Following puberty, the glandular tissue of the lobules undergoes repeated proliferation followed by involution with each menstrual cycle. With time, as ovarian function decreases, involution outweighs proliferation and the lobular parenchyma and ducts become atrophic and replaced largely by fatty and fibrous tissue. Corresponding changes may be seen in the radiodensity of mammograms which varies tremendously, but in general is increased in younger women, those who are lactating and those taking hormone replacement therapy.
Dense breast tissue is seen in a high proportion of women below the age of 40 and with decreasing frequency in patients over the age of 50. Mammographic sensitivity is inversely related to increasing breast density.
Non Dense Breast
Mammography is the first-choice breast imaging technique for women aged 40 and over. It may be used for the following indications:
- Screening of asymptomatic women
- To characterise or further assess symptomatic abnormalities
- As part of the follow-up and surveillance of women who have been treated for breast cancer
- The sensitivity of mammography for the detection of breast cancer is approximately 90%. Conversely, approximately 10% of all breast cancers will be mammographically occult.
Routine mammography should include mediolateral oblique (MLO) and craniocaudal (CC) projections. Craniocaudal projections may also be known as supero-inferior or superior-inferior (SI).
The MLO view best visualises the tissue adjacent to the chest wall and the axillary tail. A good MLO view should demonstrate the pectoral muscle at least to the level of the nipple and include the inframammary fold.
The CC (or SI) view should include the entire body of the gland with the retromammary fat visible. The nipple should be centered.
Supplementary views may include the use of extended CC projection to include more of the axillary tail and spot compression (paddle) views of an area of interest, with or without magnification.
Ultrasound is the first-choice imaging technique in women under 40 years old with focal breast problems. It is also an important adjunct to mammography in older women where it is used in a targeted manner to characterise clinical or mammographic abnormalities.
Breast ultrasound is indicated for:
- Diagnosis: characterisation of focal lesions
- Guidance for intervention: aspiration, biopsy, preoperative localisation
- Follow-up: assessment of response to chemo- or endocrine therapy
- Nodes: assessment of enlarged axillary nodes
- Implants: assessment of integrity, evaluation of overlying breast tissue
Magnetic Resonance Imaging
The exact role of breast MRI is yet to be fully established. Contrast-enhanced MRI has high sensitivity for invasive breast carcinoma (less so for ductal carcinoma in situ (DCIS)) and does not use ionising radiation. However, it has limited availability, is expensive, has a wide variation in reported specificity and there are very limited biopsy facilities for lesions seen only on MRI.
Current indications include:
- Evaluation of possible recurrence of breast cancer following breast conserving surgery
- The detection of suspected multifocal breast carcinoma
- Evaluation of response in women undergoing primary chemotherapy for breast cancer
- Screening of women at high risk of breast cancer (inherited or iatrogenic) following radiation therapy for previous lymphoma
- Assessment of breast implant integrity or the presence of suspected malignancy in women with breast implants
The imaging pathway for symptomatic women will differ depending on the age of the patient:
Patient age <40 years:
- Clinical examination
- Targeted ultrasound
Patient aged ≥40 years:
- Clinical examination
- Bilateral mammogram and targeted ultrasound
Changes to Breast during Pregnancy
During pregnancy and lactation the blood supply to breast tissue increases and glandular tissue changes from a resting state to prepare for lactation. During pregnancy, breast tissue becomes more cellular and the proportion of glandular tissue increases, resulting in increased breast density and replacement of fatty tissue with glandular tissue.
When lactation commences, the breasts become engorged with milk and the duct system is much more obvious on ultrasound when filled with milk.
During breastfeeding, sections of the breast may fail to drain fully of breast milk and collections of milk can form a galactocoele. These have ultrasound appearances of a rounded, well-defined, echogenic mass from which milk can be readily aspirated. Milk solids may separate out giving the appearance of a complex cyst.
Breast abscesses may be a complication of lactation. These present as a painful inflamed mass. For more information on breast abscesses. Mass lesions within the breast become more cellular and grow during pregnancy and lactation. These can include benign masses such as fibroadenomas, and malignancies.