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Mammography and breast ultrasound: BI-RADS in plain words

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A mammogram is a low-dose X-ray of the breast; ultrasound helps with lumps. The report ends in a BI-RADS number that says what to do next.

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What it is

Mammography compresses the breast and takes low-dose X-rays, usually two views per breast: craniocaudal (top to bottom) and mediolateral oblique (angled, including the armpit tail). Screening mammography looks for cancer in women without symptoms; diagnostic mammography adds extra views (spot compression, magnification) for a lump, an abnormal screen or other symptoms. Tomosynthesis takes several thin slices to reduce overlap. Ultrasound is the first test for a palpable lump in women under about 30 and in pregnancy or breastfeeding, and is added to mammography in older women. Every report ends in a BI-RADS category, from 0 (incomplete) to 6 (known cancer), that links the finding to an action. Screening start ages and intervals differ by guideline and country.

What to check

  • Suspicious masses: irregular shape, spiculated or indistinct margins, high density; round, smooth, well-defined masses are more often benign.
  • Suspicious calcifications: fine pleomorphic or fine linear branching calcifications, especially in a line or segment; large coarse, rim or popcorn calcifications are benign.
  • Architectural distortion (pulled-in tissue with no mass) and a new or growing asymmetry need work-up.
  • Breast density (fatty to extremely dense) lowers the sensitivity of mammography and is reported in every study.
  • On ultrasound a simple cyst is black (anechoic), round, thin-walled, with bright enhancement behind it; a solid lesion taller than wide, with angular margins and a shadow behind it, is suspicious.

Reading it step by step (and why)

  1. Check the indication and compare with prior studies — a new or growing finding matters more than a stable one.
  2. Check the views and positioning — both views must include the posterior tissue and the pectoral muscle on the oblique view.
  3. Note breast density — dense tissue can hide a cancer and may justify extra imaging.
  4. Look for masses, then calcifications, then distortion and asymmetry — the main signs of cancer.
  5. Describe any lesion by shape, margin and density, and calcifications by form and distribution — these predict benign or malignant.
  6. Correlate with ultrasound and the clinical finding, especially for a palpable lump — imaging must explain what is felt.
  7. Assign the BI-RADS category (0 incomplete, 1 negative, 2 benign, 3 probably benign, 4 suspicious, 5 highly suggestive, 6 known cancer) — it sets the next step.

Common mistakes

  • A negative mammogram does not rule out cancer in a palpable lump: a suspicious lump still needs ultrasound and often biopsy.
  • BI-RADS 0 is not a result: the woman must come back for extra views or ultrasound.
  • BI-RADS 3 means a very low chance of cancer (about 2% or less) and is followed with short-interval imaging, not biopsy.
  • BI-RADS 4 and 5 need tissue: ultrasound-guided core biopsy for masses, stereotactic biopsy for calcifications, MRI-guided for lesions seen only on MRI.
  • After biopsy the pathology must fit the imaging (radiology-pathology concordance); if it does not, repeat or surgical biopsy is needed.

Next step

  • Palpable lump in a woman under about 30, pregnant or breastfeeding: ultrasound first; from about 30, diagnostic mammography plus ultrasound.
  • BI-RADS 0: book extra views or ultrasound promptly.
  • BI-RADS 3: repeat imaging in about six months, then follow as the radiologist advises.
  • BI-RADS 4 or 5: image-guided core biopsy and referral to breast surgery; BI-RADS 6: treatment planning.
  • High-risk women (strong family history, BRCA carriers, chest radiation when young): ask about breast MRI in addition to mammography.

Test yourself

Think of the answer, then tap the question to see it.

What are the two standard mammographic views of each breast?

The craniocaudal view (top to bottom) and the mediolateral oblique view, which includes the armpit tail and the pectoral muscle.

What does BI-RADS 0 mean and what is done next?

The assessment is incomplete; the woman needs extra mammographic views or ultrasound before a final category can be given.

How is a BI-RADS 3 finding managed?

It is probably benign, with a very low chance of cancer, so it is followed with short-interval imaging (about six months) rather than biopsied.

Which first imaging test suits a palpable breast lump in a 25-year-old woman?

Breast ultrasound, because young breasts are dense on mammography and ultrasound clearly separates a cyst from a solid mass.

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Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.

Sources: Screening Mammography in Breast Cancer Detection (StatPearls (NCBI Bookshelf), 2023); Mammography BI RADS Grading (StatPearls (NCBI Bookshelf), 2023); New Palpable Breast Mass (StatPearls (NCBI Bookshelf), 2025); Image-Guided Breast Biopsy (StatPearls (NCBI Bookshelf), 2026).

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