chapter 62 reverse Flashcards
bile formation by hepatic cells begin when
12 wks
the midgut is suspended by
elongated dorsal mesentery
The Hindgut is supplied by
inferior mesenteric artery
Stomach should be seen by
14 to 16 weeks
Echogenic debris may sometimes be seen along dependent wall of stomach
Vernix
If stomach seen in right upper quadrant, condition is called
situs inversus
If fetus is in vertex presentation with spine up, both aorta and stomach should be seen to left of spine
Stomach
can be visualized in thorax during second and third trimesters as two or more parallel echogenic lines (“multilayered” pattern)
Normal esophagus
Measured at level of portal sinus and umbilical portion of left portal vein (“hockey stick” appearance on sonogram)
Abdominal Circumference
Abdominal circumference should be round, not oval.
Abdominal Circumference
Joins umbilical portion of left portal vein at caudal margin of left intersegmental fissure of liver
Umbilical Cord Insertion
Visualization of insertion site must be made to rule out presence of omphalocele, gastroschisis, hernia, and mass formation.
Umbilical Cord Insertion
Movement of gastric musculature begins in
approximately fourth to fifth month of gestation
After 15th to 16th week, meconium begins to accumulate in distal part of small intestine
Bowel
Appears as ill-defined area of increased echogenicity in mid to lower abdomen
Bowel
Hyperechoic appearance could be secondary to reflections from walls of collapsed loops of small bowel or from mesenteric fat between loops
Bowel
As pregnancy progresses: Hyperechoic area becomes less prominent Small bowel located more centrally in abdomen than colon
Bowel
Normal diameter of small bowel lumen ≤5 mm, with length of 15 mm near term
bowel
Haustral folds of colon help to differentiate it from small bowel
Bowel
In early gestation, haustral folds appear as thin linear echoes within lumen of colon Later, colon diameter increases and folds become longer and thicker
Bowel
Colon seen near end of second trimester as long tubular hypoechoic structure with well-defined walls
Bowel
Normal measurements of colon diameter range from 3 to 5 mm at 20 weeks to 23 mm or larger at term
Bowel
does not have peristalsis like small bowel
Colon
more peripheral than small bowel
Colon
After 14 weeks of gestation, lipid absorbed from fetal colon and remaining contents collect in colon as meconium
Bowel
hypoechoic relative to fetal liver and in comparison with bowel wall
Meconium within lumen of colon
Accounts for 10% of total weight of fetus at 11 weeks and 5% of total weight at term
Liver
Left lobe of liver larger than right in utero secondary to greater supply of oxygenated blood Reverses after birth
Liver
Distinguished by location to right of portal-umbilical vein and as oblong, more oval structure than “tubular” intrahepatic umbilical vein
Gallbladder
Lies in the retroperitoneal cavity anterior to the superior mesenteric vessels, aorta, and inferior vena cava (IVC)
Pancreas
Normal fetal pancreas has been seen in utero but is more difficult to routinely visualize because of the lack of fatty tissue within the gland
Pancreas
Homogeneous in texture Similar in echogenicity to kidney Slightly less echogenic than liver Increases in size during gestation Imaged on transverse plane posterior and to left of fetal stomach
Spleen
Is involved in several congenital anomalies but rarely affected by isolated hepatic lesions
Abnormalities of the Hepatobiliary System
Liver parenchymal cysts and hemangiomas of liver have been reported. Enlarges in fetuses with Rh-immune disease in response to increased hematopoiesis
Abnormalities of the Hepatobiliary System
Liver tumors, hamartoma, hepatoblastoma uncommon but may be seen
Liver
Hemangioendothelioma Most common symptomatic, vascular hepatic tumor of infancy (although rare) May cause nonimmune hydrops in fetus
Liver
Sonographic Findings of the liver
Most liver tumors appear as hypoechoic solid masses; cystic components have also been reported as mixed with solid masses
Partial situs divided into asplenia and polysplenia
Situs Inversus
Choledochal cyst (dilation of CBD) may be diagnosed when
cystic mass identified adjacent to fetal stomach and gallbladder
Agenesis of gallbladder occurs in approximately
20% of patients with biliary atresia
Absence of gallbladder can occur in association with
polysplenia and rare multiple anomaly syndromes
Combination of polyhydramnios and absent stomach over repeated studies may be suggestive of
esophageal atresia
In >50% of cases, stomach present because fistula usually present that leads to fluid filling stomach
Esophageal Atresia
About 30% of fetuses with duodenal atresia have
trisomy 21 (Down syndrome)
Anomalies occur in approximately with duodenal atresia
50%
Occurs in 1 in 3000 to 5000 live births; thought to be secondary to vascular accident, volvulus or gastroschisis or be sporadic
Bowel Intestinal Obstructions
Meconium begins to accumulate in the fetal bowel in the second trimester, at which time it can be seen sonographically as tiny echogenic reflections within the peristaltic small bowel.
Meconium Ileus
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.
Ascites
Pharynx Lower respiratory system Esophagus Stomach Part of the duodenum Liver and biliary apparatus Pancreas
foregut
Results from abnormal deviation of tracheoesophageal septum in posterior direction
Esophageal atresia
Appears as fusiform dilation of caudal part of foregut During fifth and sixth weeks, dorsal border (greater curvature) grows faster than ventral border (lesser curvature)
Stomach
Develops from caudal part of foregut and cranial part of midgut Comes to lie primarily in retroperitoneum
Duodenum
Liver, gallbladder, biliary ducts arise as bud from most caudal part of foregut in fourth week
Liver and Biliary System
(blood formation) begins during sixth week
Hemopoiesis
Blockage of bile ducts results from failure to recanalize following solid stage of development
Extrahepatic biliary atresia
Develops from dorsal and ventral pancreatic buds of endodermal cells that arise from caudal part of foregut
Pancreas
Lymphatic organ derived from mass of mesenchymal cells located between layers of dorsal mesogastrium
Spleen
Small intestines Cecum and cloaca exstrophy Ascending colon Most of transverse colon
The Midgut
All structures supplied by superior mesenteric artery
The Midgut
Usually by 10th or 11th week, midgut herniation returns to abdomen
The Midgut
Is usually located to right of umbilical cord
Gastroschisis
Forms when: Intestines return normally to abdominal cavity Herniate either prenatally or postnatally through inadequately closed umbilicus
Umbilical Hernia
Is the most common malformation of midgut Remnant of proximal part of yolk stalk that fails to degenerate and disappear during early fetal period
Meckel’s Diverticulum
Derivatives of hindgut: Left part of transverse colon Descending colon Sigmoid colon Rectum Superior portion of anal canal Epithelium of urinary bladder Most of urethra
The Hindgut
Central nervous system problem (swallowing disorders) Obstruction Oligohydramnios Atresia
if stomach is not seen RO
Distinction of large bowel from small bowel possible after 20 menstrual weeks
Bowel
After 27 weeks
peristalsis occurs
Relatively large compared with other intraabdominal organs Occupies most of upper abdomen in fetus
Liver
Hepatic veins and fissures formed by end of first trimester
Liver
May be seen sonographically after 20 weeks of gestation
Gallbladder
Normal fetal pancreas has been seen in utero but is more difficult to routinely visualize because of the lack of fatty tissue within the gland
Pancreas
Is more severe disorder May develop in two different combinations of organ reversals Thoracic viscera usually reversed Abdominal viscera may or may not be reversed
Partial situs inversus
At least two spleens present along greater curvature of stomach Heart block common in polysplenia syndrome
Polysplenia
Cardiac malformations common (99%) in asplenia syndrome; are seen with less frequency in polysplenia syndrome (90%)
Situs Inversus
Endocardial cushion defects Hypoplastic left heart Transposition of great vessels
Cardiac defects of situs inversus
usually has normal outcome
total situs inversus
extremely high; death occurs in 90% to 95% with asplenia syndrome and 80% with polysplenia syndrome
Mortality rate for partial situs inversus
right-sided heart axis and aorta; transposition of liver, stomach, spleen; left-sided gallbladder)
Total situs inversus
(right-sided stomach, left-sided liver); dextrocardia with normal stomach position (see previous section)
Partial situs inversus
Genitourinary Gastrointestinal Liver Cardiac Infections Metabolic storage disorders Idiopathic
Causes of Ascites
Cholelithiasis (gallstones)
identified in fetus when calcifications are found within gallbladder.
Develop when portion of bowel grows and infarcts Occurs anywhere in gastrointestinal tract Polyhydramnios evident on ultrasound
Atresias
back-up of amniotic fluid and hydramnios
Blockage results in
Most common form occurs in conjunction with a fistula, communicating between trachea and esophagus (tracheoesophageal fistula). allows passage of amniotic fluid into stomach
Esophageal Atresia
Gastric secretions may contribute to stomach fluid
Esophageal Atresia
Hydramnios may exist from impaired reabsorption of swallowed fluid and be associated with esophageal atresia; usually does not develop until third trimester
Esophageal Atresia
Growth restriction present in 40% of cases Chromosomal trisomies (18 and 21) reported Coexisting anomalies common in 50% to 70% of fetuses with esophageal atresia
Esophageal Atresia
Blockage of duodenal lumen by membrane that prohibits passage of swallowed amniotic fluid
Duodenal Atresia
Two echo-free communicating structures (stomach and duodenum) found in upper fetal abdomen Sonographic appearance termed “double bubble sign” Hydramnios almost always seen with duodenal atresias later in pregnancy
Duodenal Atresia Sonographic Findings
Duodenal atresia Duodenal stenosis Annular pancreas Ladd’s bands Proximal jejunal atresia Malrotation Diaphragmatic hernia
Causes of Double Bubble
Atresia or stenosis of jejunum or ileum, or both, and small bowel atresia slightly more common than duodenal atresia
Bowel Intestinal Obstructions
(jejunoileal atresia or stenosis) appears as multiple cystic structures (more than two) proximal to site of atresia within fetal abdomen
Blockage of jejunum and ileal bowel segments
General rule: The more distal the obstruction, the less severe the hydramnios, and the later it will develop.
Bowel Intestinal Obstructions
Malrotation Atresias Volvulus Peritoneal bands Cystic fibrosis Dilated bowel loops isolated or associated with other anomalies, ascites, or meconium peritonitis
Causes of fetal small-bowel obstruction include:
Intestinal obstructions appear as cystic bowel loops discontinuous with stomach Fetal intestinal obstruction should be suspected when clear cystic structures found in pelvis Vascular restriction may lead to obstruction secondary to gastroschisis
Sonographic Findings
Is a small-bowel disorder marked by presence of thick meconium in distal ileum
Meconium Ileus
10% to 15% of patients; is third most common form of neonatal bowel obstruction after atresia and malrotation
Earliest manifestation of cystic fibrosis occurring (%)
The anal sphincter prevents the passage of meconium (meconium plug) into the amniotic fluid, unless the fetus is stressed or traumatized.
Meconium Ileus
Ileum dilates because of impacted meconium (which appears echogenic) Increased production of mucus by GI organs and electrolyte imbalance explains overproduction of meconium (characteristic of cystic fibrosis)
Meconium Ileus Sonographic Findings
Presents as complex disorder of bowel and genitourinary tract Imperforate anus is disorder that occurs when membrane covers anus, prohibiting expulsion of meconium
Anorectal Atresia
Megacolon is congenital disorder in which there is abnormal innervation of large intestine
Hirschsprung’s Disease
Condition that may arise when fetus has sterile chemical peritonitis secondary to in utero bowel perforation Hydramnios present in 65% of fetuses
Meconium Peritonitis
Calcifications seen on peritoneal surfaces or in scrotum via processus vaginalis Ascitic fluid may be echogenic. Is unusual to see calcification in meconium ileus in fetus with cystic fibrosis
Sonographic FindingsMeconium Peritonitis
Grade 1: Mildly echogenic and typically diffuse Grade 2: Moderately echogenic and typically focal Grade 3: Very echogenic; similar to that of bone structures
Hyperechoic Bowel
poor in nonimmune hydrops
Prognosis is
