Appearance of Renal Replacement Lipomatosis on Computed Tomography: Rare pseudotumour.

Abstract

An 81-year-old male patient presented to the Urology Department of GATA Haydarpasa Training Hospital, Istanbul, Turkey, in May 2014 complaining of left lumbar pain and a sense of abdominal fullness. On physical examination, left lumbar tenderness and a palpable mass were observed. A urine analysis showed an increased number of red blood cells. Plain abdominal radiography demonstrated soft tissue density at the left upper quadrant pushing the colon segments medially [Figure 1]. Abdominal ultrasonography revealed a significant increase in the size and echogenicity of the left kidney and its margin could not be clearly differentiated from the surrounding fat tissue. In addition, a decrease in the left renal parenchymal thickness was noted. Figure 1: Plain abdominal radiograph showing a mass with soft tissue density in the left upper quadrant pushing the colon segments medially (arrows) in a patient with renal replacement lipomatosis. Computed tomography (CT) and magnetic resonance imaging (MRI) were performed without the administration of intravenous contrast due to elevated serum creatinine levels. The CT scan [Figure 2] and axial T2-weighted MRI images revealed a fatty mass in the left kidney (approximately 22 × 18 × 14 cm in size) with areas of linear and patchy fibrous tissue. The mass caused significant enlargement of the left kidney and distortion of the surrounding structures. There were no areas of restricted diffusion within the lesion on diffusion-weighted images. A biopsy of the mass was performed and a pathological examination revealed mature fat tissue. As a result of these findings, the left renal mass was considered to indicate renal replacement lipomatosis (RRL). Ultrasonography performed three months after the initial diagnosis revealed no changes in the size and imaging characteristics of the lesion. Figure 2: Non-contrast computed tomography showing a fatty renal mass (arrows) in a patient with renal replacement lipomatosis. The mass caused significant left renal enlargement and distortion on the surrounding structures.