Cesarean scar defect (CSD) is a long-term complication of cesarean section (CS). However, its risks for perimenopausal women remain unclear. We present a rare case of CSD involving hematometra in a perimenopausal woman, which led to emergency hysterectomy. A 51-year-old woman with a history of CS presented with acute abdominal pain. Transvaginal ultrasonography and magnetic resonance imaging identified a hematometra within a large CSD extending into the cervical myometrium. Emergent hysterectomy was performed due to persistent pain. Histopathology revealed a fresh hematoma within the CSD, with ectopic endometrial glands and hemorrhage on its walls. This case highlights the pathogenesis of hematometra within a CSD and underscores its potential to cause acute abdomen in perimenopausal women.