Rationale: Well-differentiated liposarcomas (WDLPS) are rare retroperitoneal tumors that can reach significant size as they can grow without constrains before becoming symptomatic. Laparotomic open radical tumor resection represents the most common surgical approach.
Patient concerns: A mass with "fat fluid level" was found in the right pelvis of an asymptomatic woman undergoing routine transvaginal ultrasound: the preoperative diagnosis was right mature ovarian teratoma.
Diagnosis: Postoperative histopathology confirmed the diagnosis of WDLPS.
Interventions: A radical laparoscopic excision of the retroperitoneal mass with bilateral salpingectomy was performed.
Outcomes: Patient is free of disease at 18 months after surgery.
Lesson: Despite computed tomography scan is the gold standard technique to identify WDLPS, such neoplasms can be misdiagnosed for mature ovarian teratomas. When a retroperitoneal mass is incidentally discovered during a surgery, an open core-needle biopsy is usually performed, and appropriate treatment planned only after complete staging and final pathology are available. Instead, when tumor margins are identified, resection of an incidentally diagnosed WDLPS would benefit from laparoscopic magnification that could improve distinguishing the disease from the surrounding tissues. Therefore, laparoscopy could represent a safe and effective technique to diagnose and treat retroperitoneal diseases.