Quick Links:

• Risk Stratification System hyperlink: https://www.acr.org/-/media/ACR/Files/RADS/O-RADS/O-RADS-MR-Risk-Stratification-System-Table-September-2020.pdf
• Lexicon hyperlink: https://www.acr.org/-/media/ACR/Files/RADS/O-RADS/O-RADS-MR-Lexicon-Terms-Table-November-2020.pdf
• MR O-RADS Calculator hyperlink: http://oradsmricalc.com/

1. Major Categories

Category	Term	Definition	Example
1a. Physiological observations (consistent with normal ovarian physiology)	Follicle	Simple cyst ≤ 3 cm in pre-menopausal women. A follicle is hyperintense on T2WI, hypointense on T1WI, and does not enhance.
	Corpus luteum (CL)	Cyst ≤ 3 cm with an enhancing crenulated wall on subtracted post-contrast T1WI, +/- blood flow or hemorrhagic contents.
1b. Lesions (not physiologic)	Unilocular Cyst	Single locule, without or without solid tissue.
	Multilocular Cyst	More than one locule, with or without solid tissue.
	Solid tissue	Conforms to one of the following morphologies and enhances: papillary formations, mural nodules, irregular cyst wall/septations, and solid portion.	See below
	Other solid components, not considered solid tissue	Smooth wall/septation, clot/debris/fat	See below

2. Size

3. Shape or Contour of Solid Lesion or Solid Tissue

Category	Term	Definition	Example
3a.	Smooth	Regular or even margin of a solid lesion or solid tissue
3b.	Irregular	Uneven margin of a solid lesion or solid tissue

4. Signal Intensity

5. Lesion Components

Category	Term	Definition	Example
5a. Cystic fluid descriptors	Simple fluid	Fluid content that follows CSF or urine on all sequences: hyperintense on T2WI and hypointense on T1W1
	Hemorrhagic fluid	Content can be variable depending on age
	Fluid-fluid level	Appearance when the non-dependent fluid component has a different signal intensity from the dependent fluid component with horizontal delineation (blue arrow)
	Endometriotic fluid	Content is hypointense on T2WI and hyperintense on T1WI
	Shading	Cyst fluid that is hypointense on T2WI; the extent of hypointense T2 signal intensity may be homogenous, variable within the cyst or graduated and dependent
	Proteinaceous fluid	Content is variable on T2WI and variably hypointense on T1WI
	Fat or lipid containing fluid	Hyperintense on T2WI and hyperintense on T1WI, and loses signal on fat saturated images
5b. Solid tissue descriptors (solid tissue enhances and conforms to one of the listed morphologies)	Papillary projection	Enhancing solid component arising from the inner/outer wall or septation of an adnexal lesion, with a branching architecture
	Mural nodule	Enhancing solid component, measuring ≥ 3 mm, arising from the wall or septation of an adnexal lesion, with nodular appearance
	Irregular septation	Enhancing linear strand that runs from one internal surface of the cyst to the contralateral side demonstrating an uneven margin (blue arrow)
	Larger solid portion	Enhancing component of an adnexal lesion that does not fit into the categories of papillary projection, mural nodule, or irregular septation/wall (orange arrow)
	Irregular wall	Enhancing cyst wall demonstrating an uneven margin
Other solid components, not considered solid tissue	Smooth septations/wall	Even contour or margin with no irregularities, mural nodules or papillary projections
	Blood, clot, non-enhancing debris and fibrin strands	Solid-appearing material within a cyst that does not enhance
	Fat	Lipid-containing material that does not enhance
	Hair, calcification, and a Rokitansky nodule	Other components of a dermoid not considered solid tissue

6. Enhancement: T1W1 post-contrast

6a. Dynamic contrast enhancement with time intensity curves	Low risk curve	Solid tissue shows minimal and gradual increase in enhancement over time with no well-defined shoulder and no plateau
	Intermediate risk curve	Enhancement of the solid tissue within the adnexal lesion with an initial slope less than the myometrium, moderate increase in signal intensity with a plateau
	High risk curve	Enhancement of the solid tissue within the adnexal lesion with an initial slope greater than the myometrium, marked increase in signal intensity with a plateau
6b. Non-dynamic contrast enhancement at 30-40 seconds post-injection	Less than or equal to the myometrium	Enhancement of the solid tissue within the adnexal lesion (blue arrow) is hypoenhancing to the outer myometrium (orange arrow) at 30-40 seconds post-contrast injection
	Greater than myometrium	Enhancement of the solid tissue within the adnexal lesion (blue arrow) is equal to or greater than the outer myometrium (orange arrow) at 30-40 seconds post-contrast injection

7. General and Extra-Ovarian Findings

7a. Peritoneal fluid	Physiologic	Small amount of fluid inside the pouch of Douglas or cul-de-sac or between the uterus and bladder
	Ascites	Fluid outside the pouch of Douglas or cul-de-sac or fluid extending beyond the space between the uterus and bladder
7b. Fallopian tube descriptors	Tubular	Substantially longer in one dimension than in the two perpendicular dimensions
	Endosalpingeal folds	Incomplete septations or short round projections, orthogonal to the length of the tube
7c.	Peritoneal inclusion cyst	Cyst following contour of adjacent pelvic organs; or normal ovary at the edge of/or surrounded by a cystic mass
7d. Ovarian torsion	Twisted pedicle	Swirling appearance of the broad ligament or ovarian pedicle
	Massive ovarian edema	Enlarged ovary with edematous central stroma
	Ovarian infarction	Lack of enhancement of the ovary on T1WI post-contrast (blue arrow; orange arrow shows normal left ovary for reference)
7e. Peritoneal thickening, nodules	Thickening, smooth	Uniform thickening, without focal nodularity
	Thickening, irregularity	Nonuniform thickening or focal areas of nodularity

• O-RADS MRI 0: An incomplete evaluation
• O-RADS MRI 1: Normal Ovaries
  • No ovarian lesion
  • Ovarian follicle, defined as a simple cyst ≤ 3 cm in a premenopausal* woman
  • Hemorrhagic cyst ≤ 3 cm in a premenopausal woman
  • Corpus luteum +/- hemorrhage ≤ 3 cm in a premenopausal woman
• O-RADS MRI 2: Almost certainly benign (<0.5% risk of malignancy)
  • Unilocular cyst with no enhancing solid tissue**
    • If no wall enhancement, may have any type of fluid content
    • If smooth wall enhancement, may have simple or endometriotic fluid content
  • Lesion with lipid content and:
    • No enhancing solid tissue
    • Only minimal enhancement of the Rokitansky nodule
  • Lesion with homogenously hypointense solid tissue on T2WI and DWI
  • Dilated fallopian tube with simple fluid content (hydrosalpinx) but no enhancing solid tissue. May have a thin, smooth wall/endosalpingeal folds with enhancement.
  • Para-ovarian cyst with no enhancing solid tissue. May have any type of fluid content, and may have a thin, smooth wall +/- enhancement.
• O-RADS MRI 3: Low risk of malignancy (~ 5%) 
  • Unilocular cyst with no enhancing solid tissue, smooth wall enhancement, and proteinaceous, hemorrhagic, or mucinous fluid content
  • Multilocular cyst with no enhancing solid tissue or lipid content. May have any type of fluid content, and may have smooth septae and wall with enhancement
  • Lesion with solid tissue (excluding T2 and DWI dark) with low-risk time intensity curve on DCE MRI***
  • Dilated fallopian tube with no enhancing soft tissue nodule and:
    • Non-simple fluid and thin walls/folds
    • Simple fluid with thick, smooth walls/folds
• O-RADS MRI 4: Intermediate risk of malignancy (~ 50%) 
  • Lesion with solid enhancing tissue (excluding T2 and DWI dark) with:
    • Intermediate-risk time intensity curve on DCE MRI****
    • If DCE MRI is not feasible, any lesion with enhancement ≤ myometrium at 30-40s on non-DCE MRI
  • Lesion with lipid content and large volume enhancing solid tissue
• O-RADS MRI 5: High risk of malignancy (~ 90%)
  • Lesion with solid tissue (excluding T2 and DWI dark with:
    • High-risk time intensity curve on DCE MRI*****
    • If DCE MRi is not feasible, any lesion with enhancement > myometrium at 30-40s on non-DCE MRI
  • Peritoneal, mesenteric, or omental nodularity or irregular thickening with or without ascites

*Women are categorized as pre- or postmenopausal, with postmenopausal defined as ≥ 1 year of amenorrhea
**Solid tissue is defined as a lesion component that enhances and has one of the following morphologies: papillary projection, mural nodule, irregular septation/wall, or other larger solid portions that do not conform to the aforementioned morphologies.
***Low-risk curve = minimal and gradual increase in signal over time with no well-defined shoulder and no plateau
****Intermediate-risk curve = initial slope less than myometrium, moderate increase in signal intensity with a plateau
*****High-risk curve = initial slope greater than myometrium, marked increase in signal intensity with a plateau

When lesions can be confidently diagnosed by MRI features, the final radiological diagnosis can be reported without an O-RADS risk stratification score assigned. 

An online O-RADS MRI calculator tool2 to aid in lesion characterization and O-RADS MRI assignment can be found at http://www.oradsmricalc.com.

Adnexal Findings:

For each adnexal lesion, describe:

• Size: Maximum diameter in any plane
• Morphology:
  • Unilocular cyst without solid component
  • Multilocular cyst without solid component
  • Cystic with solid component
  • Solid
• Cystic component (if applicable):
  • Fluid descriptors: simple; non-simple fluid (hemorrhagic, endometriotic, proteinaceous, fat or lipid-containing).
  • Signal descriptors: homogeneous; heterogeneous
  • If present, describe fluid-fluid level/shading and smooth wall or septal enhancement.
• Solid tissue (if applicable):
  • Solid tissue descriptors: irregular septation or wall; papillary projection; mural nodule; large solid tissue
  • Signal descriptors: T2 intensity; high b value DWI signal; enhancement less than/equal to OR greater than outer myometrium at 30-40 seconds post-contrast injection
• Other solid component (if applicable):
  • Smooth wall/septation, clot/debris, fat, hair, calcification, Rokitansky nodule
• Lipid component: Describe if present

Extra-adnexal Findings:

If present, include: ascites; peritoneal or omental stranding, thickening or nodularity.

Impression:

Lesion 1: ____. (O-RADS MRI __).
Lesion 2: ____. (O-RADS MRI __).

O-RADS MRI (Ovarian Imaging Reporting and Data System) assessment utilizes a 5-point scale to indicate the likelihood of malignancy based on a combination of multi-parametric MRI findings.

O-RADS MRI 0: Incomplete evaluation.
O-RADS MRI 1: Normal ovaries.
O-RADS MRI 2: Almost certainly benign (<0.5% PPV for malignancy).
O-RADS MRI 3: Low risk (~5% PPV for malignancy).
O-RADS MRI 4: Intermediate risk (~50% PPV for malignancy).
O-RADS MRI 5: High risk (~90% PPV for malignancy).

PPV = positive predictive value

Reference: Thomassin-Naggara I, Poncelet E, Jalaguier-Coudray A, et la. Ovarian-adnexal reporting data system magnetic resonance imaging (O-RADS MRI) score for risk stratification of sonographically indeterminate adnexal masses. JAMA Netw Open. 2020;3(1):e1919896.

Case 1

Lexicon Terms: Cystic lesion; non-simple fluid – fat or lipid-containing fluid; without solid tissue
Report Impression: Bilateral cystic lesions with lipid content without enhancing solid tissue, compatible with O-RADS MRI score 2 (almost certainly benign).
Pathology: Bilateral dermoid cysts. 

Case 2

Lexicon Terms: Cystic lesion; non-simple fluid – hemorrhagic fluid; solid tissue – mural nodule; tubular
Report Impression: Cystic adnexal lesion with solid tissue that enhances less than the outer myometrium, compatible with O-RADS MRI score 4 (intermediate risk).
Pathology: Serous adenocarcinoma likely arising from the fallopian tube. 

Case 3

Lexicon Terms: Cystic lesion; simple  fluid; solid tissue – mural nodule
Report Impression: Cystic adnexal lesion with enhancing solid tissue (mural nodule). Given enhancement less than the uterine myometrium, the lesion is classified as O-RADS MRI 4.
Pathology: Borderline serous cystadenoma.

Case 4

Lexicon Terms: Solid lesion; smooth shape/contour; heterogeneous; T2 hyperintense; T1 hypointense; peritoneal nodules
Report Impression: Adnexal lesion with solid tissue and peritoneal nodularity, compatible with O-RADS MRI score 5 (high risk).
Pathology: Borderline serous cystadenoma.

1. Thomassin-Naggara I, Poncelet E, Jalaguier-Coudray A, et la. Ovarian-adnexal reporting data system magnetic resonance imaging (O-RADS MRI) score for risk stratification of sonographically indeterminate adnexal masses. JAMA Netw Open. 2020;3(1):e1919896.
2. O-RADS MRI Lexicon Categories, Terms and Definitions. Release date: November 2002. https://www.acr.org/-/media/ACR/Files/RADS/O-RADS/O-RADS-MR-Lexicon-Terms-Table-November-2020.pdf
3. O-RADS MRI Stratification System Table. Release date: September 2020. https://www.acr.org/-/media/ACR/Files/RADS/O-RADS/O-RADS-MR-Risk-Stratification-System-Table-September-2020.pdf