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Fat in Renal Cell Carcinoma That Lacks Associated Calcifications

¹ Department of Radiology, University of Tennessee Medical Center, 1924 Alcoa Hwy., Knoxville, TN 37920.
² University Urology, University of Tennessee Medical Center, Knoxville, TN 37920.

Received July 10, 2000; accepted after revision July 16, 2001.

 
Address correspondence to J. R. Gash.

Introduction

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Distinguishing benign from malignant renal masses has always been a diagnostic dilemma for radiologists. A solitary solid mass identified in the kidney is usually considered malignant and removed surgically unless it is shown to have macroscopic fat consistent with an angiomyolipoma. A few cases of fat seen on CT in renal cell carcinomas have been reported [1,2,3,4,5,6]. Of these tumors, however, CT showed calcifications associated with the fat in all except one. The one case without calcifications revealed only a tiny focus of fat in the lesion. One pitfall of fat-containing renal masses is the wellknown occurrence of renal cell carcinoma invading and engulfing the perinephric fat. To our knowledge, no case of renal cell carcinoma with several prominent areas of macroscopic fat and without calcification visible on CT has been reported in the literature.

Case Report

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A 48-year-old man presented with painless hematuria. The patient was first evaluated with sonography that showed a large heterogeneous mass in the lower pole of the right kidney. The patient underwent further evaluation by CT. The mass measured approximately 10 cm in short-axis diameter and was well circumscribed. Several areas of low density were seen in the mass. These areas of low density were shown to be fat, which measured -75 H, by regions of interest (Fig. 1A). No calcifications were identified in the mass on CT (Figs. 1A and 1B). CT and pathologic analysis revealed no evidence of enveloping of perinephric fat. Because of the size of the lesion, the patient underwent nephrectomy the next week. Pathology reported a 10-cm renal cell carcinoma, granular cell type, arising from the lower pole of the right kidney. The lesion was tan with extensive areas of hemorrhage, adipose tissue, and focal microscopic calcifications (Fig. 1C).

View larger version (163K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —48-year-old man with painless hematuria. Contrast-enhanced CT scan with region of interest shown in focus of low attenuation in renal mass. Attenuation in this area measured -75 H.

View larger version (161K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —48-year-old man with painless hematuria. Unenhanced CT scan shows large renal cell carcinoma with macroscopic fat.

View larger version (165K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C. —48-year-old man with painless hematuria. Photograph of pathologic specimen reveals renal cell carcinoma that contains multiple areas of fat.

Discussion

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Most solid renal masses identified on imaging studies today are indeterminate as to cell type and are treated as renal cell carcinomas. There are a few exceptions to this line of treatment. One area in which radiologists have been traditionally confident in their diagnosis of a benign tumor in the kidney has been the fat-containing angiomyolipoma. For a definite diagnosis of this lesion on imaging studies, macroscopic fat must be identified. In fact, past experience suggests that when lesions contain low-density areas of -15 to -100 H, a diagnosis of an angiomyolipoma can be made confidently, and one can exclude the diagnosis of renal cell carcinoma [3, 7]. A few cases of renal cell carcinomas with identifiable fat have been reported; however, in almost all these cases, the mass had associated visible calcifications on CT [1, 2, 4,5,6, 8]. Angiomyolipomas rarely contain calcification [9, 10]. Therefore, the diagnosis of angiomyolipoma should be made with caution in the rare case in which a fat-containing renal mass also has associated calcifications. The case presented here is unique in that multiple areas of fat were found in a renal cell carcinoma and no associated calcifications were detected on CT.

In conclusion, only rarely are solid renal masses containing fat not angiomyolipomas. Rare exceptions include large renal cell carcinomas invading and enveloping the surrounding perirenal fat or containing small areas of fat associated with identifiable calcifications. We present a case of renal cell carcinoma containing multiple areas of fat without visible calcifications on CT.

References

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1. Helenon O, Chretien Y, Paraf F, Melki P, Denys A, Maoreau JF. Renal cell carcinoma containing fat: demonstration on CT. Radiology 1993;188:429 -430[Abstract/Free Full Text]
2. Henderson RJ, Germany R, Peavy PW, Eastham JA, Venable DD. Fat density in renal cell carcinoma: demonstration with computerized tomography. J Urol 1997;157:1347 -1348[Medline]
3. Lemaitre L, Claudon M, Dubrulle F, Maseman E. Imaging of angiomyolipomas. Semin Ultrasound CT MR 1997;18:100 -114[Medline]
4. Radin DR, Chandrasoma P. Demonstration of fat density in renal cell carcinoma. Acta Radiol 1992;33:365 -367[Medline]
5. Roy C, Tuchmann C, Lindner V, et al. Renal cell carcinoma with a fatty component mimicking angiolipoma on CT. Br J Radiol 1998;71:977 -979[Abstract]
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7. Davidson AJ, Hartman DS, Choyke PL, Wagner BJ. Radiologic assessment of renal masses: implications for patient care. Radiology 1997;202:297 -305[Abstract/Free Full Text]
8. Hammadeh MY, Thomas K, Philip T, Singh M. Renal cell carcinoma containing fat mimicking angiomyolipoma: demonstration with CT scan and histopathology. Eur J Radiol 1998;8:228 -229
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