Ultrasound and Obstetric/Gynecologic Imaging
Core concepts
Understand the physics of ultrasound: frequency versus resolution and penetration, artifacts (posterior acoustic enhancement, shadowing, reverberation), and Doppler principles. Master obstetric ultrasound: dating, fetal biometry, placental evaluation, and the signs of ectopic pregnancy (empty uterus, adnexal mass, free fluid). Know the appearance of ovarian cysts and masses (simple cyst vs complex), and the signs of endometriosis and adenomyosis. Recognize the findings of first-trimester complications (threatened abortion, missed abortion). Understand the role of ultrasound in evaluating the gallbladder, kidneys, and thyroid.
Traps
Do not mistake an anembryonic gestation for a normal early pregnancy; use criteria for gestational sac and embryo visualization. Posterior enhancement is not a sign of malignancy. Beware attributing adnexal pain to a simple cyst without excluding torsion (absent Doppler flow).
Rule of thumb
A gestational sac should be visible on transvaginal ultrasound by about 5 weeks; an embryo with cardiac activity by about 6 weeks.
Worked example
A patient with pelvic pain and a positive pregnancy test: transvaginal ultrasound shows an empty uterus and a complex adnexal mass, suggesting ectopic pregnancy, requiring urgent management.