Abstract: Renal angiomyolipoma (AML) is a common benign tumor in the urinary system, mainly composed of adipose tissue, blood vessels and muscle tissue. Renal AML is sporadic in most of patients, while a few are associated with tuberous sclerosis. Classical renal AML occurs predominantly in middle-aged females. Most cases are found incidentally during imaging examinations. The fat content makes AML have unique imaging characteristics and is easy to be identified with other renal tumors. However, the amount of fat varies in each tumor. AML that contains only microscopically detectable fat and whose amount of intratumoral fat may be too small to be identified on unenhanced computed tomography (CT) images is termed minimal fat or fat-poor renal AML, which appears as a high density shadow in the renal parenchyma on unenhanced CT images. Thus, it can be difficult to distinguish it from renal cell carcinoma (RCC) on imaging. Since the imaging findings are atypical, the diagnosis depends on pathological results. In addition, a few of AML can mimic malignant neoplasms. Recent studies suggested that AML might involve to peri-renal or renal sinus fat, regional lymphatics and other visceral organs, as well as inferior vena cava, which further makes the diagnosis more difficult. However, there is currently no reports about involvement of regional limphatics in minimal fat renal AML. In this article, we report a 27-year-old female patient without family history of tuberous sclerosis, who came to visit the hematologist because a high density shadow near the left kidney was found during CT scan which was accompanied by neck, armpits, groin, abdominal cavity and retroperitoneal lymph nodes enlargement. She was suspected of lymphoma in the beginning and transferred to Department of Urology to perform laparoscopic left renal mass and retroperitoneal lymph node excision and pathological examination for a definitive diagnosis. Finally, pathologic results revealed AML. Postoperative continuous lymphatic fistula developed and the retroperitoneal drainage of chylous fluid was 100-200 mL per day, lasting for 12 weeks. The fistula was successfully closed after conservative treatment including fasting and rehydration. This article summaries and discusses the diagnosis and treatment of renal AML with lymph nodes enlargement and the management of postoperative refractory lymphatic fistula by reviewing the related cases and literature.

Key words: Angiomyolipoma, Kidney, Adipose tissue, Diagnosis, differential