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