UroToday - Fat Poor Renal Angiomyolipoma: Patient, Computerized Tomography and Histological Finding

December 2, 2008

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Fat Poor Renal Angiomyolipoma: Patient, Computerized Tomography and Histological Finding

Thursday, 01 March 2007

BERKELEY, CA (UroToday.com) - In most cases, angiomyolipoma (AML) is a diagnosis that is easily made through radiographic imaging, classically described as an enhancing renal lesion that contains fat, although some studies suggest that up to 14% of AML's cannot be reliably identified on preoperative imaging.

When AML can be reliably identified on imaging, surgical intervention can be avoided except in the case of large or symptomatic AML's, or in the case of retroperitoneal hemorrhage. "Fat poor" AML's have been described previously and refer to AML's that contain a paucity of fat and therefore cannot be reliably distinguished from a renal cell carcinoma preoperatively. As a consequence, these lesions are frequently diagnosed after surgery has been performed for a presumptive renal malignancy. Several investigators have looked at a variety of imaging criteria to determine if any unifying characteristic might increase our ability to reliably detect these lesions preoperatively and therefore avoid surgery. Here Milner and colleagues examine their experience with fat poor AML's and propose a general definition to be adopted for identification of such lesions.

The authors identified over 600 patients who underwent renal surgery for suspected tumor over a 6 year period. Of these, 15 (2.5%) proved to be AML. AML's were found to be multifocal in 20% of patients. Seventy-three percent of these AML's were not identified preoperatively due to their fat poor nature, thus they were thought to be renal cell carcinoma prior to surgical extirpation. In these patients with fat poor AML's, the mean age was 54, 73% were female (50% of whom had uterine fibroids), and 64% were incidentally found. Mean tumor size was 3.2 cm (range 1.5-6 cm). On non-contrast imaging, 42% of the fat poor AML's were hyperdense, whereas 57% were isodense. When examined pathologically, the authors found that over 92% of fat poor AML's had <25% fat, as compared to only 50% of classic radiographically identifiable AML's with this characteristic (p=0.04).

The authors conclude that fat poor AML's should be defined as the failure of imaging to demonstrate fat within a lesion, thus making it unsuspected at surgery. Pathologically, these lesions appear to have less than <25% fat per high powered field. Until a reliable means of detecting these lesions preoperatively, they should be managed like any other enhancing renal mass.

Milner J, McNeil B, Alioto J, Proud K, Rubinas T, Picken M, Demos T, Turk T, Perry Jr KT

J Urol 176(3): 905-909, 2006.

UroToday.com Renal Cancer Section