Should I order a pelvic ultrasound for a patient with persistent pelvic pain after a CT scan showed no abnormalities in the female reproductive organs?

Pelvic Ultrasound is Indicated for Persistent Pelvic Pain After Normal CT

For a patient with persistent pelvic pain after a CT scan showed no abnormalities in the female reproductive organs, a pelvic ultrasound should be performed as the next diagnostic step. 1, 2

Rationale for Pelvic Ultrasound After Normal CT

• Ultrasound is considered the first-line imaging modality for evaluating gynecologic causes of pelvic pain due to its excellent visualization of pelvic structures without radiation exposure 3, 2
• Transvaginal ultrasound provides superior spatial and contrast resolution for detailed evaluation of the female reproductive organs compared to CT 1, 4
• A combined transabdominal and transvaginal ultrasound approach provides the most comprehensive assessment of pelvic structures 1, 3
• CT may miss certain gynecologic conditions that are better visualized on ultrasound, including small ovarian cysts, subtle endometrial abnormalities, and early inflammatory changes 5, 6

Specific Conditions Better Detected by Ultrasound

• Ovarian torsion may be missed on CT but can be detected on ultrasound with findings including:

  • Unilaterally enlarged ovary (>4 cm or volume >20 cm³) 7
  • Peripheral follicles (found in up to 74% of cases) 7
  • Abnormal or absent venous flow on Doppler (100% sensitivity, 97% specificity) 7
  • Whirlpool sign (90% sensitivity in confirmed cases) 7

• Pelvic inflammatory disease may be detected on ultrasound with findings of:

  • Pelvic fluid, hydrosalpinx or pyosalpinx 1
  • Inflammatory adnexal masses 1
  • Peritoneal inclusion cysts 1

• Pelvic venous disorders (pelvic congestion syndrome) can be evaluated with color and spectral Doppler ultrasound showing:

  • Engorged periuterine and periovarian veins (>8 mm) 1
  • Low-velocity flow and altered flow with Valsalva maneuver 1
  • Retrograde flow of the ovarian veins 1

Diagnostic Algorithm

1. For persistent pelvic pain after normal CT:

   • Proceed with transvaginal and transabdominal pelvic ultrasound with color Doppler 1, 3

2. If ultrasound is inconclusive but clinical suspicion remains high:

   • Consider MRI pelvis, which provides excellent soft tissue contrast and can detect subtle abnormalities not seen on CT or ultrasound 1, 3

3. If both CT and ultrasound are normal:

   • Consider non-gynecologic causes of pelvic pain (gastrointestinal, urologic, musculoskeletal) 8
   • Evaluate for functional pain disorders that may not show structural abnormalities on imaging 9

Common Pitfalls to Avoid

• Relying solely on CT findings when gynecologic pathology is suspected, as ultrasound has superior sensitivity for many gynecologic conditions 5, 2
• Failing to use both transabdominal and transvaginal approaches during ultrasound examination, as this combined approach provides the most comprehensive assessment 1
• Not including color and spectral Doppler evaluation, which is essential for assessing vascular abnormalities and distinguishing cysts from solid tissue 1, 7
• Overlooking the possibility of intermittent conditions (like ovarian torsion) that may not be apparent at the time of initial imaging 7

Conclusion

When CT shows no abnormalities but pelvic pain persists, ultrasound provides complementary information that may reveal gynecologic pathology missed on CT. The combination of transvaginal and transabdominal ultrasound with Doppler evaluation should be the next step in the diagnostic algorithm 1, 2.