Asymptomatic Retroperitoneal Lipoma with Extension to the Right Anteromedial Thigh

Background and Clinical Significance: Retroperitoneal tumors are a rare and diverse group of neoplasms, accounting for less than 1% of adult solid tumors. Retroperitoneal lipomas are particularly uncommon, with fewer than 20 cases described in the literature. Their asymptomatic growth and lack of clear anatomical boundaries can result in delayed diagnosis and substantial tumor size at clinical presentation. This case highlights a rare retroperitoneal lipoma with atypical extension into the right thigh through the muscular lacuna, mimicking a femoral hernia and compressing the femoral nerve—a presentation scarcely reported and clinically significant due to its surgical complexity and risk of recurrence. Case Presentation: We report the case of a 65-year-old woman from an urban setting who presented with progressive right thigh discomfort and lower limb pain during ambulation. The mass had been initially identified two years prior as a small, asymptomatic right inguinal formation during imaging to exclude an inguinal hernia. Computed tomography (CT) and magnetic resonance imaging (MRI) confirmed a large retroperitoneal lipomatous tumor extending to the anteromedial right thigh. Surgical excision was performed through a dual approach: midline laparotomy and thigh incision. A 30 × 30 cm encapsulated lipoma was removed without injuring adjacent nerves or vessels. Histopathological evaluation confirmed a mature lipoma without atypia but with a lipogranulomatous reaction. The patient’s postoperative course was favorable, with minimal residual paresthesia and complete wound healing. Conclusions: Although benign, retroperitoneal lipomas can mimic other pathologies and present surgical challenges when they extend beyond their typical boundaries. Early recognition and coordinated surgical management are crucial for optimal outcomes and prevention of recurrence.