Infiltrating lobular carcinoma: mammographic patterns with pathologic correlation.

Of the five identified radiographic patterns of ILC, the most common was a poorly defined asymmetric density with architectural distortion. Areas of ILC frequently are of low density, not much greater than that of the surrounding parenchyma. The mammographic appearance may reflect the behavior of ILC tumor cells, which travel in linear array ("single file") along and around the arborizing ducts that serve as scaffolding for these small, malignant cells that permeate the parenchyma without a central nidus. This feature of ILC may also help explain why tumors may be palpable as areas of vague induration or thickening rather than as discrete masses. When tumors are hidden in dense breast tissue (pattern 3) and not well imaged by mammography or when there are subtle mammographic changes (pattern 1), sonography may help confirm the presence of a solid mass. Most of the suspected tumors imaged by sonography were palpable as discrete masses or areas of induration.