Chronic Expanding Hematoma of the Postmastectomy Axilla: A Pictorial Review of Long-Term Multimodality Imaging.

Chronic expanding hematomas (CEHs) are rare, benign lesions that can persist and slowly grow following surgery or trauma. In the breast and axillary region, they may closely mimic recurrent malignancy because they may demonstrate mixed internal structures, calcifications, peripheral enhancement, and sometimes even fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET) scans. In this article, we present a long-term imaging review of a patient with a chronic left axillary lesion after bilateral mastectomy, with serial ultrasound, PET/computed tomography (CT), and magnetic resonance imaging (MRI) images and repeated histopathology over nearly two decades. The lesion evolved from a large cystic postoperative collection into a heterogeneous multilobulated mass with mixed solid and cystic components. It demonstrated mild vascularity, wall thickening, and peripheral calcification while remaining pathologically benign on repeated tissue sampling. This pictorial review highlights the imaging evolution, pitfalls, and key differentiating features that help distinguish CEH from recurrent tumors and other postoperative mimics.