Ultrasound Mass Descriptors
Shape
| Descriptor | Implication |
|---|---|
| Oval | Favors benign — fibroadenoma, cyst |
| Round | Slightly less reassuring than oval; cyst, fibroadenoma |
| Irregular | Suspicious — suggests malignancy |
Orientation
| Descriptor | Implication |
|---|---|
| Parallel (wider-than-tall) | Favors benign — growing along tissue planes |
| Not parallel (taller-than-wide) | Suspicious — growing across tissue planes |
Margin
| Descriptor | Implication |
|---|---|
| Circumscribed | Abrupt, well-defined — favors benign |
| Indistinct | No clear demarcation — suspicious |
| Angular | Sharp corners — suspicious, BI-RADS 4+ |
| Microlobulated | Short-cycle undulations — suspicious |
| Spiculated | Radiating lines — most suspicious, BI-RADS 4C–5 |
Echo Pattern
| Descriptor | Implication |
|---|---|
| Anechoic | Simple cyst if also circumscribed + posterior enhancement → BI-RADS 2 |
| Hyperechoic | Brighter than fat — typically benign (lipoma, fat lobule) |
| Isoechoic | Same echogenicity as fat — needs full assessment |
| Hypoechoic | Less echogenic than fat — suspicious if combined with other features |
| Heterogeneous | Mixed echo pattern — concerning if combined with other suspicious features |
| Complex cystic and solid | Both cystic and solid components — BI-RADS 4; biopsy required |
Posterior Features
| Descriptor | Implication |
|---|---|
| Posterior acoustic enhancement | Favors benign — cyst, fibroadenoma; increased through-transmission |
| Shadowing | Decreased through-transmission — may indicate malignancy, calcification, or scar |
| No posterior features | Neutral finding |
Not parallel (taller-than-wide) orientation is one of the most reliable individual US features for malignancy — it indicates a mass growing across rather than along normal tissue planes. Combined with irregular shape and non-circumscribed margins, it is highly suspicious.
Special Cases — Cysts and Specific Findings
| Finding | Criteria | BI-RADS | Management |
|---|---|---|---|
| Simple Cyst | Anechoic, circumscribed, no internal echoes, no solid component, posterior enhancement, thin imperceptible wall | 2 | No follow-up needed; aspiration only if symptomatic |
| Complicated Cyst | Internal echoes (too low-level to be solid), homogeneous; otherwise meets cyst criteria | 3 | 6-month follow-up if no prior and no suspicious features; if multiple bilateral → BI-RADS 2 |
| Clustered Microcysts | ≥3 anechoic foci ≤2–3 mm without solid component | 3 | 6-month follow-up; biopsy if enlarging or new solid component |
| Complex Cystic and Solid Mass | Both cystic and solid components; solid mural nodule, thick septations, or echogenic debris | 4 | Tissue sampling — intracystic papillary lesion or carcinoma must be excluded |
| Fat-Containing Mass | Hyperechoic or mixed fat-containing (lipoma, fat lobule, galactocele, hamartoma) | 2 | Routine; correlate with mammography |
| Axillary Lymph Node | Normal: reniform shape, fatty hilum, cortex ≤3 mm | 2 | Routine if normal morphology |
Abnormal axillary lymph nodes: cortex >3 mm, round shape, absent fatty hilum → suspicious. Evaluate with ultrasound-guided biopsy if clinically relevant (new diagnosis of breast cancer, palpable node). In newly diagnosed breast cancer, abnormal axillary nodes should be sampled before surgery.
Cyst aspiration: Aspirated fluid need not be sent for cytology unless bloody or associated with a residual mass after aspiration. A cyst that resolves completely on aspiration is benign. A residual solid mass after aspiration requires biopsy.
Elastography
Elastography is an adjunct US tool — stiff lesions (high shear wave velocity or strain ratio) have higher malignancy risk. It can support downgrading a BI-RADS 3 or upgrading to 4 in ambiguous cases but should not be used alone to determine BI-RADS category. Not yet a standard BI-RADS lexicon requirement.