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Fetal abdomen
The document provides guidelines and tips for evaluating the fetal abdomen using ultrasound, including normal anatomy, abnormalities like esophageal atresia and duodenal obstruction, and ventral wall defects like omphalocele and gastroschisis. Details are given on the ultrasound appearance, incidence, associated anomalies, and prognosis for various fetal abdominal abnormalities. Scanning tips are provided to aid in the ultrasound evaluation of the fetal abdomen.
Fetal abdomen
- 1. 7/19/2011 Ultrasound Evaluation Of the Fetal Abdomen Mani Montazemi, RDMS Director of Ultrasound Research & Education Geisinger Medical Center Danville, Pennsylvania Fetal Abdomen Current Official Practice Guideline • Abdomen – Anterior abdominal wall – Cord insertion – Stomach • Presence, size, situs – Kidneys – Bladder – Number of umbilical cord vessels Fetal Abdomen Scanning Tips Fetal Abdomen 1
- 2. 7/19/2011 Fetal Stomach • Wide range of shapes – Round to oval to kidney-shaped • Wide range of sizes – 4mm to 4cm • Variable filling and emptying – Based on fetal swallowing and peristalsis Fetal Abdomen Non-visualization of the Stomach • < 19 wks, 50% ABNL • > 19 wks, 100% ABNL Fetal Abdomen Esophageal Atresia Fetal Abdomen 2
- 3. 7/19/2011 Esophageal Atresia • Incidence – 1 in 2500 to 4000 live births • Overall detection rate – only 50% – Most of the polyhydramnios occur after 24 weeks – S ll stomach bubble could be dismissed as being Small h b bbl ld b di i d b i normal Fetal Abdomen Esophageal Atresia • Small stomach depend on the type of esophageal atresia • 5 types - most common with yp tracheoesophageal fistula – Fluid may cross the fistula – Gastric secretions may accumulate Fetal Abdomen Esophageal Atresia • High incidence of additional anomalies > 50% – Cardiac, other GI, GU track, CNS, Facial, skeletal, T18/21 • 40 % have IUGR • Incidence three times higher in twins • Classic findings – Polyhydramnios – Absent or small stomach bubble Fetal Abdomen 3
- 4. 7/19/2011 Non-visualization or Always Small Stomach (< 1cm) Causes: • High Gastrointestinal obstruction – Mouth to esophagus • Narrow/compressed chest • Thoracic or neck mass • Swallowing disorders • Defect or mass in the fetal mouth (clefts) • Severe neurologic or muscular abnormalities Fetal Abdomen What do you see? Fetal Abdomen Duodenal Obstruction Large, obstructed stomach and a distended proximal duodenum Fetal Abdomen 4
- 5. 7/19/2011 Duodenal Obstruction • Two cystic structures in the abdomen that communicate with each other – Classic “double bubble” Fetal Abdomen Duodenal Obstruction • Can be seen as early as 22 weeks, usually it’s not apparent up until 29-32 weeks • Polyhydramnios after 24 weeks – Detection rate = only 50% • Associated with a 30% incidence of trisomy 21 • Associated with VACTERL complex Fetal Abdomen VACTERL Complex Vertebral defects Anal atresia Cardiac defects Tracheoesophageal fistula Esophageal atresia Renal anomalies Limb defects Fetal Abdomen 5
- 6. 7/19/2011 Duodenal Obstruction Majority of cases are due to mechanical problems • Intrinsic causes – structural abnormalities – Atresia (42%) • half of all duodenal atresias occur with Down syndrome, although conversely, few cases of Down syndrome have duodenal atresia – Diaphragmatic web (10%) – Stenosis (38%) • Extrinsic causes – external cause – Annular pancreas – Malrotation – Ladd’s bands Fetal Abdomen Duodenal Obstruction • Prognosis is dependent upon whether other anomalies are present and their severity Fetal Abdomen Polyhydramnios is a constant feature in all intestinal atresia Fetal Abdomen 6
- 7. 7/19/2011 Ventral Wall Defects Omphalocele Gastroschisis – Central defect – Periumbilical defect – Associated anomalies are common – Associated anomalies are uncommon – High risk of aneuploidy – Little to no risk of aneuploidy – High rate of bowel related complications – Associated with substance abuse & medications Fetal Abdomen Omphalocele • Herniation of intraabdominal contents into the base of the cord • ALWAYS covered by a membrane Fetal Abdomen Omphalocele • Umbilical cord inserts onto membrane – In large defects may be displaced eccentrically • The herniated bowel is NOT directly exposed to amniotic fluid • Bowel usually does not thicken or dilate Fetal Abdomen 7
- 8. 7/19/2011 Is This an Omphalocele? Fetal Abdomen Pseudo-Omphalocele Caused by scanning oblique or by excessive transducer pressure Fetal Abdomen Omphalocele Can be a small or large wall defect Fetal Abdomen 8
- 9. 7/19/2011 Omphalocele • Small – Failure of normal midgut rotation – Cord midpositioned – Usually Us all contains onl bowel only bo el – Associated with chromosomal anomalies Fetal Abdomen Omphalocele • Large – Failure of anterior abdominal wall closure – Cord eccentric – May contain organs – Scoliosis – Associated with structural anomalies Fetal Abdomen Omphalocele Measurements of AC inaccurate and should be excluded from biometric calculations Fetal Abdomen 9
- 10. 7/19/2011 Omphalocele • IUGR has been reported in 20% of patients • 50% have associated anomalies (20% cardiac) • 30% are associated with trisomy 13 & 18 • Elevated maternal serum alpha-fetoprotein (70%) Fetal Abdomen Omphalocele • Omphalocele and cord cyst may co-exist – Whartons jelly cyst – mucoid degeneration of Wharton Jelly – Allantoic cyst – always near insertion site – Omphalomesenteric duct cyst – associated with intraabdominal mesenteric cysts Jane J.K. Burns, RDMS Fetal Abdomen Diagnostic Challenge Separate from but contiguous with the bladder Fetal Abdomen 10
- 11. 7/19/2011 Patent Urachus With Allantoic Cyst Urachus is an embryological remnant of the allantois which runs from the apex of the bladder through the umbilical ring to terminate in the proximal umbilical cord Yolk Stalk Allantoic Stalk Umbilical Cord Cloaca Fetal Abdomen A Ruptured Omphalocele Can Resemble Gastroschisis Fetal Abdomen Omphalocele @11 Weeks ? Potential Pitfall Fetal Abdomen 11
- 12. 7/19/2011 Normal Midgut Herniation • Fetal bowel normally herniates into the base of the umbilical cord at approx. the 7-8 weeks MA • Detected sonographically from 9-11 wks 9 11 • Should not be visible by 12 week “Possible Anomaly” CRL > 44mm with persistent herniation Maximum dimension of abdominal mass > 7mm Fetal Abdomen Normal Midgut Herniation • This appearance should not be mistaken for a ventral wall defect Fetal Abdomen Midgut (umbilical) herniation beyond the 12th week of gestation has to be considered pathological Fetal Abdomen 12
- 13. 7/19/2011 Gastroschisis Small defect to right of cord insertion No membrane over bowel Fetal Abdomen Gastroschisis • Incidence is 1 in 3000 births – Varies considerably with maternal age – Strong association reported among younger patients • Less likely for organ herniation • Variable amounts of bowel herniated • Bowel floats within amniotic fluid Fetal Abdomen Gastroschisis • Hepatic herniation is less frequent with gastroschisis than with omphaloceles Fetal Abdomen 13
- 14. 7/19/2011 Gastroschisis • Small defect (2-4cm) Fetal Abdomen Gastroschisis • Associated anomalies in about < 10% of fetuses • IUGR in up to 50% • No chromosomal abnormalities • Elevated maternal serum alpha-fetoprotein (70%) alpha fetoprotein Fetal Abdomen Gastroschisis • Oligohydramnios – More common than polyhydramnios – Suggest fetal distress • Polyhydramnios – Suggest bowel obstruction or atresia Fetal Abdomen 14
- 15. 7/19/2011 Gastroschisis • Marked bowel dilatation, which may be either external or internal to the abdominal cavity, suggests bowel obstruction and/or ischemia Fetal Abdomen Gastroschisis • Bowel can twist and cut off blood supply Fetal Abdomen Gastroschisis Fetal Abdomen 15
- 16. 7/19/2011 Gastroschisis Fetal Abdomen Gastroschisis Fetal Abdomen Ectopic Cordis “Large omphalocele coming all the way to heart” • Rare malformation • Protrusion of heart through chest wall • Association - Pentalogy of Cantrell Fetal Abdomen 16
- 17. 7/19/2011 Pentalogy of Cantrell A term used to describe the association of 5 anomalies: 1. Midline supraumbilical abdominal defect 2. Defect of the lower sternum 3. 3 Defect of the diaphragmatic pericardium 4. Anterior diaphragmatic hernia 5. Intracardiac abnormalities Fetal Abdomen Pentalogy of Cantrell – US Findings • Midline anterior wall defect usually upper abdomen • Ectopic heart • Pericardial or pleural effusion • Craniofacial anomalies • Ascites • Two vessel cord Fetal Abdomen Limb-Body Wall Complex • Also known as “body stalk” anomaly • Failure of ventral abdominal wall to close – Often left sided Jane J.K. Burns, RDMS Fetal Abdomen 17
- 18. 7/19/2011 Limb-Body Wall Complex • Abdominal organs lie in a sac outside the abdominal cavity • Short or absent umbilical cord • Fetus lies directly on placenta* • Universally fatal Fetal Abdomen Limb-Body Wall Complex • Amniotic bands attached broadly to the fetus & placenta • Large thoraco-abdominal wall defect – no covering membrane • Distorted body axis Jane J.K. Burns, RDMS Fetal Abdomen Limb-Body Wall Complex • Severe scoliosis – prominent feature • Limb defects common • Complex array of multiple malformations – Craniofacial & Internal organ anomalies Fetal Abdomen 18
- 19. 7/19/2011 Bladder & Cloacal Exstrophy • Failure of closure of lower abdominal wall resulting in exposed bladder • Omphalocele • Absent bladder • Imperforate anus • Spinal abnormalities • Malformation of the genitalia • Single umbilical artery Fetal Abdomen Bladder Exstrophy • 2o to abnormal development of the cloacal membrane • Incidence is 1:30,000 births • Eversion & exteriorization of the pelvic viscera on the abdominal surface – Inferiorly displaced umbilicus – Widely separared pubic bones Reports of T21 & 13 Fetal Abdomen Bladder Exstrophy – US Findings • Non-visible bladder • Normal kidneys • Normal amniotic fluid volume • Low CI • Bulging mass protruding from the lower abdominal wall • Small penis • Splayed iliac bones Fetal Abdomen 19
- 20. 7/19/2011 Cloacal Exstrophy Omphalocele & bladder extrophy with prolapsed ileum between the two bladder halves Fetal Abdomen Ventral Wall Defects Relation to Umbilicus • Above umbilicus – Consider pentalogy of cantrell • At umbilicus – C id gastroschisis or omphalocele Consider hi i h l l • Below umbilicus – Consider exstrophy of bladder or cloaca • Difficult to tell because of size – Consider body stalk anomaly Fetal Abdomen Normal Appearance of Bowel • Amniotic fluid is swallowed & as it gets to the small bowel it mixes with bowel mucopolysaccharide • Moves to the large bowel – water is resorbed, leaving meconium • Meconium is expelled at birth • If there is obstruction or if meconium is abnormally thick that wouldn’t pass it causes obstruction in the bowel – meconium ileus Fetal Abdomen 20
- 21. 7/19/2011 Normal Appearance of Bowel • Meconium – Variable in echogenicity (hypo to hyperechoic), can be seen throughout the later part of pregnancy, particularly in late 3rd trimester Fetal Abdomen Hyperechoic Bowel What Does That Mean? Fetal Abdomen Hyperechoic Bowel • Increased echogenicity of the mesentery and small bowel walls The bowel itself is not echogenic Fetal Abdomen 21
- 22. 7/19/2011 Hyperechoic Bowel • Often normal variant – Related to higher frequency transducers and to images with greater contrast Fetal Abdomen Fetal Abdomen Echogenic Fetal Bowel • Abnormal if – > 4 cm in size – May have mass effect – Homogeneous heterogeneo s Homogeneo s or heterogeneous – Brightness > bone (femur, spine, iliacs) Fetal Abdomen 22
- 23. 7/19/2011 Echogenic Fetal Bowel • Seen in association with: – Cystic fibrosis, trisomy 21, cytomegalovirus (CMV), parvo virus (5th disease), GI obstruction and IUGR Fetal Abdomen Echogenic Bowel • Swallowed blood (intra-amniotic hemorrhage) 4 days post-amniocentesis Fetal Abdomen Meconium Peritonitis • Leaking of bowel contents leading to an intense peritoneal reaction Fetal Abdomen 23
- 24. 7/19/2011 Meconium Peritonitis • 50% have underlying bowel pathology Fetal Abdomen Meconium Peritonitis • Calcifications 85% – Usually punctate, linear or clumped foci Fetal Abdomen Meconium Peritonitis • Calcifications 85% – Usually punctate, linear or clumped foci • Ascities 54% – U ll complex Usually l Fetal Abdomen 24
- 25. 7/19/2011 Meconium Peritonitis • Calcifications 85% – Usually punctate, linear or clumped foci • Ascities 54% – U ll complex Usually l • Bowel dilatations 27% Fetal Abdomen Meconium Peritonitis • Calcifications 85% – Usually punctate, linear or clumped foci • Ascities 54% – U ll complex Usually l • Bowel dilatations 27% • Pseudocysts 14% • Polyhydramnios 65% Fetal Abdomen Meconium Peritonitis • Calcifications can extend to thorax Fetal Abdomen 25
- 26. 7/19/2011 Meconium Peritonitis • Calcifications can extend to scrotal sac Fetal Abdomen Abdominal Calcifications • Infections: herpes, toxoplasmosis, cytomegalovirus • Tumors: teratoma, hepatoblastoma, neuroblastoma • Peritonitis: meconium leak • Infarcted bowel • Gallstones • Idiopathic Fetal Abdomen Small & Large Bowel Obstruction Obstructions below the duodenum are even harder to diagnose Fetal Abdomen 26
- 27. 7/19/2011 Small Bowel Obstruction • Jejunal & ileal obstruction is more common than duodenal obstruction! – Vascular injury • Small bowel loops can be seen specially in 3rd trimester Fetal Abdomen Small Bowel Obstruction • They peristalsis and change in configuration • Do not persist, and should not be >15 mm in length and 7 mm in diameter • Can rarely present as cyst like mass • Polyhydramnios – Timing & severity dependent Small bowels are on site of atresia centrally located Fetal Abdomen Small Bowel Obstruction Causes: • Intestinal atresia – Related to an in utero vascular accident • Stenosis • Volvulus • Meconium ileus – In fetuses with cystic fibrosis Fetal Abdomen 27
- 28. 7/19/2011 Pitfalls • Different processes can be mistaken for dilated small bowel – Cysts in an enlarged multicystic displastic kidney – Dilated tortuous ureter Fetal Abdomen Large Bowel Obstruction • Normal large bowel < 20 mm diameter • Rare - It occurs at the anal-rectal region • Additional structural & chromosomal anomalies are very common (75%) – VACTERL & caudal regression syndrome Causes: • Atresia • Stenosis Fetal Abdomen Solid Abdominal Masses Mesoblastic nephroma Neuroblastoma Hepatoblastoma Subdiaphragmatic extralobar Fetal Abdomen pulmonary sequestration 28
- 29. 7/19/2011 FetalAbdomen Abdominal Cysts Differential Diagnosis • RUQ – Hepatic/choledochal cyst • LUQ – Splenic cyst • Posterior – Renal cyst, hydronephrosis cyst • Anterior/mid-abdomen – Mesenteric cyst, umbilical vein varix • Lower abdomen – Ovarian cyst (but may migrate to mid-abdomen) – Ureterocele – Urachal cyst – Hydrometrocolpos Fetal Abdomen Diagnostic Challenge Fetal Abdomen 29
- 30. 7/19/2011 Diagnostic Challenge Fetal Abdomen There is Flow! Is it venous or arterial? Fetal Abdomen Umbilical Vein Varix • Focal dilatation of umbilical vein • Usually intraabdominal but extrahepatic may occur in association with persistent right umbilical vein • It may also occur in free floating loops of cord • Umbilical vein varix of intra-amniotic segment is rarer than intra-abdominal Fetal Abdomen 30
- 31. 7/19/2011 Umbilical Vein Varix • Focal dilatation of intra-abdominal portion – Usually near cord insertion – Abnormal if internal diameter > 9 mm or twice size of intrahepatic portion of vein – Normal size at week 20 is 3-4 mm with linear increase up 34 to 8 mm at term Fetal Abdomen Umbilical Vein Varix Fetal Abdomen Umbilical Vein Varix • Can be associated with: – Chromosome abnl (T-21, 18, 9) – Congenital malformations – Decreased growth – Hydrops H d – Thrombosis • May be first manifestation of elevated venous pressure therefore may signify increased risk of cardiac decompensation • As isolated finding: normal outcome Fetal Abdomen 31
- 32. 7/19/2011 Choledochal Cyst • Cystic dilatation of the CBD • Separate from gallbladder • No communication with stomach Fetal Abdomen Abdominal Cysts Fetal Abdomen Abdominal Cysts • Lower abdomen – Female: think ovarian: may migrate/auto-amputate • Torsion in ~ 40 % if > 5 cm Fetal Abdomen 32
- 33. 7/19/2011 Thank You Fetal Abdomen 33