Keywords
anterior coronal sonogram - congenital diaphragmatic hernia - gastrointestinal - gastroschisis
- stomach bladder proximity
Introduction
Fetal gastrointestinal tract (GIT) anomalies account for 7.35% of congenital malformations.[1] There are no well defined protocols to examine fetal GIT, unlike fetal echocardiogram
or neurosonogram. Amniotic fluid homeostasis is maintained by the balance between
the inflow from the fetal urinary tract and lung secretion and the outflow by swallowing
and absorption by the fetal GIT.[2] Hence, the fetal GIT is a dynamic system that plays a vital role in amniotic fluid
homeostasis. We present four cases that highlight the importance of the relative positions
of the stomach, small bowel, and bladder in the coronal plane of the fetal abdomen
in the diagnosis/exclusion of certain anomalies.
Case 1
A 21 year old primigravida was referred at 26 weeks with suspected congenital pulmonary
airway malformation. She had not undergone a first trimester screening and target
scan. Her antenatal course was otherwise uneventful. There was no significant medical
or surgical history. On ultrasound examination at our center, the fetal growth, liquor,
and Doppler appeared appropriate for gestational age.
The axial section of the thorax at the level of the 4 chamber view revealed a mild
mediastinal shift to the left ([Fig. 1A]). The coronal view of the fetal abdomen showed an unusual proximity of the fetal
stomach and the bladder (stomach bladder proximity sign) ([Fig. 1B]). Coronal and parasagittal views of the diaphragm revealed a discontinuity with
herniation of the small bowel and upper pole of the left kidney into the left hemithorax.
The right lung appeared mildly compressed.
Fig. 1 (A) Axial section of thorax showing mediastinal shift. (B) Anterior coronal sonogram showing the stomach in contact with the bladder. (C) The upturned superior mesenteric artery sign.
Color Doppler imaging confirmed the bowel herniation by the demonstration of an upturned
superior mesenteric artery ([Fig. 1C]).
The final diagnosis was left sided congenital diaphragmatic hernia (CDH) with small
bowel as content. The observed to expected lung area to head circumference ratio (O/E
LHR) was 80%. The couple was counseled in detail and reassured regarding a favorable
outcome. However, they chose to terminate the pregnancy.
Case 2
A 29 year old second gravida at 20 weeks of gestation was referred for a routine target
scan. Her first trimester combined screening for common aneuploidies had returned
screen negative. There was no significant past medical history. On imaging, fetal
anatomy, fetal growth, and liquor were appropriate for the gestational age. The axial
section of the thorax appeared normal ([Fig. 2A]). The anterior coronal plane of the fetal abdomen showed a normal relative position
of the fetal stomach, small bowel, and bladder ([Fig. 2B]).
Fig. 2 (A) Target scan: axial section of thorax showing normal mediastinum. (B) Anterior coronal plane showing the normal position of the stomach and bladder. (C) Growth scan, axial section of thorax showing mediastinal shift to the right. (D) Growth scan, anterior coronal plane showing the proximity of stomach and bladder.
(E) Upturned superior mesenteric artery sign.
She was referred back to us at 33 + 6 days with suspected congenital pulmonary airway
malformation. On examination, a mild mediastinal shift toward the right was noted
in the axial section of the thorax at the level of the 4 chamber view ([Fig. 2C]). Additionally, we noted the stomach bladder proximity sign ([Fig. 2D]). Coronal and parasagittal views revealed discontinuity in the left dome of the
diaphragm and displacement of the small bowel to the left hemithorax through the defect
on the left side. The right lung appeared mildly compressed. Color Doppler imaging
confirmed the bowel herniation by the demonstration of an upturned superior mesenteric
artery ([Fig. 2E]).
The final diagnosis was a late onset left sided CDH with a small bowel as content
(stomach down left CDH). The O/E LHR was 85%.
The couple was counseled at length and reassured about a favorable outcome. At 38
weeks, a male baby weighing 2,100 g was delivered by elective cesarean section. The
baby underwent surgery for a CDH on day 2 of life and was discharged on day 15. The
baby is doing well currently.
Case 3
An 18 year old primigravida was referred in view of suspected gastroschisis at 29
weeks. She had not undergone the combined first trimester screening. There was no
significant medical or surgical history and her antenatal course was unremarkable.
Upon imaging at our center, we found that the fetus was small for gestational age.
Fetal Doppler examination, liquor, and activity appeared appropriate for gestational
age.
A coronal view of the fetal abdomen demonstrated the stomach bladder proximity sign
([Fig. 3A]). The axial view revealed a ventral wall defect of size 8.9 mm to the right of a
normal appearing cord insertion. Free floating loops of small bowel were seen in the
amniotic cavity ([Fig. 3B]). There was no evidence of vascular pedicle torsion ([Fig. 3C]).
Fig. 3 (A) Anterior coronal sonogram showing the stomach in contact with the bladder. (B) Free floating bowel loops in amniotic cavity. (C) Image showing superior mesenteric artery.
The final diagnosis was gastroschisis and small for gestational age. The parents were
counseled at length in the multidisciplinary meeting, postnatal surgical management,
and favorable prognosis. The patient delivered a male baby weighing 2 kg at 38 weeks
in a tertiary institution. The baby underwent surgery on day 1 of life for gastroschisis.
Postoperatively, the baby developed an intolerance to feeds, abdominal distension,
and sepsis. Another surgery was done 4 weeks later. The baby is tolerating feeds and
is being monitored in the neonatal intensive care unit.
Case 4
A 21 year old, G4P1L1A2, was referred to us at 22 weeks with suspected gastroschisis.
She had not undergone the combined first trimester screening. There was no significant
past medical or surgical history.
Examination at our center revealed a small for gestational age fetus with normal Doppler
parameters, liquor, and activity for the gestational age. The fetal kidneys appeared
echogenic with enhanced corticomedullary differentiation.
A coronal view of the fetal abdomen showed normal relative positions of the stomach,
small bowel, and bladder ([Fig. 4A]). However, an axial view of the fetal abdomen revealed a ventral wall defect measuring
6.3 mm to the right of a normal appearing umbilical cord insertion ([Fig. 4B]). Free floating loops of small bowel were seen in the amniotic cavity ([Fig. 4C]). There was no evidence of vascular pedicle torsion ([Fig. 4D]). The final diagnosis was small for gestational age, gastroschisis, and bilateral
echogenic kidneys. Amniocentesis returned negative for copy number variations. The
couple opted for the termination of pregnancy.
Fig. 4 (A) Anterior coronal plane showing the normal position of the stomach and bladder. (B) Anterior abdominal wall defect on the right side. (C) Free floating bowel loops in the amniotic cavity. (D) Image showing superior mesenteric artery.
Discussion
The International Society for Ultrasound in Obstetrics and Gynecology has described
the 20 plus 2 planes approach to the routine mid trimester scan. Its practice guidelines
recommend three axial views of the fetal abdomen: the transverse section of the upper
abdomen with stomach and umbilical vein, the transverse section of the mid abdomen
at cord insertion, and the axial view of the fetal kidneys.[3]
Suresh and Suresh recommend an additional anterior coronal plane of the fetal abdomen
in their “7 + 3 = 10” approach for the mid trimester anomaly screening.[4] This section documents the relative positions of the fetal stomach, small bowel,
and bladder in the fetal abdomen ([Fig. 5]).
Fig. 5 Well depicted anterior coronal plane of the fetus; shows the stomach, fetal liver,
gallbladder, small bowel, and bladder. Note that the stomach is spaced from the bladder
with small bowel in between.
Aiello et al. described the abnormal position of the stomach in contact with the fetal
bladder in the anterior coronal plane of the fetal abdomen as a specific sign in the
setting of stomach down left CDH in 6 of 9 cases (67%).[5] They suggested that the visualization of the stomach in contact with the bladder
may be a specific sonographic marker of left CDH.[5] This was later reiterated by Morgan et al in their study of a larger series showing
a similar incidence in 15 of 22 cases (68%).[6]
However, as shown here, the stomach bladder proximity is a nonspecific sign observed
when there is total/near total transmigration of the small bowel out of the abdominal
cavity, such as in a case of diaphragmatic hernia or severe gastroschisis. This was
alluded to later in a letter by Aiello et al.[7] Additionally, this sign may be falsely positive in advanced gestation when the fetus
assumes a flexed attitude. Therefore, when the stomach bladder proximity sign is seen,
one should initiate a systematic search for the location of the small bowel.
We acknowledge that the principal utility of this sign will be in the diagnosis of
the stomach down left CDH, as the diagnosis is often overlooked in the mid trimester
since the echogenicity of the herniated small bowel and that of the lungs may appear
similar. The utility of this sign is not so much in diagnosing gastroschisis but would
alert the inexperienced operator not to confuse the free floating bowel loops as coils
of umbilical cord. In both cases, use of color Doppler adds additional information
regarding the position and direction of the superior mesenteric artery, thus clarifying
the situation.
It is also worthwhile noting that the normal relative position of the stomach and
bladder does not always exclude abdominal defects as depicted in our fourth case.
We contemplated that the possible absence of stomach bladder proximity was related
to early gestational age of the fetus. However, our database search revealed stomach
bladder proximity as early as 20 weeks and 5 days in a case of stomach down left CDH
([Fig. 6]).
Fig. 6 Stomach bladder proximity in 20 weeks + 5 days.
The demonstration of the fetal stomach, small bowel, and bladder in their relative
positions in the anterior coronal abdominal plane is an important practical view that
can reassure the examiner to a large extent. On the other hand, when abnormal, it
also provides a clue to the abovementioned abnormalities.
