Breast Imaging
Core framework
Almost every breast question resolves to the ACR BI-RADS lexicon, so know it cold. Screening mammography is performed in asymptomatic patients (typically annual from age 40 in the US); diagnostic mammography adds problem-solving views, spot compression, and ultrasound. Density categories a–d (almost entirely fatty → extremely dense) matter because they drive supplemental screening decisions: category c or d often triggers whole-breast ultrasound or, in some guidelines, contrast-enhanced MRI or abbreviated MRI.
Calcifications
Benign morphology: diffuse/scattered distribution, skin, vascular, coarse "popcorn," large rod-like, round, rim, dystrophic, milk-of-calcium, and suture calcifications. Suspicious morphology: amorphous, coarse heterogeneous, fine pleomorphic, and fine linear/branching. Distribution is as important as morphology - grouped, linear, and segmental distributions raise suspicion, while diffuse and regional are usually benign. Suspicious calcifications are biopsied with stereotactic vacuum-assisted technique, not excisional biopsy first.
Masses and MRI
Describe masses by shape (oval, round, irregular), margin (circumscribed, obscured, microlobulated, indistinct, spiculated), and density. Spiculated or indistinct margins are suspicious. MRI descriptors: focus, mass (with kinetics), non-mass enhancement; persistent kinetics favor benign, washout favors malignant. MRI is the most sensitive test but not specific.
Traps and rule of thumb
Traps: calling a palpable finding a "screening" exam; assigning BI-RADS 3 to a spiculated mass; forgetting that a simple cyst needs no follow-up; assuming calcifications seen only on one view are real (get a true lateral).
Rule of thumb: BI-RADS 3 means <2% malignancy risk and short-interval follow-up; BI-RADS 4 is subdivided 4A/4B/4C for 2–10%, 10–50%, and >50% risk; BI-RADS 5 is ≥95%. Worked example: a new group of fine pleomorphic calcifications in a segmental distribution is BI-RADS 4B or 4C and goes to stereotactic biopsy - never to 6-month follow-up.