Adnexal Mass Evaluation (RMI and IOTA)
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Direct answer
Adnexal mass evaluation uses ultrasound features, menopausal status and CA-125 to estimate the likelihood that an ovarian mass is malignant. The risk of malignancy index (RMI) multiplies an ultrasound score by a menopausal status score and the CA-125 level, and a value of 200 or more (250 in some guidelines) suggests high risk. IOTA simple rules classify a mass as benign or malignant from ultrasound features alone, and inconclusive or suspicious masses are referred to a gynaecologic oncology centre.
What you must remember
- RMI formula: RMI equals the ultrasound score multiplied by the menopausal status score and by the serum CA-125.
- Ultrasound score: Count the features multilocular cyst, solid areas, metastases, ascites and bilateral lesions; score 0 for none, 1 for one feature and 3 for two or more.
- Menopausal status score: 1 for a premenopausal woman and 3 for a postmenopausal woman.
- RMI cut-offs: A value of 200 or more is classically taken as high risk (RCOG and NICE use 250), and a value below 25 as low risk.
- IOTA benign features: Unilocular cyst, solid part under 7 mm, no flow in solid areas, acoustic shadows, or a smooth multilocular cyst under 10 cm.
- IOTA malignant features: Irregular solid tumour, ascites, at least four papillary structures, an irregular multilocular-solid mass of 10 cm or more, or very strong blood flow.
- Tumour markers: AFP, LDH and beta-hCG point towards germ cell tumours in young women with solid masses.
A stepwise approach from ultrasound to referral
A 52-year-old has a 6 cm solid-cystic mass with ascites and needs structured assessment before surgery. The steps show how each score feeds into the referral decision.
- Score the ultrasound: Count the five RMI features (score 0, 1 or 3) and apply the IOTA simple rules, using colour Doppler to judge blood flow in solid areas.
- Assign menopausal status: Give 1 point for premenopausal and 3 points for postmenopausal status, since the same mass carries a higher malignancy risk after menopause.
- Measure CA-125: Measure serum CA-125 and interpret it with care, because endometriosis, fibroids, pregnancy and peritoneal irritation all raise it.
- Calculate the RMI: Multiply the three scores. A result of 200 or more (250 in some guidelines) suggests high risk, below 25 suggests low risk, and intermediate values need clinical judgement.
- Decide the referral: Refer to a gynaecologic oncology centre for a malignant IOTA pattern, a high RMI, ascites with a solid mass, or inconclusive findings on an experienced scan.
Where the exam tries to catch you
Students usually lose marks by trusting one number instead of the whole picture.
- Trap: Ignoring a normal CA-125 in a solid, vascular mass Correct: Early ovarian cancer often has a normal CA-125, so the ultrasound pattern and IOTA features matter more.
- Trap: Treating a raised CA-125 as proof of cancer Correct: Benign conditions raise it, so the marker supports but does not confirm malignancy.
- Trap: Relying on RMI in a young woman with a solid mass Correct: RMI is less useful for germ cell tumours, so AFP, LDH and beta-hCG are added in young women.
Frequently asked questions
What is the cut-off value for a high risk of malignancy index?
A risk of malignancy index value of 200 or more is classically taken as high risk for ovarian malignancy, although some guidelines use 250. A value below 25 suggests low risk, and intermediate values need clinical judgement. The score combines ultrasound findings, menopausal status and CA-125.
Which ultrasound features make a mass suspicious on IOTA simple rules?
Malignant features in the IOTA simple rules include an irregular solid tumour, ascites, at least four papillary structures and very strong blood flow. An irregular multilocular-solid mass of 10 cm or more also counts. If at least one malignant feature is present with no benign feature, the mass is classed as malignant.
Why is CA-125 not diagnostic of ovarian cancer on its own?
CA-125 is raised in many benign conditions, including endometriosis, uterine fibroids, pregnancy and peritoneal irritation. Its sensitivity for early ovarian cancer is limited, so a normal value does not exclude cancer. For this reason CA-125 is combined with ultrasound scoring rather than used alone.
When should an adnexal mass be referred to a gynaecologic oncology centre?
Referral is appropriate when IOTA rules point to malignancy, the RMI is high, or ascites accompanies a solid adnexal mass. Inconclusive findings on an experienced ultrasound also justify referral. Early referral allows surgery by a team trained in ovarian cancer staging.
Which markers help in a young woman with a solid adnexal mass?
In young women with solid masses, AFP, LDH and beta-hCG help suggest germ cell tumours. These are measured alongside ultrasound because RMI is less reliable for germ cell tumours. Inhibin can support a granulosa cell tumour, which is a sex cord-stromal tumour.