Papillary endothelial hyperplasia (Masson's tumor) developed in the capsule of the implant in a breast cancer patient treated with mastectomy and radiation therapy.

Papillary endothelial hyperplasia (PEH) is an uncommon benign vascular proliferation appearing in soft tissues in different body areas including the breast, which may be related to radiation therapy. A 48-year-old woman previously treated for breast cancer with mastectomy followed by radiation therapy and reconstruction with an implant presented with a newly developing mass in the implant capsule. Pathological diagnosis was PEH. Imaging features of this rare entity are described, and lesions included in differential diagnosis are discussed.