The halo sign is not always benign

A complete or partial radiolucent ring that appears around the periphery of some breast masses has been considered a mammographic sign of a benign process most frequently seen with cysts and fibroadenomas. In 19 women the authors identified 25 malignant breast lesions with a partial or complete halo on mammography. Infiltrating ductal carcinoma was diagnosed in 11 cases (three were of the papillary subtype). Six of these were high grade and three were associated with positive axillary nodes, while a fourth was associated with distant metastases. Four other women had lymphomas, and there were single cases of metastatic melanoma, phylloides tumor, malignant fibrous histiocytoma, and breast cancer metastatic to an intrammary lymph node. The presence of the halo sign does not guarantee a benign process. The authors were able to demonstrate by densitionometric studies as well as masking the mass that the halo is due to the Mach effect