Focus (breast MRI)

Last revised by Monica Wong on 4 Sep 2019

A focus in the context of breast MRI using the BI-RADS lexicon refers to a unique enhancing dot that is too small to characterize further morphologically as a mass or nonmass enhancement. Usually, a focus is smaller than 5 mm.

  • T1 C-: no corresponding finding; possibly fatty hilum favors a benign process
  • T1 C+ FS: punctate signal that stands out from the background parenchymal enhancement, usually <5 mm
    • delayed images: persistence favors benignity 1, while plateau or washout kinetics are suspicious for malignancy 2, although kinetic data may be spurious due to partial volume averaging 3
  • T2: if present, hyperintensity (cyst-like) favors benignity, such as lymph nodes or myxomatous fibroadenomas

The radiologist must decide whether an enhancing area reflects a focus, focal area of nonmass enhancement, mass, or background parenchymal enhancement. For example, if an enhancing finding can be defined by irregular shape, noncircumscribed margins, or internal enhancement characteristics, it should be described as a mass 3. If it does not stand out from other foci, it should be described as background parenchymal enhancement.

A focus may be benign or malignant, with the estimated risk of malignancy differing widely between studies, ranging from 0.6 to 37% 1,2,4-6. At the index study, a focus is commonly assessed as probably benign and short term follow up is recommended (BI-RADS 3). Scattered multiple foci, a focus with long term stability, a decreasing or resolved focus, a focus with 100% persistent delayed kinetics, or a focus with cyst-like features may be considered benign (BI-RADS 2). Conversely, a focus that is new, enlarged, or showing washout kinetics may be viewed as suspicious (BI-RADS 4).

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