What imaging study should be ordered to rule out ovarian cyst or torsion?

Imaging for Ovarian Cyst or Torsion

Transvaginal and transabdominal ultrasound with Doppler should be ordered as the first-line imaging modality to rule out ovarian cyst or torsion due to its high sensitivity (79-80%) and specificity (76-88%). 1

Ultrasound Findings and Technique

For Ovarian Cyst Evaluation:

• Transvaginal ultrasound (TVUS) combined with transabdominal ultrasound provides optimal visualization of adnexal structures 2
• Color Doppler is considered a standard component of pelvic ultrasound examination 2
• Key ultrasound findings for cyst characterization:
  • Simple cysts: anechoic, thin-walled, no internal echoes (benign in 98.7% of premenopausal women) 2
  • Hemorrhagic cysts: spiderweb-appearing or retracting clot with peripheral vascularity 2
  • Endometriomas: low-level internal echoes, mural echogenic foci 2
  • Teratomas: echogenic attenuating component or small horizontal interfaces 2

For Ovarian Torsion Evaluation:

• Key ultrasound findings suggestive of torsion:
  • Unilaterally enlarged ovary
  • Central afollicular stroma with peripheral follicles
  • Abnormal or absent Doppler flow patterns
  • Whirlpool sign (90% specific for torsion) 2
  • Free fluid in pelvis 1

Important Caveats and Pitfalls

1. Normal blood flow does not exclude torsion - A prospective study showed that 62% of patients with normal arterial flow but abnormal venous flow had confirmed torsion 1

2. Diagnostic accuracy limitations - Ultrasound for adnexal torsion has 79% sensitivity and 76% specificity, which means false negatives can occur 2, 1

3. Whirlpool sign location matters - This sign can be located either lateral or medial to the affected ovary, with larger masses associated with a lateral whirlpool sign 2

4. Combined approach is best - Transabdominal ultrasound provides a larger field of view while transvaginal ultrasound offers better resolution of adnexal structures 2

Second-Line Imaging Options

If ultrasound is inconclusive or further characterization is needed:

CT Abdomen/Pelvis with IV Contrast:

• CT findings of ovarian torsion include:
  • Enlarged, featureless, hypoenhancing ovary
  • Swirling of vascular pedicle
  • Abnormal craniocaudal orientation of ovary
  • Uterine deviation to the affected side 2, 1
• CT evaluation has 74-95% sensitivity and 80-90% specificity for adnexal torsion 2, 3

MRI Pelvis:

• Indicated as a problem-solving examination if ultrasound or CT are inconclusive 2
• MRI findings of torsion (80-85% sensitive) include:
  • Enlarged ovary with stromal edema and surrounding fluid
  • Absent or diminished ovarian enhancement
  • Tubal knot or whirlpool sign
  • Peripheralized and/or hemorrhagic follicles 2, 1

Clinical Considerations

• Ovarian torsion is a surgical emergency requiring prompt diagnosis and intervention
• Symptoms may be nonspecific, leading to diagnostic challenges and delays 1
• In a comparative study, CT demonstrated excellent interobserver agreement (Kappa=0.85) compared to ultrasound (Kappa=0.60) for diagnosing ovarian torsion, suggesting CT may be valuable when ultrasound findings are equivocal 3
• However, ultrasound remains the cost-effective first-line imaging modality for most cystic ovarian lesions 4

In summary, while multiple imaging modalities can help diagnose ovarian cysts and torsion, the evidence strongly supports starting with combined transvaginal and transabdominal ultrasound with Doppler as the initial diagnostic approach.