Ductal adenoma of breast: imaging characteristics and radiologic-pathologic correlation of unique findings which reflect "pseudoinvasion"

To investigate the imaging characteristics of rare ductal adenoma of the breast, we evaluated the detailed imaging findings and correlated them with the pathologic features of the ductal adenomas. In particular, we describe in detail the imaging findings derived from "pseudoinvasion," one of the histological features unique to this tumor. We reviewed the imaging findings including magnetic resonance imaging (MRI) in three patients with ductal adenomas of the breast and correlated the findings with the detailed histological features. All patients exhibited well-demarcated nodules with smooth margins on mammography. On ultrasonography, two patients exhibited mural nodules within cysts. The bases of mural nodules protruded into the mammary glands. On contrast-enhanced MRI, these margins were smooth. Histologically, the bases showed foci of tumor cells scattered into collagenous materials (pseudoinvasion), the tumor foci were located along the collagen fibers; therefore, the margins were smooth. Distinguishing ductal adenoma from invasive carcinoma is an urgent issue. A clear margin of 'pseudoinvasion' on MRI is both a unique finding and a useful diagnostic clue.