Clinical Correlates of Renal Angiomyolipoma Subtypes in 209 Patients: Classic, Fat Poor, Tuberous Sclerosis Associated and Epithelioid

Purpose

Angiomyolipomas classically present radiographically as fat containing lesions but some fail to demonstrate fat content. Histologically confirmed angiomyolipomas uniformly follow a benign course but rare epithelioid variants of angiomyolipoma can recur and metastasize. We investigated the clinical, radiographic and histological characteristics of each angiomyolipoma subtype.

Materials and Methods

Pertinent data were recorded for 209 patients surgically treated for angiomyolipoma in 219 kidneys from 1981 to 2007. Classic and fat poor angiomyolipomas were classified radiographically based on the presence or absence of fat and classified histologically based on the presence of triphasic, monophasic or epithelioid histology.

Results

Median radiographic size was 3.2, 4.9 and 10 cm in patients with a single angiomyolipoma (59% of patients), multiple angiomyolipomas and tuberous sclerosis (probable or definite), respectively. In these 3 groups 65%, 47% and 33% of lesions were not suspected radiographically (fat poor angiomyolipoma). Fat poor angiomyolipomas were more commonly single, smaller and in older patients. Triphasic histology was evident in 76% of angiomyolipomas with 16% demonstrating a predominance of 1 component and 8% containing epithelioid features. Despite potentially aggressive findings in 18% (eg presence within the perinephric fat, lymph node involvement) no angiomyolipoma recurred during a mean followup of 3.4 years (range 0 to 24). A total of 28 (13%) patients with angiomyolipoma had concomitant renal cell carcinoma.

Conclusions

A surprisingly high number of resected angiomyolipomas was not suspected radiographically indicating the importance of precise radiographic characterization to minimize nephrectomy for fat poor angiomyolipoma, which should remain a research priority. In this sizeable single institution series no triphasic, monophasic or epithelioid angiomyolipoma recurred despite potentially aggressive findings in a substantial proportion of cases.

Key Words: kidney neoplasms, angiomyolipoma, pathology, tuberous sclerosis

Abbreviations and Acronyms: AML, angiomyolipoma, CT, computerized tomography, IQR, interquartile range, MR, magnetic resonance, RCC, renal cell carcinoma, TSC, tuberous sclerosis complex