Pediatric Radiology

, 41:1117

Fetal MRI clues to diagnose cloacal malformations

Authors

    • Department of Radiology, MLC 5031Cincinnati Children’s Hospital Medical Center
  • Beth M. Kline-Fath
    • Department of Radiology, MLC 5031Cincinnati Children’s Hospital Medical Center
  • Marc A. Levitt
    • Colorectal Center for Children, Pediatric SurgeryCincinnati Children’s Hospital Medical Center
  • Foong-Yen Lim
    • Fetal Care Center of Cincinnati, Pediatric SurgeryCincinnati Children’s Hospital Medical Center
  • Leann E. Linam
    • Department of RadiologyArkansas Children’s Hospital
  • Manish N. Patel
    • Department of Radiology, MLC 5031Cincinnati Children’s Hospital Medical Center
  • Steven Kraus
    • Department of Radiology, MLC 5031Cincinnati Children’s Hospital Medical Center
  • Timothy M. Crombleholme
    • Fetal Care Center of Cincinnati, Pediatric SurgeryCincinnati Children’s Hospital Medical Center
  • Alberto Peña
    • Colorectal Center for Children, Pediatric SurgeryCincinnati Children’s Hospital Medical Center
Original Article

DOI: 10.1007/s00247-011-2020-8

Cite this article as:
Calvo-Garcia, M.A., Kline-Fath, B.M., Levitt, M.A. et al. Pediatr Radiol (2011) 41: 1117. doi:10.1007/s00247-011-2020-8

Abstract

Background

Prenatal US detection of cloacal malformations is challenging and rarely confirms this diagnosis.

Objective

To define the prenatal MRI findings in cloacal malformations.

Materials and methods

We performed a retrospective study of patients with cloacal malformations who had pre- and post-natal assessment at our institution. Fetal MRI was obtained in six singleton pregnancies between 26 and 32 weeks of gestation. Imaging analysis was focused on the distal bowel, the urinary system and the genital tract and compared with postnatal clinical, radiological and surgical diagnoses.

Results

The distal bowel was dilated and did not extend below the bladder in five fetuses. They had a long common cloacal channel (3.5–6 cm) and a rectum located over the bladder base. Only one fetus with a posterior cloacal variant had a normal rectum. Three fetuses had increased T2 signal in the bowel and two increased T1/decreased T2 signal bladder content. All had renal anomalies, four had abnormal bladders and two had hydrocolpos.

Conclusion

Assessment of the anorectal signal and pelvic anatomy during the third trimester helps to detect cloacal malformations in the fetus. The specificity for this diagnosis was highly increased when bowel fluid or bladder meconium content was identified.

Keywords

CloacaCloacal malformationPrenatal diagnosisFetal MRIAnorectal malformationPrune belly syndrome

Introduction

Cloacal malformations represent a spectrum of developmental defects 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. It is seen typically in girls with an incidence of 1 in 40,000–50,000 births and is thought to result from failure of the urorectal septum to join the cloacal membrane during the 4th to 6th weeks of embryonic development [1, 2]. It can lead to bladder obstruction, hydrometrocolpos and colonic dilatation [3, 4].

Because of its prognostic and therapeutic implications, Peña et al. [5, 6] subdivided these anomalies into two major subgroups based on the length of the common channel. Cloacal malformations with common channel shorter than 3 cm have lower incidence of associated defects and less difficult repair. Cloacal malformations with a long common channel (longer than 3 cm) have a high incidence of associated defects, complex anatomy, difficult repair and inferior functional results [5, 6].

A prenatal diagnosis is challenging and rarely confirmed before birth. However, the ability to define these conditions in utero is essential as it allows improved parental counseling in the presence of colorectal surgeons and pediatric urologists. Knowledge of the lesion and type is also important as it can guide site of delivery in order that appropriate surgical intervention and supportive care is instituted [68].

In recent years, several authors have helped to define the normal appearance of the colon and the rectal cul-de-sac with fetal MRI (Fig. 1) and have proposed its use to characterize gastrointestinal (GI) tract abnormalities [9, 10].
https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig1_HTML.jpg
Fig. 1

Fetal MRI in a normal rectum after 20–21 weeks’ GA. The rectum is close to the bladder and its cul-de-sac at least 10 mm below the bladder neck [9]. The rectal content is dark on T2-W images (a), has intermediate signal intensity on steady-state free-precession sequences (b) and has bright signal on T1-W images (c). Rectum (arrow), bladder (asterisk)

We intended to define the spectrum of fetal MRI findings in cloacal malformations in order to improve its detection so that a confident prenatal diagnosis can be provided.

Materials and methods

This study was approved by the Internal Review Board at our institution and patient written consent was waived.

We performed a retrospective review in seven patients treated for cloacal malformation at our institution. Fetal MRI was indicated based on US abnormalities in all cases (Table 1). Third trimester MRI was performed in six fetuses, between 26 and 32 weeks of gestation (mean: 28 weeks) and was included in the study. One case was excluded as fetal MRI was performed at 19 weeks, too early to define abnormal distribution of meconium in the colon and rectum.
Table 1

Summary of findings in six fetuses with cloacal malformation

Case

US diagnosis prior to fetal MRI

Gestation-al age at MRI (weeks)

Fetal MRI findings

Postnatal final diagnosis (Type of cloacal malformation)

#1

Concern for cloacal malformation:

27

• High rectum

Long common channel cloacal malformation

Hydrocolpos, oligohydramnios

• Normal signal in distal bowel (↑T1, ↓T2)

• Cloacagram: 4.5 cm

• Hydrocolpos

• No surgery/cystoscopy

• Small bladder

• Absent right kidney/small LK with cysts

•Oligohydramnios

 

#2

CHD, MCDK

26

• High rectum

Long common channel cloacal malformation

Normal amniotic fluid

• Abnormal fluid in distal bowel (↑T2)

• Cloacagram: 3 cm

• Normal bladder and RK

• Cystoscopy: 3.5 cm

• Left MCDK

•Normal amniotic fluid

 

#3

Concern for cloacal malformation:

26

• Normal rectum

Posterior cloacal malformation variant

Hydrocolpos, oligohydramnios, bladder outlet obstruction prior to development of ascites

• Normal signal in distal bowel (↑T1, ↓T2)

2 perineal orifices:

• Septated hydrocolpos

Posteriorly located urogenital sinus and normal to slightly anteriorly placed anus

• Ascites

• Thick, smooth-walled bladder with normal size

• Mild bilateral hydronephrosis

• Oligohydramnios

 

#4

Concern for cloacal malformation:

29

• High rectum

Long common channel cloacal malformation

Bladder outlet obstruction, oligohydramnios and fluid in bowel

• Abnormal fluid in distal bowel (↑T2)

• Cloacagram: 5 cm

• Layering (↑T1, ↓T2) bladder content

• Cystoscopy: 6 cm

• Megacystis with lobulated contour

And bladder outlet obstruction:

• Mild bilateral hydronephrosis. LK cyst

Prune belly syndrome variant (absence of abdominal muscles)

• Oligohydramnios

 

#5

Concern for cloacal malformation:

32

• High rectum

Long common channel cloacal malformation (5 cm by cloacagram and cystoscopy)

Bilobed bladder and oligohydramnios

• Abnormal fluid in distal bowel (↑T2) + meconium (↓T2 nodular foci)

• Layering (↑T1, ↓T2) bladder content

• Common channel with intermittent fluid

• Megacystis with large right diverticulum

• Absent left kidney

• Oligohydramnios

#6

Bladder outlet obstruction, CHD, normal amniotic fluid

28

•High rectum

Long common channel cloacal malformation

• Normal signal in distal bowel (↑T1, ↓T2)

• Cloacagram: 6 cm

• Common channel with fluid

• Cystoscopy: 5 cm

• Megacystis thick wall, patent urachus, left diverticulum

Prune-belly type features of the anterior abdominal wall

• Right MCDK, mild left hydronephrosis

• VACTERL/normal amniotic fluid

CHD congenital heart disease, MCDK multicystic dysplastic kidney, LK left kidney, RK right kidney

MRI studies were obtained utilizing a phase-array body coil in a 1.5-tesla scanner (Horizon, GE Healthcare, Milwaukee, WI, USA; and Avanto, Siemens Medical Solutions, Erlangen, Germany). T2-W, single-shot fast spin-echo (SSFSE)/HASTE and fast gradient echo T1-W FSPGR/FLASH 2-D sequences were obtained in all three planes for each anatomical region. No maternal or fetal sedation was required.

The images were reviewed by two pediatric radiologists. The analysis focused on the distal bowel, the urinary system and the genital tract, identifying signs of hydrocolpos and ascites. The GI MRI parameters included distal meconium level (using as anatomical landmark the bladder base), presence of focal distal dilatation and abnormal bowel signal content. Bowel dilatation was determined to be present if the diameter of the most distal segment was greater than the adjacent proximal bowel. Bowel dimensions were also compared with normal fetal MRI standards described in the literature [9, 10] as well as with normal macroscopic fetal standards [11]. In the assessment of the urinary system, the bladder shape, size and content signal was analyzed. The appearance of the renal parenchyma and presence of collecting system dilatation were recorded. Potential identification of the common channel as a vertical tubular structure inferior to the bladder and detection of associated malformations were also documented.

The amount of amniotic fluid was subjectively evaluated with MRI and confirmed by the amniotic fluid index on the most recent prior sonogram.

The working diagnosis at the time of imaging, prenatal counseling in the presence of colorectal surgeons and pediatric urologists and fetal interventions were recorded.

The fetal MRI findings were compared with postnatal clinical, radiological (including plain films, sonograms and cloacagrams) and surgical (cystoscopy/vaginoscopy and exploratory laparotomy) evaluations. Chromosome analysis was performed at the time of the work-up and repeated at birth in all patients, confirming normal 46 XX karyotype. Congenital adrenal hyperplasia was excluded in all patients. The type of cloacal malformation was defined postnatally based on the length of the common channel (distance from the perineal orifice to the level of the bifurcation or trifurcation, depending on the type of malformation), shorter or longer than 3 cm following the classification of Peña [5]. The length of the common channel and the level of connection of the distal bowel were assessed with cloacagrams as well as surgically. The clinical outcome was also recorded. Infants were followed for several months. Creatinine levels at birth and at last follow-up were determined. These data are summarized in Tables 1, 2, 3 and 4.
Table 2

Distal bowel dilatation analysis

Case # (GA)

Level of terminal bowel

Caliber (mm)

Expected mean by fetal MRI*

Expected mean by macroscopic analysis**

Maximum colonic diameter/gestational age***

Beaked vs. blunted end of distal bowel

Signal of the distal bowel/bladder

1 (27w)

Expected descending colon

10.24

6 mm

6.11 mm

8 mm

Beaked

• Both normal

2 (26w)

Expected sigmoid

18.67

6 mm

7.33 mm

7 mm

Blunted

• Rectum: Intermediate T2/↑ T1)

• Bladder: normal

4 (29w)

Expected descending colon

16

7 mm

7.10 mm

10 mm

Blunted

• Rectum: ↑ T2

• Bladder: ↓T2/ ↑ T1 layering bladder content

5 (32w)

Expected sigmoid

15.44

8 mm

9.44 mm

11 mm

Beaked

• Rectum: ↑ T2 + meconium concretions (↓T2 nodular foci)

• Bladder: ↓T2/↑T1 layering bladder content

6 (28w)

Expected sigmoid

18.28

6.5 mm

8.22 mm

10 mm

Beaked

• Both normal

GA = gestational age in weeks *Couture et al., **Malas et al., ***Saguintaah et al

Table 3

Summary of postnatal findings in six patients with cloacal malformation

Case #

Months of follow- up

Neonatal renal US

VUR (on cloacagram/VCUG)

Creatinine at birth

Creatinine at last follow-up

Complete repair

#1

0.5 demise (renal insufficiency)

• Absent RK, 2 small cysts on left renal fossa

No

1.6 mg/dl

4.8 mg/dl

No

• Small bladder

• Dilated distal bowel

 

#2

43

•Left MCDK

No

0.6 mg/dl

0.2 mg/dl

Yes

• Normal RK and bladder

• Dilated distal bowel

 

#3

36

•Left cystic renal dysplasia and mild bilateral pelvocalyectasis

Yes (grade 3–4 left/grade 3 right)

4.1 mg/dl

1 mg/dl (GFR:38 mL/min/m2)

Yes

• Thick, smooth-walled bladder with normal size

Persistent (grade 1 left/grade 4 right) at last follow-up

• Hydrocolpos/duplicated vagina

• No ascites

• No bowel dilatation

 

#4

34

•Bilateral echogenic kidneys, cystic dysplasia on the left and mild bilateral pelvocalyectasis

Yes (bilateral grade 4, persistent at last follow-up)

1.4 mg/dl

0.8 mg/dl (GFR:64 ml/min/m2)

Yes

• Megacystis with echogenic debris

 

#5

28

• Solitary RK with mild to moderate hydroureteronephrosis

No

0.9 mg/dl

0.5 mg/dl

Yes

• Megacystis with echogenic debris and large right diverticulum (both filled with air on plain film)

 

#6

16, Demise (respiratory insufficiency and candida sepsis)

• Megacystis thick-walled, patent urachus, left diverticulum

Yes (grade 4 from ectopic insertion into bladder diverticulum)

1.5 mg/dl

1.2 mg/dl

No

• Right MCDK, echogenic LK with worsening hydronephrosis

Also UPJ obstruction

RK right kidney, LK left kidney, MCDK multicystic dysplastic kidney, VUR vesicoureteral reflux, UPJ ureteropelvic junction

Table 4

Genital tract assessment and presence of hydrocolpos

Case #

Prenatal hydrocolpos

Postnatal hydrocolpos

Müllerian structures/vagina on cloacagram

Müllerian structures/vagina on cystoscopy/vaginoscopy

Surgical findings during final repair

#1

Yes

Yes

Large hydrocolpos

N/A

N/A

#2

No

No

Tiny müllerian structure to the left of the bladder base

Small left blind-ending area, but no obvious vagina

• 2 normal ovaries

• Underdeveloped and non-patent müllerian structures (hemiuteri and tubes) that were removed

• No significant vagina (anorectal vaginostomy performed)

#3

Yes

Yes

Low posterior urogenital sinus with septated vaginas s/p vaginostomy tube and partial septum resection

2 hemivaginas (5/5.5 cm in length) with patent bilateral müllerian structures

• 2 normal ovaries

• Normal/patent müllerian structures

• 2 hemivaginas

#4

No

No

Not identified

2 small blind-ending hemivaginas connected to posterior wall of the bladder

• 2 normal ovaries

• Fairly atretic left fallopian tube, hemiuterus and hemivagina (removed)

• Slightly better-developed right fallopian tube, hemiuterus on the right with right vaginal remnant, but patency of the lumen could not be confirmed with saline injection (not removed)

The right vaginal remnant was anastomosed to colonic neovagina

#5

No

No

Not identified

Not identified

• Normal right ovary and small but patent right müllerian structures

• Left ovary with inadequate blood supply and tiny left müllerian remnant (both removed)

• No significant hemivaginas

#6

No

No

Not identified

Not identified

N/A

N/A (not performed)

Results

Rectal assessment

There was apparent high position of the rectum in 5/6 fetuses with the distal end at the bladder base or above this level. It was also noted that all five had associated focal dilatation with a blunted (2) or beaked (3) distal bowel end. The caliber of the dilated distal segment always exceeded the maximum expected colonic diameter for gestational age (Table 2). On postnatal assessment these infants had a high rectum and a long common channel measuring 3.5 cm to 6 cm (Table 1) (Figs. 2, 3, 4, 5, 6 and 7).
https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig2_HTML.jpg
Fig. 2

Case 6, VACTERL association. Fetal MRI sagittal SSFSE (a) coronal 2-D FIESTA, (b) T2-W and (c) sagittal T1-W images. a The bladder is decompressed status post drainage (asterisk). Patent urachus (black arrow) and esophageal atresia with upper pouch distention (arrowhead). a–c The rectum is dilated (white arrow) with beaked end. It does not extend below the bladder (asterisk). Multicystic dysplastic right kidney (RK)

https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig3_HTML.jpg
Fig. 3

Case 6, VACTERL association, postnatal imaging. a First day of life chest-abdomen radiograph. Enteric tube is in upper esophageal pouch (arrowhead). Distended bladder (asterisk) and distal bowel (black arrow). There is mesocardia, congenital scoliosis and protuberant abdomen. b Lateral 3-D rendering cloacagram. There is high origin of the common channel (white arrow). Distal bowel (black arrow) and bladder (asterisk)

https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig4_HTML.jpg
Fig. 4

Case 5. Fetal MRI. Axial T2-W (a and b), sagittal T1-W (c) and T2-W (d) images. There is fluid-filled dilated distal bowel with concretions of meconium (white arrow) and dark T2/bright T1 layering bladder content (short black arrows). Large right bladder diverticulum (asterisk). d The rectal fistulous connection (long black arrow) and partial fluid distention of the common channel (white arrowhead) are shown

https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig5_HTML.jpg
Fig. 5

Case 5 postnatal assessment. a Supine abdominal radiograph. Large bladder (black arrow) and right diverticulum (asterisk) are filled with air. b Surgical anatomy of the bladder. c Cloacagram, lateral view. Rectal fistulous connection (long white arrow) and partial opacification of the common channel (arrowhead). Catheter through single perineal opening (anterior radiopaque marker) and vesicostomy are reaching the bladder. A Foley catheter is also in the colostomy (short white arrow). Posterior perineal marker (expected position of the anus)

https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig6_HTML.jpg
Fig. 6

Case 2 fetal MRI. Sagittal T1-W (a, b) and T2-W (c) images. The focally dilated left colon (white arrow) reaches the pelvis, caudal to a multicystic dysplastic left kidney (LK) and posterior to the bladder (asterisk). The rectal cul-de-sac is high and shows abnormal increased T2 signal

https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig7_HTML.jpg
Fig. 7

Case 2 postnatal imaging. a Frontal chest-abdomen radiograph on first day of life. Very dilated distal bowel (white arrows). Segmentation vertebral anomalies are present throughout the spine. b Cloacagram, lateral view. Contrast agent has been injected through the colostomy (arrowhead) and bladder catheter (asterisk) through a single perineal opening (anterior perineal marker). High rectum (white arrow) and tiny müllerian structure (black arrow)

A posterior cloacal variant (normal rectum with posterior location of a urogenital sinus) was the only case in which a normal meconium-filled rectum extended distal to the bladder without dilatation. There was, however, posterior displacement of the rectum from the bladder wall by a septated hydrocolpos and ascites (Fig. 8).
https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig8_HTML.jpg
Fig. 8

Case 3 fetal MRI. Sagittal T2-W (a) and sagittal T1-W (b) images and postnatal fluoroscopic contrast exam lateral view (c). There is normal appearance of the rectum (R) but it is displaced from the bladder (asterisk) by a hydrocolpos (H). There is fetal ascites (FF) and postnatal vesicoureteral reflux (VUR). Placenta (P) and liver (L). The perineal marker (arrowhead) is in the opening of the urogenital sinus, immediately anterior to the anus

In three fetuses, increased T2 signal content in the distal bowel was noted. Two of them also had dark T2/bright T1 layering bladder content (Figs. 4 and 9). These findings were supportive of the presence of a recto-urinary fistula. Interestingly, in one patient the bladder was distended with air after birth, as well (Fig. 5).
https://static-content.springer.com/image/art%3A10.1007%2Fs00247-011-2020-8/MediaObjects/247_2011_2020_Fig9_HTML.jpg
Fig. 9

Case 4. a Fetal MRI coronal/oblique T2-W image. Megacystis with layering lower T2 signal content (white arrow). b Frontal chest-abdomen radiograph on first day of life. Protuberant abdomen and pelvic mass effect with displacement of the transverse colon (black arrow) caused by megacystis. There were prune-belly-type features of the abdominal wall with absence of abdominal muscles and only skin and attenuated fascia on surgery

Genitourinary system assessment

In concordance with prior reports, multiple abnormalities of the urinary system were detected (Tables 1 and 3). Abnormal bladder shape was present in four, which included large bladder diverticulum in two and wall trabeculation and patent urachus in one (Figs. 2 and 4). There were also renal anomalies in all cases. Hydronephrosis was seen in four, unilateral renal agenesis in two, unilateral cystic renal dysplasia in two and unilateral multicystic dysplastic kidney (MCDK) in two (Figs. 2 and 6). Hydrocolpos was present in two fetuses, in one of them with transient ascites (Fig. 8). The other four fetuses had no hydrocolpos. Three of these four had no significant vagina during the final repair and one patient without a final repair had no identifiable vagina during cloacagram and vaginoscopy (Fig. 3) (Table 4).

Persistent bladder dilatation (megacystis) was seen in three fetuses, two in the setting of oligohydramnios (Figs. 4 and 9) and one with normal amniotic fluid but esophageal atresia/VACTERL association. Postnatal prune-belly-type features of the abdominal wall were present in two of them (Figs. 3 and 9).

Thin tubular fluid signal inferior to the bladder base was intermittently identified in two fetuses and correlated with a portion of the common channel on cloacagram (Figs. 4 and 5).

Detection of other malformations

In one fetus, MRI defined associated malformations with findings in the spectrum of VACTERL association (Fig. 2) including scoliosis, mesocardia, esophageal atresia and renal abnormalities and limb anomalies comprising hypoplasia of right lower limb and bilateral clubfoot. Low position of the conus concerning for tethering of the cord was also confirmed.

Parental counseling/clinical management

The correct diagnosis was prospectively missed in one patient (case 2), although retrospective review of the fetal MRI demonstrated high position of the rectal cul-de-sac and dilated distal bowel segment with increased fluid signal content (Fig. 6), which should have supported cloaca diagnosis. This baby was the only full-term infant who also had normal amniotic fluid in utero, allowing for normal lung development. The patient had no vesicoureteral reflux and has had normal renal function to 3½ years of age (Table 3).

Fetal MRI was able to confidently detect anorectal malformation in two patients (cases 1 and 6) and gave a confident diagnosis of rectourinary fistula in two patients (cases 4 and 5), only prospectively suspected by US in one patient (case 4). Fetal MRI and sonography were concordant in case 3. In all these cases the parents were properly counseled and met with the colorectal surgeons and pediatric urologists who explained the surgical planning. These babies were also accordingly delivered at a level 3 facility and transferred to our institution after initial stabilization following the prenatal plan. They were between 32 and 36 weeks at the time of delivery and all but one suffered oligohydramnios in utero. The baby with normal amniotic fluid in this second group was diagnosed in utero with esophageal atresia. In all cases, the renal assessment was improved with fetal MRI (Table 1).

With regard to in utero intervention, one fetus with severe megacystis was treated with vesicoamniotic shunt and amnioinfusion in an attempt to improve the anhydramnios and decompress the urinary system (case 5). Another fetus with megacystis received several bladder taps (case 6).

Discussion

The classic diagnosis of a cloacal malformation starts with the inspection of the perineum. Unfortunately, Peña et al. [12] found patients misdiagnosed and mistreated as neonates with “recto-vaginal fistula” or intersex anomalies. As such, heightened knowledge about this malformation among the medical community is still needed [13]. These infants need urgent clinical and radiological evaluation by an experienced pediatric surgeon, pediatric urologist and radiologist during the first day of life [13]. Renal function is usually impaired at birth and without early treatment bowel obstruction will follow and lead to metabolic complications. This situation can become more critical in the setting of prematurity, lung hypoplasia related to oligohydramnios and associated respiratory distress if there is a large hydrocolpos. Prenatal diagnosis is essential to ensure appropriate parental counseling and to improve the management of these neonates, by directing site of delivery and immediate postnatal care [8].

Prenatal US diagnosis of cloacal malformation is extremely challenging and usually considered when a pelvic cystic lesion is detected in a female fetus. However it frequently leads to a wide differential diagnosis that includes isolated hydrocolpos, urogenital sinus, obstructive uropathy and even other cystic pelvic lesions such as ovarian cyst, enteric duplication cyst and bowel atresia [14]. Alternative etiologies include cystic type IV sacrococcygeal teratoma or an anterior myelomeningocele [15]. The sequence of findings on serial sonograms of transient ascites, progressive hydrocolpos, hydronephrosis and oligohydramnios is suggestive of this malformation but not specific [7, 8, 16, 17]. The only reported specific prenatal US signs supporting the communication between the distal bowel and the urinary system are rectal fluid distention, intraluminal calcifications [8, 16, 18] and the detection of calcified meconium in the urinary tract [19]. However these sonographic findings are not always present or easily detected.

Fetal MRI allows excellent depiction of the GI tract. It provides a resource to assess the rectum and its content and to differentiate isolated hydrocolpos from cloacal malformations [9, 20, 21].

Several case reports of cloacal malformation imaged with MRI in utero have been described; however, none has provided a detailed description of the rectal signal, caliber or position [4, 8, 17, 2224]. There is only one case report of cloacal variant with complete fetal MRI assessment and postnatal imaging correlation [25].

We have presented the fetal MRI findings of six patients with cloacal malformation with postnatal clinical, radiological and surgical correlation. A systematic assessment of the anorectal region and position of the rectal cul-de-sac resulted in a confident diagnosis of anorectal malformation. Our series, although short, is the largest providing detailed assessment of cloacal malformation and we found concordance between the levels of the most distal bowel visualized in the third trimester and after birth.

Rectourinary fistula can be seen in male fetuses with some forms of imperforate anus and in female patients with cloacal malformation [5]. A very important prenatal clue supporting this communication is abnormal distal bowel signal in the form of increased fluid content [3]. We saw this in three of our patients. Two of them also had meconium signal layering in the bladder.

Rectal dilatation has been described in anorectal malformations [10], including two cases of cloacal malformations detected by sonography [4, 19] and two cases by fetal MRI [9, 24]. In our series, rectal dilatation and high rectal cul-de-sac was noted in all cases with the exception of a case of posterior cloacal variant. This rare form of cloacal malformation has an essentially normal or slightly anterior rectum and anus and a urogenital sinus opening immediately anterior to it, as opposed to at the expected level of the urethra. Although it would be strictly considered a urogenital sinus it is thought to be an anatomical variant of an unusual malformation named posterior cloaca. In this condition a urogenital sinus drains into the rectum at the anus or immediately anterior to it [2, 26]. In our patient, we detected in utero a septated hydrocolpos increasing the distance between the posterior bladder wall and the meconium-filled non-dilated rectum, alerting us to possible urogenital sinus but not ruling out cloacal malformation with low position of the distal bowel.

More than 50% of patients with cloacal malformation have different degrees of septation of the internal genitalia and hydrocolpos [5]. The fact that we only found two cases with hydrocolpos is most likely related to the small size of our sample. It is also possible that in the setting of a severely atretic genital tract, as in four of our patients, hydrocolpos could not develop.

Megacystis, present in three cases, is rare but possible in the setting of cloacal malformation. This pathology can develop because of mechanical obstruction created by a narrow common channel or neurogenic bladder dysfunction related to associated tethered cord [27]. It is also seen in prune belly syndrome, characterized by deficient abdominal wall musculature, urinary tract anomalies (especially megacystis and hydroureter) and cryptorchidism in males or major genital tract malformations in females. Prune belly syndrome is frequently associated with malformations in other organ systems, including the GI tract, and among those, anorectal malformations [2830]. In fact, two of the three cases presenting with megacystis had postnatal abdominal wall prune belly features and one of the two, VACTERL association. Simultaneous occurrence of abdominal wall prune belly features, cloacal malformation and VACTERL, as in one of our patients, is rare with only one case previously described. It has been postulated that they are linked by a common defect in the differentiation of mesoderm early in embryonic development [31]. Megacystis is also seen in the setting of megacystis-microcolon-intestinal hypoperistalsis syndrome, and third-trimester fetal MRI can be extremely helpful in defining the presence of microcolon [3, 9, 10].

Given the not infrequent association of malformations involving other systems, sometimes overlapping with the VACTERL association or caudal regression syndrome [8], a complete fetal evaluation should always be performed.

Conclusion

Third-trimester fetal MRI can detect cloacal malformations with high position of the distal bowel and long common channel. In this scenario, the rectum is focally dilated and does not extend below the bladder base. Although the rectal content can demonstrate normal meconium signal, sometimes it will exhibit increased T2 signal (fluid) with or without bladder layering containing decreased T2 and increased T1 (meconium) signal. Abnormal signal in the colon or in the bladder is consistent with a rectourinary fistula, which in a female fetus is characteristic of cloacal malformation. Additionally third-trimester megacystis in a female fetus with decreased or normal amniotic fluid should raise concern for this malformation, and attention to the appearance of the colon should be paid to alternatively exclude megacystis-microcolon-intestinal hypoperistalsis syndrome.

Potential limitations to our analysis include cloacal malformations with low position of the distal bowel in the absence of hydrocolpos. We expect that further experience with a larger series could provide more imaging clues in these situations.

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© Springer-Verlag 2011