Ultrasound: Pelvic

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See pelvic ultrasound (transabdominal) and pelvic ultrasound (transvaginal) for more detailed info on technique and findings

Background

  • Ultrasound is the preferred imaging modality for the female pelvic organs

Indications

  • To evaluate female reproductive organs in pediatric patients or those that are not sexually active or refuse transvaginal exam
  • Start with transabdominal ultrasound when evaluating to rule out ectopic (less invasive than transvaginal), particularly if bHCG >6,000

General

Uterus

Ovaries and adnexa

Pregnancy


Technique

Transabdominal

  • 3.5 MHz curvilinear probe
  • Start above pubic symphysis in longitudinal axis
  • Locate endometrial stripe (echogenic line) which represents the center of the uterus
  • Scan through longitudinal axis of uterus and sweep laterally to try to visualize ovaries (though often difficult to visualize on transabdominal ultrasound)
  • Rotate probe to transverse plane above pubic symphysis and scan through uterus from cervix to fundus
  • Scan hepatorenal recess to assess for free fluid

Transvaginal

General

  • Use 5 MHz endocavitary probe (high frequency, low penetration)
  • Apply surgical lubricant inside and outside probe cover
  • Place patient in lithotomy position
  • Gently advance probe into vaginal canal and position adjacent to cervix
    • May be more comfortable for patient to insert probe into vagina herself
  • Apply gentle pressure to lower abdominal wall with one hand and manipulate probe with other hand

Longitudinal scan

  • Probe marker pointing at 12:00
  • Shows anterior structures on left side of screen
  • Begin midline at endometrial stripe
  • Scan from right to left through uterus
  • Move probe laterally to view adnexa and ovaries

Transverse scan

  • Rotate probe 90 degrees counterclockwise so probe marker is pointing at 9:00
  • Shows right-sided structures on left side of screen
  • Start at endometrial stripe and scan throughout uterus
  • Locate cornual flare (junction of uterus and fallopian tubes)
  • Move probe laterally along fallopian tube to locate ovary
  • Ovaries identified by follicular (anechoic or hypoechoic) structures

  • Uterus in longitudinal plane

  • Cornual flare (uterus and fallopian tube junction) in transverse plane

  • Normal ovary with follicles

Normal Findings

Uterus

  • Anteverted: Fundus pointing to anterior abdominal wall
  • Retroverted: Fundus pointing to posterior wall
  • Endometrial stripe: Measured from thickest echogenic area (from one basal endometrial interface to the other, including canal)
    • Pre-menopausal:
      • During menstruation: 2-4mm
      • Early proliferative phase: 5-7mm
      • Late proliferative phase: 11mm
      • Secretory phase: 7-16mm
      • After D&C or SAB: >5mm
        • Consider retained POC if thicker
    • Post-menopausal:
      • With vaginal bleeding: <5mm
      • Without vaginal bleeding: <11mm

  • Normal thickened endometrial stripe during secretory phase

  • Normal thin endometrial stripe during menses

Ovaries

  • Physiologic cysts present
    • <3 cm diameter
    • Ovarian follicle or corpus luteum
    • Typically don't cause complications

Pregnancy (1st trimester)

  • 4-5 weeks
    • Gestational sac
      • First sign of early pregnancy, usually seen between 3-5 weeks gestation
    • "Double decidual sac" sign
      • Two concentric rings (uterine lining and gestation lining) around anechoic gestational sac)
      • Highly suggestive of intrauterine pregnancy (before yolk sac or embryo embryo visualized
    • "Intradecidual sign"
      • Thickened decidua on one side of uterine cavity surrounding anechoeic sac
  • 5-6 weeks:
    • Yolk Sac
      • Circular (or sometimes as two parallel lines) echogenic structure with thick walls within gestational sac
      • Definitive evidence of intrauterine pregnancy
      • Multiple yolk sacs is earliest sign in multiple gestational pregnancy
    • "Double bleb" sign
      • Yolk sac and amniotic cavity that look like two bubbles within gestational sac
  • 6-7 weeks
    • Fetal Pole
      • First visual manifestation of fetus (or "embryo")
      • Thickening of margin on yolk sac
    • Cardiac activity present (FHR ~100-115 bpm)
    • Crown rump length: ~5mm
  • 8-9 weeks
    • Limb buds appear
    • Head identifiable
  • 9-10 weeks
    • FHR ~170-180 bpm
    • Fetal movement visible
    • End of embryonic period
In a normal pregnancy, the gestational sac appears as a hypoechoic structure encircled by an echogenic border within the endometrial cavity at 4-5 weeks
IUP at 6 wks

  • Double decidual sac sign

  • Intradecidual sign

  • Double bleb sign (yolk sac and amniotic cavity)

  • Fetal pole (Thickening of yolk sac on one side)

Abnormal Findings

Abnormal Pregnancy

  • Gestational sac >10mm without visible yolk sac
  • Gestational sac >18mm without fetal pole
  • Collapsed gestational sac
  • Pseudogestational sac
    • Endometrial breakdown during ectopic pregnancy
    • May be erroneously interpreted as true gestational sac in ectopic pregnancy
    • Irregularly shaped
    • Located in endometrial cavity, instead of eccentrically within endometrium
    • No yolk sac present
    • May not have double decidual sac sign
  • Absence of fetal heart beat in embryo with CRL >5mm
  • FHR <90 bpm
  • Molar pregnancy
    • Many small, irregular cystic structures in endometrium
    • "Snowstorm appearance"

  • Gestational sac greater than 10mm without yolk sac

  • Gestational sac greater than 18mm without fetal pole

  • Collapsed gestational sac

  • Pseudogestational sac

  • Molar pregnancy with multiple cystic lesions in endometrium ("snowstorm appearance")

Ectopic pregnancy

  • Implantation of blastocyst outside of endometrium
  • Occur in fallopian tubes, cervix, ovaries, peritoneal cavity, or scar of prior uterine surgery
  • Most definitive sonographic sign is gestational sac with yolk sac, embryo, or fetal heart beat outside of the endometrium
  • Tubal pregnancy
    • "Tubal ring" sign: echogenic thick-walled anechoic sac visualized between uterus and ovary (separate from ovary when pressure applied to fallopian tube with probe)
  • Interstitial Pregnancy
    • Implantation of gestational sac in muscular wall of uterus at proximal regional of fallopian tubes
    • "Interstitial line" sign: hyperechoic line from endometrial stripe to cornual region adjacent to interstitial gestational sac
  • Cervical Pregnancy
    • Implantation of gestational sac below internal cervical os
    • Can cause life-threatening hemorrhage
    • Must distinguish between cervical ectopic and spontaneous abortion at level of cervix:
Cervical ectopic Spontaneous abortion at cervix
Hour-glass shaped uterus Elongated gestational sac
Gestational sac with yolk sac, fetal pole, or heartbeat Absent embryonic cardiac activity
Closed internal os Dilated internal os
Color doppler showing hypervascular trophoblastic ring Sac moves in cervix with gentle probing (“Sliding sac sign”)
Empty uterine cavity Loss of sac on serial imaging

  • Ectopic pregnancy

  • Free fluid in cul-de-sac with no gestational sac visualized in uterus

  • Ectopic pregnancy between ovary and uterus, suggestive of tubal ectopic

  • Interstitial pregnancy

  • Cervical pregnancy

Ovarian Torsion

  • Bimodal age distribution: young women (15-30yo) and post-menopausal women
  • Typically occur in enlarged ovaries (>5cm)
    • Benign mature cystic teratomas
    • Hemorrhagic/large ovarian cysts
    • Cystic neoplasms
    • Cystadenomas
    • Polycystic ovarian syndrome
  • Sonographic signs associated with torsion
    • Enlarged ovary from edema, engorgement, hemorrhage
    • Midline ovary
    • Free pelvic fluid
    • Underlying ovarian lesions
    • Peripherally displaced follicular cysts
    • Doppler findings:
      • Decreased/absent venous or arterial flow
      • Absent/reversed diastolic flow
      • Can have normal flow (from dual supply from uterine and ovarian arteries)

  • Large ovarian cystadenoma

  • Hemorrhagic ovarian cyst with blood clot

  • Large midline ovary with multiple peripherally located follicular cysts (torsion)

  • Absent color doppler and venous and arterial waveforms (torsion)

Pearls and Pitfalls

  • Free pelvic fluid with positive hCG is ectopic pregnancy until proven otherwise
  • Presence of doppler flow cannot rule out ovarian torsion

See Also

References

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