Interpretation
| Result | Meaning |
|---|---|
| No M, >2 B features | Very low risk (<0.01–0.29%) |
| No M, 2 B features, or B1 alone | Low risk (0.19–3.1%) |
| No M, 1 B feature (not B1) | Intermediate risk (2.4–15.2%) |
| No features, equal M and B, or more B than M (>0 M) | Elevated risk |
| More M than B features | Very high risk (42–>99.9%) |
Formula
Risk = e^RS / (1 + e^RS), RS = −0.97 − 3.41·B1 − 2.25·B2 − 1.66·B3 − 2.75·B4 − 1.86·B5 + 2.19·M1 + 2.65·M2 + 1.53·M3 + 0.98·M4 + 1.55·M5 + 0.92·(oncology centre). Each feature = 1 if present, 0 if absent (Timmerman 2016, Table 8).
Clinical pearls
- Features must be assessed with standard IOTA terminology by a trained sonographer; B4 is a smooth multilocular tumour <100 mm and M4 an irregular multilocular-solid tumour ≥100 mm.
- Oncology centre status reflects the higher prevalence of malignancy in referral populations (43% vs 17%), not scan quality.
- Worked example from the paper: B3 + M2 + M5 at an oncology centre gives a regression score of 2.49 and a 92.3% risk of malignancy.
Examples
iota simple rules acoustic shadows, ascites, very strong flow at oncology centreIOTA risk for a unilocular cyst with no flow, community hospitaladnexal mass with irregular solid tumour and ascites, not an oncology center, what is the malignancy risk
FAQ
What are the IOTA Simple Rules B and M features?
B: unilocular cyst, solid components <7 mm, acoustic shadows, smooth multilocular tumour <100 mm, no blood flow. M: irregular solid tumour, ascites, ≥4 papillary structures, irregular multilocular-solid tumour ≥100 mm, very strong blood flow.
How is the Simple Rules risk different from the original Simple Rules?
The original rules classify a mass as benign, malignant or inconclusive. The 2016 risk model gives a percentage risk for every combination, including the inconclusive ones.