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American College of Radiology 3

BI-RADS MRI

s in the mammography BI-RADS lexi-con, there are sources of confusion inusing the ACR BI-RADSMRI lexicon.

Some confusion occurs because descriptors maybe used more than once to describe different fea-tures of a mass. Specifically, the descriptor IR-REGULAR is both a mass shape and a massmargin, which could conceivably result in an ir-regularly shaped mass with an irregular mar-gin. For this situation, we recommend that theterm IRREGULAR be used only once to de-scribe the mass shape or mass margin.

Differentiation between a very large, irregu-lar heterogeneous mass and a large heterogeneousarea of regional enhancement also has been both-ersome to the committee, since both termsdescribe abnormally enhancing large volume-occupying findings. To help in this distinction,a MASS should have definable margins witha separable distinct edge from the surroundingglandular tissue. In general, a MASS isusually composed of a pathologic process in aball-like three-dimensional structure. On the otherhand, REGIONAL ENHANCEMENT is notas distinct from the surrounding elements,REGIONAL ENHANCEMENT may representnormal or pathologic changes, depending onthe character of the enhancement within the

region. For example, STIPPLED REGIONALENHANCEMENT describes tiny separated dotsof enhancement over a large area, suggestive of fibrocystic change within the structure of the glan-dular elements, displayed as tiny enhancing fociseparated by islands of fat and nonenhancing glan-dular tissue. REGIONAL ENHANCEMENTcan also represent abnormal pathologic processes

such as a large heterogeneously enhancing ex-tensive breast cancer, or a wide area of RE-GIONAL CLUMPED ENHANCEMENT repre-senting ductal carcinoma in situ (DCIS). How-ever, even using these guidelines, categorizationof large enhancing findings into MASS or RE-GIONAL ENHANCEMENT may still proveproblematic, since one persons large mass maybe another persons regional enhancement.

There has been confusion regarding the nounsFOCI or FOCUS, which describe a specifictiny dot or dots of enhancement that cannototherwise be characterized, compared to thedistribution descriptor FOCAL AREA, describ-ing a small region of NON-MASS-LIKE abnor-mal enhancement. A FOCUS is a small isolatedspot of enhancement, generally less than 5 mmin size, that is so tiny that no definitive morpho-logic descriptors can be applied to it, and so smallthat ROI dynamic data may be spurious due topartial volume averaging with surrounding nor-mal tissue. FOCI describe several such tinyspots separated widely by normal tissue so thateach tiny spot of enhancement can be considereda separate entity.

A FOCAL AREA of enhancementdescribes a small area of abnormal enhancement(larger than a FOCUS) that contains a specific

characteristic morphologic enhancing pattern thatcan be distinguished from the surroundingnormal tissue, has isolated spots of fat or normalglandular tissue within it (to distinguish it froma MASS), and is larger than a FOCUS.In general, a FOCAL AREA occupies less than25% of a breast quadrant volume. For example,a 1 cm FOCAL AREA of CLUMPED enhance-

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ment near the chest wall might be used todescribe a small region of DCIS, whereas a1 cm FOCAL AREA of STIPPLED enhance-ment might describe a small region of fibrocysticchange.

Other questions arose regarding the termsLINEAR, DUCTAL, and SEGMENTAL.The term LINEAR describes enhancementin a line that is not definitely in a duct andcannot be otherwise characterized. On three-dimensional images, LINEAR enhancementdescribed from a sagittal image might be seen torepresent a sheet of enhancement that is seen asa line on the sagittal tomographic slice. DUC-

TAL enhancement describes abnormal enhance-ment in a linear distribution that may branch, mayhave smooth or irregular margins, and is point-ing toward the nipple, representing enhancementin breast ducts and its branches. DUCTALenhancement can best be discerned on imageswith enough high spatial resolution to define andseparate individual ducts.

SEGMENTAL enhancement is enhance-ment in single ductal system resulting in a cone

or triangular area of enhancement with itsapex pointing at the nipple. SEGMENTALenhancement may be seen more frequently onthicker sections, but the same process mightshow individual DUCTAL enhancement if the spatial resolution were high enough. BothDUCTAL and SEGMENTAL enhancementrepresent enhancement in ductal structures, how-

ever, the morphologic appearance of the ductalsystem on MRI depends on spatial resolution aswell as the orientation of the viewing plane.

Breast MRI is a developing field, and it isexpected that technical advances will allow fastertemporal acquisitions and higher spatial resolu-tion, easier acquisition of physiologic images, andnew types of image display. The current ACR BI-RADSMRI lexicon reflects current technology,but it is to be expected that the Breast MRI lexi-con will be a living document, that the lexiconwill be continually updated and changed as newsequences and imaging techniques develop.

The ACR BI-RADSMRI lexicon is

arranged to be used in everyday practice. Con-stant use of the lexicon should make it possibleto issue meaningful, unambiguous breast MRIreports. As a document that is expected to changewith advances in morphologic and dynamicimaging techniques, the committee welcomes anycomments and/or suggestions, and requests thatthey be addressed in writing to the ACR.

ACR BI-RADSMRI Lexicon Committee

American College of Radiology1891 Preston White Drive

Reston, Virginia 20191Fax: (703) 246-5287

E-Mail: carlam@acr.orgDebra M. Ikeda, M.D., Committee Chair Nola Hylton, Ph.D., Committee Co-Chair