Dilated Bowel



Dilated Bowel


Paula J. Woodward, MD



DIFFERENTIAL DIAGNOSIS


Common



  • Normal Third Trimester Bowel


  • Duodenal Atresia


  • Jejunal, Ileal Atresia


  • Meconium Ileus


Less Common



  • Anal Atresia


  • Volvulus


Rare but Important



  • Cloacal Malformation


ESSENTIAL INFORMATION


Key Differential Diagnosis Issues



  • Try to determine point of obstruction (proximal vs. distal)


  • Assess peristalsis



    • Hyperperistalsis of obstructed bowel often seen in real-time evaluation


    • Infarcted bowel loses ability for peristalsis


  • Polyhydramnios common with atresia, but timing & severity dependent on site of obstruction



    • Earlier presentation & more severe with proximal atresia


    • Usually not present before 24 weeks



      • Most present in 3rd trimester


    • Amniotic fluid is often echogenic from fetal regurgitation of intraluminal contents


  • Intrauterine growth restriction (IUGR) common with atresia



    • Proximal atresias more likely to have IUGR


    • Ingested amniotic fluid important for fetal growth in latter half of gestation


  • Always look for normal rectum/anus in setting of obstruction



    • Normal rectum has hypoechoic walls with a hyperechoic mucosa


    • Follow down to perineum in coronal or sagittal plane


    • “Target” appearance in axial plane


Helpful Clues for Common Diagnoses



  • Normal Third Trimester Bowel



    • Colon, especially sigmoid, often prominent in 3rd trimester


    • Normal colon diameter ≤ 18 mm


  • Duodenal Atresia



    • Fluid-filled stomach & duodenum create classic “double bubble” appearance in axial plane


    • Stomach & duodenum can be connected during real-time imaging


    • No fluid in distal bowel loops


    • 30% will have trisomy 21


    • May also have an associated esophageal atresia



      • If a tracheoesophageal fistula is not present, fluid may accumulate in distal esophagus, stomach, & duodenum, forming a “C loop”


      • Normal secretions accumulate in this closed loop


      • Accumulated secretions may cause marked dilatation, much greater than typically seen with just duodenal atresia


  • Jejunal, Ileal Atresia



    • Roughly equal involvement between jejunum and ileum


    • “Triple bubble” for proximal jejunal atresia


    • “Sausage-shaped” bowel loops


    • Hyperperistalsis of obstructed segments often seen in real time


    • At risk for perforation and meconium peritonitis (≈ 6%)


  • Meconium Ileus



    • Obstruction of distal ileum due to abnormally thick, tenacious meconium


    • Seen in fetuses with cystic fibrosis


    • Echogenic bowel in 2nd trimester



      • Increased echogenicity likely secondary to inspissated, mucus secretions in bowel lumen


    • Progresses to dilated small bowel in 3rd trimester



      • Appearance often indistinguishable from ileal atresia


    • May perforate & present with meconium peritonitis


    • Systic fibrosis is a autosomal recessive disorder



      • If diagnosis is suspected, test parents for carrier status


      • Can also do amniocentesis for direct detection of mutation in fetus


    • If not detected in utero, may present in newborn period with failure to pass meconium



    • 10-20% of newborns with cystic fibrosis have meconium ileus


Helpful Clues for Less Common Diagnoses



  • Anal Atresia



    • May go undetected prenatally



      • Dilatation does not typically occur until 3rd trimester


    • Difficult to distinguish large from small bowel



      • U- or V-shaped bowel in pelvis suggestive of anorectal atresia


    • Scan in both coronal and axial planes looking for normal rectum



      • May see rectum end above perineum


      • Normal “target” appearance will not be present


    • Often associated with urinary tract fistulae



      • Mixing of meconium with urine creates enteroliths (may see calcified meconium “marbles” moving within bowel)


    • Part of VACTERL association



      • Vertebral anomalies


      • Anal atresia


      • Cardiac anomalies


      • Tracheo-esophageal (TE) fistula


      • Renal anomalies


      • Limb malformations


  • Volvulus



    • Single “kinked” loop is very suggestive but often difficult to determine


    • May see multiple, dilated loops from proximal obstruction



      • Often difficult to differentiate from bowel atresia


    • May have had a normal scan earlier in gestation



      • Volvulus is an abrupt event


    • Compromise of vascular supply leads to infarction & necrosis



      • Echogenic, intraluminal contents from sloughing of necrotic mucosa


      • Real-time evaluation important: Infarcted bowel loses ability for peristalsis


Helpful Clues for Rare Diagnoses

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Aug 10, 2016 | Posted by in OBSTETRICS | Comments Off on Dilated Bowel

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