A White Paper of the ACR Ovarian-Adnexal Reporting and Data

ORIGINAL ARTICLE

Clinical Practice Management

Ovarian-Adnexal Reporting Lexicon for

MRI: A White Paper of the ACR

Ovarian-Adnexal Reporting and Data

Systems MRI Committee

Caroline Reinhold, MD, MSc

1,a

, Andrea Rockall, MRCP, FRCR

1,b

, Elizabeth A. Sadowski, MD

Evan S. Siegelman, MD

, Katherine E. Maturen, MD, MS

, Hebert Alberto Vargas, MD

Rosemarie Forstner, MD

, Phyllis Glanc, MD

, Rochelle F. Andreotti, MD

Isabelle Thomassin-Naggara, MD, PhD

Abstract

MRI is used in the evaluation of ovarian and adnexal lesions. MRI can further characterize lesions seen on ultrasound to help decrease

the number of false-positive lesions and avoid unnecessary surgery in benign lesions. Currently, the reporting of ovarian and adnexal

ﬁndings on MRI is inconsistent because of the lack of standardized descriptor terminology. The development of uniform reporting

descriptors can lead to improved interpretation agreement and communication between radiologists and referring physicians. The

Ovarian-Adnexal Reporting and Data Systems MRI Committee was formed under the direction of the ACR to create a standardized

lexicon for adnexal lesions with the goal of improving the quality and consistency of imaging reports. This white paper describes the

consensus process in the creation of a standardized lexicon for ovarian and adnexal lesions for MRI and the resultant lexicon.

Key Words: Adnexal lesion, adnexal mass, MRI, ovarian mass, structured reporting

J Am Coll Radiol 2021;18:713-729. Copyright ª 2021 American College of Radiology

Credits awarded for this enduring activity are designated “SA-CME” by the American Board of Radiology (ABR) and qualify toward fulﬁlling

requirements for Maintenance of Certiﬁcation (MOC) Part II: Lifelong Learning and Self-assessment. To access the SA-CME activity visit

https://cortex.acr.org/Presenters/CaseScript/CaseView?Info=nStKx24vrpKvbbrTdQgjmYsJIIlAcszeEOoMvAj%2bF6c%253d. SA-CME

credit for this article expires May 2, 2024.

Codirector, Augmented Intelligence & Precision Health Laboratory of the

Research Institute of McGill University Health Center, McGill University,

Montreal, Canada.

Division of Surgery and Cancer, Imperial College London and Depart-

ment of Radiology, Imperial College Healthcare NHS Trust, London, UK.

Departments of Radiology, Obstetrics and Gynecology, University of

Wisconsin School of Medicine and Public Health, Madison, Wisconsin.

Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania.

Departments of Radiology and Obstetrics and Gynecology, University of

Michigan Hospitals, Ann Arbor, Michigan.

Memorial Sloan Kettering Cancer Center, New York, New York.

Department of Radiology, Universitätsklinikum Salzburg, PMU Salzburg,

Salzburg, Austria.

University of Toronto, Sunnybrook Health Science Center, Toronto,

Ontario, Canada.

Department of Radiology and Radiological Sciences, Vanderbilt University

Medical Center, Nashville, Tennessee.

Sorbonne Université, Assistance Publique—Hôpitaux de Paris, Hôpital

Tenon, Service d’Imagerie, Paris, France.

Corresponding author and reprints: Caroline Reinhold, MD, MSc, McGill

University Health Center, McGill University, 1001 Decarie Boul, Mon-

treal, Quebec, Canada, H4A 3J1; e-mail: [email protected].

Dr Rockall reports travel support from Guerbet Laboratories, France

outside the submitted work. Dr Thomassin-Naggara reports personal fees

from General Electric, personal fees from Hologic, from Canon, from

Guerbet, personal fees from Siemens, outside the submitted work. The

other authors state that they have no conﬂict of interest related to the

material discussed in this article. Dr Reinhold is a partner. Dr Rockall, Dr

Sadowski, Dr Siegelman, Dr Maturen, Dr. Vargas, Dr Forstner, Dr

Andreotti, and Dr Thomassin-Naggara are nonpartner, non–partnership

track employees.

Joint ﬁrst author with equal contribution.

1546-1440/21/$36.00

https://doi.org/10.1016/j.jacr.2020.12.022 713

INTRODUCTION

Ultrasound (US) is widely consi dered the primary imaging

modality in the evaluation of women with suspected adnexal

pathology [1-5]. Standardized terms and deﬁnitions to

describe the sonographic features of adnexal lesions have

been proposed, and several US reporting models can aid

in differentiating benign from malignant adnexal masses

[4,6-11]. However, approximately 20% to 25% of adnexal

masses remain indeterminate after the initial sonographic

evaluation [4,7,12]. Furthermore, studies have demonstrated

variable positive predictive values for the detection of ovarian

cancer using US, with some studies showing low positive

predictive values in the general population in which the

incidence of ovarian cancer is low [6,8,13]. Secondary tests

such as MRI could help decrease the number of false-positive

lesions when using US in certain settings and avoid unnec-

essary surgery in benign lesions [6,13-16].

The number of adnexal lesions that remain indeterminate

after MRI is 5% to 7%, with high sensitivity and speciﬁcity

for characterizing both benign and malignant lesions [17-22].

In 2010, the European Society of Urogenital Radiology

proposed an algorithmic pathway using standardized MRI

morphological descriptors for predicting the risk of

malignancy for adnexal lesions [23,24]. Their goal was to

improve lesion characterization by MRI to assist in

treatment planning. However, a standardized lexicon and

risk stratiﬁcation system was not developed in conjunction

with the proposed algorithmic pathway. In 2013, an MR

scoring system (AdnexMR score) was developed in a

retrospective, single-center French study of 497 sono-

graphically indeterminate adnexal masses on US [25]. The

AdnexMR score used a standardized lexicon to describe

MRI features and proposed a 5-point score according to

the positive likelihood ratio for malignancy derived from

features with high positive and negative predictive values in

distinguishing benign from malignant masses [25-27].

The ACR Ovarian-Adnexal Reporting and Data Systems

(O-RADS) MRI Committee has developed an evidence-

based lexicon and risk stratiﬁcation system for MRI evalua-

tion of adnexal lesions, employing the AdnexMR score as the

basis for the lexicon and the results of a subsequent large

prospective multicenter study as the foundation of the risk

stratiﬁcation system [28]. The ACR and other partners have

led the efforts to standardize imaging reporting in many other

anatomical regions, leading to the adoption of uniform

reporting descriptors and improved interpretation agreement

and providing the basis for structured reporting and best

clinical practice [29-33]. Standardized reporting and use of

consistent morphologic imaging descriptors and deﬁnitions

can result in improved accuracy for lesion characterization

and improved communication between radiologists

and clinicians, as well as allowing for high-impact research

[34-38]. The current article describes the formation of a

standardized lexicon by the ACR O-RADS MRI

Committee and the methodology used in its development.

METHODS

Under the direction of the Comm ission on US of the ACR

headed by Commission Chair, Beverly Coleman, MD, the

O-RADS Committee was created in 2015.

Committee Membership

Led by Rochelle F. Andreotti, MD, the multidisciplinary

international consortium was ﬁrst convened in November

2015. The committee includes a diverse, international group

of experts that represent specialties and organizations that

would be key to developing the O-RADS lexicon and risk

stratiﬁcation systems. The list of committee members is

listed in e-only Appendix 1 and the organizations that were

represented in the process in e-only Appendix 2.

After the initial meeting in November 2015, the O-RADS

committee decided in consensus that the lexicon and stratiﬁ-

cation systems would be developed for US and MRI, given the

important role of both modalities in adnexal mass character-

ization. Because of the different expertise required for both

imaging modalities, two parallel working committees were

formed to develop separate but consistent groups of terms

speciﬁc to each modality (Appendix). The O-RADS MRI

Committee is led by Dr. Caroline Reinhold, MD and the O-

RADS US Committee is led by Dr. Rochelle Andreotti, MD.

Process

The development of the O-RADS MRI standardized

reporting system used a two-step process. The ﬁrst step was to

develop an evidence-based, standardized lexicon using uni-

versally accepted terms for describing the imaging character-

istics of adnexal masses on MRI. Committee members and

nonmember gynecological imaging specialists contributed to

this phase. The methodology regarding the development of

the standardized MRI lexicon will be described in this article.

The second step was to develop the O-RADS MRI risk score,

and this is the topic of a separate publication [28].

Literature Search and Development of

Lexicon Terms

The development of the MRI lexicon involved a systematic

literature search from 1995 through 2019 performed by the

ACR with search terms provided by the members of the O-

RADS MRI Committee (CR, AR, IT, ES). This list was

cross-referenced with bibliographies assembled from the

Committee Members’ own literature searches. The articles

were reviewed independently by the O-RADS MRI Com-

mittee via an online questionnaire, and only articles that

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Table 1. ACR O-RADS MRI terminology, deﬁnitions, and corresponding image for lexicon categories 1 to 7

Category Term Subterm Deﬁnition Comments

1. Major categories

1a Physiological observations (consistent with normal physiology)

Follicle Simple cyst  3cmin

premenopausal age

group; follicle

hyperintense on T2WI,

hypointense on T1WI,

and does not enhance

on postcontrast T1WI

Premenopausal women

only

Corpus luteum Cyst  3 cm, with an

enhancing crenulated

wall on subtracted

postcontrast T1WI,

with or without blood

clot or hemorrhagic

contents

Premenopausal women

only

1b Lesions (not physiological)

Cystic lesion Unilocular cyst Single locule, with or

without solid tissue

Multilocular cyst More than one locule, with

or without solid tissue

Lesion with solid

component

Solid tissue Conforms to one of the

following morphologies

and enhances: papillary

formations, mural

nodules, irregular cyst

wall or septations, and

solid portion

Other solid components,

not considered solid

tissue

Smooth wall or septation,

clot or debris, fat

Not considered solid tissue

Solid lesion Consists of at least 80%

solid tissue with <20%

of lesion volume being

cystic

2. Size

Maximum diameter Largest diameter of the

lesion or solid

component in any

imaging plane

3. Shape or contour of solid lesion or solid tissue

3a Smooth Regular or even margin of a

solid lesion or solid

tissue

(continued)

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Table 1. Continued

Category Term Subterm Deﬁnition Comments

3b Irregular Uneven margin of a solid

lesion or solid tissue

4. Signal intensity

4a Homogeneous Uniform appearance of the

signal observed in an

adnexal ﬁnding

Heterogeneous Nonuniform or variable

appearance of the

signal observed in an

adnexal ﬁnding

4b T2 hypointense Adnexal observation with

signal intensity lower or

equal to iliopsoas

muscle

T2 intermediate Adnexal observation with

signal intensity higher

than iliopsoas and

lower than CSF

T2 hyperintense Adnexal observation with

signal intensity equal or

higher to CSF

4c T1 hypointense Adnexal observation with

signal intensity that

follows simple ﬂuid

T1 intermediate Adnexal observation with

signal intensity similar

or higher to iliopsoas

and lower than fat

T1 hyperintense Adnexal observation with

signal intensity equal or

higher to fat

4d DWI high B-value low

signal

Adnexal lesion with signal

similar to urine or

cerebral spinal ﬂuid

DWI high B-value high

signal

Adnexal lesion with signal

clearly higher than

urine or CSF

5. Lesion components

5a Cystic ﬂuid descriptors

Simple ﬂuid Fluid content that follows

CSF or urine on all

sequences:

hyperintense on T2WI

and hypointense on

T1WI

(continued)

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Table 1. Continued

Category Term Subterm Deﬁnition Comments

Nonsimple ﬂuid Hemorrhagic ﬂuid Content can be variable

depending on age

Late subacute hemorrhage

hyperintense on T2WI

and hyperintense on

T1WI

Endometriotic ﬂuid Content is hypointense on

T2WI and hyperintense

on T1WI

Proteinaceous ﬂuid Content is variable in signal

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

If microscopic fat present,

there will be signal loss

on out-of-phase

images and there may

not be any signal loss

on fat-saturated

images

Additional speciﬁc

descriptors for

nonsimple ﬂuid

Fluid-ﬂuid level Appearance in which the

nondependent ﬂuid

component has a

different signal

intensity from the

dependent ﬂuid

component with

horizontal delineation

Shading Cyst ﬂuid that is

hypointense on T2WI;

extent of hypointense

T2 signal intensity may

be homogeneous,

variable within the cyst

or graduated and

dependent

5b Solid component descriptors

Solid tissue: enhances and conforms to one of the listed morphologies

Solid tissue descriptors Papillary projection Enhancing solid component

arising from the inner

or 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

(continued)

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Table 1. Continued

Category Term Subterm Deﬁnition Comments

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

Irregular wall Enhancing cyst wall

demonstrating an

uneven margin

Larger solid portion Enhancing component of an

adnexal lesion that

does not ﬁt into the

categories of papillary

projection, mural

nodule, or irregular

septation or wall

Other solid components, not considered solid tissue

Smooth septations or wall Even contour or margin with

no irregularities, mural

nodules, or papillary

projections

Blood clot, nonenhancing

debris, and ﬁbrin

strand

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: T1WI postcontrast

6a Dynamic contrast enhancement with time intensity curves

Low-risk curve Enhancement of the solid

tissue within the

adnexal lesion with

minimal and gradual

increase in signal over

time with no well-

deﬁned shoulder and

no plateau

Intermediate-risk curve Enhancement of the solid

tissue within the

adnexal lesion with an

(continued)

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Table 1. Continued

Category Term Subterm Deﬁnition Comments

initial slope less than or

equal to 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 Nondynamic contrast enhancement at 30-40 s postinjection

Less than or equal to the

myometrium

Enhancement of the solid

tissue within the

adnexal lesion that is

less than or equal to

the outer myometrium

at 30-40 s postcontrast

injection

Greater than the

myometrium

Enhancement of the solid

tissue within the

adnexal lesion that is

greater than the outer

myometrium at 30-40 s

postcontrast injection

7. General and extra-ovarian ﬁndings

7a Peritoneal ﬂuid Physiological 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

(continued)

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were hypothesis driven and contained MRI ovarian lesion

descriptors were maintained. An online questionnaire was

used to (1) document the methodology of each study that

provided evidence for all descriptors of ovarian lesions, (2)

assess the frequency of usage of the terms, and (3) assess the

evidence as pertains to differentiating benign from malig-

nant adnexal lesions.

From this online questionnaire, the O-RADS MRI

Committee developed a preliminary set of terms and deﬁ-

nitions that could be applied to all adnexal lesions derived

from the key articles. For each term, a recommendation to

either include or omit the term was undertaken based upon

analysis of all available pertinent descriptors and the evi-

dence underlying their usage. Major categories of morpho-

logical descriptors were developed, and a list of individual

descriptors related to each major category was created. Some

of the titles of the major categories, as well as individual

descriptors, evolv ed during ensuing committee discussions

to reﬂect their meaning more accurately or to maintain

consistency with the terms proposed by the O-RADS US

Committee [10].

The next step involved a modiﬁed Delphi process that

involved 14 gynecological MR imaging experts, eight of

whom were O-RADS MRI Committee members (CR, AR,

IT, ES, EAS, KM, RF, AV). The purpose of the modiﬁed

Delphi process was to rate the usage of descriptor terms using

an online survey in which individual descriptors were rated

using a 1 to 5 scale (strongly disagree to strongly agree). The

committee sought a minimum 80% consensus to determine

if a term would be included (rating consensus of 4-5) or

excluded (rating consensus of 1-2). Spreadsheets that

included the original reference articles from the literature were

available to each member for evaluation, to allow evidence-

based and usage-driven responses while minimizing individ-

ual bias. On occasion, the committee agreed that even a

frequently used term should be intentionally excluded when

deemed vague or confusing (eg, “complex cyst”). Descriptor

terms that did not achieve the minimum 80% consensus on

the initial round underwent a rerating and voting process via

teleconference, group emails, and online survey. Only those

terms that reached the ultimate target of 80% consensus were

incorporated into the lexicon.

A lexicon of MRI descriptor terms was derived and

organized into seven major categories (Table 1). MRI-speciﬁc

terms and descriptor terms for the solid and ﬂuid components

of adnexal lesions were compiled. This permitted us to go

forward with evidence-based standardized terminology for

major categories of adnexal lesions, which could then be

Table 1. Continued

Category Term Subterm Deﬁnition Comments

7c Peritoneal inclusion cyst Cyst following contour of

adjacent pelvic organs,

or normal ovary at the

edge of or surrounded

by a cystic collection

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

postcontrast

7e Peritoneal thickening,

nodule

Thickening, smooth Uniform thickening, without

focal nodularity

Thickening, irregularity Nonuniform thickening or

focal areas of

nodularity

MRI sequences are speciﬁcally noted in the descriptive text only if they are important to the term being deﬁned. For example, the ﬂuid content

of a follicle is hyperintense on T2WI; however, unilocular is deﬁned regardless of the imaging sequence. CSF ¼ cerebral spinal ﬂuid; DWI ¼

diffusion- weighted image; O-RADS ¼ Ovarian-Adnexal Reporting and Data Systems; T1WI ¼ T1- weighted imaging; T2WI ¼T2- weighted

imaging.

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modiﬁed by additional MRI-speciﬁc characteristics, including

T2 signal intensity, T1 signal intensity, diffusion-weighted

imaging (DWI), and enhancement characteristics.

O-RADS MRI TERMINOLOGY AND

DEFINITIONS

Table 1 provides terms and deﬁnitions in the seven lexicon

categories, with pictorial representations of the major

concepts in Figures 1 to 4. A general MRI protocol for adnexal

mass characterization is provided in e-only Appendix 3.

Category 1: Major Categories

Findings in the ovaries and adnexa can be unilateral or

bilateral. When multiple ﬁndings are present, a separate

process of description and characterization should be per-

formed for each individu al observation.

The ovary undergoes substantial morphologic change each

month during reproductive life [39]. Therefore, the ﬁrst

fundamental distinction is between physiological observations

and nonphysiological observations, known as lesions.

1a: Physiological Observations.

i. Follicles are present in ovaries of premenopausal women

and deﬁned as unilocular simple cysts 3 cm.

ii. Corpus luteum is a transient hormone-producing structure

at the site of a follicle that has released an ovum. The wall

is thicker than that of a follicle and enhances after contrast

administration, often with a characteristic pattern of reg-

ular infoldings known as crenulation. If the wall reseals

after ovulation, simple or hemorrhagic internal contents

may accumulate and form a corpus luteum cyst.

1b: Lesion. Part of an ovary or adnexa that is not normal

physiology (ie, not follicles or corpus luteum cysts). Lesions

Fig 1. Lesion is a ﬁnding in the adnexa that is not normal

physiology (ie, not a follicle or corpus luteum cyst). (A)

Unilocular cyst without solid tissue. (B) Multilocular cyst

without solid tissue. (C) Lesion with solid tissue, papillary

projection. (D) Lesion with solid tissue, nodule. (E) Lesion

with solid tissue, irregular septation or wall. (F) Lesion with

solid tissue, larger solid portion. (G) Solid lesion.

Fig 1. Continued.

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Ovarian-Adnexal Reporting Lexicon for MRI

may be further cha racterized as cystic without solid

component, cystic with solid comp onent, or solid (Fig. 1).

i. Cystic lesions are ﬂuid-ﬁlled structures with or without

solid components.

1. Unilocular cystic lesions contain a single locule, with

no complete septations. A complete septation is a

linear strand that runs across a cyst cavity, from one

internal surface to the contralateral side, and

enhances. Unilocular cysts, however, may contain

incomplete septations deﬁned as septations that are

interrupted or discontinuous.

2. Multilocular cystic lesions contain one or more

complete septations, dividing the lesion into more

than one locule.

ii. “Solid component” ref ers to any nonﬂuid component

of a lesion. There are two types of solid components:

Fig 2. Solid tissue and nonsolid tissue. (A) Solid tissue conforms to one the following morphologies (white arrows) on T2-

weighted imaging: papillary formation (left), mural nodules (middle), irregular cyst wall or septation, and solid portion (right).

By deﬁnition, solid tissue enhances (black arrows) on T1-weighted imaging postcontrast. (B) Nonsolid tissue: debris that does

not enhance on T1-weighted imaging postcontrast (black arrows, left), thin septations (arrowheads, middle) that may or may

not enhance, and fat (white arrow, top right), which decreases in signal intensity on fat-saturated images (black arrow,

bottom right).

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solid tissue and other solid components (not solid

tissue).

1. “Solid tissue” is deﬁned as exhibitin g postcontrast

enhancement and conforms to one of the following

morphologies: papillary projections, mural nodules,

irregular septations or walls, and a larger solid portion

(Figs. 2 and 3).

2. Other solid components (not solid tissue) include

smooth wall or septation, clot, debris, and fat within a

lesion (Fig. 2).

iii. A solid lesion consists of at least 80% solid tissue with

<20% of lesion volume being cystic or nonsolid tissue.

Category 2: Size

O-RADS MRI lexicon recommends measuring the

maximum diameter of the lesion in any plane as the stan-

dard. If there is solid tissue, the maximum diameter of the

solid tissue should be measured. The volume obtained from

the largest three diameters is not recommended,because no

evidence exists that it predicts behavior.

Category 3: Shape or Contour of Solid Lesion

or Solid Tissue

Two descriptors categorize the contour of a solid lesion or

solid tissue: smooth and irregular. Evaluation of the contour

Fig 3. Low-risk (A), intermediate-risk (B), and high-risk (C) time intensity curves are derived from the dynamic postcontrast

series. The curves are generated by placing one region of interest on the earliest enhancing region of the solid tissue in the

adnexal lesion and one region of interest on the outer myometrium avoiding the arcuate vessels.

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can be performed with any MR pulse sequence that opti-

mally shows the interface of the solid tissue with the sur-

rounding tissues or adjacent ﬂ uid.

3a: Smooth. Regular or even shape or contour of the

margin.

3b: Irregular. Uneven shape or contour of the margin.

i. Spiculated: inﬁltrative appearance to the margin.

ii. Lobular: undulation or scalloped appearance of the margin.

Category 4: Signal Intensity

There are four subcategories of signal intensity described.

These categories include homogeneous versus heterogeneous

signal intensity and the relative signal intensity on T1, T2,

and high B-value diffusion-weighted images.

4a: Homogenous Versus Heterogeneous. The signal

intensity of the solid and ﬂuid components can be described

as homogeneous or heterogeneous. “Homogeneous signal

intensity” refers to uniformness of the signal observed, and

“heterogeneous signal intensity” refers to nonuniform or

variable appearanc e of the signal observed.

4b: T2 Signal Intensity. T2 signal is subdivided into

three categories: hypointense, intermediate, and hyperin-

tense. T2 hypointense observations have similar or lower

signal intensity than iliopsoas muscle. T2 intermediate ob-

servations have higher signal intensity than the iliopsoas

muscle and lower than cerebral spinous ﬂuid (CSF).

Hyperintense observations are similar in signal intensity to

CSF.

4c: T1 Signal Intensity. T1 signal intensity is subdivided

into three categories: hypointense, intermediate, and

hyperintense. T1 hypo intense observations have signal in-

tensity that follows CSF. T1 intermediate observations have

similar or higher signal than iliopsoas and lower signal than

fat on non–fat-saturated pulse sequences. T1 hyperintense

observations have equal or higher signal intensity to fat on

non–fat-saturated pulse sequences.

4e: High B-Value DWI Signal Intensity. Signal in-

tensity on the high B-value (B  1,000) DWI is subdivided

into two categories: low and high. “Low ” refers to signal on

a high B-value DWI that is relatively similar to simple ﬂuid

(urine or CSF). “High” refers to signal that is higher than

simple ﬂuid (urine or CSF). The presence of restricted

diffusion is not speciﬁc for malignancy because hemorrhagic

portions of benign endometriomas, infected ﬂuid, and fatty

portions of mature cystic teratomas can be high signal on

high B-value images and low signal on the corre sponding

Fig. 4. Fluid descriptors. (A) Simple: ﬂuid content that fol-

lows CSF or urine on all sequences; hyperintense on T2-

weighted imaging (T2WI) (black asterisk) and hypointense

on T1-weighted imaging (T1WI) (white asterisk). (B) Hem-

orrhagic ﬂuid: variable depending on age; late subacute

hemorrhage is hyperintense on T2WI (black asterisk) and

hyperintense on T1WI (white asterisk). (C) Endometriotic

ﬂuid: hypointense on T2WI (white asterisk) and hyperin-

tense on T1WI (black asterisk). (D) Proteinaceous: variable

in signal on T2WI (white and black asterisks; left image)

and variably hypointense on T1WI (white and black aster-

isks right image). (E) Fat or lipid containing: hyperintense on

T2WI and hyperintense on T1WI (black asterisk), and loses

signal on fat-saturated images (white asterisk).

Fig. 4. Continued.

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apparent diffusion coefﬁcient (ADC) maps [40,41]. Solid

tissue will enhance, whereas blood, infected ﬂuid, and fat

will not enhance.

Category 5: Lesion Components (Cystic and

Solid)

5a: Cystic Fluid Descriptors. The ﬂuid within a cystic

lesion can be categorized as either simple or nonsimple,

based on the observed signal intensity of the ﬂuid on T1-

weighted imaging (T1WI) and T2-we ighted imaging

(T2WI) (Fig. 4).

i. Simple ﬂuid follows the signal intensity of CSF on all

sequences.

ii. Nonsimple ﬂuid has signal intensity that does not meet

criteria for simple ﬂuid. The signal intensity is variable to

CSF and may reﬂect blood, lipid, or proteinaceous ﬂuid.

1. Hemorrhagic ﬂuid demonstrates variable signal in-

tensity on T2WI, T1WI, and DWI. The signal in-

tensity depends on the age of the blood [42-44].

2. Classic endometriotic ﬂuid is homogeneous and T1

hyperintense and demonstrates either hypointense or

intermediate T2 signal intensity called shading.

Diffusion signal intensity and restriction are variable.

In endometriotic cysts or endometriomas, there may

be the speciﬁc ancillary ﬁnding on T2WI of black

nodules or linear foci in the wall.

3. Proteinaceous ﬂuid (mucinous or purulent or colloid)

demonstrates variable T2 hypo-intensity, varia ble T1

signal intensity, and variable DWI signal intensity.

4. Fat- or lipid-containing ﬂuid (eg, dermoid or benign

mature teratoma) is T2 hyperintense and T1 hyper-

intense with signal dropout on fat-saturated imaging.

Microscopic or intravoxel fat can be identiﬁed by loss

of signal intensity on out-of-phase images and may

not exhibit signal loss on fat-saturated images.

iii. Additional speciﬁc descriptors for nonsimple ﬂuid:

1. “Fluid-ﬂuid level” describes an appearance in which

the nondependent portion has a different signal in-

tensity from the dependent portion with horizontal

delineation. This may be seen when there is a mixture

of two ﬂuid types of different intensity within the

same lesion.

2. “Shading” is characteristic of endometrioma and

older hemorrhagic ﬂuid [45]. This describe s cyst ﬂuid

that is hypointense or intermediate T2 signal

intensity; the signal intensity may be homogeneous,

variable within the cyst, or graduated and dependent.

5b: Solid Component Descriptors. Cysts are delineated

by a wall and may contain septations or solid components,

all of which may be seen to enhance on postcontrast T1WI.

The cyst wall and any septations may be described as smooth

or irregular, depending if there are any irregularities, papillae,

or mural nodules present. The presence of an enhancing

irregular wall or septations or papillary projections or mural

nodules indicates the presence of solid tissue (Figs. 2 and 3).

i. “Solid tissue” is deﬁned by the presence of enhancement and

conforms to one or more of the following morphological

appearances listed below (1-4) (Figs. 1 and 2). If solid tissue

is present in a lesion, the lesion may be further characterized

by evaluating the time intensity curve (TIC) within the solid

tissue (see Category 6) (Fig. 3).

1. Papillary projection has a distinct appearance on MRI

that is deﬁned by a protrusion with a stalk, an acute

angle with the cyst wall, septation or surface of the

ovary, with typically a visible branching architecture.

A papillary projection may lie within a cyst, arise from

a septation (endocystic), or may arise on the external

surface of the ovary or cyst (exophytic).

2. Mural nodule is a focal protrusion along the wall or

septation of a cystic lesion that has a height of 3mm

and has outward convex borders and a more obtuse

angle in relation to the cyst wall or septation than a

papillary projection.

3. Irregular septation or wall demonstrates uneven

margin that varies in thickness along its length.

4. Larger solid portion enhancing component of an

adnexal lesion that does not ﬁt into the categories of

papillary projection, mu ral nodule, or irregular sep-

tation or wall. A solid lesion consists of at least 80%

solid tissue.

ii. Other solid components not deﬁned within the term

“solid tissue” include any components of the lesion that

are not ﬂuid and do not conform to the deﬁnition of

solid tissue described previously (Fig. 2). Other solid

components may or may not enhance. For solid

components such as thin septations or Rokitansky

nodules that enhance, comparisons to the enhancement

of the myometrium should not be performed or

reported as part of the O-RADS MRI risk score [28].

1. Smooth septation or wall has an even contour. Smooth

septations may enhance after contrast administration.

2. Blood clot can be variable in signal intensity depending

on the age of the clot and does not enhance post-

contrast. Debris and ﬁbrin strands are lacelike or

cobweb-type strands seen in hemorrhagic or proteina-

ceous cysts and do not enhance after contrast

administration.

3. Fat, hair , and calciﬁcations as part of a dermoid cyst.

Fat, hair, and calciﬁcations do not enhance after

contrast enhancement. A Rokitansky nodule is a solid

component within a dermoid cyst and it may

Journal of the American College of Radiology 725

Clinical Practice Management

Reinhold et al

Ovarian-Adnexal Reporting Lexicon for MRI

enhance; however, it is not termed solid tissue. A

Rokitansky nodule usually contains fat and may be

associated with multiple septations.

Category 6: Enhancement

In an adnexal lesion, it is important to identify the presence

of any enhancement. If there is no enhancement (no increase

in signal on T1WI after intravenous gadolinium-based

contrast injection), the lesion is almost certainly benign

[15,16,25,28]. To evaluate for the presence of enhancement,

especially in a lesion that contains any high T1W signal,

subtracted images are optimal. Any portion of the lesion

may enhance, including the wall, septations, and solid tissue.

The recommended method for assessing enhancement is

performing a dynamic contrast enhancement (DCE) MRI

acquisition (e-only Appendix 3). Alternatively, a nondynamic

contrast MR acquisition is acquired precontrast and at 30 to

40 seconds after contrast injection (e-only Appendix 3). A

DCE MRI acquisition is a postcontrast 3-D T1WI fat-

saturated sequence with a minimal spatial resolution of 3

mm and a temporal resolution of 15 seconds and allows

complete coverage of the lesion. A TIC can be obtained by

placing one region of interest on the earliest enhancing region

of the solid tissue in the adnexal mass and one region of

interest on the outer myometrium avoiding the arcuate vessels

(as an internal reference standard). If DCE MRI is not

available, the analysis of relative enhancement on the 3-D

T1WI at 30 to 40 seconds after contrast injection of the

solid tissue related to outer myometrium may be used.

6a: Dynamic Enhancement With TICs.

i. “Low-risk TIC” is deﬁned as a gradual increase in the

signal of solid tissue, slower than the myometrium,

without a well-deﬁned shoulder and no plateau (corre-

sponds to TIC type 1) [28].

ii. “Intermediate-risk TIC” is deﬁned as a moderate initial

rise in the signal of solid tissue, slower than or equal to

the myometrium, followed by a plateau (corresponds to

TIC type 2) [28].

iii. “High-risk TIC” corresponds to an initial rise in the signal

of solid tissue that is faster (steeper) than myometrium,

followed by a plateau (corresponds to TIC type 3) [28].

6b: Nondynamic Enhancement Visual Analysis at 30

to 40 Seconds After Contrast Enhancement.

i. Less than or equal to the outer myometrium

ii. Greater than the outer myometrium

In the absence of a uterus, a low-risk TIC can be

recognized by its progressive enhancement (no plateau),

whereas intermediate- and high-risk TICs cannot be

distinguished. The level of enhancement should be esti-

mated according to the expertise of the radiologist. The

committee agreed to change the name of TICs to low, i nter-

mediate, or high risk rather than using a number as in previous

publications to be more descriptive and avoid potential

confusion with O-RADS MRI risk score assignment [28].

Solid tissue may be encountered in benign lesions as well

as in borderline or malignant lesions. The nature of the

enhancement may help to differentiate benign from malig-

nant lesions, which is the purpose of the O-RADS MRI

score for risk score of adnexal lesions [28].

Category 7: General and Extra-Ovarian

Findings

Several general ﬁndings are relevant to the description of

adnexal lesions on MRI that we include in the lexicon.

7a: Peritoneal Fluid. Physiological ﬂuid should be used to

describe a small amount of ﬂ uid inside the pouch of Douglas

(ie, cul-de-sac) or ﬂuid in the space between the uterus and

bladder. “Ascites” is deﬁned as abdominal or pelvic ﬂuid

outside of the pouch of Douglas (ie, cul-de-sac) or ﬂuid

extending beyond the space between the uterus and bladder.

7b: Fallopian Tubes. These may be visualized on MRI,

particularly when ﬂuid ﬁlled (ie, hydrosalpinx). The

morphologic descriptor “tubular” is deﬁned as a structure

that is substantially longer in one dimension than in the two

perpendicular dimensions. Endosalpingeal folds may also be

visualized on MRI and are orthogonal to the length of the

tube (short axis), typically appearing as incomplete septa-

tions or short round projections. Fallopian tubes should

have thin walls measuring <3 mm and the wall is considered

thickened when it measures 3 mm.

7c: Peritoneal Inclusion Cyst. These cysts occur in

women with a history of pelvic surgery, trauma, or chronic

pelvic inﬂam mation from various causes including endo-

metriosis. The term should be used to describe a cyst that

follows the contour of the peritoneal cavity and adjacent

pelvic organs or in the presence of a normal ovary at the

edge of or surrounded by a cystic collection of ﬂuid.

7d: Ovarian Torsion. Ovarian torsion can mimic ovarian

malignancy on other imaging modalities, particularly when

it is chronic in nature. Ovarian torsion occurs when the

blood ﬂow to the ovary is impeded by “twisting” of the

vascular pedicles. If the twisting is not reversed, ovarian

infarction can occur. Chronic ovarian torsion may result in

the appearance described as “massive ovarian edema,”

deﬁned by an enlarged ovary with edematous central stroma

and peripherally displaced follicles.

7e: Peritoneal Thickening or Nodules. Peritoneal

thickening describes prominence of the peritoneal surfaces

that become discretely visible on MRI and should be

726 Journal of the American College of Radiology

Volume 18

Number 5

May 2021

categorized as “smooth” when thickening is unifo rm or

“irregular” when there is nonuniform thickening or there are

focal areas of nodularity.

DISCUSSION

The added value of MRI lies in its ability to accurately

characterize adnexal lesions that are deemed sonographically

indeterminate, despite the use of advanced analytics and

high-level sonographic expertise [18,25, 46,47] Studies

support the use of MRI as a secondary test to (1) decrease

the number of false-positive diagnoses of cancer when us-

ing US and (2) to potentially reduce the number of un-

necessary surgeries performed for benign lesions [6,13,14].

Recently, Thomas sin-Naggara et al found that the O-

RADS MRI score achieved a sensitivity of 93% and speci-

ﬁcity of 91%, for diagnosing malignant adnexal lesions that

were sonographically indeterminate. In addition, the same

study found that a lesion without any enhancement has a

positive likelihood of malignancy of <0.01 [28].

In a continued effort toward global standardization of

radiological reporting, the ACR O-RADS committee was

established, an international multidisciplinary working

committee for ovarian-adnexal mass characterization using

US and MRI. This process included the development of a

universally accepted set of standardized terms and deﬁni-

tions. Such a lexicon would provide the basis for a stan-

dardized reporting and risk strati ﬁcation system of adnexal

or ovarian masses. The ACR O-RADS US lexicon and risk

stratiﬁcation system has recently been published by

Andreotti et al [10,11]. In keeping with the use of MRI as a

secondary modality in adnexal lesion evaluation, the O-

RADS US management schema includes the

recommendations for MRI lesion characterization in

multiple risk categories.

The ACR O-RADS MRI lexicon presented in this

article encompasses seven categories of descriptors of adnexal

masses that were derived by consensus of expert radiologists

in the ﬁeld of female pelvic MRI using a modiﬁed Delphi

process. These categories include general descriptors, as well

as morphological and functional MRI properties of ﬂuid and

tissue. The combination of these descriptors allows for

speciﬁc characterization of adnexal masses. Although cate-

gories 2 to 6 include descriptions of the lesion, category 7

summarizes secondary ﬁndin gs important for tumor

dissemination as well as cystic lesions that can be speci ﬁcally

characterized by imaging (eg, fallopian tube dilation, ovarian

torsion, and peritoneal inclusion cyst). Despite its common

use in the literature, the nonspeciﬁc term “complex adnexal

lesion” was eliminated and replaced by concise descriptors of

the lesion morphology. This is in keeping with the approach

taken by the O-RADS US lexicon [10].

Characterization of adnexal lesions is mainly based on

the combination of morphologic features with its functional

properties on DWI and DCE. Contrast dynamics compared

with the myometrium using TIC have been shown as a

pivotal feature for predicting malignancy [22,48

]. Of note,

this can onl y be applied to the solid tissue within an

adnexal mass. Thi s warranted clariﬁcation of the term

“solid tissue,” which conforms only to papillary

projections, mural nodules, irregular cyst wall and

septations, and larger solid portions within an adnexal

mass. In contrast, other solid components (smooth

enhancing cyst wall or septations, nonenhancing debris,

clot, fat or Rokitansky nodule) are not considered solid

tissue.

The ACR O-RADS MRI lexicon was developed to

provide a comprehensive set of terms and deﬁnitions for the

broad spectrum of adnexal ﬁndings ranging from physio-

logical to malignant entities. Its widespread implementation

as a standardized lexicon will improve reporting and inter-

disciplinary communication by eliminating uncertainties in

term usage and thus help optimize patient management.

The consistent use of these descriptors may also provide a

basis for future research and serve as a means for multi-

institutional collaborations.

TAKE-HOME POINTS

- The O-RADS MRI lexicon is a multidisciplinary in-

ternational initiative with the goal of developing

standardized terminology for the evaluation of ovarian

and adnexal lesions with MRI.

- Consistent application of the O-RADS MRI lexicon

terms in a standardized report has the potential to

increase accuracy of lesion characterizatio n, improve

interdisciplinary communication, and promote opti-

mized patient management of adnexal and ovarian

lesions.

- Thi s lexicon is used in the O-RADS MRI risk strati-

ﬁcation system to assign a malignancy risk to adnexal

lesions and provide actionable information in the

imaging report.

ACKNOWLEDGMENTS

This document was developed with nation ally and interna-

tionally recognized experts in gynecological imaging, gyne-

cological clinical services, and gynecological cancer care,

representing Canadian Association of Radiologists (CAR)

and European Society of Radiology (ESR). The ACR ac-

knowledges Société d’Imagerie de la Femme (SIFEM) as a

promoter of the EURAD study, which provided data for the

basis of this lexicon development. The acknowledgment

Journal of the American College of Radiology 727

Clinical Practice Management

Reinhold et al

Ovarian-Adnexal Reporting Lexicon for MRI

afﬁrms the ACR’s appreciation to the ESR, and SIFEM but

does not imply, infer, or denote approval or endorsement of

the document. The authors acknowledge the contribution of

specialist consultants Drs. Stephen Rose, Bradford Whit-

comb, Wendy Wolfman, and Blake Gilks for their partici-

pation on the O-RADS Committtee. The members of the

Steering Committee of O-RADS MRI were not compensated

for their time. We acknowledge the support of the O-RADS

Steering Committee from the American College of Radiology

and the European Society of Radiology. We are also grateful

for the assistance given by ACR staff Mythreyi Chatﬁeld,

Lauren Attridge, Dipleen Kaur and Cassandra Vivian-Davis.

Dr Rockall acknowledges the support of the National Insti-

tute of Health Research Imperial Biomedical Research

Centre and the Cancer Research UK Imperial Centre.

ADDITIONAL RESOURCES

Additional resources can be found online at: https://doi.

org/10.1016/j.jacr.2020.12.022

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