IMAGING

Renal angiomyolipoma: relationships between tumor size, aneurysm formation, and rupture
Yamakado K, Tanaka N, Nakagawa T, Kobayashi S, Yanagawa M, Takeda K
Departments of Radiology and Urology, Mie University School of Medicine, Tsu, Mie, Japan
Radiology 2002; 225:78-82

• 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 5mm 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.
  
  
• Editorial Comment
  This study was conducted in a group of 23 patients with renal angiomyolipoma (AML), in order to establish the correlation between tumor size, aneurysm formation, and spontaneous rupture. Renal AML are benign neoplasms composed of mature adipose tissue, thick-walled blood vessels, and smooth muscle, in varying proportions. Spontaneous renal bleeding secondary to an AML usually occurs when the tumor is larger than 4 cm (51%), although in a recent review of our material, 3 (27%) of 11 hemorrhagic tumors measured 2.5 to 4.0cm in diameter (1). It is well known that the early phase of selective angiography demonstrates aneurysms in the interlobar or interlobular arteries in about 70 % of AMLs (2). These pseudoaneurysms appear to be very difficult to detect when a non-hemorrhagic renal angiomyolipoma is evaluated only by US, CT, or MRI. In a hemorrhagic renal AML, color-flow Doppler sonography may demonstrate large pseudoaneurysm (= or >2cm in diameter) within the lesion, and consequently is able to predict if the hemorrhagic tumor is at risk of early recurrent bleeding (3). As we know, the presence of a large aneurysm in renal AML has shown to be cause of life threatening hemorrhage in few patients in the literature (4). In this situation, heminephrectomy or therapeutic embolization has been performed as therapeutic modalities .This fact emphasizes the authors’ conclusion that aneurysm formation is probably related to the size of the tumor, and that large pseudoaneurysms are related to a higher probability of rupture.

References
1. Prando A: Renal angiomyolipomas: an imaging review and a radiologic classification. Scientific Exhibit, RSNA, 2002.
2. Arima K, et al.: Renal angiomyolipoma: diagnosis and treatment. Hinyokika Kiyo 1995; 41:737-43.
3. Lapeyre M, et al.: Color-flow Doppler sonography of pseudoaneurysms in patients with bleeding renal angiomyolipoma. AJR, 2002; 179:145-7.
4. Adler J: Macro aneurysm in renal AML: two cases, with therapeutic embolization in one patient. Urol Radiol, 1984; 6:201-3.

Dr. Adilson Prando
Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil