The patient had undergone breast reconstruction with expander and saline implant after skin-sparing mastectomy for multicentric DCIS 9 years earlier.

After 9 years, a blunt chest trauma produced a periprosthetic fluid collection (seroma) detected by ultrasound but did not result in a rupture of the saline implant, which would have caused a change in the size and shape of the affected breast.

An ultrasound-guided fluid aspiration and cytological evaluation, required to rule out breast implant-associated anaplastic large cell lymphoma (BIA-ALCL), an extremely rare form of lymphoma, were indicated but refused by the patient.

The history of chest trauma, the extreme rarity of BIA-ALCL and the collection of fluid without solid nodules to suggest BIA-ALCL, were considered sufficient for the diagnosis. This was confirmed by the stability of the seroma after 4 years.