Renal angiomyolipoma: relationships between tumor size, aneurysm formation, and rupture.

PURPOSE: To evaluate the relationships between tumor size, aneurysm formation, and spontaneous rupture in renal angiomyolipomas. MATERIALS AND METHODS: Twenty-three patients with renal angiomyolipoma were examined with angiography and computed tomography (CT). The single largest lesion in each kidney was evaluated. Tumor size was measured at CT, and aneurysm size was measured at renal angiography. Tumor and aneurysm sizes were compared between the group with ruptured angiomyolipoma and the group with unruptured angiomyolipoma. Multiple regression analysis was performed to identify factors affecting rupture. RESULTS: Twenty-nine kidneys with angiomyolipoma were identified. Eight angiomyolipomas were hemorrhagic; the remaining 21 were not hemorrhagic. Tumor size was larger than 4 cm and aneurysm size was 5 mm or larger in all hemorrhagic lesions. There were significant differences in mean tumor size (11.4 cm +/- 5.5 [SD] vs 5.0 cm +/- 3.1, P <.02) and mean aneurysm size (13.3 mm +/- 6.2 vs 2.4 mm +/- 2.9, P <.02) between the ruptured and unruptured tumor groups. When tumor size of 4 cm or larger and aneurysm size of 5 mm or larger were used as predictors of rupture, sensitivity and specificity, respectively, were 100% and 38% with the former criterion and 100% and 86% with the latter criterion. Multiple regression analysis indicated that aneurysm size was the most important factor linked to rupture. CONCLUSION: Aneurysm formation appears to be related to tumor size, and large aneurysms confer a higher probability of rupture.