Radiology in Obstetrics

Question 1

x-rays: are they safe?

Answer 1

• “All-or-none” phenomenon
• Location of irradiation
• Amount of radiation
• Timing (during pregnancy) of exposure

Question 2

harmful effects of ionizing radiation

Answer 2

• Cell death and birth defects (Teratogenesis)
• Carcinogenesis
• Genetic effects

Question 3

HDR and Carcinogenesis: weak data

Answer 3

• Unclear risk, probably very small
• At 10-20 mGy, 1/2000 develop childhood leukemia
  
  • Background risk is 1/3000
• Non-irradiated siblings also have higher risk of leukemia
• Termination of pregnancy should not be based on exposure to typical dosing

Question 4

genetic effects of radiation

Answer 4

• May increase frequency of natural mutations, not create de novo mutations
• No increased risk of genetic disorders has been noted in any human population at any dose
• “Little or no evidence exists for estimating the frequency or magnitude of genetic effects on future generations”

Question 5

nuclear medicine and pregnancy

Answer 5

• “Tagging” a chemical agent with a radioisotope
• Fetal exposure depends on radioisotope’s physical and biochemical properties
  
  • Tc 99m – used in brain, bone, renal, CV scans
    
    • Exposure < 0.5 rads
  • VQ Scans – Tc 99m for perfusion, ¹²⁷Xe or ¹³³Xe for ventilation
    
    • Exposure ~ 50 mrad (0.05 rads)

Question 6

MRI contrast agents

Answer 6

• Gadolinium and iron oxide based agents are most commonly used
• Gadolinium is associated with nephrogenic systemic fibrosis (NSF), especially in “free” form
  
  • AKA nephrogenic fibrosing dermopathy (NFD)
  • Disease of fibrosis of the skin and internal organs

Question 7

safety of ultrasound in pregnancy

Answer 7

• Sound waves, not ionizing radiation
• No reports of adverse fetal effects
• FDA arbitrarily limits energy exposure

Question 8

indications for first trimester ultrasound

Answer 8

• Confirm fetal viability and dates
• Rule out ectopic pregnancy
• Diagnose multifetal pregnancy
• Guidance for removal of IUD
• Rule out molar pregnancy
• Guidance for chorionic villous sampling
• Nuchal translucency testing

Question 9

pregnancy dating

Answer 9

• Error of ultrasound:
  
  • ≤ 8-6/7 weeks: 5 days
  • 9 to 15-6/7 weeks: 7 days
  • 16 to 21-6/7 weeks: 10 days
  • 22 to 27-6/7 weeks: 14 days
  • 28 to term: 21 days
• Assessment of fetal growth patterns linked to ultrasound error

Question 10

pregnancy with IUD

Answer 10

• Higher risk of ectopic
• 50-60% risk of miscarriage if left inside uterus
• String retraction hampers removal

Question 11

ectopic pregnancy and ultrasound

Answer 11

• Most ectopic pregnancies are tubal
• Presentation: 7-8 weeks
• Clinical triad: Pain, bleeding, amenorrhea
• Ultrasound cannot definitively rule OUT an ectopic pregnancy, but can rule IN an intrauterine pregnancy
• Other less common sites: cornual, cervical

Question 12

molar pregnancy and ultrasound

Answer 12

• Molar gestation – neoplastic placental growth
• Fetus present (partial) or absent (complete)
• Inheritance: uniparental disomy
• Lab: high levels of HCG
• Symptoms: hyperemesis, hyperthyroidism
• US: “Snowstorm” or “Grape-like” clusters
• High incidence of fetal CNS anomalies
• Uniparental disomy – both chromosomes come from dad or both come from mom

Question 13

CVS and ultrasound

Answer 13

• Biopsy of placental tissue at 10-13 weeks
• Diagnoses chromosomal or genetic disorders for which DNA testing is available
• Ultrasound guides needle/catheter into placental tissue

Question 14

fetal nuchal translucency

Answer 14

• 11.5 and 14.5 weeks
• Abnormal edema associated with chromosomal and fetal structural abnormalities
  
  • Down syndrome
  • Fetal anomalies mostly cardiac
• If pt has test that shows nuchal translucency that is greater than 3, this is BAD

Question 15

1st trimester cystic hygroma

Answer 15

• Commonly associated with Downs, trisomy 18, and turner syndrome

Question 16

2nd trimester ultrasound uses

Answer 16

• Assessing gestational age
• Multifetal pregnancy detection
• Screening for fetal anomalies
• Placental localization and evaluation
• Amniotic fluid evaluation
• Guidance for amniocentesis

Question 17

components of a 2nd trimester ultrasound

Answer 17

• Gestational age / fetal growth
• Fetal position
• Fetal number
• Placental location
• Amniotic fluid volume
• Uterine evaluation – fibroids, anomalies
• Cervical evaluation
• Fetal anatomy

Question 18

placenta

Answer 18

• Where is it?
  
  • Anterior
  • Posterior
  • Fundal
  • Covering the cervical os
• Is it abnormal?
  
  • Molar pregnancy
  • Has it separated?
  • Abruptio placenta

Question 19

placenta previa

Answer 19

• Higher incidence in assisted reproductive technologies (insemination, IVF)

Question 20

placental location and appearance

Answer 20

• Placenta previa
  
  • Complete, partial or marginal
  • Common in 2^nd (5%) and rare in 3^rd trimester (0.5%)
  • Higher incidence in multiparas, elderly, previous cesarean section or abortion
• May detect retroplacental or retromembranous clot – abruptio placenta
• If placenta is within 2 cm of the os, the possibility of bleeding is 50%

Question 21

amniotic fluid assessment

Answer 21

• Increased: Polyhydramnios
  
  • Diabetes
  • Upper GI tract obstruction
  • Chromosomal abnormalities
  • Muscular lesions affecting swallowing
• Decreased: Oligohydramnios
  
  • Rupture of the membranes
  • Absent fetal renal tissue or lower urinary tract obstruction
  • Intrauterine growth restriction

Question 22

uterine evaluation during obstetical sonography

Answer 22

• Overall shape and size
• Presence of anomalies
  
  • Uterus didelphys (including double cervix)
  • Uterine septa, bicornuate uterus
• Presence of tumor – leiomyoma

Question 23

cervical evaluation during 2nd trimester

Answer 23

• Normal cervical length: > 2.5 cm
• Borderline area: 2.0-2.5 cm
• Abnormally short: < 2.0 cm
• Normal shortening process during gestation
• Most helpful evaluation between 18-22 weeks
• Funneling
• “Hourglassing” membranes
• Placement of cervical cerclage

Question 24

fetal anatomic survey

Answer 24

• Systematic survey for fetal anomalies
• Performed usually between 16 and 22 week
• CNS
• Cardiopulmonary
• Gastrointestinal
• Genitourinary
• Musculoskeletal
• Umbilical cord
• Fetal exterior

Question 25

fetal anatomy: CNS and Spine

Answer 25

• Cerebral ventricles
• Posterior fossa and cerebellum
• Cavum septum pellucidum
• Cranium
  
  • Encephalocele
  • Hypo- and hypertelorism
• Spina bifida
  
  • Myelocele
  • Myelomeningocele

Question 26

cardiopulmonary assessment

Answer 26

• 4 chamber heart, outflow tracts
• Echogenic foci
• Cardiac masses – myxoma, rhabdomyoma
• Pulmonary evaluation
  
  • Diaphragmatic herniation
  • Masses:
    
    • Cystic adenomatoid malformations (CCAM)
    • Bronchopulmonary sequestration
  • Effusions

Question 27

gastrointestinal assessment

Answer 27

• GI tract obstruction
  
  • Absence of stomach “bubble”
    
    • Tracheo-esophageal fistula
  • “Double bubble”
    
    • Duodenal atresia
  • Anal atresia
• Ascites
• “Echogenic” bowel – brightness = bone brightness
  
  • Trisomy 21
  • Cystic fibrosis
  • Intrauterine bleeding
  • Intrauterine infections – CMV, toxoplasmosis

Question 28

genitournary assessment

Answer 28

• Normal anatomy
  
  • Kidneys and bladder seen
  • Ureters and urethra not seen
• Abnormal:
  
  • Dilated renal pelvis – obstructive, “flaccid”
  • Obstructions: UPJ, UVJ, urethral (bladder outlet), hydronephrosis
  • Renal, ovarian cysts
  • Hypospadias, penile anomalies
  • Cystic renal changes

Question 29

umbilical cord assessment

Answer 29

• Number of vessels
  
  • 2 vessel cord associated with chromosomal, skeletal, GU tract abnormalities – up to 50%
• Insertion site into abdomen
  
  • Defects
    
    • Gastroschisis
    • Omphalocele

Question 30

musculoskeletal assessment

Answer 30

• Calvarium
• Long bones
  
  • Presence or absence
  • Length
  • Bowing
  • Fractures
• Digits – Number and orientation
• Abnormalities: - skeletal dysplasias, spondylolystheses, ichythyoses

Question 31

fetal exterior/integument assessment

Answer 31

• Craniofacial
  
  • Cleft lip and palate
  • Cystic hygroma
• Teratomas
  
  • Sacrococcygeal

Question 32

3rd trimester assessment

Answer 32

• Fetal growth
  
  • Biometry
  • Fluid assessment: AFI
• Fetal well-being
  
  • Biophysical profile
  • Doppler studies
• Fetal pulmonary maturity studies
  
  • LBC, SA Ratio, LS ratio, PG level

Question 33

macrosomia greater than 90th percentile for GA

Answer 33

• Often associated with diabetes
• CPD/Shoulder dystocia
• US widely used to estimate fetal weight
• Cesarean section recommended for:
  
  • 4750 gm (non-diabetic)
  • 4250 gm (diabetic)

Question 34

fetal growth assessment: IUGR <10th percentile for GA

Answer 34

• Chromosomal abnormalities
• Renal disease and hypertension
• Connective tissue diseases – lupus
• Perinatal infections – CMV, toxoplasmosis, etc.
• Thrombophilia – clotting abnormalities
• Placental abnormalities

Question 35

fetal well-being by ultrasound: fluid assessment

Answer 35

• Amniotic fluid volume is an indicator of fetal renal output
• Decreased amniotic fluid is associated with increased rate of perinatal mortality

Question 36

biophysical profile

Answer 36

• Excellent predictor of fetal well being
• 4 ultrasound parameters + NST
  
  • Fetal breathing
  • Fetal tone
  • Fetal movement
  • Amniotic fluid volume (2 cm pocket)
• 2 points for each normal parameter
• Normal: ≥ 7 points

Question 37

MRI and pregnancy

Answer 37

• Magnets alter energy state of hydrogen protons
• May be helpful in diagnosis of fetal CNS defects and IUGR
• May also help in detecting placenta accreta
• Some agencies advise against use in 1st trimester but no reports of adverse effects