In an adult female with acute lower abdominal pain, can a non‑contrast computed tomography (CT) of the abdomen detect ovarian torsion?

Non-Contrast CT for Ovarian Torsion Detection

Non-contrast CT abdomen is not the appropriate imaging modality for detecting ovarian torsion and should not be used for this purpose. Ultrasound (transvaginal and transabdominal) is the first-line imaging study, and if CT is needed, it must be contrast-enhanced to adequately evaluate ovarian enhancement patterns and vascular structures 1.

Why Non-Contrast CT is Inadequate

Contrast enhancement is essential for detecting the key CT findings of ovarian torsion, which include:

• Hypoenhancing or absent enhancement of the affected ovary – this critical finding cannot be assessed without intravenous contrast 1
• Enlarged, featureless ovary with abnormal craniocaudal orientation 1
• Twisted vascular pedicle ("whirlpool sign") 1, 2
• Uterine deviation to the affected side 1, 3

The diagnostic accuracy of CT for ovarian torsion relies heavily on evaluating enhancement patterns, which requires contrast administration 1. In a retrospective study of 167 surgically proven ovarian torsion cases, all CT scans showed abnormalities of the involved ovary (enlarged ovary, ovarian cyst, or adnexal mass), but these studies were contrast-enhanced 4.

Recommended Imaging Algorithm

For suspected ovarian torsion in an adult female with acute lower abdominal pain:

1. First-line: Transvaginal and transabdominal ultrasound with Doppler 1, 2

   • Sensitivity of 70-80% and specificity of 87-88% 2, 5
   • Key findings: unilaterally enlarged ovary (>4 cm), peripheral follicles, whirlpool sign, abnormal/absent venous flow 2
   • Critical caveat: Normal arterial flow does NOT exclude torsion – 61% of right ovarian torsion cases and 27% of left ovarian torsion cases had normal Doppler flow 5

2. Second-line: CT abdomen/pelvis WITH intravenous contrast (if ultrasound is inconclusive or non-diagnostic) 2, 6

   • Sensitivity of 74-95% and specificity of 80-90% 2
   • A negative contrast-enhanced CT has 100% negative predictive value for ovarian torsion 6

3. Alternative: MRI without and with contrast (if available and patient stable) 1, 2

   • Sensitivity of 80-85% 2
   • Useful when ultrasound is equivocal but avoids radiation 1

Clinical Pitfalls to Avoid

• Do not rely on Doppler flow alone – presence of arterial flow does not exclude torsion, as torsion can be intermittent or partial 2, 5
• Do not order non-contrast CT – it cannot assess the critical enhancement patterns needed for diagnosis 1
• Do not delay surgery for imaging – if clinical suspicion is high despite negative or equivocal imaging, proceed with laparoscopy, as this is a surgical emergency requiring ovarian preservation 2
• Obtain β-hCG before imaging in all reproductive-age women to narrow the differential and guide imaging choices 1

When CT May Be Encountered

CT is increasingly performed in emergency departments for non-specific abdominal pain, and ovarian torsion may be incidentally discovered 7, 3. However, this should be contrast-enhanced CT, not non-contrast 7. If a non-contrast CT was already obtained and shows an enlarged ovary or adnexal mass, proceed directly to ultrasound or contrast-enhanced imaging rather than assuming torsion is excluded 4.