Duct ectasia - literally (lactiferous) duct widening is a very common and thus rather unspecific finding, increasing with age.
Also called Zuska's disease (only nonpuerperal case), is a frequently aseptic inflammation and has been associated with squamous metaplasia of the lactiferous ducts.
Characteristic for granulomatous mastitis are multinucleated giant cells and epithelioid histiocytes around lobules. Often minor ductal and periductal inflammation is present. The lesion is in some cases very difficult to distinguish from breast cancer.
Comedo mastitis is a very rare form similar to granulomatous mastitis but with tissue necrosis. Because it is so rare it may be sometimes confused with comedo carcinoma of the breast although the conditions appear to be completely unrelated.