Apocrine metaplasia: mammographic and sonographic appearances

Our objective was to evaluate the mammographic and sonographic appearances of apocrine metaplasia and correlate imaging and histopathologic findings.

Retrospective review of 408 lesions in 318 consecutive patients undergoing core needle biopsy (n = 370) or fine needle aspiration (n = 38) revealed 46 cases of apocrine metaplasia. In 17 of these cases, apocrine metaplasia represented more than 50% of the lesion sampled; these 17 lesions formed the basis for analysis.

On mammography, all 17 cases appeared as new or enlarging equal-density (n = 15) or low-density (n = 2) masses with an average size of 12.8 mm. Borders were microlobulated in 59% (10/17), macrolobulated in 29% (5/17), and circumscribed or oval in 12% (2/17). Sonography revealed a lobulated mass containing a cluster of small (2- to 5-mm) anechoic foci and intervening septae in 77% (10/13) of cases. A discrete hypoechoic solid component was seen in 23% of cases (3/13). Posterior acoustic enhancement was seen in 85% of cases (11/13). In 65% of lesions (11/17), we noted a decrease in size or total resolution during biopsy or fine needle aspiration. Histopathologic examination showed the typical appearance of dilated cystic acini lined by apocrine metaplastic epithelium.

On mammography, the combined findings of an equal- or low-density microlobulated or lobulated mass that corresponds on sonography to a cluster of small (2- to 5-mm) anechoic foci with intervening septae should suggest the diagnosis of focal apocrine metaplasia. With radiologists' increasing experience, follow-up, rather than biopsy, of such typical-appearing lesions may be adequate.