O-RADS MRI risk stratification system: pearls and pitfalls

Abstract

In 2021, the American College of Radiology (ACR) Ovarian-Adnexal Reporting and Data System (O-RADS) MRI Committee developed a risk stratification system and lexicon for assessing adnexal lesions using MRI. Like the BI-RADS classification, O-RADS MRI provides a standardized language for communication between radiologists and clinicians. It is essential for radiologists to be familiar with the O-RADS algorithmic approach to avoid misclassifications. Training, like that offered by International Ovarian Tumor Analysis (IOTA), is essential to ensure accurate and consistent application of the O-RADS MRI system. Tools such as the O-RADS MRI calculator aim to ensure an algorithmic approach. This review highlights the key teaching points, pearls, and pitfalls when using the O-RADS MRI risk stratification system.Critical relevance statement This article highlights the pearls and pitfalls of using the O-RADS MRI scoring system in clinical practice.Key points• Solid tissue is described as displaying post- contrast enhancement.• Endosalpingeal folds, fimbriated end of the tube, smooth wall, or septa are not solid tissue.• Low-risk TIC has no shoulder or plateau. An intermediate-risk TIC has a shoulder and plateau, though the shoulder is less steep compared to outer myometrium.

Keywords: MRI; O-RADS; Ovarian lesion; Stratification.

Fig. 1

Optimal MRI protocol to perform O-RADS MRI Risk scoring. a Sagittal T2-weighted sequence without fat saturation. b Axial T2-weighted lombo-pelvic sequence. c Axial DWI lombo-pelvic scan (b: 1400 s/mm²). d Corresponding axial ADC map. e Axial unenhanced T1-weighted in-phase. f Axial unenhanced T1-weighted opposed-phase. g Axial unenhanced T1-weighted Fat sequence. h Axial unenhanced T1-weighted water sequence. i Axial late-gadolinium T1-weighted sequence. j, k DCE T1-weighted sequence with myometrial curve (yellow curve) and region of interest within the solid ovarian tissue (blue curve) (l). This was classifified as an O-RADS MRI 4, and hypothesized to represent a serous borderline cystadenoma

Fig. 2

O-RADS classification with most common errors. Please refer to reference 7 for positive predictive values

Fig. 3

Useful sign to evaluate the relationship between a lesion and adjacent organ: a Axial T2-weighted sequence with a “beak sign” (white arrow head). b Sagittal T2-weighted sequence showing a “claw sign” (white star). c, d Sagittal and Axial T2-weighted sequence with “bridging vessel sign” (arrow)

Fig. 4

Example of MRI appearance of a corpus luteum cyst. a Axial T2-weighted sequence. b Axial DWI abdominal and pelvic scan (b: 1200 s/mm²). c Axial unenhanced T1-weighted water sequence. d Axial late-gadolinium T1-weighted sequence. Left ovarian corpus luteum cyst (maximal diameter: 35 mm) (white arrow)

Fig. 5

Example of MRI appearance of a para-ovarian cyst. a Axial T2-weighted sequence. b Axial DWI lombo-pelvic scan (b: 1200 s/mm²). c Axial unenhanced T1-weighted in-phase sequence. d Axial late-gadolinium T1-weighted sequence. Left para-ovarian cyst (maximal diameter: 17 mm) white arrow

Fig. 6

MRI assessment of non-simple fluid. First column corresponding to T2-weighted signal. Second column corresponding to T1-weighted in-phase sequence. Third column corresponding to T1-weighted water-phase sequence. Fourth column corresponding to diffusion-weighted sequence. Last column corresponding to late gadolinium T1-weighted sequence. a Hemorrhagic fluid. b Endometriotic fluid. c Proteinaceous fluid in this case: pus inside an abscess. d Lipid-containing fluid

Fig. 7

Illustration of the dark T2/DWI appearance on MRI. a Axial T2-weighted sequence. b Axial DWI abdominal and pelvicscan (b: 1200 s/mm²). c Axial unenhanced T1-weighted in-phase sequence. d Axial late gadolinium T1-weighted sequence. Right ovarian lesion classified O-RADS2 corresponding to a right ovarian fibroma (maximal diameter: 47 mm) (white arrow)

Fig. 8

Example of MRI appearance of a Rokitansky nodule which does not account for a solid tissue. a Axial T2-weighted sequence. b Axial DWI abdominal and pelvic scan (b: 1200 s/mm²). c Axial unenhanced T1-weighted in-phase sequence. d Axial late-gadolinium T1-weighted sequence. Right ovarian dermoïd cyst with a small Rokitansky nodule (white arrow)

Fig. 9

Example of solid tissue descriptors: a Axial T2-weighted sequence without fat saturation. b Axial unenhanced T1-weighted Water sequence showing papillary projections in bilateral serous borderline ovarian lesions (arrows). c Axial T2-weighted sequence without fat saturation. d Axial unenhanced T1-weighted Water sequence showing a large mural nodule (arrows) in a high-grade serous ovarian cancer. e Axial T2-weighted sequence without fat saturation. f Axial unenhanced T1-weighted Water sequence showing irregular septations (arrows) in bilateral serous borderline ovarian lesions. g Axial T2-weighted sequence without fat saturation. h Axial unenhanced T1-weighted Water sequence showing irregular wall (arrows) in a serous borderline bilateral ovarian tumor. i Axial T2-weighted sequence without fat saturation. j Axial unenhanced T1-weighted Water sequence showing irregular septations showing large solid component (arrows) high-grade serous ovarian cancer

Fig. 10

Example of mature cystic teratoma. a Axial T2-weighted sequence without fat saturation. b Axial unenhanced T1-weighted Water sequence. c Axial DWI scan (b: 1200 s/mm²). d Axial late-gadolinium T1-weighted sequence. e, f DCE T1-weighted sequence with corresponding curve of the external myometrium: yellow curve and Rokitansky protuberance: purple curve corresponding to a type I curve

Fig. 11

Example of MRI appearance endosalpingial folds. a Axial T2-weighted sequence. b Axial DWI lombo-pelvic scan (b: 1200 s/mm²). c Axial unenhanced T1-weighted water sequence. d Axial late-gadolinium T1-weighted sequence. Multiple endosalpingial folds (white arrow) potentially leading to a misinterpretation with ovarian vegetations. Note the hypersignal on the DWI scan corresponding to pus inside the fallopian tube (white star)

Fig. 12

Fimbrial end of the tube between a dilated hydrosalpynx and the right ovarian structure. a Axial T2-weighted sequence. b Sagittal T2-weighted sequence. Stellar morphology of the fimbrial end of the tube (white arrow)

Fig. 13

MRI appearance of a thick (first row, white arrow) and a thin septa (second row). a Axial T2-weighted sequence showing a thickened septa with tissular component. b Axial late-gadolinium T1-weighted sequence showing a tissular enhancement. c Axial DWI abdominal and pelvic scan (b: 1200 s/mm²) with hypersignal of the tissular component. d Axial T2-weighted sequence showing a thin septa. e Axial late-gadolinium T1-weighted sequence showing a thin enhancement. f Axial DWI abdominal and pelvic scan (b: 1200 s/mm²) showing no hypersignal

Fig. 14

Example of left ovarian lesion with a solid component with a type I dynamic enhancement curve. a Axial T2-weighted sequence without fat saturation. b Axial DWI scan (b: 1200 s/mm²). c Axial unenhanced T1-weighted water sequence. d Axial late-gadolinium T1-weighted sequence. e, f DCE MRI T1-weighted sequence with corresponding curve of the tissular component showing a type I curve. This was favored to be a benign cystadenofibroma

Fig. 15

Difference between a type I curve and a type II curve. Same case as illustrated previously: a Axial T2-weighted sequence without fat saturation. b,c DCE MRI T1-weighted sequence with corresponding curve of the tissular component showing a type I curve corresponding to a cystadenofibroma. Other case with (d) Axial T2-weighted sequence without fat saturation. e, f DCE MRI T1-weighted sequence with corresponding curve of the tissular component showing a type II curve corresponding to a borderline serous cystadenoma

Fig. 16

Example of bilateral ovarian lesion with a solid tissue with a type II dynamic enhancement curve (e) and type III dynamic enhancement curve (e). a Axial T2-weighted sequence without fat saturation and (b) Axial unenhanced T1-weighted water sequence show a mixed right cystic and solid lesion with (c) large enhancing solid tissue portion (d) with corresponding curve of the tissular component showing a type III curve (orange curve) (e) consistent with an O-RADS MRI 5 score. c Axial T2-weighted sequence without fat saturation and (f) DCE MRI T1-weighted sequence show a large left cystic lesion with solid tissue represented by papillary projections (arrow), corresponding to a type II curve (pink curve). Note the myometrium is represented by the yellow curve. The hypothesis of a low-grade serous ovarian cancer was made and later proven on histology