What is the utility of obtaining CT (Computed Tomography) and US (Ultrasound) to evaluate appendicitis and ovarian torsion in a 28-year-old female with right lower quadrant abdominal pain?

Imaging Strategy for RLQ Pain in a 28-Year-Old Female

Start with ultrasound as the first-line imaging modality, followed by CT with IV contrast if ultrasound is nondiagnostic or equivocal—this sequential approach provides optimal diagnostic accuracy for both appendicitis and ovarian torsion while minimizing radiation exposure in a young woman of reproductive age. 1, 2

Initial Imaging: Ultrasound First

Ultrasound should be the primary imaging modality for a 28-year-old female with RLQ pain because it:

• Provides excellent visualization of both gynecologic and gastrointestinal structures without radiation exposure 2
• Requires a combined transabdominal and transvaginal approach for comprehensive pelvic assessment 2
• Must include color and spectral Doppler evaluation, which is essential for detecting ovarian torsion and distinguishing vascular abnormalities 2

Ultrasound Performance for Key Diagnoses

For ovarian torsion, ultrasound can detect:

• Unilaterally enlarged ovary with peripheral follicles
• Abnormal or absent venous flow on Doppler imaging
• Whirlpool sign of the vascular pedicle 2

For appendicitis, ultrasound demonstrates 76% sensitivity compared to CT's 94% sensitivity, making it adequate for initial screening but less reliable than CT 1

When to Proceed to CT

Obtain CT abdomen and pelvis with IV contrast when:

• Ultrasound is nondiagnostic, equivocal, or technically limited 1
• Clinical suspicion remains high despite negative ultrasound 3
• The patient presents with nonspecific or poorly localized pain suggesting a broader differential diagnosis 1

CT Performance Characteristics

CT with IV contrast demonstrates:

• 89% sensitivity for urgent diagnoses versus 70% for ultrasound in abdominopelvic pain 1
• 100% sensitivity for appendicitis in some studies, significantly outperforming ultrasound 4
• Superior detection of complications such as perforation, abscess formation, and alternative diagnoses 1, 5

CT Findings for Ovarian Torsion

While ultrasound remains the preferred modality for ovarian torsion, CT can identify:

• Enlarged, featureless, hypoenhancing ovary
• Swirling appearance of the vascular pedicle
• Abnormal craniocaudal orientation of the ovary
• Uterine deviation to the affected side 1, 6, 7

Critical caveat: CT findings of ovarian torsion may be subtle and easily missed—radiologists and emergency physicians must actively look for these features when evaluating young women with RLQ pain 7

Role of MRI as Problem-Solving Tool

MRI should be considered when:

• Both ultrasound and CT are inconclusive but clinical suspicion remains high 3
• There is concern about radiation exposure and time permits (MRI is not typically available emergently) 1

MRI demonstrates:

• 100% sensitivity for acute appendicitis and 86% sensitivity for ovarian torsion in patients with pelvic pain 1, 3
• 99% overall accuracy for detecting acute abdominal pathology 3

However, MRI feasibility depends heavily on institutional availability, expertise, and rapid acquisition protocols optimized for acute presentations 1, 3

Practical Algorithm

1. Perform combined transabdominal and transvaginal ultrasound with Doppler as initial imaging 2

2. If ultrasound is diagnostic (clearly shows appendicitis, ovarian torsion, or alternative diagnosis), proceed with appropriate management

3. If ultrasound is negative or equivocal and clinical suspicion remains moderate to high, obtain CT abdomen and pelvis with IV contrast 1, 3

4. If both ultrasound and CT are nondiagnostic but clinical concern persists, consider MRI if available, or close clinical observation with repeat examination 3

Common Pitfalls to Avoid

• Failing to use both transabdominal and transvaginal approaches during ultrasound—this combined technique is essential for comprehensive assessment 2

• Omitting Doppler evaluation on ultrasound, which is critical for detecting ovarian torsion and assessing vascular flow 2

• Ordering CT without IV contrast—the bulk of evidence supporting CT diagnostic accuracy specifically refers to contrast-enhanced imaging 1, 8

• Missing ovarian torsion on CT because radiologists and clinicians are not actively looking for it—this diagnosis is frequently overlooked when CT is performed for suspected appendicitis 7

• Assuming normal blood flow on Doppler excludes ovarian torsion—arterial flow may be preserved even with venous obstruction in early or intermittent torsion 2