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Saudi Journal of Kidney Diseases and Transplantation
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LETTER TO THE EDITOR  
Year : 2013  |  Volume : 24  |  Issue : 5  |  Page : 1027-1030
Metanephric adenoma: A case report and review of the literature


Department of Urology, Institute of Post Graduate Medical Education and Research, Kolkata, (W.B.), India

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Date of Web Publication12-Sep-2013
 

How to cite this article:
Sharma PK, Tiwari P, Singh JP, Bera MK. Metanephric adenoma: A case report and review of the literature. Saudi J Kidney Dis Transpl 2013;24:1027-30

How to cite this URL:
Sharma PK, Tiwari P, Singh JP, Bera MK. Metanephric adenoma: A case report and review of the literature. Saudi J Kidney Dis Transpl [serial online] 2013 [cited 2019 Nov 16];24:1027-30. Available from: http://www.sjkdt.org/text.asp?2013/24/5/1027/118088
To the Editor ,

Metanephric adenoma (MA) is a rare neoplasm accounting for 0.2% of adult renal epithelial neoplasms. [1] It is seen predominantly in females, with a ratio of 2:1. [2] The mean age and age-range of patients with MA was 41 years and 5-83 years, respectively, in a study by Davis et al [2] and 48.6 years and 38-64 years, respectively, in another study by Jones et al. [3] MA has a characteristic histopathological appearance and a benign course. Only one case of metastasis to lymph nodes has been described in the literature. [4] Herein, we present a 44-year-old female who was diagnosed as having a small lower polar renal mass and underwent partial nephrectomy for the same. On histopathological evaluation, the tumor was found to be an MA.

The patient, a 44-year-old female, a known diabetic, presented to us with a chief complaint of dull aching pain in the left flank region. On ultrasonographic evaluation, a 3.8 cm × 3.6 cm solid hyper-echoic mass was seen arising from the lower pole of the left kidney. On contrast enhanced computerized tomography (CT) scan, the patient was found to have a well-circumscribed, mildly enhancing, homogenous mass measuring 3.3 cm × 3.2 cm and arising from the lower pole of the left kidney [Figure 1]. There was no evidence of lymphadenopathy. The red blood cell and the white blood cell counts as well as the differential counts were essentially normal. Urinalysis, renal function tests and liver function tests were all within normal limits. Considering the small size and the polar location of the tumor, a partial nephrectomy was performed. Per-operatively, a well-defined mass of about 4 cm in diameter was found at the lower pole of the left kidney. No lymphadenopathy was seen. On histopathological examination, the tumor was found to be well circumscribed, but without a fibrous capsule [Figure 2]. The tumor consisted of cuboidal to columnar cells with bland histological features, which were arranged in long tubular structures. No nucleoli or mitosis were seen, neither was there any evidence of necrosis or hemorrhage, points favoring the benign nature of the lesion [Figure 3]. The histopathological findings were consistent with MA.
Figure 1: Computerized tomography scan of the patient (coronal section) showing a well-circumscribed tumor located at the lower pole of the left kidney.

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Figure 2: Histology of the renal mass (H & E stain, low-power view) showing tumor on the left side while on the right side normal renal tissue can be seen. Note the cuboidal to columnar cells arranged in tubular structures as well as the absence of a capsule.

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Figure 3: High-power view showing the tumor containing cuboidal to columnar cells with bland histological features.

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The patient progressed well after the surgery. Follow-up CT scan performed after six months showed no evidence of any residual or recurrent tumor [Figure 4].
Figure 4: Follow-up computerized tomography scan after six months. No evidence of recurrent or residual tumor is seen.

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Metanephric neoplasms are part of a spectrum of kidney tumors that contain renal epithelial or stromal cells, or both. They are derived from the metanephric blastema. At one end of the pathologic spectrum are tumors that are composed exclusively of epithelial nephroblastic cells, the MAs, and at the other end are tumors that are composed exclusively of stromal elements, the metanephric stromal tumors. Tumors that include a combination of both are termed metanephric adenofibromas. Wilm's tumor, which is also derived from the nephrogenic rests, is thought to represent the malignant end of this spectrum. The concept of MA was recognized as a distinct entity by Mostofi et al in 1988. [5]

However, Brown et al, on fluorescent in situ hybridization analysis of MA found frequent chromosome 7 and 17 gain and loss of sex chromosome thus relating these tumors to papillary renal cell adenoma and papillary renal cell carcinoma. [6]

MA is a rare, benign epithelial neoplasm of the kidney, accounting for 0.2% of all renal neoplasms, [1] and is more common in females (M:F = 1:2). [3] Although benign, difficulty lies in its pre-operative differentiation from other malignant neoplasms. Only one case of metastasis from MA to the lymph nodes has been reported. [4] Pins et al reported three MA-like tumors that had metastasized; however, these tumors revealed certain histological features that helped in their differentiation from MA. [7]

Symptoms include flank pain, gross hematuria or a palpable mass. However, most of the tumors are now diagnosed incidentally during imaging for other problems. Less-common features are dysuria, fever or hypertension. [8] It may also be associated with para-neoplastic syndromes like polycythemia and hypercalcemia.

On imaging studies, it is difficult to differentiate MA from renal cell carcinoma. Felding et al evaluated the ultrasonographic features and CT appearance of three patients with MA and found that the tumors appear hyperechoic on ultrasonography with enhanced through transmission, while on unenhanced CT, the tumor had increased attenuation relative to the adjacent parenchyma. [9] However, Bastide et al. in their study of nine patients found that the tumor may appear hyper-, iso- or hypo-echoic on ultrasonography and that they were hypovascular on color Doppler evaluation. On unenhanced CT, majority of the tumors were of higher attenuation than the adjacent renal parenchyma, but on enhanced CT, the tumors were of lower attenuation than the adjacent renal parenchyma. [10]

On gross pathological examination, the tumors are usually small in size. The mean size and range of sizes of the tumor were 5.5 cm and 0.3-15 cm, respectively, in a study by Davis et al [2] and 4.7 cm and 0.6-8 cm, respectively, in a study by Jones et al. [3] Grossly, the tumor is solid in appearance, although cystic MA has also been described. [11] The cut-surface usually appears tan to grey or yellow in color with foci of hemorrhage. Calcifications are seen in approximately 20% of the cases. The tumor usually lacks a fibrous capsule. [2] Microscopically, MA is composed of tightly packed, uniform, small epithelial cells with small regular nuclei, a basophilic cytoplasm, a high nuclei-to-cytoplasm ratio and no mitotic figures. The cells may be arranged in tubular or papillary architectural patterns and glomeruloid bodies may be found. The stroma ranges from an inconspicuous to a pauci-cellular edematous appearance. Psammomatous calcifications are common. In our case, uniform cuboidal to columnar cells were arranged in a tubular pattern. The distinction of MA from renal cell carcinomas, particularly papillary carcinomas, is important. The presence of fibrovascular cores, a number of macrophages or hemosiderins in the stroma and marked cytological atypia make the tumor more likely to be a papillary renal cell carcinoma than MA. [12] No such features were seen in our case, confirming the diagnosis of MA. Immunohistochemical staining with CD57, WT1 and CK7 may be useful to differentiate MA from papillary renal cell carcinoma when distinction by histological features alone proves difficult.

 
   References Top

1.Amin MB, Amin MB, Tamboli P, et al. Prognostic impact of histologic subtyping of adult renal epithelial neoplasms: An experience of 405 cases. Am J Surg Pathol 2002;26:281-91.  Back to cited text no. 1
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2.Davis CJ, Barton JH, Sesterhenn IA, Mostofi FK. Metanephric adenoma: Clinicopathological study of fifty patients. Am J Surg Pathol 1995;19:1101-14.  Back to cited text no. 2
    
3.Jones EC, Pins M, Dickersin GR, Young RH. Metanephric adenoma of the kidney: A clinicopathological, immunohistochemical, flow cytometric, cytogenetic, and electron microscopic study of seven cases. Am J Surg Pathol 1995; 19:615-26.  Back to cited text no. 3
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4.Renshaw AA, Freyer DR, Hammers YA. Metastatic metanephric adenoma in a child. Am J Surg Pathol 2000;24:570-4.  Back to cited text no. 4
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5.Kuroda N, Toi M, Hiroi M, Enzan H. Review of metanephric adenoma of the kidney with focus on clinical and pathobiological aspects. Histol Histopathol 2003;18:253-7.  Back to cited text no. 5
    
6.Brown JA, Andrel KL, Barell TJ, Qian J, Bostwick DG, Jenkins RB. Simultaneous chromosome 7 and 17 gain and sex chromosome loss provide evidence that Renal Metanephric Adenoma is related to Papillary Renal Cell Cracinoma. J Urol 1997;158:370-4.  Back to cited text no. 6
    
7.Pins MR, Jones EC, Martul EV, Kamat BR, Umlas S, Renshaw AA. Metanephric adenomalike tumors of the kidney: Report of 3 malignancies with emphasis on discriminating features. Arch Pathol Lab Med 1999;123:415-20.  Back to cited text no. 7
    
8.Obulareddy SJ, Xin J, Truskinovsky AM, Anderson JK, Franklin MJ, Dudek AZ. Metanephric adenoma of the kidney: An unusual diagnostic challenge. Rare Tumors 2010;2:e38.  Back to cited text no. 8
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9.Fielding JR, Visweswaran A, Silverman SG, Granter SR, Renshaw AA. CT and ultrasound features of metanephric adenoma in adults with pathologic correlation. J Comput Assist Tomogr 1999;23:441-4.  Back to cited text no. 9
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10.Bastide C, Rambeaud JJ, Bach AM, Russo P. Metanephric adenoma of the kidney: Clinical and radiological study of nine cases. BJU Int 2009;103:1544-8.  Back to cited text no. 10
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11.Patankar T, Punekar S, Madiwale C, Prasad S, Hanchate V, Metanephric adenoma in a solitary kidney. Br J Radiol 1999;72:80-1.  Back to cited text no. 11
    
12.Granter SR, Fletcher JA, Renshaw AA. Cytologic and cytogenetic analysis of metanephric adenoma of the kidney. Am J Clin Pathol 1997;108:544-9.  Back to cited text no. 12
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Correspondence Address:
Pramod Kumar Sharma
Department of Urology, Institute of Post Graduate Medical Education and Research, Kolkata, (W.B.)
India
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DOI: 10.4103/1319-2442.118088

PMID: 24029279

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