Uncommon presentation of a giant psoas muscle lipoma: a case report and brief literature review.

Giant retroperitoneal lipomas, particularly within the psoas muscle, are a rare condition. We herein present one such case of a 45-year-old Italian man and a literature review. There are only two case reports published in the literature, thus posing challenges for the appropriate diagnosis and treatment. Our patient was admitted to the emergency department with colicky abdominal pain. Computerized tomography (CT) with contrast enhancement revealed kidney stones and a 19.5×13.6×18 cm mass of adipose tissue with septa located in the right retroperitoneum, in close continuity with the right psoas major muscle. Magnetic resonance imaging showed a voluminous neoformation with predominantly adipose content and a compressive effect on adjacent vascular structures. The CT-guided biopsy indicated spindle cell mesenchymal neoplasm, not otherwise specified. Surgical resection of the retroperitoneal mass with the capsule was performed, and a histopathology examination confirmed the diagnosis of spindle cell lipoma. Despite the fact that CT and MRI are the main diagnostic tools, this case report emphasizes the need for a CT-guided core needle biopsy prior to surgery for appropriate diagnosis.