Ch 10 Abdomen Flashcards
By what trimester have the fetal abdominal organs attained their normal adult position + structure?
Early in the 2nd trimester
List the landmarks for the right + left parasagittal views?
RT: lung, liver + right kidney
LT: stomach + left kidney
What echogenicity is the fetus’s skin + muscles?
Skin: echogenic
Muscles: hypoechoic (can be confused with ascites - pseudoascites)
Which arteries carry most of the fetal aortic blood to the placenta?
2 umbilical arteries
The 2 umbilical arteries can be followed caudad from the anterior abdominal wall cord insertion site to which arteries?
To the internal iliac arteries (which are just lateral to the bladder)
What 4 structures develop from the embryonic foregut?
-Liver
-GB
-Ducts
-Pancreas
In the 4th week, what develops on the caudal portion of the foregut?
An outgrowth
When does rapid growth of the liver occur?
From 5-10th week - this results in the liver occupying most of the abdominal cavity
What percentage of total weight does the liver make up in the 2nd trimester + at term?
2nd trimester: 10%
Term: 5%
Bile secretion begins in what week?
12th week
During what week does the liver look bright red due to the start of hematopoiesis?
6th week
Is the GB passive or active in fetal life?
Passive - it does not respond to fat ingested by the mother
Where is the GB in a fetus?
To the right of midline - it separates the right lobe from the medial left lobe (as does the middle HV)
How can we differentiate the GB from the tubular intrahepatic portion of the umbilical vein?
CD (the GB should have no color flow)
List 4 ways the GB can be distinguished?
-Teardrop shape
-Off midline position (to the right of it)
-Extrahepatic location (posteroinferior to liver)
-Lack of communication b/w GB + vessels of umbilical cord
Does the umbilical vein or GB reach the anterior abdominal wall?
Umbilical vein does, GB does not
What is the echogenicity of the pancreas + spleen?
Pancreas: hyperechoic
Spleen: hypoechoic
(these are rarely discretely imaged)
What can help aid in the identification of the pancreas?
The stomach + the location of the pancreas being anterior to the splenic vein
Is the pancreas echogenicity slightly greater or less than the liver?
Greater
List 3 ways we can help identify the spleen?
-Is homogeneous, posterior to stomach + superior to LK in left upper abdomen
-Best seen on TRV scans
-Is similar in echogenicity to kidney + slightly less echogenic than liver
Does an absent stomach require a follow up?
Yes - the stomach periodically fills + empties but it must be seen throughout the exam
What causes echoes in the stomach?
Hyperechoic debris - is a normal finding
(m/c seen in the 2nd trimester + disappears on follow up exams)
Echogenicity within the stomach has been seen in cases of 3rd trimester ____ ____?
Placental abruption
(may represent swallowed blood or vernix)
Before fluid enters the small bowel, how will it appear?
As a heterogeneous, echogenic pseudomass w/o shadowing (occupies a substantial portion of abdomen)
What is the echogenicity of small bowel?
-More echogenic than liver, but less echogenic than bones
-Becomes less echogenic in 3rd trimester + more sharply defined
Where may peristalsis be seen?
In small bowel that occupies central abdomen
Does normal small bowel increase or decrease in diameter as gest age increases?
Increases
What is the colon?
Long, continuous, tubular structure with a hypoechoic lumen at the abdominal periphery
In what trimester is the colon seen?
As early as the late 2nd trimester, but more consistently seen in 3rd trimester
Does the colon increase or decrease in diameter throughout the 3rd trimester?
Increase
How can we tell if we are looking at the colon or cysts?
If it is all linked together than it is bowel
What is meconium composed of?
The materials the fetus ingests during gestation (mucous, amniotic fluid, bile, etc)
What is the echogenicity of meconium?
Less echogenic than bowel walls
(may be seen in discrete portions of the colon)
Colon with liquid meconium in it is often mistaken for what anomalies?
Cysts, dilated bowel, etc.
The 2 m/c types of abdominal wall defects are?
-Omphalocele
-Gastroschisis
What type of malformations are one of the sources of elevated AFP levels in the amniotic fluid or maternal serum?
Abdominal wall malformations
What is an omphalocele?
Midline defect occurring in 1 in 4,000 births
A normal migration of bowel into the umbilical cord occurs during which weeks of embryologic development?
B/w 8-12 weeks
Sometimes bowel does not migrate back into the abdomen + remains in extraembryonic coelom of umbilical cord. Explain what type 1 + type 2 are?
Type 1: fusion failure of lateral ectomesodermal folds
Type 2: failure of muscle, fascia + skin to fuse
(omphalocele)
List 4 SFs for an omphalocele?
-Abdominal viscera
-Bowel protruding into base of cord
-Can range from 2-10cm in size
-Always covered by a membrane + centrally located
A definitive 1st trimester diagnosis of an omphalocele is only made when?
The omphalocele is larger than the abdomen itself
An omphalocele may be suggested in pregnancy if the cord containing the midgut has a max dimension of what?
7mm or greater
Are omphaloceles associated with other anomalies?
Yes 50-70% are, which worsen the prognosis
GI anomalies are found in 30-50% of omphaloceles, which anomaly is m/c?
Bowel malrotation
40-60% of pt’s with omphaloceles have chromosomal abnormalities. Which ones?
-Trisomy 13, 18 + 21
-Turner, Klinefelter + triploidy syndromes
Is there skin surrounding an omphalocele?
No! The abdominal wall has parted. The omphalocele is covered by a thin translucent membrane.
Is an umbilical hernia covered by skin?
Yes! Completely covered by skin + subcutaneous tissue.
What is the distinguishing feature of an umbilical hernia vs an omphalocele?
Position of cord insertion:
Hernia = alongside cord
Omphalocele = in cord
What is gastroschisis?
Smaller abdominal wall defect measuring 2-4cm + m/c occurs to the right of the cord insertion
(is unrelated to the umbilical cord)
Do younger or older mothers m/c have fetus’s with gastroschisis?
Young - 1 in 3,000 pregnancies
The maternal use of what substances cause increased risk of fetal gastroschisis?
Vasoactive substances like nicotine + cocaine
Except for bowel malrotation + jejunal or ileal atresia, associated anomalies with gastroschisis are m/c related to what?
Vascular compromise of the malrotated bowel + are way less common than with an omphalocele
Is AFP increased or decreased with gastroschisis?
Increased - due to direct contact of bowel with amniotic fluid
How early can we detect gastroschisis on u/s?
As early as 14-16 weeks, b/c of the free floating loops of bowel within the amniotic fluid
Gastroschisis causes what 2 things to occur due to the lack of internal organs?
-Right sided cord insertion
-Small AC
(mass is not associated with umbilical cord)
Does gastroschisis occur with other anomalies outside of bowel malformations?
No, rarely
Are the survival rates high or low with gastroschisis?
High - 85-95%
Differentiate b/w an omphalocele, umbilical hernia + gastroschisis?
Hernia: covered by skin + subcutaneous tissue, is located to the side of cord
Omphalocele: covered by translucent membrane, is located in base of cord
Gastroschisis: not covered by any membrane, free floating bowel, m/c to the right of the cord
Ascites represents what?
Fluid within peritoneum
Is true fetal ascites always abnormal?
Yes!
-Large amounts can surround + shift intraperitoneal structures superiorly, inferiorly or laterally
Urinary ascites results from what?
-Bladder outlet obstruction
or
-Renal forniceal rupture
List 4 conditions that can cause ascites?
-Heart failure
-Infections
-Tumors
-Twin to twin transfusions
The liver enlarges in association with what?
Immune or nonimmune hydrops
(result of increased hematopoiesis)
What would cause fetus to have a small or large liver?
Small: IUGR
Large: diabetic mothers + macrosomic fetus’s
Why might solitary liver cysts develop?
B/c of interruption of the development of the intrahepatic biliary tree
Diffuse liver calcifications occur in fetus’s with what?
Intrauterine infections
(especially TORCH infections, toxoplasmosis + herpes simplex infection)
Will gallstones in fetus’s always have posterior shadowing?
No
Do fetal gallstones usually resolve?
Yes, possibly due to postnatal hydration or from changes in bile metabolism
In some cases fetal gallstones are not true gallstones, what are they?
Tumefactive sludge or thickened bile
Rapid growth/proliferation of the esophageal epithelium during the embryonic period creates an almost complete closure of what structure?
The esophageal lumen
Esophageal atresia is m/c in male or female infants?
Male
What is the m/c type of esophageal atresia?
-It consists of a proximal esophageal pouch that communicates with the more distal GI tract through a fistula
-The fistula follows a track b/w the tracheobronchial tree (near tracheal bif) + the distal esophagus which allows amniotic fluid to pass into stomach
-Communication with the distal GIT reduces # of fetuses with polyhydramnios b/c of impaired swallowing
-Associated with trisomy 21
What 2 factors may cause an absence of stomach fluid?
-Oligohydramnios
-Stress of nonimmune hydrops
If there is no stomach, or an unusually small stomach, after 18 weeks with normal amniotic fluid levels what is this associated with?
A guarded prognosis
(meaning we do not have enough information to know what the outcome will be)
If we can’t identify the stomach during the exam, this raises suspicion for what abnormality?
Chromosomal abnormalities (however m/c the fetus has a normal karyotype)
What is a volvulus?
An obstruction caused by bowel twisting upon its blood supply
If the sm bowel fails to return to the abdominal cavity + rotate properly, the bowel may twist around the axis of which artery?
The SMA - resulting in poor vascular flow distal to the point of obstruction or volvulus
When is midgut volvulus usually diagnosed?
In first days of life
(infant may present with distention or obstruction, but m/c with bilious vomiting)
What is the whirlpool sign?
A fluid-filled proximal duodenum with an arrowhead twist at the point of the descending or TRV duodenal obstruction
Fluid filling the stomach + duodenum at the site of obstruction creates what classic sign?
The double-bubble sign - represents duodenal atresia + is m/c associated with trisomy 21
What is duodenal atresia?
Failure of duodenum to change from a solid cord of tissue during development to a tube
List the 3 types of duodenal recanalization anomalies?
-Duodenal diaphragm or web (resulting in stenosis)
-Solid cord with atresia
-Segmental or partial absence of duodenum
What type of tissue may surround the 2nd portion of the duodenum, causing obstruction or stenosis?
Pancreatic tissue
What is the m/c echogenic mass found in the fetal abdomen?
Echogenic bowel
(m/c found in 2nd trimester, 50% resolve spontaneously)
What trimester is echogenic bowel considered a normal finding?
In late 3rd trimester - b/c of presence of meconium in bowel
Bowel echogenicity greater than bone indicates greater risk for meconoium ileus/cystic fibrosis + other pathologic processes. What does this cause an increased association with?
-Fetal demise
-IUGR
(follow these fetuses closely)
List what grade 1, 2 + 3 mean for echogenic bowel?
1: bowel is NOT as bright as bone (normal)
2: bowel is AS bright as bone (moderate)
3: bowel is BRIGHTER than bone (worst)
How can we differentiate the GB from the umbilical vein?
GB has teardrop shape, it does not reach abdominal wall, use CD
T/F: An omphalocele is covered by skin + subcutaneous tissue?
False: they are covered by a membrane (peritoneum/amnion)
When assessing for echogenic bowel, how can you be sure it is truly echogenic?
Compare to nearby bone + do split screen image while turning gains down (to compare echogenicity of bowel to bone)
