Breast Ultrasound and BI-RADS: What Sonographers Need to Know

Breast ultrasound is often performed by sonographers in general imaging departments, not just breast-dedicated centers. Whether you're called to evaluate a palpable lump, complete a screening ultrasound (in high-risk patients), or characterize a mammographically detected finding, you need to know the BI-RADS lexicon and how to describe what you see.

When Breast Ultrasound Is Performed

• Palpable mass (all ages, but especially women under 30 where mammography has lower sensitivity)
• Characterization of mammographic finding (is it cystic or solid?)
• Supplemental screening in dense breast tissue (per individual practice/ACR guidelines)
• Problem-solving after equivocal mammography
• Guidance for biopsy, aspiration, or localization
• Evaluation of axillary lymph nodes
• Implant integrity evaluation

Equipment and Technique

Probe: 10–18 MHz linear transducer. Use the highest frequency that gives adequate depth — most breast masses are superficial. For larger breasts, you may need to drop to 8–10 MHz for posterior tissue.

Position: Supine with ipsilateral arm raised above the head for the outer breast quadrants. Roll patient to contralateral oblique for the medial quadrants. The goal is to flatten the breast against the chest wall for uniform depth.

Gel: Use plenty. No compression is needed — light contact only. Excessive pressure can deform masses and obscure their true shape.

Systematic scanning: Cover the entire breast quadrant by quadrant. Document with radial (from nipple) and antiradial planes. Always include the axilla.

Clock position and distance notation: Document findings as "right breast, 2 o'clock position, 3 cm from nipple" — this is the standard ACR notation that correlates with mammography and biopsy planning.

BI-RADS Lexicon: Describing What You See

The ACR BI-RADS (Breast Imaging Reporting and Data System) lexicon provides standardized descriptors. Radiologists write the report, but sonographers benefit from knowing this language so they know what images to capture and what features to document.

Shape

• Oval: Elliptical or egg-shaped. Favorable.
• Round: Spherical. Neutral.
• Irregular: Neither round nor oval. Suspicious.

Orientation

• Parallel (wider than tall): Long axis parallel to skin. Favorable — most benign masses grow in the plane of breast tissue.
• Not parallel (taller than wide): Long axis perpendicular to skin. Suspicious — suggests growth across tissue planes, more typical of malignancy.

Margin

• Circumscribed: Well-defined, abrupt interface with surrounding tissue. Favorable.
• Not circumscribed (suspicious margins):
  • Indistinct: no clear demarcation
  • Angular: sharp corners
  • Microlobulated: small bumps
  • Spiculated: radiating lines (highly suspicious for malignancy)

Echo Pattern

• Anechoic: Simple cyst — no internal echoes
• Hyperechoic: Brighter than fat — often benign (lipoma, fat necrosis)
• Complex cystic and solid: Contains both cystic and solid components — needs further evaluation
• Hypoechoic: Darker than fat — can be benign or malignant, depends on other features
• Isoechoic: Same echogenicity as fat — rare, often fibroadenoma
• Heterogeneous: Mixture of echo patterns — suspicious

Posterior Features

• No posterior features: Neutral
• Enhancement: Increased through-transmission posterior to the mass. Seen with cysts and some fibroadenomas. Generally favorable.
• Shadowing: Decreased through-transmission. Classic for malignancy (desmoplastic response) but also seen with some fibroadenomas and calcifications.
• Combined pattern: Both enhancement and shadowing present.

BI-RADS Categories

Category	Descriptor	Malignancy Risk	Recommendation
0	Incomplete	N/A	Additional imaging needed
1	Negative	0%	Routine screening
2	Benign	0%	Routine screening
3	Probably benign	< 2%	Short-interval follow-up (6 months)
4A	Low suspicion	2–10%	Tissue sampling
4B	Moderate suspicion	10–50%	Tissue sampling
4C	High suspicion	50–95%	Tissue sampling
5	Highly suggestive of malignancy	> 95%	Tissue sampling
6	Known biopsy-proven malignancy	N/A	Treatment planning

Simple Cyst vs Complex Cyst vs Solid Mass

Simple cyst:

• Anechoic (no internal echoes)
• Circumscribed
• Posterior acoustic enhancement
• Thin imperceptible walls
• BI-RADS 2 — benign, no further workup needed

Complicated cyst:

• Internal echoes (low-level, homogeneous)
• Otherwise cyst-like
• BI-RADS 3 — follow-up in 6 months if no history of malignancy

Complex cystic and solid:

• Intracystic mass or mural nodule
• Thick irregular walls or septations
• Suspicious — needs aspiration or biopsy

Solid mass (likely benign — fibroadenoma):

• Oval, parallel, circumscribed
• Posterior enhancement or no change
• Homogeneous, isoechoic or mildly hypoechoic
• BI-RADS 3 if classic features, or 4A if slightly atypical

Solid mass (suspicious for malignancy):

• Irregular, not parallel (taller than wide), spiculated margins
• Posterior shadowing
• Heterogeneous, markedly hypoechoic
• BI-RADS 4 or 5

Axillary Lymph Nodes

Always evaluate the axillary nodes when scanning breast.

Normal node: Reniform (kidney-shaped), echogenic hilum visible, cortex < 3 mm Suspicious node:

• Cortical thickening > 3 mm (especially focal)
• Absent hilum (replaced by tumor)
• Round shape replacing kidney shape
• Vascularity in cortex rather than hilum

Measuring a Mass

Document:

• Three perpendicular dimensions: length × width × height (in cm)
• Always measure in two planes (transverse and longitudinal — or radial and antiradial)
• Depth from skin surface to anterior margin

Images to Capture

For any solid or complex lesion:

1. Long axis (radial plane) — with calipers
2. Short axis (antiradial plane) — with calipers
3. Clock position annotation on image
4. Color Doppler (internal vascularity)
5. With and without calipers images
6. Adjacent tissue for comparison
7. Axillary lymph nodes of that side

A Note on Scope

Sonographers describe what they see using BI-RADS lexicon. The BI-RADS category (1 through 6) and clinical recommendations are assigned by the radiologist in the final report. Some institutions have sonographers state the BI-RADS category on the worksheet; others do not. Follow your department's protocol.

---

SonoBuddy covers measurement reference tables for breast imaging and other specialties. Search "breast" in the Measurements tab for normal values.