Simple Rules can classify ~75% of masses. Masses that don't fit (neither or both types) should be analyzed using IOTA ADNEX / Specialist assessment.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
Primary Clinical Uses
Sonographic characterization of adnexal/ovarian masses
Triaging surgical referrals (general gynecology vs. gynecologic oncology)
Standardizing global ultrasound terminology regarding ovarian cysts
Why it Exists
Prior to IOTA, radiologists used highly subjective terminology ("complex", "worrisome", "thickened") that caused massive over-operation by oncologists for universally benign cysts, and accidental rupture of malignant cysts by generalists.
Section 2
Formula & Logic
B-Features (Benign)
B1: Unilocular
B2: Presence of solid components, but largest is < 7 mm
B3: Presence of acoustic shadows (classic for dermoids)
B4: Smooth multilocular tumor with largest diameter < 100 mm
B5: No blood flow on Doppler (Color Score 1)
M-Features (Malignant)
M1: Irregular solid tumor
M2: Presence of ascites
M3: At least 4 papillary structures
M4: Irregular multilocular solid tumor with largest diameter ≥ 100 mm
M5: Very strong blood flow on Doppler (Color Score 4)
Section 3
Pearls/Pitfalls
The Diagnostic Algorithm
Rule 1 (Benign): Must have at least one B-feature AND zero M-features.
Rule 2 (Malignant): Must have at least one M-feature AND zero B-features.
Rule 3 (Inconclusive): If it has both B and M features, or NEITHER, the rules do not apply.
Inconclusive Masses
The Simple Rules are highly accurate (~90-95%) but only applicable to about 76% of all adnexal masses.
For the ~24% that are inconclusive, you MUST defer to an expert ultrasound examiner, an MRI, or apply advanced mathematical models (like IOTA ADNEX).
Section 4
Next Steps
Clinical Triage
01
Benign: Safe for conservative management, surveillance, or cystectomy/oophorectomy by a general gynecologist depending on symptoms.
02
Malignant: Absolute requirement for referral to a trained Gynecologic Oncologist. Attempting surgery by a generalist risks capsule rupture, upgrading the staging and ruining survival odds.
03
Inconclusive: Escalate diagnostic imaging (Pelvic MRI with contrast) or utilize the continuous ADNEX model.
Section 5
Evidence Appraisal
Phase 2 IOTA Study
Simple ultrasound-based rules for the diagnosis of ovarian cancer.
Timmerman D et al. • Ultrasound Obstet Gynecol.. 2008;Developed the 10 rules using 1938 women, proving a 95% sensitivity and 91% specificity for the masses where the rules could be conclusively applied.
Section 6
Literature
The IOTA Group
The International Ovarian Tumor Analysis (IOTA) consortium revolutionized ultrasound. Rather than relying on tumor markers like CA-125 (which has catastrophic false positive rates in premenopausal women due to endometriosis), they forced objective morphology to dictate risk.
