The breast implant capsule is a dynamic structure that forms following the implantation of a device. Although normally benign, increased awareness of breast implant-associated anaplastic large-cell lymphoma (BIA-ALCL) highlights that disease may arise from the capsule. BIA-ALCL presents as a late seroma or mass but explains few of the late seromas found in breast implant patients. To date, many of these seromas lack a clear cause and are often described as "idiopathic." Several benign and malignant breast implant capsular diseases can cause a late seroma or mass, including breast implant-associated squamous cell carcinoma. Similar to early reports of BIA-ALCL, these conditions are rare and largely limited to case reports or series. The purpose of this special topic is to present a narrative review highlighting capsular abnormalities that contribute to the formation of late seroma or mass in an attempt to broaden the differential diagnosis and help plastic surgeons identify the cause. Specifically, we review the presentation and management of BIA-ALCL, synovial metaplasia, capsular epithelialization, late hematoma, double capsule, breast cancer, squamous cell carcinoma, mesenchymal tumor, and B-cell lymphoma. Although rare, plastic surgeons should consider these capsular conditions as causes of late seromas and masses. Usually, these conditions may be diagnosed by following the National Comprehensive Cancer Network screening guidelines for BIA-ALCL. Thorough evaluation and workup of late seromas and masses may lead to improved characterization of these rare breast implant capsular conditions and improve our understanding of their pathophysiology and management.
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