CLINICS 2011;66(2):359-361 CASE REPORT DOI:10.1590/S1807-59322011000200030 Metanephric Adenoma: clinical, imaging, and Histological findings Fa´ bio Ce´ sar Miranda Torricelli,I Giovanni Scala Marchini,I Rodrigo Sousa Madeira Campos,II Antoˆ nio Otero GilIII I Urologic Surgeon, Urology Department, Faculdade de Medicina da Universidade de Sao, Sao Paulo - SP – Brazil. II Urologic Surgeon, Urology Department, Hospital do Servidor Pu´ blico Estadual, Sao Paulo - SP – Brasil. III Urology - Instituto Dante Pazanezzi, Sao Paulo, S a˜o Paulo, Brazil. Email: fabio_torri@yahoo.com.br Tel.: 55 11 5533-4900 INTRODUCTION Metanephric adenoma (MA), also designated nephrono- genic nephroma or renal epithelial tumor resembling immature nephron, has just been recently recognized as a special type of benign renal epithelial tumor. Only few reports are found in the literature regarding this rare renal tumor. The purpose of this paper is to describe our clinical, imaging and histological / immunohistochemical observa- tions of MA diagnosed in two patients and compare these data to previous information reported in medical databases. CASE REPORT The first case refers to a 70-years-old female patient, who except by systemic arterial hypertension was completely healthy. During routine examinations, a mass of 4.5 cm located on the lower third of her right kidney was incidentally found. At that time, the patient presented only low-grade fever and weakness for about two weeks. Abdominal ultrassonography (USG) showed hypoechoec mass with solid aspect and irregular limits. It was heterogeneous and exofitic, containing septation and cystic areas in its interior. Magnetic resonance imaging (MRI) showed a solid mass 5.2 cm for its higher dimension located in right kidney with same hemorrhagic foci and no sign of peri-renal invasion (Figure 1). Also, simple renal cysts were evidenced. The patient was submitted to a successful partial nephrectomy by open surgery, evolving uneventfully. Pathologic examination of surgical specimen revealed a firm lesion of light brown tissue with reticulated central area and clear delimitation from the adjacent parenchyma. Microscopic evaluation showed no cellular atypical or mitotic activity. Peri-renal adipose tissue was free from neoplasic invasion. The second patient was a 23-year-old man with no previous heath problem, who presented with flank pain for one month. Abdominal USG showed a 464 cm nodular, solid and heterogenic lesion with hyperecogenic areas and exofitic characteristics in the lower third of right renal parenchyma. Computed tomography (CT) confirmed the presence of a 4 cm expansive tumoral formation with Copyright 2011 CLINICS – This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non- commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. intermediate attenuation and minimum venous contrast enhancing at that anatomic site (Figure 2). Partial nephrect- omy was again the therapeutic choice. The patient evolved well but an arterial-venous fistula clinically manifested by hematuria was diagnosed in post-operative (PO) day five. The fistula was successfully embolized by arteriography and no other complications occurred. Immunohistochemical study employing incubation of histological cuts with mono and polyclonal antibodies (panels) showed a profile focally and positive to WT-1, EMA and CK7. Both patients are free of neoplasic disease with no signs of recurrence after 2 years of follow up. DISCUSSION MA is a renal tumor with benign behavior. The classification is based on a combination of histological, immunohistochemical, and genetic features. Most small MA tumors are well circumscribed, firm, and white; larger tumors may be hemorrhagic and softer. The cytology of a few cases has been described1 and is composed of tight, short papillae and loose sheets of cells with scant cytoplasm, round nuclei, fine chromatin and rare small nucleoli. By analyzing all described findings at immunohistochemical and lectin histochemical studies, MA has shown reactivity for keratin (CK7 is the most common), CD 57, vimentin, S-100 protein, EMA, lysozyme, 359 Figure 1 - MRI - solid mass 5.2 cm in higher dimension located in right kidney with same hemorrhagic foci and no sign of perirenal invasion