Early US Prenatal Diagnosis and Serial Imaging Confirmation of Hydrometrocolpos with Uterine Didelphys and Cloacal Malformation: A Rare Case of Combined Müllerian Duct and Anorectal Anomaly

Introduction

The prenatal diagnosis of congenital anomalies is a critical aspect of obstetric care, particularly in the identification of anorectal malformations such as anal atresia.¹ During the first trimester, ultrasound findings play a pivotal role in the assessment of cystic accumulations in the pelvic region, specifically those located posterior to the bladder.² Such cystic structures that align with the characteristics of anal atresia can be distinguished by the unique pattern of the distal end of the cyst, which, upon sagittal view examination, tends to extend towards the perineum.²

A key parameter utilized in differentiating anal atresia from other cystic lesions is the anteroposterior diameter of the rectosigmoid segment compared to that of the bladder.³ Specifically, at no point in gestation should the rectosigmoid diameter exceed that of the bladder.³ An altered ratio, particularly an increase at 18 weeks gestation, raises the suspicion of anorectal obstruction, necessitating further evaluation.³

Moreover, advancements in imaging, such as fetal MRI, enhance the accuracy of diagnosis in the third trimester.⁴ In a typical scenario, the rectum should be positioned at least 10 mm below the bladder level; any deviation from this norm, including elevation or alignment of the rectum with the bladder, strongly suggests the presence of an anorectal obstruction.^5,6

Furthermore, the visualization of the target anus following 23 weeks of gestation serves as an important marker in prenatal assessments.⁶ It emerges as a hypoechoic annular area with a small central echogenic focus, and the absence of this finding is indicative of an imperforate anus.⁶ This article aims to explore the nuances of these imaging findings and their implications for prenatal diagnosis and management of anal atresia and related disorders.

Methods

This case report describes the first-trimester diagnosis of hydrometrocolpos associated with uterine didelphys and cloacal malformation, representing a rare combination of Müllerian duct and anorectal anomalies. All clinical, imaging, and histopathological data were collected retrospectively from the patient’s medical records. Ethical approval for this study was obtained from the Research Ethics Committee of Mashhad University of Medical Sciences (Approval No: IR.MUMS.REC.1404.245). Written informed consent to publish the clinical information and any identifying images was obtained from the legal guardians (parents), in accordance with international ethical publishing standards.

Case Presentation

In the first-trimester screening ultrasound, a cystic accumulation was observed in the fetal pelvis posterior to the bladder. In a male fetus, such a finding typically suggests a dilated rectum, whereas in a female fetus, it indicates a distended uterus compatible with hydrometrocolpos (Figure 1 and Video S1). These cysts are usually associated with anorectal atresia. In male fetuses, the finding often relates to an anorectal–urethral fistula, while in females it is typically due to Hydrometrocolpos secondary to cloacal malformation.

Figure 1 Midline cystic masses in the first trimester indicate anorectal malformations most often due to anorectal–urethral fistula in males and Hydrometrocolpos from cloacal malformation in females.

At the 18-week second-trimester screening, it was confirmed that the fetus is female. A cystic structure with a thick and echogenic wall was visualized posterior to the bladder. The distal part of this cystic area extended along the midline toward the perineum, which is again in favor of an anorectal malformation (Video S2). Since the fetus is female, the observed midline cystic pelvic structure appears to represent a fluid-filled distension of the vaginal canal extending to the uterus and cervix, consistent with Hydrometrocolpos.

Ultrasound evaluation at 30 weeks of gestation demonstrated a midline cystic pelvic structure with internal echoes and a thick echogenic wall located posterior to the bladder, consistent with Hydrometrocolpos. A thick longitudinal septum was visualized within the cystic structure, resulting in duplication of the cervix (double cervix). Additionally, two small uteri were identified superior to the cystic mass, consistent with uterine didelphys. The distal extension of the cystic structure toward the perineum, together with the absence of a normal anorectal canal, indicated a persistent cloacal anomaly. In addition, the kidneys were normal and showed no dysplastic changes.

Echogenic ascites containing debris and internal echoes was also detected, representing chemical peritonitis, caused by urine reflux into the uterus and subsequent spillage through the fallopian tubes into the peritoneal cavity. Echogenic bowel loops were noted secondarily (Figures 2–4 and Video S3, Video S4). This constellation represents a rare and complex combination of Müllerian duct anomaly (uterine didelphys) and cloacal malformation.

Figure 2 30-week female fetus with cloacal anomaly, Hydrometrocolpos, uterine didelphys, and echogenic ascites with debris causing secondary echogenic bowel. The arrow indicates echogenic ascites.

Figure 3 The arrow indicates the distended cervix 1, and the arrowhead indicates the uterus 1.

Figure 4 The arrow indicates the distended cervix 2, and the arrowhead indicates the uterus 2. A depth scale (cm) is displayed on the left side of the ultrasound image.

Discussion

Persistent cloacal anomaly (PCA) represents the most severe and uncommon form of anorectal malformation, occurring at an incidence of approximately 1 in 50,000 live births.⁷ This anomaly is exclusively observed in female fetuses and typically manifests during the second and third trimesters of gestation.⁸ Sonographic evaluations may reveal the presence of a pelvic cyst characterized by a distinctive thick longitudinal septum.⁹ The complexity of this condition necessitates multidisciplinary management to address associated urogenital and gastrointestinal anomalies.

Hydrocolpos is seen in about 30% of instances where urine and meconium enter the vaginal canal.^6,10 Furthermore, a small percentage of cases present with ascites, which usually arises when cloacal contents flow backward from the fallopian tubes into the peritoneal cavity.^11,12 Hydrocolpos is frequently associated with urinary obstruction, which can result in bilateral pyelectasis.¹³ When the obstruction occurs at the bladder outlet, it can lead to the development of megacystitis.^14,15 Conversely, if the obstruction is situated at the level of the trigone, the bladder may present as either normal in size or diminished.^6,16

The presence of certain features alongside hydrocolpos may suggest a persistent cloacal anomaly rather than isolated hydrocolpos.¹⁷ These features include the identification of a thick longitudinal septum within the hydrocolpos and the observation of a fluid-fluid interface with echogenic particles.¹⁷ Such echogenic findings are indicative of a mixture of meconium and urine, which can assist in differentiating between these two conditions.⁶

The presence of bilateral pyelectasis, absence of a visible anal target, dilatation of the distal colon and rectum, and the detection of ascites with echogenic particles in the abdominal and pelvic regions are indicative of a cloacal malformation.¹⁷ These findings suggest the possibility of meconium leakage from the fallopian tubes into the peritoneal cavity.¹⁸ The presence of abdominal calcifications resulting from meconium peritonitis further supports the diagnosis of a cloacal anomaly as opposed to isolated hydrocolpos.¹⁹ Persistent cloaca is associated with a variety of congenital anomalies, including dysplastic multicystic kidneys, ectopic kidneys, Single umbilical artery (SUA), uterus didelphys, and spinal cord abnormalities. These associations highlight the complex developmental implications of persistent cloacal malformations.⁶

The earliest times for diagnosing gastrointestinal atresias are as follows: duodenal atresia and jejunoileal atresia are typically detectable in the late second trimester, around 25 weeks of gestation. Conversely, anorectal atresia can be diagnosed earlier, in the first trimester at approximately 12 weeks. According to the “Diagnostic Ultrasound” textbook, the prenatal detection rate for anal atresia using ultrasound is reported to range from 7% to 24%.²⁰

This case report sheds light on a rare confluence of congenital anomalies—hydrometrocolpos (fluid accumulation within the uterus and cervix), uterus didelphys, and cloacal malformation—which presented significant challenges in both diagnosis and management.

Conclusion

This case highlights the importance of early and systematic prenatal imaging in the detection of rare congenital anomalies. The coexistence of hydrometrocolpos, uterine didelphys, and cloacal malformation represents a complex spectrum of Müllerian and anorectal anomalies that can be identified as early as the first trimester. Careful evaluation of midline cystic pelvic structures, recognition of distinguishing sonographic features, and the integration of advanced modalities such as fetal MRI are essential for accurate diagnosis. Early recognition not only improves perinatal management but also allows for timely parental counseling and multidisciplinary planning. Reporting such rare presentations expands the current understanding of prenatal manifestations of cloacal malformations and their associated anomalies, ultimately contributing to improved diagnostic accuracy and outcomes.