Adnexal mass — characterisation and risk stratification

ACR O-RADS US v2022; O-RADS MRI

Risk-stratifying an adnexal lesion so that benign disease is left alone and malignant disease reaches a gynaecological oncology service. Ultrasound assigns the risk; MRI is the problem-solver for the genuinely indeterminate lesion; CT stages, and only once malignancy is likely.

An adnexal lesion found on ultrasound, on cross-sectional imaging done for another reason, or on examination — with or without symptoms.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Pelvic ultrasound — transabdominal and transvaginal

Ultrasound pelvis (transabdominal ± transvaginal)

What we'd amend, and why

Transvaginal ultrasound resolves the features that drive risk — septations, solid components, papillary projections and their vascularity — at a spatial resolution no cross-sectional modality matches for a small pelvic lesion. Most lesions are classifiable as almost certainly benign on ultrasound alone, and that is what prevents a cascade of unnecessary imaging and surgery.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayany — All patients

Decision support only. Local protocol takes precedence.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

Is the patient pre- or postmenopausal?
The same morphology carries a different malignancy risk either side of the menopause, and the follow-up recommendation changes with it.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

All patients

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Ultrasound pelvis (transabdominal ± transvaginal) Pelvic ultrasound — transabdominal and transvaginal usually appropriate	Transvaginal ultrasound resolves the features that drive risk — septations, solid components, papillary projections and their vascularity — at a spatial resolution no cross-sectional modality matches for a small pelvic lesion. Most lesions are classifiable as almost certainly benign on ultrasound alone, and that is what prevents a cascade of unnecessary imaging and surgery.
Second line	MRI Pelvis (Gynaecological) MRI Pelvis — general gynaecological	MRI is the correct next step for the lesion ultrasound has called indeterminate. It identifies fat, blood products and fibrous tissue directly, which is how a dermoid, an endometrioma and a fibroma are separated from a malignancy, and dynamic contrast behaviour of any solid component adds specificity. It reclassifies a large share of indeterminate lesions as benign and so prevents operations.
Problem solving	CT Abdomen and Pelvis CT Abdomen and Pelvis — Portal Venous Phase	CT is for staging once the lesion is already considered likely malignant — peritoneal disease, omental deposits, nodes and the upper abdomen. It is a poor characterisation tool for the adnexa itself, so ordering it to decide whether a cyst is benign answers the wrong question.

Pitfalls

Characterising an adnexal lesion on CT. A simple-looking cyst on CT can be a mucinous or borderline tumour, and a haemorrhagic cyst routinely looks solid.
Requesting MRI for a lesion that ultrasound has already called almost certainly benign — the additional study adds cost and anxiety without changing management.
Reporting an adnexal lesion without saying which risk category it falls into and what follow-up that implies; an unclassified description transfers the decision back to a clinician with less information.
Forgetting that a postmenopausal ovary should be small and quiet: the thresholds that are reassuring before the menopause are not reassuring after it.
Answering a completed indeterminate ultrasound with a request to repeat the ultrasound. The scan has already done its job — it has said the lesion is indeterminate — and the next study is MRI; sending the patient round the loop again delays a possible ovarian cancer for no gain.

Priors — what to pull first

Find the earliest imaging that shows the lesion. Stability over years is strong evidence of benignity and can end the pathway outright.
Retrieve any CA125 and, in a young woman with a solid lesion, the germ cell markers — they change the pre-test probability that the report is written against.

What makes a good request

Menopausal status changes both the prior probability and the reporting thresholds, so it belongs on the request.
The useful question is not "is this cancer" but "which pathway does this lesion belong to": discharge, interval ultrasound, MRI, or gynaecological oncology referral.
A structured risk-stratification report (O-RADS or an IOTA-based description) is what makes the answer actionable for the referring team.
This is the characterisation question, not the acute one. An adnexal mass with sudden severe pain and vomiting is a torsion request and belongs on that pathway, at that tempo — characterisation follows the ovary being saved, not the other way round.
Say on the request when the ultrasound has already been done and called the lesion indeterminate. That is the fact that makes MRI the correct next study rather than a study skipped ahead to, and without it the request comes back asking for the scan the patient has already had.

Scoring this once it is done

The classification and risk tools this question ends in.

O-RADS Ultrasound (Adnexal Lesion Risk Stratification)O-RADS MRI Risk Stratification (Adnexal Lesion)IOTA Simple Rules (Adnexal Mass)ADNEX Model (IOTA)RMI (Risk of Malignancy Index)RECIST 1.1 Tumor Response

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

Pelvic ultrasound — transabdominal and transvaginal MRI Pelvis — general gynaecological CT Abdomen and Pelvis — Portal Venous Phase

Confirm locally

Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.