Ultrasound: Pelvic
(Redirected from Pelvic US)
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
- Pelvic pain
- Abnormal pelvic or abdominal exam
Uterus
- Vaginal bleeding
- Fibroids
- IUD placement
Ovaries and adnexa
- Ovarian cyst
- Ovarian torsion
- Ovarian masses
- Tubo-ovarian abscess
- Hydrosalpinx
Pregnancy
- Confirm intrauterine pregnancy
- Gestational dating
- Fetal monitoring and surveillance
- Evaluation of placenta
- Spontaneous abortion
- Intrauterine fetal demise
- Ectopic pregnancy
- Heterotopic pregnancy
- Molar 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
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
- Pre-menopausal:
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
- Gestational 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
- Yolk 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
- Fetal Pole
- 8-9 weeks
- Limb buds appear
- Head identifiable
- 9-10 weeks
- FHR ~170-180 bpm
- Fetal movement visible
- End of embryonic period
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"
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 |
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)
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
- Ultrasound (Main)
- Pelvic ultrasound (transabdominal)
- Pelvic ultrasound (transvaginal)
- Ectopic Pregnancy