Myxolipoma of the renal capsule: A case report

INTRODUCTION: Although lipomas are the most common mesenchymal tumors of the human body, primary intrarenal lipomas are quite rare. In this report we present a case of benign mesenchymal tumor with lipomatous and myxoid components. PRESENTATION OF CASE: A sixty one years old male patient was admitted to our outpatient clinic for a general control since he had a right radical nephrectomy operation due to renal cell carcinoma (RCC) eight years ago and he did not have any urological control for last 3 years. However the urinary ultrasound revealed a mass lesion on left kidney and then on axial contrast-enhanced computed tomography (CT) scan, there were two masses on the left kidney. In the magnetic resonance imaging (MRI), the tumor on cortex was depicted as a homogeneous low-signal intensity on the T1-weighted pulse sequence and as a heterogeneous high-signal intensity on the T2-weighted pulse sequence. In pathological evaluation, the biopsy material of the cortical mass was a tumoral lesion containing lipomatous and mixoid areas without atypia, mitosis or necrosis which was diagnosed as myxolipoma. DISCUSSION: Myxolipoma, an uncommon type of lipoma, is a benign tumor composed mainly of fat cells with myxoid (mucus-like) components. In our case, the tumor was composed of mature adipocytes together with areas rich in mucoid substances and there were no malignant features including lipoblasts, mitosis or abundant capillary network. CONCLUSION: Herein we present a case of a fatty tumor originating from the renal capsule with the histologic diagnosis of myxolipoma. To the best of our knowledge, myxolipoma, a very rare form of lipoma, is not reported in kidney, in the literature before.