To improve understanding of the clinical features of renal angiomyolipoma (AML) accompanied by tumor thrombus (TT).

From January 2017 to February 2022, 18 patients with AML and TT were enrolled. We retrospectively analyzed them and there were 6 cases of epithelial AML (EAML) and 12 of classical AML (CAML). We compared the key variables between the two cohorts.

The mean age of the 18 cases was 42.0 (standard deviation [SD] 13.4) years and 14 (77.8%) were female. Eleven (61.1%) tumors were on the right side. Only two (11.1%) cases presented with flank pain. The mean follow-up time was 33.6 (IQR: 20.1−48.5) months. All participants were alive at the end of follow-up. One case developed lung metastases 21 months after operation but entered remission after 2 years of everolimus treatment. The imaging diagnoses of all CAML cases were consistent with the pathology, while all imaged EAML cases were diagnosed with carcinomas. Five EAML cases, but only one CAML case, exhibited necrosis (83.3 vs. 8.3%, P = 0.001). The Ki-67 index of the EAML group was significantly higher than that of the CAML group (7 vs. 2, P = 0.004).

Compared to CAML, EAML tended to be associated with a higher imaging misdiagnosis rate, and was more commonly associated with necrosis and a higher Ki-67 index. Surgery remains the prime treatment for nonmetastatic AML with TT; such cases have a relatively good prognosis despite the malignant potential.