Background parenchymal uptake during molecular breast imaging and associated clinical factors

Abstract

OBJECTIVE. The purposes of this study were to describe the prevalence of background parenchymal uptake categories observed at screening molecular breast imaging (MBI) and to examine the association of background parenchymal uptake with mammographic density and other clinical factors. MATERIALS AND METHODS. Adjunct MBI screening was performed for women with dense breasts on previous mammograms. Two radiologists reviewed images from the MBI examinations and subjectively categorized background parenchymal uptake into four groups: photopenic, minimal-mild, moderate, or marked. Women with breast implants or a personal history of breast cancer were excluded. The association between background parenchymal uptake categories and patient characteristics was examined with Kruskal-Wallis and chi-square tests as appropriate. RESULTS. In 1149 eligible participants, background parenchymal uptake was photopenic in 252 (22%), minimal-mild in 728 (63%), and moderate or marked in 169 (15%). The distribution of categories differed across BI-RADS density categories (p < 0.0001). In 164 participants with extremely dense breasts, background parenchymal uptake was photopenic in 72 (44%), minimal-mild in 55 (34%), and moderate or marked in 37 (22%). The moderate-marked group was younger on average, more likely to be premenopausal or perimenopausal, and more likely to be using postmenopausal hormone therapy than the photopenic or minimal-mild groups (p < 0.0001). CONCLUSION. Among women with similar-appearing mammographic density, background parenchymal uptake ranged from photopenic to marked. Background parenchymal uptake was associated with menopausal status and postmenopausal hormone therapy but not with premenopausal hormonal contraceptives, phase of menstrual cycle, or Gail model 5-year risk of breast cancer. Additional work is necessary to fully characterize the underlying cause of background parenchymal uptake and determine its utility in predicting subsequent risk of breast cancer.

Keywords: MRI; breast density; hormone therapy; menstrual cycle; molecular breast imaging.

Fig. 1

Examples of background parenchymal uptake categories. A, 65-year-old postmenopausal woman with no current exogenous hormone use. Molecular breast image shows photopenic background parenchymal uptake. B, 55-year-old postmenopausal woman with no current exogenous hormone use. Molecular breast image shows minimal-mild background parenchymal uptake. C, 50-year-old postmenopausal woman with no current exogenous hormone use. Molecular breast image shows moderate background parenchymal uptake. D, 75-year-old postmenopausal woman with no current exogenous hormone use. Molecular breast image shows marked background parenchymal uptake. E–H, Mammograms corresponding to A–D are categorized as heterogeneously dense and have quantitative percentage densities of 33–35%.

Fig. 2

Mosaic plots show distribution of background parenchymal uptake categories in molecular breast imaging as function of BI-RADS breast density (p < 0.0001) (A), menopausal status (p < 0.0001) (B), and use of postmenopausal hormone therapy (p < 0.0001) (C).

Fig. 3

59-year-old woman with bilateral breast cancer obscured by marked background uptake at molecular breast imaging (MBI). A and B, Right (A) and left (B) mediolateral oblique MB images show bilateral moderate to marked background uptake. Both mammographic and MBI findings were interpreted as benign. Workup of palpable areas in both breasts resulted in diagnosis of 8-mm invasive ductal carcinoma in 12-o’clock position of right breast and 7-mm invasive lobular carcinoma in periareolar region of left breast.

Fig. 4

62-year-old postmenopausal woman discontinuing hormone therapy with systemic estradiol. A, Molecular breast image shows moderate background parenchymal uptake while patient is using hormone therapy. B, Molecular breast image obtained 4 months after hormone therapy was discontinued shows minimal-mild background parenchymal uptake.