Fetal Abdomen an Genitourinary System

stomach

• in LUQ

• seen by 16w

• amniotic, fluid-filled structure

• if no fluid seen, evaluate 20-30 minutes

• used as a marker for taking AC measurement

evaluating stomach

• scanned in TRV plane (short axis)

• anechoic (fluid-filled)

• if stomach is empty, move on and come back later or have patient come back another day

• can also image stomach and bladder together in LONG

small bowel

• mid-lower abdomen; centrally located echogenic areas inferior to liver

• SONO: varies with menstrual age

  • mid gut herniation (<12wks)

  • early pregnancy=hypoechoic

  • late pregnancy=more echogenic

• hyperechoic bowel is NOT normal

  • echogenicity should always be less than bone

• may see peristalsis in 3rd trimester (normal)

abnormality?

large bowel

• seen after 22w (can discern between small and large)

• more peripherally than small bowel

• hypoechoic tubular structure (meconium)

  • meconium=baby stool

• well-defined walls

• haustral folds appear as thin linear echoes within lumen

liver

• large compared to other abdominal organs

• occupies upper right abdomen

• left lobe is larger in utero

• SONO:

  • homogeneous, moderate echogenicity

  • helpful for determining situs and obtaining AC measurement

gallbladder

• seen after 20 weeks

• SONO: elongated anechoic structure in long-axis; circle in short-axis

• in right abdomen near liver

• more oval than intrahepatic umbilical vein

• document presence

spleen

• in LUQ

• increases in size during gestation (biggest in 3rd trimester)

• best images in TRV plane; to left of stomach

• SONO:

  • homogeneous

  • similar echogenicity to kidney

  • less echogenic than liver

abdominal cord insertion (ACI)

• becomes belly button after born

• umbilical cord seen entering fetal abdomen just above level of bladder

• UV courses to liver within falciform ligament

• UAs course on either side of bladder

  • 2VC can cause IUGR or is an indication of chromosomal abnormality

• SONO:

  • image ACI with and without color Doppler

  • ensure smooth abdominal cord insertion (should be nothing “pooching” out)

  • rule out gastroschisis and omphalocele

gastroschisis

• “loose bowel pooching out—floating outside abdomen”

omphalocele

• bowl or other organs come out, BUT difference is… it will be encased in a membrane

  • looks like a contained mass with smooth borders b/c of membrane

kidneys

• kidneys form in pelvis and ascent into abdomen

• urine formation around 11-2 weeks

  • excrete into amniotic cavity (component of amniotic fluid)

• visible by 12-13wks

• by 25wks distinction between renal cortex and sinus

• must evaluate both kidneys

  • presence, number, position

  • size (is one bigger than the other?)

  • collecting system dilation (??hydro)

  • appearance (echogenicity; compared to liver and spleen)

**if hydro seen, measure renal pelvis (AP) in TRV plane

kidneys develop from what 3 excretory organs in embryo?

• pronephros

• mesonephros

• metanephros

SONO: kidneys

• homogeneous cortex

• hypoechoic pyramids

• anechoic collecting system

imaging the kidneys (TRV, SAG, coronal)

transverse (easiest plane)

• kidneys visualized on either side of spine

• measure AP diameter of renal pelvis

sagittal

• long axis of kidney

coronal

• demonstrates a longer axis image of both kidneys

**always throw color Doppler on

what plane was this taken in?

transverse

what plane was this taken in?

coronal

what plane was this taken in?

longitudinal

mild pyelectasis (dilation) vs. hydronephrosis in utero

• before 27w = >4mm is abnormal

• after 27w = >7mm is abnormal

renal pelvis measurement for hydro

>4mm = hydro

what is the pathology?

ARPKD (autosomal recessive polycystic kidney disease)

adrenals

• adrenal glands can be prominent in fetus and neonate

• located medially and superior to fetal kidneys

• SONO:

  • best seen in TRV

  • superior pole of kidneys

  • hypoechoic cortex

  • echogenic medulla

bladder

• distended bladder should be seen by 13wks

• empties and fills at least once every 30 minutes

• if not identified on exam; exam must be repeated within 24 hours

• empty bladder is an indication of abnormality

• SONO:

  • anechoic (fluid-filled)

  • document in LONG and TRV
    

genitalia

• sexual characteristics develop between 9-12 weeks

• fetal testes produce androgens that cause masculinization of external genitalia (baby start as a girl)

• fetal external genitalia can be definitively identified with US after 18wks

SONO: genitalia (male vs. female)

male

• both scrotum and penis identified

• “turtle sign”

female

• vulva/labia lips identified

• “three-line sign”

• “hamburger sign”