Non-mass enhancement (breast MRI)

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.

Pathology

Etiology

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

• fibrocystic changes
• pseudoangiomatous stromal hyperplasia (PASH)
• apocrine metaplasia
• radiation therapy effect
• flat epithelial atypia
• atypical ductal hyperplasia
• radial scar/complex sclerosing lesion
• intraductal papilloma
• ductal carcinoma in situ
• invasive carcinoma of no special type (ductal carcinoma not otherwise specified)
• invasive lobular carcinoma

Radiographic appearance

MRI

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

• 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

Treatment and prognosis

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

Differential diagnosis

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

• focus
• background parenchymal enhancement
• mass

Practical points

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 . In one newer study, a linear distribution of non-mass enhancement <1 cm that is not branching is probably benign . Anecdotal experience suggests homogeneous non-mass enhancement in a focal, regional, or multiple regions distribution on baseline examination may also fit this category .

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 .