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British Journal of Radiology (2007) 80, e193-e195
© 2007 British Institute of Radiology
doi: 10.1259/bjr/79274414
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Case report

CT and MRI in fat-containing papillary renal cell carcinoma

J M Garin, MD I Marco, MD A Salva, MD F Serrano, MD J M Bondia, MD and M Pacheco, MD

Department of Radiology, University Hospital Carlos Haya, Avda. Andalucia 21, Malaga 29002, Spain

Correspondence: Dr Jorge M Garin, Department of Radiology, University Hospital Carlos Haya, Avda. Andalucia 21, Malaga 29002, Spain. E-mail: jmgarin{at}ozu.es


   Abstract
Top
 Abstract
Introduction
 Case report
 Discussion
 References
 
We present a case, pathologically proven, of a patient with multiple papillary renal cell carcinoma (PRCC) with bilateral and synchronous affectation. CT showed fatty tissue inside one of the lesions and numerous calcified lesions. The study with MR demonstrated multiple and hypointense lesions in T2 and contrast enhancement in T1. Our observations confirm that the presence of multiple lesions with fat and calcified deposits and poor contrast enhancement should be diagnosed as PRCC, rather than renal clear cell carcinoma (RCCC) or renal angiomyolipoma.


   Introduction
Top
 Abstract
 Introduction
Case report
 Discussion
 References
 
Papillary renal cell carcinoma (PRCC) is the second most common carcinoma of the proximal renal tubules, accounting for 10–15% of renal neoplasms. The 5-year survival rate is very high (80–90%). Affected individuals may develop bilateral multifocal papillary renal carcinoma that can be sporadic, inherited or associated with acquired cystic kidney disease secondary to chronic renal failure [1–5]. It is diagnosed histologically and by its characteristic enhanced pattern on CT and MRI. A number of similarities with other types of renal cell carcinoma (RCC), such as clear cell carcinoma, have been found [6–10]. The identification of fatty tissue within a solid renal mass by CT and MRI suggests development of an angiomyolipoma; however, fat deposits have been reported in other types of renal neoplasms [11–21]. We report a case of synchronous bilateral multifocal PRCC showing calcifications with intratumoral fat in one of the lesions. We evaluate the use of CT and MRI for the diagnosis of PRCC.


   Case report
Top
 Abstract
 Introduction
 Case report
Discussion
 References
 
The patient was a 58-year-old man with hypertension, hypercholesterolaemia and macroscopic haematuria. There was no family history of kidney tumours. Renal ultrasound revealed a round, sharply delineated and partly calcified mass of 50 mm in diameter in the external interpolar area of the right kidney. Triphasic renal helical CT consisting of an unenhanced phase and two contrast-enhanced phases (30 s and 90 s delay) was performed with a scanner (Aura; Philips, The Netherlands). Unenhanced CT examination revealed multiple and bilateral renal masses of 15–50 mm in diameter. Two lesions in the right kidney had a dense calcification. The lesion of diameter 50 mm was hyperdense with respect to the adjacent parenchyma. It showed an area of diameter lower attenuation measuring –65 HU (Figure 1aGo). The left kidney showed multiple lesions that were iso- and hyperdense. Five of the smaller lesions (less than 10 mm in diameter) were heavily calcified and were located cortically (Figure 1bGo).


Figure 1
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  		Figure 1. (a) Unenhanced CT scan shows a hyperdense tumour of the right kidney with intratumoral fat density (–65 HU) and annular calcification (arrow). (b) Unenhanced CT scan shows two cortical calcified tumours of the left kidney (arrows).

 
Contrast-enhanced CT imaging of the kidney showed multiple bilateral hypodense cortical lesions. All but one of the non-calcified lesions larger than 10 mm in diameter had a contrast enhancement that ranged from 9 HU to 20 HU. The tumour–parenchyma and tumour–aorta contrast enhancement rates were estimated for two of the lesions in the right kidney and one of the lesions in the left kidney according to the method described by Herts et al [8]. Values of less than 25% were obtained in all cases.

The lesion containing macroscopic fat deposits did not incorporate any contrast medium. Neither macroscopic necrosis nor invasion of the perirenal tissue was observed. Contrast enhancement could not be precisely determined for the calcified lesions in the left kidney and for those lesions smaller than 10 mm in diameter. Nine tumours were removed from the right kidney. The histopathological analysis revealed six papillary renal cell carcinomas (Fuhrman grade 1) and three papillary adenomas. One of the tumours that was removed was 50 mm in diameter and was found to be necrotic. The histological examination revealed extensive necrotic tissue with macrophages and psammoma bodies (lipid necrosis and lipid vacuoles; Figure 1aGo).

The patient was monitored every 6 months by MRI and the left kidney was removed a year later. T1 and T2 weighted MRI was performed at 1.5 T (Gyroscan Intera; Philips, The Netherlands). On T1 weighted MR images several bilateral lesions were isointense relative to the renal parenchyma. On T2 weighted MR images all lesions were hypointense (Figure 2aGo). Changes in the lesions were not observed in the fat-suppressed sequences on either T1 or T2 weighted images. It was not possible to distinguish which lesions were calcified. All lesions identified on T1 and T2 weighted imaging, including those that were calcified, were slightly hyperintense after contrast medium injection, to a lesser degree than the normal renal parenchyma (Figure 2bGo).The histological examination of the 12 tumours isolated revealed Fuhrman grade 2 PRCC.


Figure 2
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  		Figure 2. (a) Coronal half Fourier single-shot turbo spin echo (HASTE) T2 weighted MR image showing four masses in the left kidney. All lesions have low signal intensity (arrows). (b) Axial post-gadolinium T1 weighted Gradient echo MR image showing cortical lesions with enhancement inside the tumour (arrows).

 

   Discussion
Top
 Abstract
 Introduction
 Case report
 Discussion
References
 
PRCC is the second most frequent renal epithelial malignancy after renal clear cell carcinoma (RCCC). It represents 10–15% of all tumours of the renal tubular system. It can be sporadic, inherited or associated with phakomatosis or haemodialysis [1–5]. On ultrasound PRCC is characterized by homogeneous iso- or hypoechogenic behaviour, making its identification difficult [6, 7]. In this patient, one single 50 mm calcified lesion was found. The other lesions were probably too small in size, or were isoechogenic, to be accurately identified.

CT scans of PRCCs characteristically show poor contrast enhancement compared with RCCCs [6–10]. In this case, lesions larger than 10 mm in diameter in diameter had a contrast enhancement of 9–20 HU, not really reaching the 10–20 HU thresholds. Contrast enhancement in calcified and non-calcified lesions smaller than 10 mm was undetectable. This might be because of their small size and the dense calcification of the lesion.

The presence of intratumoral fat is associated with a benign angiomyolipoma. Intratumoral fat, whether macro- or microscopic, has been reported in other renal tumours [11–22]. In this case, one tumour showed fat deposits inside the lesion and a calcified wall. The tumour did not show contrast enhancement in any of the phases assessed. The histological examination revealed extensive necrotic tissue with macrophages and psammoma bodies (lipid necrosis and lipid vacuoles).

To our knowledge, only three cases of PRCC with macroscopic fat have been reported in the literature [13, 18, 20]. The coexistence of fat deposits and tumoral calcifications in the renal lesions allows us to exclude a diagnosis of angiomyolipoma.

By MRI, most RCCCs are iso- or hypointense on T1 weighted images and have an increased signal intensity on T2 weighted images. A small number of PRCCs studied by MRI have been described as having hypointensity on T2 weighted images [23]. In this case, all lesions were isointense on T1 weighted images and hypointense on T2 analysis.

In conclusion this case illustrates: (1) the limitations of ultrasound for the correct identification of PRCC, as demonstrated by the fact that only one tumour was detected; (2) the importance of co-localizing fat and calcium deposits in the absence of any contrast enhancement; (3) that renal calcifications are undetectable by MRI although MRI can be useful in detecting changes in contrast enhancement in small lesions that are heavily calcified; (4) that the presence of multiple lesions with fat and calcified deposits and poor contrast enhancement should be interpreted as PRCC rather than RCCC or renal angiomyolipoma.

Received for publication October 4, 2005. Revision received March 20, 2006. Accepted for publication July 14, 2006.


   References
Top
 Abstract
 Introduction
 Case report
 Discussion
 References
 

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This Article
Right arrow Abstract Freely available
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Right arrow Articles by Garin, J M
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Right arrow Articles by Garin, J M
Right arrow Articles by Pacheco, M

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