Background parenchymal enhancement (breast MRI)

Background parenchymal enhancement on breast MRI refers to the normal contrast enhancement of fibroglandular tissue.

Epidemiology

Background parenchymal enhancement is more common in younger patients with dense breasts ^1,8. Reflecting hormonal influence, background enhancement is decreased after menopause ².

Radiographic appearance

MRI

Background parenchymal enhancement is depicted on T1 weighted images with fat suppression. Subtraction maximal intensity projections can be helpful.

Background enhancement usually appears as a homogeneous or stippled area (multiple tiny dots separated by nonenhancing parenchyma), in a bilateral diffuse or regional distribution. Due to preferential vascular supply, greater enhancement is seen in the upper outer quadrant and along the inferior aspect of the breast ¹.

The level of background enhancement is assessed on the first postcontrast acquisition, at approximately 90 seconds. On delayed images, background enhancement is persistent (progressive/increased in intensity compared to the first postcontrast phase).

Radiology report

The BI-RADS lexicon provides standard descriptors for the level and symmetry of background parenchymal enhancement ¹:

• level (evaluated relative to the amount of fibroglandular tissue and not total breast volume)
  • minimal
  • mild
  • moderate
  • marked
• symmetry
  • symmetric (equal in both breasts)
    • suggestive of normal, benign background parenchymal enhancement
  • asymmetric (more prominent in one breast than the other)
    • due to unilateral processes such as prior radiation therapy or mastitis
    • should be distinguished from pathologic causes of a large area of nonmass enhancement

Treatment and prognosis

Because background enhancement is more prominent during the luteal phase of the menstrual cycle, elective breast MRI should be scheduled at days 7-14 during the follicular phase of a woman's cycle.

As it may be confused for suspicious lesions, increased background parenchymal enhancement increases the rate of abnormal interpretations (BI-RADS category 0, 3, 4, or 5 assessments) but does not decrease the sensitivity and cancer detection rate ^3,4.

Increased background parenchymal enhancement is an imaging biomarker of higher risk of breast cancer, independent of the amount of fibroglandular tissue, in women at high risk ^5,6,10. In patients who undergo adjuvant endocrine therapy, high background parenchymal enhancement in the nonaffected breast predicts poorer cancer outcomes ⁷. Similarly, in the setting of neoadjuvant chemotherapy, reduction in level of background parenchymal enhancement correlates with pathological tumor response ⁹.

Differential diagnosis

A larger area of background parenchymal enhancement overlaps in appearance with a focal area of nonmass enhancement, which requires further assessment and management ¹⁰.