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O-RADS MRI › O-RADS MRI

Adnexal MRI assessment

Understand the system

How O-RADS MRI works for adnexal masses

O-RADS MRI (Ovarian-Adnexal Reporting and Data System for MRI) is an ACR consensus system to standardize reporting and risk stratification of adnexal masses on MRI. There is no differentiation for pre and post menopause. Scores 0 to 5 correspond to Incomplete Evaluation, Normal Ovary, Almost Certainly Benign, Low Risk, Intermediate Risk, and High Risk.

From the normal ovary to high risk

O-RADS MRI category scale and PPV for malignancy

O-RADS MRI 2
<0.5%
Almost certainly benign
O-RADS MRI 3
~5%
Low risk
O-RADS MRI 4
~50%
Intermediate risk
O-RADS MRI 5
~90%
High risk
O-RADS MRI 0 — Incomplete evaluation
Off the risk scale: not assessable.
O-RADS MRI 1 — Normal ovary
Off the risk scale: no ovarian lesion.

Categories and PPV for malignancy

CategoryTypical findingsPPV for malignancy
O-RADS MRI 0Incomplete evaluation.Not assessable
O-RADS MRI 1Normal ovary. No ovarian lesion; includes a follicle defined as a simple cyst ≤3 cm, a hemorrhagic cyst ≤3 cm, or a corpus luteum ± hemorrhage ≤3 cm in a premenopausal woman.Normal
O-RADS MRI 2Unilocular cyst with no wall enhancement and no enhancing solid tissue; thick smooth enhancing wall but no solid tissue; lipid-containing lesion without enhancing solid tissue; "T2 dark/DWI dark" solid tissue (homogeneous T2 and DWI hypointensity); thin-walled dilated tube or paraovarian cyst without enhancing solid tissue.<0.5%
O-RADS MRI 3Unilocular cyst with proteinaceous, hemorrhagic, or mucinous content, thick smooth enhancing wall, no enhancing solid tissue; multilocular cyst with smooth enhancing septa/wall, no solid tissue; lesion with solid tissue (excluding T2 dark/DWI dark) with a low-risk time-intensity curve on DCE-MRI.~5%
O-RADS MRI 4Lesion with solid tissue (excluding T2 dark/DWI dark) with an intermediate-risk time-intensity curve on DCE-MRI (or, if DCE is not feasible, enhancement ≤ myometrium at 30–40s); lipid-containing lesion with a large volume of enhancing solid tissue.~50%
O-RADS MRI 5Lesion with solid tissue (excluding T2 dark/DWI dark) with a high-risk time-intensity curve on DCE-MRI (or, if DCE is not feasible, enhancement > myometrium at 30–40s); peritoneal, mesenteric, or omental nodularity or irregular thickening, with or without ascites.~90%

Key lexicon terms

  • DCE (Dynamic Contrast Enhancement): evaluates the time-intensity curve of solid tissue enhancement.
  • DWI (Diffusion Weighted Imaging): "T2 dark/DWI dark" tissue is typically benign (endometrioma, dermoid).
  • Rokitansky nodule: in lipid-containing lesions (dermoid), minimal enhancement of Rokitansky nodules does not change the category to O-RADS MRI 4.
Common questions

Frequently asked questions about O-RADS MRI

What is the O-RADS MRI system?+
It is an American College of Radiology (ACR) consensus system to standardize reporting and risk stratification of adnexal masses on MRI, with scores from 0 to 5. There is no differentiation for pre or post menopausal status.
What is the difference between O-RADS MRI and O-RADS US?+
Both ACR systems stratify the malignancy risk of adnexal masses on a 0-to-5 scale, but they use criteria from different modalities: O-RADS US is based on ultrasound features (IOTA lexicon), while O-RADS MRI uses MRI findings, including the dynamic contrast enhancement (DCE) pattern of solid tissue.
What is the time-intensity curve on DCE-MRI?+
DCE (Dynamic Contrast Enhancement) evaluates the solid tissue enhancement pattern over time via a time-intensity curve, and it is the central criterion that differentiates O-RADS MRI categories 3 (low risk), 4 (intermediate risk), and 5 (high risk).
What does "T2 dark/DWI dark" tissue mean?+
It is solid tissue that is homogeneously hypointense on both T2 and DWI (Diffusion Weighted Imaging), typically associated with benign lesions such as endometrioma and dermoid. This finding is excluded from the DCE time-intensity evaluation, since this tissue does not follow the typical enhancement behavior.
Does a Rokitansky nodule always raise the category to O-RADS MRI 4?+
Not necessarily. In lipid-containing lesions (such as a dermoid), minimal enhancement of Rokitansky nodules does not change the category to O-RADS MRI 4 — a large volume of enhancing solid tissue is needed for that change.
What is the PPV (positive predictive value) for malignancy in each O-RADS MRI category?+
O-RADS MRI 2: <0.5%. O-RADS MRI 3: ~5%. O-RADS MRI 4: ~50%. O-RADS MRI 5: ~90%. Categories 0 (incomplete evaluation) and 1 (normal ovary) fall outside this risk scale.