24.1 Breast & Axilla

The Role of Breast Ultrasound

Mammography remains the screening tool of choice, but breast ultrasound fills critical gaps. It is the first-line imaging study for women younger than 30, for pregnant or lactating patients, and for evaluating palpable lumps in radiographically dense breasts, where fibroglandular tissue can obscure a mass on mammography. Ultrasound distinguishes cystic from solid lesions with very high accuracy, guides biopsies in real time, and involves no ionizing radiation. It is an adjunct, not a replacement, for mammography: microcalcifications — the hallmark of ductal carcinoma in situ — are a mammographic finding that ultrasound detects poorly.

Technique and Documentation

Use a high-frequency linear-array transducer (typically 12-18 MHz) for maximum near-field resolution. Key technique points:

• Radial and antiradial scanning: scan along the long axis of the ducts (radial, like spokes of a wheel) and perpendicular to them (antiradial) to demonstrate intraductal pathology
• Clock-face documentation: every lesion is reported by clock position (e.g., 3 o'clock, right breast) plus its distance in centimeters from the nipple
• Position the patient supine or in contralateral posterior oblique with the ipsilateral arm raised above the head; a stand-off pad or a thick gel layer helps evaluate very superficial lesions
• Image each lesion in two orthogonal planes, with and without calipers; add color Doppler to document vascularity, since malignant masses often show internal or penetrating vessels

Breast Anatomy

From anterior to posterior, the breast contains skin (normally under 3 mm thick — thickening suggests edema or inflammatory carcinoma), subcutaneous fat, the mammary (glandular) zone of 15-20 lobes drained by lactiferous ducts converging on the nipple, and the retromammary space separating glandular tissue from the pectoralis major fascia and chest wall. Cooper's ligaments (suspensory ligaments) are fibrous septa anchoring the skin to the underlying fascia; they normally appear as thin echogenic lines, but tethering or straightening of these ligaments suggests an invasive process. Fat is hypoechoic and glandular tissue is relatively echogenic — this contrast makes masses visible. The axillary tail of Spence extends glandular tissue toward the axilla and must be included in any complete survey. When describing a mass, always use the standardized descriptors: shape (oval, round, irregular), margin (circumscribed or not), orientation (parallel/wider-than-tall versus nonparallel/taller-than-wide), echo pattern, and posterior features (enhancement, shadowing, combined, or none).

Cystic Masses

A simple cyst meets all of these criteria: an anechoic interior, an imperceptible (thin, smooth) wall, and posterior acoustic enhancement, often with thin edge refraction shadowing at the lateral margins. A true simple cyst is benign (BI-RADS 2) and requires no follow-up and no aspiration. A complicated cyst contains low-level internal echoes or debris but has no thick wall, septation, or solid component; it is probably benign (BI-RADS 3) and is managed with short-interval (6-month) follow-up. A complex cystic-solid mass — thick wall or septa, an intracystic solid component, or mixed cystic and solid architecture — requires biopsy (BI-RADS 4), because a minority prove to be cystic papillary carcinomas or necrotic solid tumors.

Fibroadenoma

The fibroadenoma is the most common solid breast mass in young women. Sonographically it is oval, circumscribed, gently lobulated, wider-than-tall (parallel orientation), and homogeneously hypoechoic, often with mild posterior enhancement. After menopause it may involute and develop coarse "popcorn" calcifications.

Malignant Features

Malignant masses show the opposite morphology: irregular shape, non-circumscribed margins (spiculated, angular, or microlobulated), taller-than-wide orientation, marked hypoechogenicity, posterior acoustic shadowing, and surrounding architectural distortion with Cooper's ligament tethering. Invasive ductal carcinoma (IDC) is the most common breast malignancy (roughly 70-80% of cases); invasive lobular carcinoma is subtler and may present only as shadowing and distortion.

Other Entities

An intraductal papilloma is the most common cause of bloody nipple discharge — a small solid nodule within a dilated duct near the nipple, best demonstrated with radial scanning. In men, gynecomastia (the most common male breast disorder) appears as flame-shaped or discoid retroareolar tissue with no discrete mass; male breast cancer typically presents as an irregular solid mass eccentric to the nipple. Axillary lymph nodes are benign when they retain an echogenic fatty hilum and a thin, uniform cortex; focal or diffuse cortical thickening greater than 3 mm or loss of the fatty hilum is suspicious for metastatic involvement.

BI-RADS and Biopsy

The Breast Imaging Reporting and Data System (BI-RADS) standardizes reporting: 0 = incomplete (needs additional imaging), 1 = negative, 2 = benign, 3 = probably benign (under 2% malignancy risk, 6-month follow-up), 4 = suspicious (biopsy; subdivided 4A/4B/4C by rising suspicion), 5 = highly suggestive of malignancy (95% or greater), and 6 = biopsy-proven malignancy. Ultrasound-guided core needle biopsy (typically a 14-gauge spring-loaded device) samples the mass under real-time visualization; a radiopaque clip is deployed at the biopsy site to mark it for follow-up or surgical localization. Compared with stereotactic guidance, ultrasound guidance is faster, uses no radiation, and is preferred whenever the lesion is visible sonographically.

Clinical Indications and Limits

Common indications for a diagnostic breast ultrasound include a palpable abnormality, evaluation of a mammographic finding, nipple discharge, breast pain with a focal trigger point, assessment of implants and peri-implant fluid, and axillary staging before breast surgery. During the exam, always correlate the imaging with the clinical history — prior surgery, trauma, lactation status, and hormone therapy all alter the expected appearance — and compare with any prior studies, since long-term stability (two years or more) is itself a benign feature. Remember the modality's blind spots: ultrasound is operator-dependent, and a normal ultrasound does not exclude malignancy when the mammogram or physical exam is suspicious, so discordant findings still warrant biopsy.