We present a case of cystic renal cell carcinoma( RCC) mimicking a benign complicated renal cyst. In thepresent case, the cystic renal mass was classified as Bosniak classification category II on computed tomography(CT), but magnetic resonance imaging (MRI) demonstrated additional septa and enhancement, whichled to an upgraded Bosniak classification( category III). The patient underwent radical nephrectomy. Histologicalexamination showed the cystic necrosis type of RCC

Akinori Masuda

Department of Urology, Dokkyo Medical University

Department of Urology, Dokkyo Medical University Nikko Medical Center

Ken-ichiro Yoshida

Mikihiko Honda

Takao Kamai

Tomonori Yamanishi

Toyoaki Toyoshima

Yoshitatsu Fukabori

English

Dokkyo Medical University Repository / 獨協医科大学リポジトリ

prostatic enlargement. A right renal mass with a solid 
component was incidentally found during the examina-
tion （Fig. 1）. Unenhanced CT showed a cystic renal 
INTRODUCTION
Differentiation between a benign complicated renal 
cyst and a cystic renal cell carcinoma （RCC） remains 
one of the more common problems in renal imaging. 
Using computed tomography （CT）, Bosniak developed 
a useful classification scheme that divides cystic renal 
masses into four categories 1）. Differentiating category 
II from category III is important because the recom-
mended management for these categories is different. 
Herein, we report a case of cystic RCC mimicking a 
benign complicated renal cyst.
CASE REPORT
A 74-year-old man presented with difficulty in uri-
nating. Ultrasonography （US） demonstrated benign 
111
Received October 27, 2010；accepted December 24, 2010
Reprint requests to：Akinori Masuda, MD.
Department of Urology, Dokkyo Medical 
University, Mibu, Tochigi, 321-0293, Japan
Dokkyo Journal of Medical Sciences
38（1）：111〜114，2011
A Case of Cystic Renal Cell Carcinoma Mimicking a 
Benign Complicated Renal Cyst on Computed 
Tomography；Usefulness of Magnetic Resonance Imaging
Akinori Masuda, Toyoaki Toyoshima, Takao Kamai, Yoshitatsu Fukabori,  
＊Mikihiko Honda, Tomonori Yamanishi and Ken-ichiro Yoshida
Department of Urology, Dokkyo Medical University, Mibu, Tochigi, Japan 
＊Department of Urology, Dokkyo Medical University Nikko Medical Center, Nikko, Tochigi, Japan
SUMMARY
We present a case of cystic renal cell carcinoma （RCC） mimicking a benign complicated renal cyst. In the 
present case, the cystic renal mass was classified as Bosniak classification category II on computed tomogra-
phy （CT）, but magnetic resonance imaging （MRI） demonstrated additional septa and enhancement, which 
led to an upgraded Bosniak classification （category III）. The patient underwent radical nephrectomy. Histo-
logical examination showed the cystic necrosis type of RCC.
Key Words： Cystic renal cell carcinoma, Renal cyst, Bosniak classification
Case Report
Figure 1　 Ultrasonography demonstrated a renal mass 
with a solid component （arrow） in the right 
kidney （arrowhead）.
Akinori Masuda
ment of the inferior septa （Fig. 4b, 4c）, although the 
lesion showed a low intensity on T1-weighted image 
（Fig. 4a）. On MRI examination, the cystic renal mass 
was classified as category III. A staging workup dem-
onstrated no other evidence of disease. The patient un-
derwent radical right nephrectomy. Macroscopically, 
the cystic space was filled with necrotic debris. Histo-
logically, under low magnification, the renal mass 
showed virtually complete tumor necrosis with rare 
nests of tumor cells. These cells were identified at the 
site of the inferior septa that had been visualized as an 
enhanced region on MRI. On high magnification, these 
mass with minimal marginal calcification （Fig. 2a）. 
The cystic renal mass was round and sharply margin-
ated without evidence of enhancement after the ad-
ministration of contrast material （Fig. 2b）. The cystic 
renal mass was 8 cm in diameter. On CT examination, 
it was classified as category II using the Bosniak clas-
sification. T1-weighted axial MRI demonstrated a 
right renal mass that was slightly hyperintense rela-
tive to the renal parenchyma （Fig. 3a）, and a T2-
weighted axial image demonstrated a hyperintense 
mass with a thickened septa （＞1 mm） （Fig. 3b）. The 
administration of Gd-DTPA demonstrated enhance-
112 DJMS
Figure 2　 （a）　Unenhanced CT showed a right cystic renal mass with minimal marginal 
calcification （arrowhead）. （b） The right cystic renal mass was round and 
sharply marginated without evidence of enhancement after administration of 
contrast material.
Figure 3　 （a）On MRI examination, T1-weighted axial image view demonstrated a right 
renal mass that was hyper-intense relative to the renal parenchyma. （b） 
T2-weighted axial image view demonstrated a right hyper-intense mass with 
thickened septa （＞1 mm）.
Cystic Renal Cell Carcinoma Mimicking Benign Complicated Renal Cyst
his original classification system to add a subset of cat-
egory II lesions, category IIF （F for follow-up） le-
sions5）.
In our case, the cystic renal mass was classified as 
category II using the Bosniak classification on CT. 
However, MRI demonstrated additional thickened sep-
ta and contrast enhancement that caused the lesion to 
be upgraded （category III）. These findings agree with 
Israel et al. who reported that gadolinium-enhanced 
MRI has superior contrast resolution compared with 
CT6〜7）. When cystic renal masses contain hemorrhage 
or debris, they may demonstrate a wide range of sig-
nal intensities on T1- and T2-weighted images. In 
these instances, it is not possible to differentiate com-
plex renal cyst from cystic RCC using morphological 
features and signal intensities only. The only determin-
ing factor to accurately differentiate these lesions is 
the presence or absence of enhancement. Therefore, 
the ability to confidently identify enhancement on MRI 
tumor cells represented clear cell type of adenocarci-
noma, Grade 1＞Grade 2 （Fig. 5）. The patient has re-
mained free of disease for 96 months since surgery.
DISCUSSION
Cystic RCC account for 1％ to 2.5％ of all renal neo-
plasms2〜3）. Hartman et al. classified cystic RCC as 
showing either （i） intrinsic multiloculated growth；（ii） 
intrinsic unilocular growth；（iii） cystic necrosis；or 
（iv） originating from the epithelial lining of a preexist-
ing simple cyst 4）. Differentiation between cystic RCC 
and benign complicated renal cyst remains one of the 
more common problems in renal imaging. Using CT, 
Bosniak proposed a new classification system in 1986 
based on the division of renal cystic lesions into four 
categories1）. Differentiating more complex category III 
lesions from somewhat less complex category II lesions 
is important because the recommended approaches to 
management are different. In 1993 , Bosniak revised 
38（1） （2011） 113
Figure 5　 （a） Under low magnification, the renal mass showed virtually complete tumor 
necrosis with only rare nests of tumor cells. （b） High power magnification, 
these tumor cells were consistent with clear cell type adenocarcinoma, G1＞G2.
Figure 4　 Administration of Gd-DTPA demonstrated enhancement of the inferior septa 
（arrowhead） （Fig. 4b, 4c）, although the lesion showed a low intensity on 
T1-weighted image （Fig. 4a）.
Akinori Masuda
REFERENCE
 1） Bosniak MA：The current radiological approach to 
renal cysts. Radiology 158：1-10, 1986.
 2） Emmett JL, Levine SR, Woolner LB：Co-existence of 
renal cyst and tumor；incidence in 1007 cases. Br J 
Urol 35：403-410, 1963.
 3） Hayakawa M, Hatono T, Tsuji A et al：Patients with 
renal cysts associated with renal cell carcinoma and 
clinical implications of renal puncture：a study of 223 
cases. Urology 47：643-646, 1996.
 4） Hartman CD, Davis CC, Johns CT et al：Cystic renal 
cell carcinoma. Urology 28：145-153, 1986.
 5） Bosniak MA：Problems in the radiologic diagnosis of 
renal parenchymal tumors. The urologic clinics of 
North America. Saunders, Philadelphia, pp.217-230 , 
1993.
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cystic renal masses：comparison of CT and MR imag-
ing by using the Bosniak’ classification system. Radiol-
ogy 231：365-371, 2004.
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masses. Magnetic Resonance Imaging Clinics of North 
America 12：403-412, 2004.
 8） Kochhar R, Brown RK, Wong CO, et al：Role of FDG 
PET/CT in imaging of renal lesions. J Med Imaging 
Radiat Oncol 54：347-57, 2010
 9） Ishikawa I, Morita K, Hayama S, et al：Imaging of ac-
quired cystic disease-associated renal cell carcinoma 
by contrast-enhanced ultrasonography with perlubu-
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is critical for the appropriate characterization of cystic 
renal masses.
Although the Bosniak renal cyst classification sys-
tem was developed based on CT findings, Bosniak clas-
sification is appropriate for use with MRI in the evalu-
ation of most cystic renal masses. A potential 
drawback of MRI is its inability to depict calcification 
within the septa or wall of a cystic lesion. However, 
neither the diagnosis of malignancy nor the decision to 
surgically excise a cystic renal mass can be made 
based on the presence or amount of calcification. 
Therefore, this potential limitation should not affect pa-
tient management.
The Bosniak classification system using CT has 
proved to be useful because it is often definitive in 
many instances, providing a starting point for the eval-
uation of complex cystic renal masses and a frame-
work for a logical approach to the treatment of pa-
tients with cystic lesions. However, the classification 
system is not always definitive because renal cystic 
disease can often show complex imaging and histologi-
cal findings. Such factors as the size of the lesion, age 
of the patient and presence or absence of renal inflam-
mation also dictate the treatment options. Gallium-67 
scintigraphy may be useful for differentiating infected 
cystic renal mass from cystic RCC. Furthermore, there 
were reports that positron emission tomography 
（PET） and computed tomography （CT） is useful for 
differentiating cystic renal cell carcinoma from renal 
cyst8〜9）. Ascenti et al.10） proposed that the use of the 
Bosniak classification with contrast-enhanced US is 
also appropriate for classifying renal cysts. The Bos-
niak classification is based primarily on CT findings 
but decisions regarding management should be based 
on a consideration of the findings of other imaging 
studies, such as MRI and US.
114 DJMS


A Case of Cystic Renal Cell Carcinoma Mimicking a Benign Complicated Renal Cyst on Computed Tomography;Usefulness of Magnetic Resonance Imaging

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A Case of Cystic Renal Cell Carcinoma Mimicking a Benign Complicated Renal Cyst on Computed Tomography;Usefulness of Magnetic Resonance Imaging

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