Abdominal Abnormalities (Ch. 62-63)

embryology review

• physiologic midgut herniation occurs between 8-12 weeks gestation

  • some of the bowel temporarily migrates into the base of the umbilical cord

  • around 12 weeks gestation, bowel rotates and returns back into the abdominal cavity

• if this process (normal development of abdominal wall) does not occur correctly, abdominal organs may remain at the base of the umbilical cord, leading to abdominal wall abnormalities

how to image abdominal wall

• image the cord insertion site

  • note presence/absence of defects

  • what is the relation of cord to defect?

• MC abdominal wall defects:

  • omphalocele

  • umbilical hernia

  • gastroschisis

• in presence of abdominal wall defects, look for other abnormalities

omphalocele

• during 8-12th weeks of development, fetal bowel normally migrates into umbilical cord from abdominal cavity

  • bowl-containing omphalocele occurs when bowel loops fail to return to abdomen

• intra-abdominal structures herniate into the base of the umbilical cord

  • herniation is covered by membrane that consists of amnion and peritoneum

  • cord goes through the omphalocele

• AFP is within normal limits (may be slightly elevated)

omphalocele: bowel-containing vs liver-containing

bowel-containing

• intestines fail to return

• higher risk of associated chromosomal abnormalities and other anomalies

• variable amount of bowel (only) in the herniation

liver-containing

• defect affects the abdominal wall closure (closure of muscles, fascia, and skin)

• herniation includes fetal liver and sometimes variable amount of bowel

SONO: omphalocele

• abdominal wall mass should be continuous with umbilical cord

  • Doppler to demonstrate intrahepatic umbilical vein coursing through defect

• membranous sac should be identified covering contents

  • document size; increased AC

• identify contents of membranous sac

  • bowel only; liver in and out of sac

• hydramnios is common

pathology?

omphalocele

pathology?

omphalocele

gastroschisis

• periumbilical opening in abdominal wall

  • allows for protrusion of bowel through the defect

  • herniation of bowel and, infrequently, stomach and genitourinary organs (rarely the stomach)

• defect is nearly always to the right of the umbilical cord

• umbilical cord insertion is normal

• no skin or membrane covering the defect or herniated contents

• AFP levels are significantly higher compared to omphalocele

why are AFP levels higher in gastroschisis?

because it does not have a membrane to cover the internal organs of fetus—organs are exposed

SONO: gastroschisis

• right paraumbilical defect of abdominal wall

  • rarely a left-side defect

• normal fetal cord insertion

• free-floating herniated bowel

  • other organs may be involved

  • herniated bowel may be dilated or thick-walled; may be obstructed

pathology?

gastroschisis

omphalocele vs gastroschisis summary chart

which is omphalocele? which is gastroschisis?

amniotic band syndrome (ABS)

• rupture of amnion → entrapment or entanglement of fetal parts by “sticky” chorion

  • early entrapment → severe craniofacial defects and internal malformations

  • late entrapment → amputations or limb restrictions

• increased AFP

• associated abdominal wall anomalies

  • gastroschisis; omphalocele

SONO: amniotic band syndrome (ABS)

• echogenic bands within amniotic cavity

  • follow band from uterine wall to fetal attachment

  • if bands are small, may not be able to visualize

• any missing extremities or facial deformities should raise suspicion of ABS

• document normal appearance of extremities and fetal contour

  • help to rule out ABS

limb-body wall complex

• aka body stalk anomaly, or short umbilical cord syndrome

  • extends as sheet from margin of cord

• rare malformation caused by failure of closure of ventral body wall

• involves: limb or spinal defects, wall defects, thoracic/abdominal defects, craniofacial defects, scoliosis

• left-sided body wall defects 3x more common than right-sided defects

• prognosis: fatal

SONO: limb-body wall complex

• large ventral wall defect of abdomen and thorax (usually left-sided)

• eviscerated organs form a complex mass entangled with membranes

• cranial anomalies

• limb defects

• short umbilical cord

• fetus is inseparable from placenta (fetus is right on top of it)

pentalogy of Cantrell

• rare syndrome causing defects involving 5 abnormalities:

  • anterior diaphragmatic hernia

  • high omphalocele (primary finding)

  • intracardiac defect

  • ectopia cordis (cleft defect in lower sternum)

  • defect of diaphragmatic pericardium

• prognosis: very poor

• associated with various defects

ectopia cordis

• exposed heart outside chest wall through cleft sternum

• most dramatic finding is presence of heart outside thoracic cavity

• anomalies most frequently associated with ectopia cordis:

  • omphalocele

  • cardiovascular malformations

  • craniofacial defects

Beckwith-Wiedemann Syndrome

• rare syndrome results in a grossly large fetus

• characterized by:

  • macroglossia

  • omphalocele

  • embryonic tumors

  • visceromegaly

  • macrosomia

• associated with hepatic, renal, and adrenal tumors; also ear creases

SONO: Beckwith-Wiedemann Syndrome

• large for dates fetus with enlarged kidneys, omphalocele, and macroglossia on 2nd trimester US

• may have an enlarged spleen, liver, and adrenal glands

bladder exstrophy

• defect in lower abdominal wall and anterior wall of urinary bladder

  • caused by incomplete closure of inferior part of abdominal wall

  • causes bladder to protrude outside abdomen

• defects of the urethra, bladder

• may be mild or severe (accompanied by omphalocele, inguinal hernia, undescended testes, anal problems)

SONO: bladder exstrophy

• absence of fluid-filled bladder in pelvis

• lower abdominal bulge

• cord insertion is normal or low

• kidneys and AFI usually normal

cloacal exstrophy

• more rare, complex, and more extreme

• condition occurs early in development that involves the primitive gut and persistent cloaca

• defects urethra, bladder, and bowel are present

• results in:

  • exstrophy of the bladder (with 2 hemibladders separated by muscosa)

  • omphalocele (upper part of defect)

  • lower abdominal wall defect

SONO: cloacal exstrophy

• absence of normal bladder

• lower abdominal defect

• herniation of bowel between halves of bladder

• omphalocele

liver (hepatobiliary abnormality)

• rarely affected by isolated hepatic lesions

  • if lesions seen, cysts and hemangiomas are MC

• fetal liver tumors are uncommon

  • hemangioendothelioma is MC if one is found

• liver enlarges in fetuses with Rh-immune disease in response to increased hematopoiesis

SONO: liver (hepatobiliary abnormalities)

• most fetal liver tumors appear as solid masses, sometimes with cystic components; may be calcified

• liver calcification may be observed as isolated echogenic focus

  • is usually a benign finding

  • if multiple calcifications seen within liver, other organs such as brain and spleen may be affected

spleen (hepatobiliary abnormalities)

asplenia

• absence of spleen

• accompanied abnormal positions of liver, GB, and stomach

polysplenia

• more than one spleen

• associated with situs inversus

• GB is typically absent

splenomegaly

• usually associated with Rh-immine disease

GB (hepatobiliary abnormalities)

cholelithiasis

• uncommon in fetus; usually resolve in utero or childhood

choledochal cyst

• dilation of CBD

• presents as cystic mass adjacent to GB

biliary atresia

• absence of GB

• may be associated with polysplenia

pancreas (hepatobiliary abnormalities)

• fetal pancreatic anomalies are rare

• pancreatic cysts are uncommon

  • when present, will appear as midline cystic mass

GI tract abnormalities tips

• check bowel diameter

• bowel dilation not evident until 20w

• polyhydramnios commonly with obstruction

  • why? b/c fetus can’t swallow normally due to obstruction

• lack of stomach: possible “upstream abnormality”

esophageal atresia (GI tract abnormality)

• congenital absence/blockage of esophagus

  • esophagus fails to develop as a continuous passage

  • trachea and esophagus don’t separate → fistula

• often occurs with tracheoesophageal fistula

• associated with trisomy 18, 21

• often occurs with VACTERL syndrome

what is VACTERL syndrome?

• V: vertebral defects

• A: anal atresia

• C: cardiac anomalies

• TE: tracheoesophageal fistula

• R: renal anomalies

• L: limb defects

SONO: esophageal atresia (GI tract abnormality)

• stomach not visualized

• polyhydramnios

• IUGR appearance (sometimes)

  • not always seen prenatally because TE fistula results in normal size stomach and normal AFI

duodenal atresia (GI tract abnormality)

• constricted duodenum located distal to ampulla of Vater

  • dilation of duodenum due to stenosis/atresia

  • amniotic fluid enters stomach and upper duodenum (dilation of both)

• MC bowel obstruction in fetus

• unknown cause

• associated with T21 and cardiac anomalies

• prognosis: excellent (if isolated)

SONO: duodenal atresia (GI tract abnormality)

• double bubble sign

  • dilated stomach and duodenum

• polyhydramnios

• AC will be large

small bowel atresia/obstruction (GI tract abnormality)

• congenital narrowing or obstruction of small bowel

• MC in proximal jejunum or distal ileum

• general rule: the more distal the obstruction, the less severe the polyhydramnios

• causes of fetal small-bowel obstruction

SONO: small bowel atresia/obstruction (GI tract abnormality)

• dilated loops of bowel (cystic dilation)

• persistently full stomach and dilated bowel loops

• absence of peristalsis

  • pay attention to whether or not there’s movement

• hydramnios

what do you see? pathology?

small bowel atresia/obstruction

anorectal atresia (GI tract abnormality)

• complex disorder of bowel and genitourinary tract

• imperforate anus (membrane covers anus, prohibiting expulsion of meconium—meconium cant get out)

• maybe associated with VACTERL or caudal regression

• poor prognosis

SONO: anorectal atresia (GI tract abnormality)

• fluid-filled, dilated colon

• calcified meconium

• normal AFI

  • can be decreased if renal problems are present

meconium peritonitis

• fetus has sterile chemical peritonitis secondary to in utero bowel perforation

• hydramnios present in 65% of fetuses

SONO: meconium peritonitis

• calcifications seen on peritoneal surfaces or in scrotum via processus vaginalis

• ascitic fluid may be echogenic

pathology?

meconium peritonitis

meconium ileus

• small-bowel disorder with thick meconium in distal ileum

• ileum dilates because of impacted meconium

• most infants with this have cystic fibrosis

SONO: meconium ileus

• usually apparent in 3rd trimester

• dilation of small bowel

• echogenic bowel

• calcifications may be present

hyperechoic bowel

• echogenicity similar to bone

• typically compared to iliac crest

  • grade 1: mildly echogenic and typically diffuse

  • grade 2: moderately echogenic and typically focal

  • grade 3: very echogenic, similar to that of bone structures

SONO: hyperechoic bowel

• usually apparent in the 3rd trimester

• dilation of small bowel

• echogenic bowel

• calcifications may be present

ascites

• true ascites in fetal abdomen always abnormal

• other conditions that may cause ascites to develop include bowel perforation or urinary ascites secondary to bladder rupture

SONO: ascites

• fluid collects between 2 leaves of unfused omentum → cyst-like appearance in abdomen

• ascitic fluid may be echogenic

Meckel’s diverticulum

• remnant of proximal part of yolk stalk that fails to degenerate and disappear during early fetal period

• MC malformation of midgut

• it is usually a small finger-like sac, about 5cm long, that projects from border of ileum

hydrops fetalis

• life-threatening, severe condition

• abnormal fluid builds up in two or more fetal compartments (e.g. abdomen, lungs, heart), causing total body swelling

• usually diagnosed via prenatal ultrasound and treated by addressing the underlying cause

• prognosis: poor

  • often fatal, with about 50% survival rate for live-born babies

  • high mortality rate before or shortly after birth

• tx: in-utero interventions like…

  • blood transfusions

  • draining fluids

  • early delivery

causes of hydrops fetalis

1. non-immune hydrops (NIHF): MC type, caused by heart/lung problems, genetic abnormalities, or infections like Parvovirus B19

2. immune hydrops: occurs due to Rh blood incompatibility between mother and fetus, though this is less common due to RhoGAM treatments

S/S of hydrops fetalis

• severe swelling

• severe anemia

• jaundice

• heart failure

SONO: hydrops fetalis

• fluid in abdomen (ascites)

• around the lungs (pleural effusion)

• around the heart (pericardial effusion)

• polyhydramnios

fetal anasarca

• rare, severe, often fatal form of hydrops fetalis

• characterized by massive, subcutaneous edema (fluid accumulation) in fetus

• end-stage condition featuring total body swelling, skin thickening, and often visceral effusions

  • intense. widespread swelling throughout the body—including head, limbs, torso

• typically measuring more than 5mm in tissue thickness

• associated with non-immune or immune hydrops fetalis (e.g. erythroblastosis fetalis)

• prognosis: often indicated imminent fetal death

causes of fetal anasarca

• driven by underlying factors such as…

  • severe fetal cardiovascular impairment

  • chromosomal abnormalities

  • infections

  • metabolic conditions

SONO: fetal anasarca

• in severe cases, this condition can cause serious complications such as

  • polyhydramnios

  • placental edema