Giant renal hilar angiomyolipoma with Mayo level II venous tumor thrombus: a rare case report and literature review.

We present the case of a 54-year-old woman with an incidentally discovered left renal hilar mass. Imaging examination revealed a large, heterogeneous mass of fat density in the left renal pelvis, accompanied by a tumor thrombus extending into the renal vein and inferior vena cava (IVC), consistent with a Mayo level II thrombus—a finding reported in fewer than 50 cases worldwide. A preoperative diagnosis of renal angiomyolipoma (RAML) was established. Despite the patient’s strong preference for nephron-sparing surgery (NSS), intraoperative findings of extensive hilar invasion and calyceal involvement, along with significant hemorrhage, necessitated conversion to radical left nephrectomy with IVC thrombectomy. Histopathological examination confirmed the diagnosis of classic RAML, as indicated by positive immunohistochemical staining for Human Melanoma Black 45 (HMB45), Melanoma Antigen Recognized by T-cells 1 (Melan-A), and Smooth Muscle Actin (SMA), and negative staining for Cytokeratins (CK), S-100 Protein (S-100), and Desmin. The tumor thrombus was derived from the RAML. The patient recovered well postoperatively, with no recurrence or metastasis observed at the 8-month follow-up. This case underscores the surgical challenges of large hilar RAMLs with venous extension and highlights the importance of preoperative planning and intraoperative adaptability.