Sporadic, classic-type renal angiomyolipoma with renal vein and inferior vena cava extension: an incidental case

Renal angiomyolipomas (AMLs) were first described in the early 1900s by Gravitz, but it was not until 1951 that they were named renal AML. These kidney tumours are rare, occurring in 0.13%-0.44% of the population. These mesenchymal tumours are composed of smooth muscle-like, adipocyte-like and epithelioid cells. Depending on the predominant cell population, it can be further subclassified into classic, epithelioid and AML with epithelial cyst. A 32-year-old woman presented with mild, intermittent, epigastric and right upper quadrant abdominal pain. Abdominal ultrasound revealed an incidental lesion within the inferior vena cava (IVC). A CT scan showed a lesion within the left renal vein extending into the IVC with 40% narrowing and a fat-containing mass in the lower pole of the left kidney of 15 mm suggesting an AML. Thrombectomy was performed. The specimen resulted positive for classic variant renal AML. Initial diagnosis is centred on imagining studies, based in fatty tissue concentration. The AML expresses melanocytic markers. This helps differentiate from renal cell carcinoma. Although AML is considered a benign condition, there is evidence of malignant transformation. Active surveillance is recommended for lesions <4 cm. Nephron sparing surgery is the procedure of choice. Nephrectomy is recommended if there is a high probability of malignancy. Mammalian target of rapamycin (mTOR) inhibitors have been proposed to be an alternative treatment.