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Case Report

Urol Int 2013;90:369–372 DOI: 10.1159/000341940

Renal Metanephric Adenoma Mimicking Papillary Renal Cell Carcinoma on Computed Tomography: A Case Report

Akinori Masuda a Takao Kamai a Tomoya Mizuno a Tsunehito Kambara a

Hideyuki Abe a Shigeki Tomita b Yoshitatsu Fukabori a Tomonori Yamanishi a

Yasushi Kaji c Ken-ichiro Yoshida a

Departments of a Urology, b Surgical and Molecular Pathology and c Radiology, Dokkyo Medical University, Mibu , Japan

Introduction

Metanephric adenoma (MA) is a rare benign renal tu-mor. The histological similarity between renal MA and type I papillary renal cell carcinoma (PRCC) has long been recognized. Both of these tumors feature tubular-papillary structures and psammoma bodies, but there are some immunophenotypic and cytogenetic differences that can assist in the differential diagnosis. On the other hand, differentiating between renal MA and PRCC on the basis of radiological findings is difficult. Both tumors frequently show calcification and are visualized as hypo-vascular masses. Jinzaki et al. [1] reported that there was a correlation between the pattern of enhancement of re-nal tumors on double-phase enhanced computed tomog-raphy (CT) and the pathological features. Enhancement on CT scans shows various patterns among the subtypes of renal tumors because the extent of contrast enhance-ment is influenced by differences of tumor angiogenesis. Here, we report a case of renal MA mimicking PRCC on CT. We also review previous reports of the findings on multiphase enhanced CT to clarify the enhancement pat-tern of renal MA.

Key Words

Renal metanephric adenoma � Papillary renal cell carcinoma � Computed tomography

Abstract

We present a case of renal metanephric adenoma (MA) mim-icking papillary renal cell carcinoma (PRCC) on computed to-mography (CT). In the present case, double-phase enhanced CT showed a hypovascular right renal tumor with gradual and prolonged enhancement. The renal tumor was surgical-ly removed. Histological examination of the resected speci-men showed renal MA. Although the radiological features of renal MA have been described by some authors, only a few reports have mentioned the pattern of enhancement on multiphase enhanced CT. The pattern of enhancement of a renal tumor is likely to be correlated with its pathological features. Since renal MA is thought to be genetically related to PRCC, these two tumors are likely to demonstrate similar radiological features, so that differentiating between them becomes difficult. In patients with a hypovascular renal mass that shows gradual and prolonged enhancement on multi-phase enhanced CT, the diagnosis of renal MA should be considered. Copyright © 2012 S. Karger AG, Basel

Received: May 31, 2012 Accepted: July 18, 2012 Published online: October 17, 2012

InternationalisUrologia

Akinori Masuda, MD Department of Urology, Dokkyo Medical University 880 KitakobayashiMibu-machi, Shimotsuga-gun, Tochigi 321-0293 (Japan) Tel. +81 282 86 1111, E-Mail a.masuda.dmu   @   gmail.com

© 2012 S. Karger AG, Basel0042–1138/13/0903–0369$38.00/0

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Case Report

A 57-year-old woman was referred to our hospital for evalua-tion of a right renal tumor that had been incidentally detected by ultrasonography. She had hypertension, fatty liver, and diabetes mellitus. Plain CT showed a 2.5-cm right renal mass without cal-cification ( fig. 1 a). After administration of contrast medium, at-tenuation in the corticomedullary phase (CMP) was significantly less marked for the tumor than the renal parenchyma ( fig. 1 b), while the tumor showed gradual and prolonged enhancement in the late nephrographic phase (NP) ( fig. 1 c). We considered that the tumor was likely to be PRCC. After a staging workup demon-strated no other evidence of disease, radical right nephrectomy was performed. Histologically, the tumor was characterized by monomorphic proliferation of small and uniform tumor cells with round nuclei and scanty cytoplasm. The tumor was com-posed of numerous small tubular structures, some of which con-tained glomeruloid bodies ( fig. 2 ). From these findings, a diagno-sis of renal MA was made. The patient has remained free of dis-ease for 102 months since surgery.

a b

c

Fig. 1. a Plain CT showed a 2.5-cm right renal mass without cal-cification. b After administration of contrast medium, attenua-tion during the CMP was significantly less marked in the renal tumor than the renal parenchyma. c The tumor showed gradual and prolonged enhancement during the late NP.

Fig. 2. Histologically, the tumor is composed of numerous small tubular structures, some of which show glomerular differentia-tion.

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A Case of Renal Metanephric Adenoma Urol Int 2013;90:369–372 DOI: 10.1159/000341940

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Discussion

MA accounts for only 0.2% of epithelial renal tumors in adults [2] . In 1995, Davis et al. [3] reported a clinico-pathological study of 50 renal MAs from the files of the Armed Forces Institute of Pathology. They found that re-nal MA was predominantly detected in females by over 2: 1 (36 females vs. 14 males). The mean age of the patients was 41 years (range: 5–83). In 20 patients, the tumor was found incidentally during evaluation of other disease, as in our case, and the other disease was polycythemia in 6 patients. An association between polycythemia and renal MA has been reported, and Yoshioka et al. [4] have pro-vided direct evidence that renal MA cells can produce erythropoietin and other cytokines.

In our case, double-phase enhanced CT showed a hy-povascular mass that displayed gradual and prolonged enhancement similar to that seen in patients with PRCC. Jinzaki et al. [1] reported that there were correlations between the pattern of enhancement on double-phase enhanced CT and the pathological findings of renal tu-mors. They reported that attenuation during the CMP was higher for clear renal cell carcinoma than for other renal tumor subtypes, while clear renal cell carcinoma showed early washout during the late NP. On the other hand, PRCC showed less attenuation during the CMP than other tumor subtypes, and demonstrated gradual enhancement during the late NP. Jinzaki et al. [1] re-ported that attenuation during both the CMP and late NP was higher in their 2 cases of renal MA than in PRCC, and that higher attenuation during each phase may be an important difference between renal MA and PRCC. To clarify the enhancement pattern of renal MA on multiphase enhanced CT, we reviewed previously re-

ported cases [1, 5–7] . Table 1 summarizes the enhance-ment patterns of 7 renal MAs on multiphase enhanced CT. In 6 cases, the findings agreed with those of Jinzaki et al. [1] , who reported that renal MA was a hypovascu-lar mass with gradual enhancement on multiphase en-hanced CT.

Recent cytogenetic and molecular genetic studies of renal tumors have provided important information about the origin, progression, and behavior of these tumors. Brown et al. [8] demonstrated that gain of a chromosome 7 and 17, and loss of the Y chromosome, are the charac-teristic genetic alterations in papillary renal adenoma, re-nal MA, and PRCC. Tickoo et al. [9] suggested that onco-cytoma and chromophobe renal cell carcinoma may arise from common progenitor lesions. Jinzaki et al. [1] dem-onstrated that oncocytoma showed a similar pattern of attenuation to chromophobe renal cell carcinoma, while renal MA showed a similar pattern to PRCC on double-phase enhanced CT. Similarity of the pattern of attenua-tion of these renal tumors on multiphase enhanced CT appear to be consistent with the similarities of cytoge-netic and molecular genetic findings.

Kuroda et al. [10] reported that gain of chromosomes 7 and 17, loss of the Y chromosome, and additional gains (of chromosomes 3q, 8p, 12q, 16q, and 20q) are frequent-ly observed in type 1 PRCC, but the chromosomal aber-rations found in type 2 PRCC seem to be more heteroge-neous. To our knowledge, there have been no reports about radiological findings that differentiate type 1 PRCC from type 2 PRCC. Although Jinzaki et al. [1] reported that attenuation during both CMP and late NP was high-er in their 2 cases of renal MA than in PRCC, differenti-ating factors for renal MA on multiphase enhanced CT compared with types 1 and 2 PRCC have not been ade-

Table 1. P attern of enhancement on multiphase enhanced CT

Reference Plane CT Enhancement pattern on multiphase enhanced CT Ultrasonography

Araki et al. [5] (1 case) calcification (+) hypovascular mass with gradual enhancement pattern hypoechoic massJinzaki et al. [1] (2 cases) (not described) hypovascular mass with gradual enhancement pattern (not described)Hwang and Choi [6](1 case)

calcification (–) hypovascular mass with gradual enhancement pattern isoechoic compared with the renal parenchyma

Zhang et al. [7] (2 cases) case 1 (not described) hypovascular mass with gradual enhancement pattern hypoechoic masscase 2 (not described) progressive moderate enhancement of a well-defined mass hypoechoic mass

Present case (1 case) calcification (–) hypovascular mass with gradual enhancement pattern isoechoic compared with the renal parenchyma

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References

1 Jinzaki M, Tanimoto A, Mukai M, Ikeda E, Kobayashi S, Yuasa Y, Narimatsu Y, Murai M: Double-phase helical CT of small renal parenchymal neoplasms: correlation with pathologic findings and tumor angiogenesis. J Comput Assist Tomogr 2000; 24: 835–842.

2 Amin MB, Amin MB, Tamboli P, Javaidan J, Stricker H, de-Peralta Venturina M, Desh-pande A, Menon M: Prognostic impact of histologic subtyping of adult renal epithelial neoplasms. Am J Surg Pathol 2002; 26: 281–291.

3 Davis CJ, Barton JH, Sesterhenn IA, Mostofi FK: Metanephric adenoma: clinicopatholog-ical study of fifty patients. Am J Surg Pathol 1995; 19: 1101–1114.

4 Yoshioka K, Miyakawa A, Ohno Y, Namiki K, Horiguchi Y, Murai M, Mukai M, Tachiba-na M: Production of erythropoietin and multiple cytokines by metanephric adenoma results in erythrocytosis. Pathol Int 2007; 57: 529–536.

5 Araki T, Hata H, Asakawa E, Araki T: MRI of metanephric adenoma. J Comput Assist Tomogr 1998; 22: 87–90.

6 Hwang SS, Choi YJ: Metanephric adenoma of the kidney: case report. Abdom Imaging 2004; 29: 309–311.

7 Zhang LJ, Yang GF, Lu GM: CT and ultra-sound findings of metanephric adenoma: a report of two cases and literature review. Br J Radiol 2011; 84:e51–e54.

8 Brown JA, Anderi KL, Borell TJ, Qian J, Bostwick DG, Jenkins RB: Simultaneous chromosome 7 and 17 gain and sex chromo-some loss provide evidence that renal meta-nephric adenoma is related to papillary renal cell carcinoma. J Urol 1997; 158: 370–374.

9 Tickoo SK, Reuter VE, Amin MB, Srigley JR, Epstein JI, Min KW, Rubin MA, Ro JY: Renal oncocytosis: a morphologic study of four-teen cases. Am J Surg Pathol 1999; 23: 1094–1101.

10 Kuroda N, Toi M, Hiroi M, Enzan H: Review of papillary renal cell carcinoma with focus on clinical and pathological aspects. Histol Histopathol 2003; 18: 487–497.

quately discussed. Data from more patients should be ac-cumulated in order to allow definite conclusions to be reached. Since renal MA is thought to be genetically re-lated to PRCC, these two diseases are likely to demon-strate similar radiological findings. Almost all renal MAs reported in the literature were surgically resected because

malignancy was diagnosed by preoperative radiological evaluation. However, in patients with a hypovascular re-nal mass that shows gradual and prolonged enhancement on multiphase enhanced CT, a diagnosis of renal MA should be considered.

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