Breast Ultrasound

Anatomy and Physiology

Breast ultrasound is often used to localize palpable and non-palpable masses before surgical excision.[3]

The basic breast anatomy comprises 15 to 20 lobules, each consisting of smaller breast ducts, known as the terminal duct lobular units (TDLUs). All the ducts drain into a single lactiferous sinus towards the nipple.

The three main anatomical zones of the breast are the pre-mammary, mammary, and retro-mammary zones, consisting of fatty tissue, fibroglandular tissue, and muscular tissue.

From a sonographic point of view (Image 2), the breast is divided into various hypoechoic and hyperechoic layers:

• Skin (hyperechoic, white fibrous bands)
• Fat (hypoechoic, subcutaneous fat lobules)
• Breast parenchyma (hyperechoic, fibroglandular soft tissue)
• Retromammary fat (hypoechoic fat lobules)
• Pectoralis major muscle (hyperechoic fibrous tissue)[4] 

Indications

Common indications for breast ultrasound are:[5]

• Palpable lump during clinical breast evaluation
• Axillary lymphadenopathy present on mammogram imaging
• Women younger than 40 years with the clinical presentation of certain anomalies
• Pregnant or lactating women
• Suspicious abnormality identified on mammogram imaging
• Nipple discharge
• Skin retraction or inversion of the nipple
• Surgical scarring evident in mammogram imaging
• Suspicion of rupture breast implants used to differentiate between intra-and-extracapsular ruptures
• Needle-guided percutaneous breast biopsy
• Follow up patients receiving neoadjuvant chemotherapy

Contraindications

The use of breast ultrasound as a sole screening tool is inappropriate.[6]

Equipment

High-frequency ultrasound has improved over the past decade with standard linear frequency probes ranging from 7.5 MHz to 23 MHz, with high density or single crystal probe components, which improves lateral resolution. Tissue harmonic imaging (THI) is also a standard feature of most entry-level ultrasound units for a reduction in reverberation and near field artifacts. Real-time compound scanning aids in improved contrast resolution.

Panoramic imaging provides an increased longitudinal imaging perspective of breast lesions in relation to the surrounding breast tissue.

The latest technology from ultrasound vendors now also boasts stand-alone linear frequency probes connecting wirelessly to mobile imaging application software.[7]

Most ultrasound software allows computer-aided detection (CAD) to assist in the segmentation and identification of suspicious mass lesions. This technology allows for increased improvement in diagnostic proficiency.

Proper technical consideration is required to produce quality ultrasound images such as the depth of the focal zone, time gain compensation measures, and overall gain used during mass lesion assessment.[8]

Personnel

Breast ultrasound is performed by an ultrasound technician, radiologist, or a referring clinician with adequate technical and clinical competency for ultrasound evaluation.

Preparation

Breast ultrasound is a non-invasive procedure with none or very little special preparation required. Jewelry in the anatomical region of interest should be removed, and the patient is encouraged to wear loose clothing to be able to undress the upper half of the torso before the examination.[9]

Technique or Treatment

Initial breast imaging of the patient should include a full clinical breast self-examination (BSE) to assess and validate all palpable masses, either identified by the patient or by the physician. Following BSE, a bilateral breast ultrasound is performed with a sequential sweeping of the breast surface.

The breast is assessed in the four main quadrants, namely outer upper, outer inner, lower outer, and lower inner quadrants. Any lesions identified during the examination should be marked as a breast 'o clock position for future follow up sessions.

The most common imaging technique used is a radial, star-shaped, or superior to inferior sweep of the entire breast, extending to the axillary space, parasternal, and clavicular surfaces.

The retro areolar space should also be evaluated systematically; the dense tissue causes posterior acoustic shadowing, limiting visibility posterior to its surface. This anatomical limitation can be overcome by either angling the probe upwards towards the retro areolar ducts or using a gel standoff pad with decreased focal zone and altering of the tissue gain compensation controls, visualizing the soft tissue posterior to the dense nipple tissue.[10]

Complications

Breast ultrasound is a safe, non-invasive procedure without any complications of the procedure itself.

Clinical Significance

Ultrasound as part of follow up imaging for masses reported as breast imaging reporting and data system (BI-RADS) 2 or 3 (probably benign) has shown great value in assessing morphological changes to the sonographic appearance.

Through the use of ultrasound as a standard follow up imaging tool, it could promote recharacterization of lesions during initial imaging assessment.

Full ultrasound examination requires the recording of results in a standard breast report, including the patient indications, findings, and results with differential diagnosis.

Any lesions noted during the examination should be measured in both transverse and longitudinal planes. Location, measurement, echogenicity of all masses should be described as either hypoechoic, hyperechoic, or heterogeneous.

The various mass descriptors are used according to the ultrasound breast imaging and reporting system (US BIRADS) lexicon which includes six main morphological descriptors for breast masses:[11]

The most common morphologic features associated with benign sonographic findings are:[12]

• Smooth and well-circumscribed margins
• Hyperechoic, isoechoic or mildly hypoechoic in echogenicity
• Thin echogenic capsule or well-defined capsule border
• Ellipsoid shape, wider than tall appearance
• Macrolobulated; less than three lobulated margins
• Posterior acoustic enhancement

The most common morphologic features associated with malignant findings are:

• Hypoechoic mass, on occasion, hyperechoic in appearance
• Spiculated margins
• Ill-defined borders, architectural distortion of surrounding soft tissue
• Posterior acoustic shadowing
• Taller than wide appearance
• Microcalcifications present[13]

Enhancing Healthcare Team Outcomes

As part of interprofessional education (IPE), point of care ultrasound (POCUS) has been expanding its use over many medical specialties.

For appropriate interprofessional collaboration, role clarification of each practitioner and profession should be assessed. Conflict resolution methods between learner and practitioner should be provided for the best outcomes.

Nursing, Allied Health, and Interprofessional Team Monitoring

Pre-workshop assessments should include demographics as well as the attitudes of professions regarding the use of IPE. During training and collaborative teaching events, simulation of activities could promote increased awareness and interest in ultrasound imaging. Following workshop integration, a follow up regarding attitudes of IPE should be encouraged to assess if the resulting work leads to contextual learning and assessment across all fields of medicine.