What is more accurate for diagnosing uterine anomalies, 3-D (three-dimensional) ultrasound or SIS (Saline Infusion Sonography)?

3-D Ultrasound is More Accurate Than SIS for Diagnosing Uterine Anomalies

For diagnosing and classifying congenital uterine anomalies, 3-D ultrasound is the superior choice over SIS, with near-perfect diagnostic accuracy (sensitivity and specificity approaching 100%) that rivals MRI and is recommended by the American College of Radiology as the primary diagnostic modality. 1, 2, 3

Diagnostic Performance of 3-D Ultrasound

3-D ultrasound demonstrates exceptional accuracy for uterine anomaly classification:

• Sensitivity of 100% and specificity of 92-100% for septate uterus, which is the most common anomaly requiring differentiation 2
• Perfect diagnostic accuracy (Kappa index = 0.945) when compared to the gold standard of combined hysteroscopy/laparoscopy 2
• Superior sensitivity (99%) compared to MRI (81%) for detecting septate uterus, and higher specificity for bicornuate (99% vs 92%) and didelphys uterus (100% vs 87%) 3
• Similar accuracy to MRI for detecting Müllerian anomalies overall, as noted by the American College of Radiology 1

Why 3-D Ultrasound Outperforms SIS

The critical advantage of 3-D ultrasound is its ability to visualize the external fundal contour, which is essential for differentiating between anomaly types:

• 3-D ultrasound provides coronal plane imaging that clearly shows both the uterine cavity AND the external contour, allowing differentiation of septate from bicornuate uterus (fundal cleft >1 cm for bicornuate vs <1 cm for septate) 1, 4
• SIS only evaluates the uterine cavity and cannot assess the external fundal contour, limiting its ability to classify anomalies accurately 1
• In one study, 3-D ultrasound was 100% accurate in classifying bicornuate, septate, and arcuate uteri when combined with SIS (3-D SIS), but this accuracy was not statistically different from 3-D transvaginal ultrasound alone 1

Clinical Algorithm for Uterine Anomaly Diagnosis

Start with 3-D transvaginal ultrasound as the primary diagnostic tool:

• 3-D ultrasound is non-invasive, quick, cost-effective, and does not expose patients to radiation 5, 6
• It provides immediate coronal plane reconstruction showing both internal cavity and external contour 4
• Reserve MRI for complex cases where 3-D ultrasound findings are equivocal or when detailed soft tissue characterization is needed 6
• Reserve combined hysteroscopy/laparoscopy for surgical planning after diagnosis is established, not as a primary diagnostic tool 6, 2

Role of SIS in the Diagnostic Pathway

While SIS has limitations for anomaly classification, it remains valuable for specific indications:

• SIS is excellent for detecting intrauterine pathology including polyps, submucosal fibroids, and adhesions (75% accuracy for fibroids vs 52.6% for HSG) 1
• Combining 3-D ultrasound with SIS (3-D SIS) can overcome limitations when endometrium is thin, providing enhanced cavity visualization 4
• SIS and MRI were equally effective for detecting intracavitary abnormalities and both superior to conventional 2-D transvaginal ultrasound 1

Common Pitfalls to Avoid

• Do not rely on 2-D ultrasound or HSG alone for anomaly classification—they cannot adequately visualize the external fundal contour needed for accurate diagnosis 5
• HSG is particularly poor for uterine anomalies (only 16.7% accurate for Müllerian duct anomalies) and should not be used for this purpose 1
• Ensure adequate endometrial thickness when performing 3-D ultrasound; if endometrium is thin, add saline infusion to improve cavity delineation 4
• Always image for renal anomalies when a uterine anomaly is diagnosed, as they frequently coexist 6