A 49-year-old woman who had surgery for left breast cancer and subsequently underwent a two-stage deep inferior epigastric perforator(DIEP)flap reconstruction. One month postoperatively, she became aware of abdominal distention and visited a local hospital. CT scan revealed subcutaneous fluid accumulation with capsular formation in the lower abdomen. Imaging findings and physical examination showed no abdominal wall scar hernia. After multiple puncture aspirations, fluid accumulation was observed again, and the possibility of a chronic expanding hematoma was considered. Later, hematoma removal, including the capsules, was performed; pathological findings showed no evidence of malignancy. No fluid retention was observed postoperatively. In cases where imaging evaluation reveals hematoma formation with capsules, hematoma removal, including the capsules, should be performed to avert the possibility of a chronic expanding hematoma.