca variant, and posterior cloaca variant, the rectum opens into the perineum; hence, the meconium is expected to reach the perineum. This fact can be utilized as an important point of differentiation between the classic cloaca and urogenital sinus/cloaca variants during antenatal MRI, by noting the level of T1 hyperintense meconium signal in the pelvis. However, in cases of classic cloaca with a very short common channel, the meconium can extend up to the perineum and give an erroneous impression of urogenital sinus/cloaca variants.[25]

Postnatal Imaging

Plain radiographs of the chest, abdomen, and spine are initially obtained to rule out VACTERL association. Ultrasonography of the abdomen and pelvis with screening of the spine should also be performed.

Plain radiograph: In the neonate, a pelvic density may be seen due to distended vagina secondary to obstruction. Gas lucencies within the density may point to rectovaginal communication. Spillage of the meconium through the fallopian tubes into the peritoneal cavity may result in meconium peritonitis, which is visualized as linear calcifications in the abdomen lining the peritoneal surfaces.

Ultrasound: Sonography can demonstrate the distended and obstructed vagina in cases of hydrocolpos. However, its main use lies in determining the severity of urinary tract obstruction, assessment of the status of the ureters and upper urinary tract, and evaluation of renal parenchymal echogenicity. It is also useful in serial follow-up of urinary tract dilatation in these patients.

Before Definitive Surgery

Defining the anatomy of the pelvic structures and their relationship is of critical importance during preoperative assessment of cloacal malformations because it determines the technique of surgical repair.

Various methods for preoperative evaluation are available such as fluoroscopic contrast study and MRI. The role of contrast-enhanced ultrasound has also been described in the evaluation of cloacal malformations.[29]

Fluoroscopic contrast study: It is an important method of assessing the anatomy in general, and abnormal communications in particular (due to excellent spatial resolution), which may otherwise be difficult to visualize on cross-sectional imaging. Moreover, it also provides a measure of functional assessment by demonstrating vesicoureteric reflux and status of continence. Catheterization of the perineal opening is done using an 8-Fr feeding tube. Upon injection of water-soluble nonionic iodinated contrast, image is first acquired in the lateral or oblique projection ([Fig. 3]). This is done to demonstrate the subtle fistulous communications in the initial stages before they get obscured by contrast-filled pelvic structures. Frontal projections are helpful in identifying vaginal or bladder duplication, which may show overlap on lateral projection. Barium is best avoided as it can reflux in the peritoneal cavity, and it may be unsuccessful in delineation of small communications due to higher viscosity.

Fig. 3 Classic cloaca with short common channel. (A) Oblique projection of contrast genitogram with distal cologram study reveals a fistulous communication (arrow) between the rectum (r) and vagina (v). (B) Sagittal T2-weighted MR image in the same patient shows a distended rectum (r) communicating with the vagina (v) through a rectovaginal fistula (red arrow). The urethra (green arrow) and bladder (b) are seen with surface vesicostomy (white arrow). The urethra opened into the vaginal cavity at its distal most aspect resulting in a short common channel (not shown). Associated vertebral anomalies like partial sacral agenesis (orange arrow) and L4–L5 block vertebra (yellow arrow) are also present. (C) Coronal T2-weighted image reveals bilateral moderate hydroureteronephrosis (blue arrows) in the same patient.

Distinguishing between the vagina and the urinary bladder can be challenging but is of utmost importance. The position of these structures is not entirely reliable since the vagina can show abnormal position in many cases. To circumvent this, visualization of cervical impression, if present, can be useful in the identification of the vagina. The presence of the septum also increases the chances that the structure is the vagina. On the contrary, demonstration of reflux into the ureter or passage of contrast into a urachal remnant identifies the structure as urinary bladder. If the contrast reaches the bladder neck during injection and the urinary bladder fails to opacify, then this might be indicative of a competent sphincter.

An imaging-based description of the cloacal malformations describes various types of cloacal configurations, urinary–cloacal communications, and levels of rectal communication.[16]

The cloacal configuration is categorized into two types:

• Urethral: The cloaca resembles a continuation of the urethra and appears as a long, narrow, and curved structure with a small perineal opening.

• Vaginal: The cloaca is wider and straighter and tends to resemble the continuation of the vagina.

Two types of urinary–cloacal communications are described:

• Urethral: The urethra is well developed with the presence of a normal sphincter, and connects the bladder with the cloaca.

• Vesical: There is a complete absence of the urethra resulting in direct communication between the bladder and the cloaca.

Level of rectal communication can be of the following three types:

• Vaginal: Communication occurs at the posterior wall of the lower vagina or at the lower end of the vaginal septum (in cases of vaginal duplication). Rare sites of communication include the upper vagina or the anterior vaginal wall.

• Cloacal: There is direct communication between the rectum and the cloaca, with the presence of a small chamber acting as a passage between the rectum and the cloaca in some cases. Other variants include rectal communication with the bladder in cases of absent or abnormal position of the vagina.

• Cloacal variant: The rectum opens into the perineum through an anteriorly located anal orifice.

In patients who have undergone colostomy, an augmented pressure contrast injection into the distal loop should be performed. A Foley catheter is inserted into the distal loop, the balloon is inflated, and water-soluble nonionic iodinated contrast is injected. It demonstrates the level of rectal communication by providing adequate rectal distension and pressure to depict the fistulous communication and is helpful in distinguishing the rectum from the vagina, which can be difficult on a cloacogram/genitogram.

A voiding cystourethrogram may be performed for the assessment of the bladder and vesicoureteric reflux. This may be attempted by advancing the catheter into the bladder; however, it may not always be possible due to sharp angulation of the urethra with the urogenital sinus.[30] In such cases, the study may only be feasible at the time of cystoscopy or after vesicostomy.

There are certain limitations of conventional 2D fluoroscopy. There may be difficulty in interpretation due to overlap of structures. Foreshortening and magnification can pose difficulty in image interpretation and taking measurements. It can be technically challenging to perform and also carries the risk of radiation exposure.

This drawback of conventional fluoroscopy can be overcome using rotational fluoroscopy with 3D reconstruction. Although 3D fluoroscopy entails a higher radiation dose, it provides much more precise anatomical information to the pediatric surgeon before repair. 3D fluoroscopy in combination with general anesthesia has been described as a useful method of preoperative evaluation. Cystoscopy and vaginoscopic examination under anesthesia enables the surgeon to visualize the internal anatomy and place the catheters in the appropriate lumens. Following this, nonionic iodinated contrast is injected through the catheters to dilate the pelvic structures for imaging. Reconstruction of rotational images in three dimensions helps provide precise information regarding the location of the common channel, distance to the perineum, and other such critical information. It enables the assessment of bladder capacity, vesicoureteric reflux, vaginal size and morphology, length of the common channel, length of the urethra from the bladder neck, and site of confluence.[31] Although it does provide a distinct advantage over conventional fluoroscopy, interpretation of images can still be challenging even with 3D rotational fluoroscopy.[32]

MRI: Use of MRI as a single investigation or adjunct to fluoroscopy is gaining favor with better correlation with surgical findings as compared with fluoroscopic examinations. The role of computed tomography has largely been relegated to the margins, and the only justifiable use appears to be when it is the only imaging modality available or osseous details need to be studied.[33]

MRI provides excellent soft tissue contrast and allows clear visualization of pelvic structures and their relations. The accuracy of MRI in identifying the site of confluence has been reported to be similar to genitoscopy and fluoroscopy. The key elements that need to be evaluated include morphology and relationship of pelvic structures, namely, urinary bladder, urethra, uterus, vagina, rectum and anal canal, perineal body, levator muscle and sphincter development, and length of the urethra and common channel. MRI also enables evaluation of other structures like the gonads, kidneys, and adrenals. Additionally, spinal imaging is recommended to determine the need for neurosurgical intervention. Depending upon the severity, spinal involvement is considered a poor prognostic factor for achieving adequate future bladder and bowel control.

The pelvic images are acquired with a slice thickness of 3 mm and interslice gap of 0.5 mm. Images are acquired in all three orthogonal planes, namely, axial, coronal, and sagittal plane, perpendicular to the pelvic floor. T1- and T2-weighted images are acquired along with T2 fat-suppressed images. Complementary imaging of the upper abdomen (for kidneys and adrenals) and screening of spine is also performed.

Midsagittal T2-weighted images are useful in determining the level of rectal termination and confluence of the urogenital tract. The hyperintense mucosa of the urethra, vagina, and rectum is better appreciated on T2 fat-suppressed images. In the absence of frank visualization of rectal communication with the vagina/cloaca, features like distal tapering of the rectum and its anterior displacement toward the vagina/cloaca can point toward the level of communication ([Figs. 4] and [5]). These findings can then be corroborated with the axial T2-weighted images. The length of the common channel is measured as a straight-line distance between the inferior end of the visualized vagina and the perineum/labia minora.

Fig. 4 Classic cloaca with short common channel. (A) Frontal and (B) lateral projections of distal cologram study reveal fistulous communication between the rectum (yellow arrow) and vagina (red arrow). (C) Coronal T2-weighted MR image shows two uterine cervices (red arrows) opening into separate fluid-distended vaginas (v) with rectum (r) coursing in midline between the uteri. (D) Axial T2-weighted image reveals a small fistulous communication (blue arrow) between the rectum (r) and vagina (v). (E) Sagittal T2-weighted image shows abrupt truncation of the spinal cord (red arrow) and complete coccygeal agenesis (white arrow). (F) Coronal T2-weighted image reveals right renal agenesis.

Fig. 5 Classic cloaca with short common channel. (A) Coronal T2-weighted MR image reveals müllerian duplication with two uterine bodies and cervices (red arrows) opening into separate fluid-filled distended vaginal cavities (v). There is a longitudinal nonobstructing vaginal septum in the upper two-thirds of the vagina. The distended rectum (r) is seen in midline superiorly between the two müllerian structures. (B) Sagittal T2-weighted image demonstrates anteroinferior tapering of the rectum (yellow arrow) opening into the vaginal cavity (v). The urethra (green arrow) opens into the vagina inferiorly to form a short common channel. Partial sacral agenesis (white arrow) is also noted. (C) Lateral and (D) frontal projections of voiding cystourethrogram study demonstrate contrast opacification of the vagina (red arrow) during micturition suggesting urethrovaginal communication. Grade 4 vesicoureteric reflux (blue arrows) is also noted on the right side.

There exists a probability of interobserver variability when measuring the length of the common channel, especially in very small children, making it challenging to obtain accurate values. However, standardizing the measurements based on important landmarks can help circumvent these issues and produce more reliable and reproducible measurements. As an indicator, it may be useful to remember the normal lengths of anatomical structures—an adult female urethra measures approximately 3 cm in length, while in a neonate, its length may be as little as 12 mm. Between the age of 6 months and 3 years, the minimum length of the urethra is 1.5 cm and the mean length is 2.5 cm, with minimal change in this period. From this, it may be extrapolated that to maintain postsurgical continence, the urethra must measure at least 1.5 cm after surgical reconstruction.[34]

Müllerian anomalies like hypoplastic/absent uterus, vaginal atresia/hypoplasia, hydrometrocolpos, and müllerian duplication can also be identified on T2-weighted images. Various urinary tract anomalies like renal agenesis/ectopia, cross-fused renal ectopia, hydroureteronephrosis, and ectopic insertion of the ureter ([Fig. 6]) can be present.

Fig. 6 Urogenital sinus with anterior ectopic anus (cloaca variant). (A) Axial and (B) coronal T2-weighted MR images show the urethra opening (arrowhead) into the vagina (v) with partial septate bladder (arrow). (C) Sagittal and (D) axial T2-weighted images reveal anomalous course of the left ureter (red arrows) between the bladder (b) and the vagina (v) with ectopic ureteric insertion into the hypertrophied bladder neck (yellow arrow).

MRI can also evaluate the status of the pelvic hiatus in cloacal malformations. The pelvic hiatus denotes the opening in the pelvic floor through which the urogenital and digestive tracts reach the perineum. A narrow hiatus results from poor development of the vagina and rectum, resulting in obstruction and dilatation of these structures. Similarly, increase in the length of the common channel and decrease in urethral length, as seen in high cloacal confluence, lead to narrower hiatus and increase the chance of obstruction.[35]

MRI is also the imaging modality of choice for postoperative assessment of technical adequacy of surgery.[36]

The following imaging checklist may be included in the MRI report to provide comprehensive information regarding cloacal malformations to the operating surgeon:

• Level of rectal termination.

• Urogenital confluence.

• Common channel length.

• Urethral length.

• Pelvic hiatus.

• Striated muscle complex.

• Perineal body.

• Vaginal anatomy.

• Müllerian structures.

• Accessory urethra.

• Renal anomalies.

• Vertebral column and spinal cord.

On the basis of MRI and cystoscopy findings, urogenital confluence can be of the following three types[20]:

• Low confluence (type 1): Urogenital confluence at or below the level of the lower border of the pubic symphysis with a short common channel.

• Intermediate confluence (type 2): Urogenital confluence behind the midpart of the pubic symphysis.

• High confluence (type 3): Urogenital confluence at or above the level of the upper border of the pubic symphysis.

In some studies, MRI has been considered an inaccurate method for measurement of the common channel length because thin tubular structures like the urethra, rectovaginal fistula, and common channel are difficult to visualize in the absence of dilatation.[37] [38] [39] Also, it can be difficult to precisely define the site where the pelvic structures coalesce. However, preoperative measurement of the common channel using MRI has been found to be comparable to fluoroscopic contrast study and cystoscopy, with MRI measurements being more accurate than fluoroscopy in patients with short common channel (<1 cm) than in those with longer common channel. In patients with common channel length between 1 and 3 cm, MRI and fluoroscopy have the same accuracy.[40] MR cloacogram/genitogram is a modification of routine MRI in which diluted gadolinium is injected into the common channel, rectum, vagina, and urinary bladder to dilate these structures and extract greater anatomical information.[41] Another limitation of MRI is the need for sedation/anesthesia in very young children.

Together, MRI and contrast fluoroscopy provide adequate assessment of various structures and their relationships. Perhaps the best outcome is obtained when these different imaging modalities (ultrasound, contrast fluoroscopy, and MRI) are used in a complementary fashion so as to derive maximum and accurate information to enable the surgeon in the planning of reconstructive surgery.

Conclusion

Cloacal malformations are a rare but complex developmental condition encompassing a diverse spectrum of anomalies. MRI has a significant and indispensable role in the preoperative evaluation of cloacal malformations, apart from its utility in antenatal and postoperative period. Its excellent soft tissue contrast and multiplanar capabilities allow accurate description of anatomy and pathology, rendering it invaluable in surgical decision-making. It is ably complemented by other imaging modalities such as fluoroscopy and ultrasound, which together with MRI form an integral part of the diagnostic armamentarium. A multidisciplinary approach with close collaboration between the radiologist and pediatric surgeon is of critical importance to ensure accurate diagnosis and effective management of these patients.

Conflict of Interest

None declared.

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Artikel online veröffentlicht:
10. April 2025