Non-mass enhancement (breast MRI)

Last revised by Henry Knipe on 14 Apr 2020

Non-mass enhancement at breast MRI is defined in the BI-RADS lexicon as an area of enhancement that does not meet criteria for a mass, such as by having nonconvex borders or intervening fat or fibroglandular tissue between the enhancing components.

A wide variety of benign, high risk and malignant processes can manifest as non-mass enhancement 2,6:

The BI-RADS lexicon (5th edition) provides standard descriptors for the distribution and internal pattern of non-mass contrast enhancement 1.

  • distribution
    • focal: confined area less than a breast quadrant characterized by a non-mass internal enhancement pattern
    • linear: straight, curved, or branching arrangement of enhancement, suggestive of ductal or periductal involvement
    • segmental: triangular or conical arrangement with the apex directed toward the nipple, suggestive of ductal or periductal involvement
    • regional: area larger than a breast quadrant
    • multiple regions: more than one large area, separated by normal tissue, not conforming to a ductal distribution (patchy)
    • diffuse: randomly arranged throughout the breast
  • internal enhancement patterns
    • homogeneous: confluent and uniform
    • heterogeneous: randomly separated by normal tissue in a nonuniform pattern
    • clumped: small aggregates of enhancement ("cobblestone" like)  in various sizes and shapes, suggestive of ductal involvement; used in combination with focal, linear, segmental, or regional distribution
    • clustered ring: multiple small ring shapes closely arranged, suggestive of periductal involvement

In general, a substantial minority of non-mass enhancement proves to be malignant 3-5. Second-look breast ultrasound is prudent to look for a correlate that can be targeted for ultrasound-guided rather than MRI-guided breast biopsy.

Alternative considerations for describing an enhancing area depends on the size, shape, and distinctness from the rest of the breast parenchyma:

Non-mass enhancement is usually assessed as suspicious and managed with core needle biopsy (BI-RADS 4). 

There are limited data supporting a probably benign assessment for certain types of non-mass enhancement (BI-RADS 3), which remains a matter of intuition for most radiologists 1. In one newer study, a linear distribution of non-mass enhancement <1 cm that is not branching is probably benign 7. Anecdotal experience suggests homogeneous non-mass enhancement in a focal, regional, or multiple regions distribution on baseline examination may also fit this category 8,9.

In some clinical situations, enhancement could be transient and related to hormonal status. For instance, a premenopausal patient may be scanned in a suboptimal part of her cycle, or a postmenopausal patient may be taking hormone replacement therapy. If this is suspected but the finding is not clearly background parenchymal enhancement, the non-mass enhancement may be assessed as probably benign (BI-RADS 3) with a recommendation for a very short interval follow up (2-3 months), timed for week 2 of the patient's cycle or after suspending hormonal therapy 1.

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