Rare breast lesions: correlation of imaging and histologic features with WHO classification.

Mammographers occasionally are surprised by the diagnosis of a rare lesion at breast biopsy. The imaging features of some breast lesions are unfamiliar because they are rarely seen in routine mammographic practice and they are not well described or well documented in the radiologic literature. Moreover, there may be wide variation in the appearances of rare breast lesions at mammography and ultrasonography (US). In addition, although a few rare breast lesions have a typical imaging appearance, most have mammographic and US features similar to those of breast carcinomas, and a needle biopsy is almost always necessary to obtain a diagnosis. However, even when a rare breast lesion is diagnosed on the basis of a needle biopsy, knowledge of the imaging features of such lesions may help the radiologist decide whether the results of pathologic analysis concur with the imaging findings and whether surgical excision is necessary. It is therefore important that radiologists be familiar with the broad spectrum of imaging features of rare breast lesions as well as with the correlation between their histopathologic features and their current classification according to the World Health Organization classification system. (c) RSNA, 2008.