OB/GYN & PELVIC

Pelvic US Pearls & Pitfalls

TRANS-ABDOMINAL SCANS  & GENERAL ADVICE

• The ED physician rarely needs to do a trans-vaginal scan.  With a trans-abdominal you can usually tell if there is an IUP or not (to rule out ectopic), and if there is free fluid or not (to rule out rupture).  This, and evaluation for cardiac motion should be the extent of a limited bedside ultrasound.
• An IUP (Intra Uterine Pregnancy) usually rules out an ectopic pregnancy unless the patient is on fertility drugs or your suspicion is very high.
• The order of appearance of changes within the uterus in pregnancy is enlargement followed by a gestational sac (beware of pseudosacs) then a yolk sac, then finally a fetal pole which will eventually have cardiac motion and development of a variety of anatomical structures.
• A cornual ectopic, which is the most dangerous type, is also the closest to the uterus. Don’t be fooled into thinking it’s an IUP
• Free fluid in the pelvis or abdomen should be considered blood until proven otherwise. Blood and ascitic fluid may look the same on ultrasound. In the proper clinical scenario, such a hemodynamically stable patient with no history of trauma and a benign exam, ascites may be more likely. Other causes of free fluid include bowel or bladder rupture.

TRANS-VAGINAL SCANS (Usually formal, Non-ED studies)

• To make trans-vaginal ultrasound less painful, let the patient put the probe in her vagina herself. Make sure you have a chaperone.
• Here’s is what you should see on transvaginal ultrasound depending on the number of weeks gestation: 5-6wks: Sac 6-7wks: Pole & Cardiac Motion.
• Ultrasound is only 40% sensitive for placental abruption
• Avoid trans-vaginal imaging if the patient had a recent gynecologic procedure
• Always assess for vascular flow to ovaries in order to rule-out ovarian torsion.

BLADDER SCANS (SEE KIDNEY & BLADDER SECTION)

• You can estimate bladder volume by assuming it approximates a sphere and using the “diameter-cubed/2″ rule. The volume of a sphere is (4/3)P(r-cubed). Alternately use the “ABC/2″ rule where A, B and C are the three diameters of the bladder in three planes.
• Turn down the far gain when looking for free fluid behind the bladder. This will help compensate for the acoustic enhancement that occurs distal to fluid filled structures. Fluid collections will most frequently take the form of “dog-ears” or a “bow tie”

Want more educational images? Check out the ED Atlas on CD

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PELVIC ULTRASOUNDS

Normal Uterus in Transverse

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Ectopic Pregnancy with clot around uterus

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Empty Uterus

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Cornual Ectopic Pregnancy.  Mid-uterus is empty.  Sac is in the right horn of the uterus

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Cornual Ectopic Pregnancy.  If your not careful, this can look like an IUP

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Using B/M mode split screen to measure Fetal Heart Rate

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Pseudosac in a patient with Ectopic Pregnancy (Courtesy of Julie Vajnar, PA-C)

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Ruptured ectopic with free fluid in pouch of Douglas

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Hydatidiform Mole

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Tubo Ovarian Abscess read more about this case

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