A rare case of malignant epithelioid angiomyolipoma: involvement of the lumbar vein pathway with downward extension to the iliac veins.

[INTRODUCTION AND IMPORTANCE] Epithelioid angiomyolipoma (EAML) is a rare renal perivascular epithelioid cell tumor (PEComa) with malignant potential in up to one-third of cases. Venous invasion usually involves the renal vein or inferior vena cava, while extension through the lumbar venous pathway is exceedingly uncommon.

[CASE PRESENTATION] We describe a 51-year-old woman with malignant EAML presenting with a left renal mass and extensive tumor thrombus extending via the lumbar venous complex into the bilateral iliac veins. Preoperative CT angiography demonstrated collateral venous drainage, and MRI venography was omitted due to adequate CT detail. The patient underwent radical nephrectomy and thrombectomy following preoperative embolization. Histopathology confirmed malignant EAML with negative margins and intraluminal tumor thrombus without venous wall invasion. Postoperative recovery was uneventful, and no recurrence was observed at 12 months. Next-generation sequencing revealed TP53, TSC, and MTOR mutations.

[CLINICAL DISCUSSION] This case illustrates a unique venous invasion route of EAML via the lumbar vein, an anatomic pathway not previously reported. Recognition of this pattern is essential for preoperative planning and surgical decision-making. The findings also highlight the molecular underpinnings of EAML and potential therapeutic implications of mTOR and PD-1 pathways.

[CONCLUSION] Malignant EAML can invade atypical venous routes such as the lumbar vein. Comprehensive imaging, multidisciplinary evaluation, and long-term follow-up are crucial for successful management.