Gynecomastia is common, reportedly occurring in 57% of men older than 44 years of age (2). Gynecomastia is the enlargement of the male breast with secondary branching of the
subareolar ducts and proliferation of the surrounding stroma. Patients present with a subareolar mass that may be tender. The process may be unilateral or bilateral, symmetric or asymmetric. Cooper and colleagues (1) described unilateral involvement in 33% of their patients with gynecomastia, and in another 33% involvement was asymmetric. Appelbaum and co-workers (2) reported 61 patients with gynecomastia, 55 of whom had bilateral mammograms. In 84% of the patients, the gynecomastia was asymmetric; in 2%, it was symmetric; and in 14%, it was unilateral. Increases in serum estradiol levels, combined with decreases in testosterone levels, are thought to be the etiologic factors governing the development of gynecomastia. At this time, there is no known association between gynecomastia and male breast cancers. Some of the causes of gynecomastia are listed in Box 9.1.

Three patterns have been described for gynecomastia mammographically (1, 2, 3, 4, 5). The nodular pattern is characterized by increased tissue focally in the subareolar area (Figure 9.1) that fans out symmetrically from the nipple. It has been suggested that this represents the early phase of gynecomastia and corresponds to florid gynecomastia histologically. The epithelial lining of the ducts is hyperplastic, and the surrounding stroma is edematous, loose, and cellular. The fibrous or dendritic pattern appears as retroglandular tissue with prominent fibrous extensions that radiate out into the fatty tissue (Figure 9.2). Histologically, this is fibrous gynecomastia and reflects long-standing changes; there is ductal proliferation with dense fibrotic stroma. Diffuse glandular gynecomastia is the third pattern; it simulates the heterogeneously dense female breast pattern (Figure 9.3). Appelbaum and co-workers (2) described 61 patients with histologically proven gynecomastia: 77% had nodular, 20% dendritic, and 3% diffuse patterns mammographically. In some men presenting with breast enlargement and tenderness, fatty tissue alone is imaged mammographically (Figure 9.4).