Case report

A 35-year-old (G2P1) was referred at 18 weeks and 4 days gestation for sonographic evaluation due to a suspicion of omphalocele.

Ultrasound examination in our center revealed the following findings:
A small bowel loops containing omphalocele extended inferiorly to genitalia with ambiguous genitalia and absence of bladder suggestive for cloacal exstrophy
Skin covered splaying of sacral vertebras with normal posterior fossa appearance in favor of closed type neural tube defect.
Conus was at the level of L4-L5 suggestive for tethered cord.
A segmentation abnormality in mid thoracic vertebra in central ossification nucleus suspected for butterfly vertebra.

Based on these findings OEIS complex was diagnosed. Parents chose termination of the pregnancy.

Images 1 and 2; videos 1, 2 and 3: 2D and Doppler images of omphalocele (wide vertical arrow) extended inferiorly to genitalia.

Images 4, 5 and 6; videos 4 and 5: 2D images in different planes showing splaying of sacral vertebras with overlying normal skin suggestive of closed type neural tube defect, tethered cord and segmentation abnormality in mid thoracic vertebra.

Definition: Omphalocele-Exstrophy-Imperforate anus-Spinal defects (OEIS) is the most severe form of  cloacal exstrophy. which is a complex anomaly resulting in exstrophy of both bowel and bladder. ¹

Prevalence: between 1/200,000 and 1/400,000.¹,²

Etiology: unknown

Pathogenesis: the cloaca is the common chamber and is origin of intestinal, urinary, and genital tracts. The urorectal septum grows caudally and divides the cloaca into anterior and posterior chambers (the urogenital sinus and the rectum respectively) between the 6th–7th weeks of gestation. After that time the cloacal membrane ruptures and forms the external orifices. Failure of this mesenchymal tissue migrations or early cloacal membrane ruptures are proposed as a Cloacal exstrophy pathogenesis.² Some believe OEIS may result from a single defect in early caudal mesoderm during first 4 weeks of development.

Prenatal diagnosis: prenatal diagnosis of a cloacal exstrophy is very challenging due to the lack of a reliable sign and antenatally only around 25% of them can accurately be diagnosed. The initial observation usually is an omphalocele but in cloacal exstrophy inferior to the omphalocele there is a more complex abdominal wall defect which involves genitalia.²,³ Omphalocele presents in 70-90% of cloacal exstrophy and vertebral anomalies in 46% of them. But in OEIS syndrome both of them should be present for diagnosis.¹,³Prenatal US clues in diagnosis of OEIS complex: ¹,²,³:

-Absence of a bladder is a crucial sign for confirming the diagnosis.
-A solid mass in the lower fetal abdomen due to bladder exstrophy and bowel herniation between them with umbilical arteries running around the mass.
-Low position of umbilical cord insertion.
-Ambiguous genitalia: A normal external genitalia will probably exclude this diagnosis. Karyotyping may be necessary for determination of fetal sex. 
-Omphalocele.-Spinal abnormalities (usually occult spinal dysraphism as meningocele, lipomeningocele, and lipomyelocystocele). Other findings include abnormalities of the vertebral column or tethered cord.

Differential diagnosis:²

-Gastroschisis and isolated omphalocele: bladder should be present in both of them.
-Bladder exstrophy: the abdominal wall defect inferior to the cord insertion site and bladder halves are everted with irregular contour which extend to genitalia and results in ambiguous genitalia. Differentiating clues: No associated anomaly, bowel loops are never extruded, no rectum abnormality.
-Amniotic band sequence: its sonographic findings are highly variable and occur in a nonanatomic distribution. Each part can be involved.
-Limb-body wall complex: The fixed position of fetus, often with abdominal wall defect and adherence to the placental surface. No identifiable cord insertion site with no free-floating loops of cord. Often with severe kyphoscoliosis. A wide spectrum of limb abnormalities.

References

1- Z. Ben-Neriah, S. Withers, M. Thomas et al. OEIS complex: prenatal ultrasound and autopsy findings, Ultrasound Obstet Gynecol 2007; 29: 170–177
2-Reza Pakdaman, MD; Paula J. Woodward, MD; Anne Kennedy, MBBCh. Complex Abdominal Wall Defects: Appearances at Prenatal Imaging. . RadioGraphics 2015; 35:636–649
3-Ching-Yu Chou , Ying-Chih Tseng , Tsung-Hsuan Lai. Prenatal Diagnosis of Cloacal Exstrophy: A Case Report and Differential Diagnosis with a Simple Omphalocele. Journal of Medical Ultrasound (2015) 23, 52e55