You'll see it when you know it: granulomatous mastitis.

Granulomatous mastitis (GM) is an under-recognized and under-diagnosed disease. Patients with GM often present to the emergency room with a painful breast mass, nipple retraction, and skin changes. This pictorial essay will review the clinical presentation and imaging appearance of GM, BI-RADS reporting parameters, differential diagnoses, and diagnostic challenges posed by this disease. Early and accurate diagnosis is essential, as misdiagnosis can result in repeated core biopsies, leading to fistulae and sinus tract formation. A classic history and typical sonographic appearance allow the emergency radiologist to confidently make this diagnosis.