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Background
Metanephric adenoma is a rare renal tumor that is generally detected in adults and occasionally in children. These tumors usually behave in a benign fashion although rare cases have been reported with metastases.
OUTLINE
DISEASE ASSOCIATIONS CHARACTERIZATION EMBRYONAL HYPERPLASIA OF BOWMAN'S CAPSULE
Metanephric adenoma with embryonal hyperplasia of Bowman's capsular epithelium: previously unreported association.
Keshani de Silva V, Tobias V, Kainer G, Beckwith B.
Department of Anatomical Pathology, South Eastern Area Laboratory Service at Sydney Children's Hospital, Sydney, New South Wales 2031, Australia.
Pediatr Dev Pathol. 2000 Sep-Oct;3(5):472-8. Abstract quote
We report a case of a 9-year-old boy with focal, segmental glomerulosclerosis who, following peritoneal dialysis, underwent renal transplantation and bilateral nephrectomy.The kidneys showed histological features of embryonal hyperplasia of Bowman's capsular epithelium, an uncommon lesion that is seen most often in patients with chronic renal failure who are being maintained on dialysis. In addition, a 1-cm tumor in the left kidney showed features of metanephric adenoma.
Although both lesions are uncommon, they share many similarities on a morphological, immunohistochemical, and ultrastructural basis. This association has not been previously reported and may shed some light on the histogenesis of these recently described lesions.
KIDNEY CANCER
Simultaneous diagnosis of a metanephric adenoma and a clear cell carcinoma of the contralateral kidney.
Anastasiadis AG, Ebert T, Gerharz CD, Ackermann R.
Department of Urology, Heinrich Heine University Medical Center, Dusseldorf, Germany.
Eur Urol. 2001 Feb;39(2):236-9. Abstract quote
Metanephric adenoma of the kidney is a rare, newly recognized entity of a unique benign renal tumor. Clinically, pain, hematuria and palpable mass are the most common presenting signs. Females predominate by well over 2:1. A higher incidence of polycythemia is often found in these patients.
Only a few cases of this type of adenoma have been reported in the literature. We report on a 78-year-old female patient with a metanephric adenoma of the left kidney, which showed typical clinical, radiologic, microscopic and immunohistochemical findings. A clear cell carcinoma of the contralateral kidney was also discovered and treated.
PATHOGENESIS CHARACTERIZATION CHROMOSOMAL ALTERATIONS
Metanephric adenoma lacks the gains of chromosomes 7 and 17 and loss of Y that are typical of papillary renal cell carcinoma and papillary adenoma.
Brunelli M, Eble JN, Zhang S, Martignoni G, Cheng L.
Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120, USA.
Mod Pathol. 2003 Oct;16(10):1060-3. Abstract quote
Metanephric adenoma has morphologic similarities to papillary renal cell neoplasms. Cytogenetic studies of papillary renal cell carcinoma and papillary adenoma have shown frequent gains of chromosomes 7 and 17 and loss of the Y chromosome. Some cytogenetic studies have supported the hypothesis that metanephric adenoma is related to papillary renal cell neoplasia; others have not.
Seven metanephric adenomas were studied with fluorescence in situ hybridization in paraffin sections using centromeric probes for chromosomes 7, 17, and Y diluted 1:100 with tDenHyb1 buffer. The signals in 100 to 200 nuclei were counted in each tumor. Samples of histologically normal renal cortical tubule epithelium were used as controls. In all seven metanephric adenomas, the results for chromosomes 7 and 17 were similar: a high percentage of nuclei with two signals (range, 75 to 85%; median, 79%). Normal kidney showed similar results (range, 78 to 88%; median, 84%). The Y chromosome was present in all three of the tumors from males (range, 86 to 89% of nuclei; median, 87%). Normal kidney gave similar results (range 82% to 91%, median 84%). The presence of chromosomes 7, 17, and Y in metanephric adenomas is similar to their presence in normal kidney.
Metanephric adenoma lacks the frequent gains of chromosomes 7 and 17 and losses of the Y chromosome that are typical of papillary renal cell neoplasms, supporting the notion that metanephric adenoma is not related to papillary renal cell carcinoma and papillary adenoma. Genetic analysis of chromosomes 7, 17, and Y may facilitate discrimination of metanephric adenoma from papillary renal cell carcinoma in difficult cases.
Mapping a tumor suppressor gene to chromosome 2p13 in metanephric adenoma by microsatellite allelotyping.
Pesti T, Sukosd F, Jones EC, Kovacs G.
Laboratory of Molecular Oncology, Department of Urology, Ruprecht-Karls-University, Heidelberg, Germany.
Hum Pathol. 2001 Jan;32(1):101-4 Abstract quote.
Twelve metanephric adenomas (MA) were studied for allelic imbalance at chromosomal regions known to be involved in the genetics of papillary renal cell tumors (RCT) and Wilms' tumors as well as for loci on chromosome 2p13-21. DNA was isolated from paraffin slides, and allelic status was established by fluorescently-labeled microsatellite markers. No allelic changes were seen in the Wilms' tumor gene region at chromosome 11p13 and in the papillary RCT gene region at chromosome 17q21.32.
We delineated a tumor suppressor gene region of approximately 8-centimorgan genetic distance between loci D2S2153 and D2S380 on chromosome 2p13. Allelic changes at this region occurred in 56% of informative cases.
Our results provide molecular evidence that MA is a genetic entity, and it can be differentiated from both Wilms' tumor and papillary renal cell adenoma.
LABORATORY/RADIOLOGIC/
OTHER TESTSCHARACTERIZATION RADIOLOGIC
CT and ultrasound features of metanephric adenoma in adults with pathologic correlation.
Fielding JR, Visweswaran A, Silverman SG, Granter SR, Renshaw AA.
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
J Comput Assist Tomogr. 1999 May-Jun;23(3):441-4. Abstract quote
PURPOSE: The purpose of this work was to correlate the CT, ultrasound, and pathologic features of metanephric adenoma, a rare benign renal tumor in adults.METHOD: Retrospective review of medical records (1990-1997) revealed three adult female patients who had both preoperative imaging and nephrectomy with pathologic diagnosis of metanephric adenoma performed at our institution. CT (n = 3) and ultrasound (n = 2) features were reviewed in consensus by two radiologists and correlated with pathologic findings.
RESULTS: In all three cases, the metanephric adenoma was of increased attenuation relative to adjacent renal parenchyma on unenhanced CT scans. No septa or calcifications were seen. Ultrasound images showed both tumors to be hyperechoic with enhanced through-transmission.
CONCLUSION: The CT and ultrasound findings correlate with the pathologic features of a high nuclear-to-cytoplasmic ratio and psammomatous calcifications. In the adult population, it is unlikely that metanephric adenoma can be prospectively differentiated from renal cell carcinoma based on imaging features.
HISTOLOGICAL TYPES CHARACTERIZATION GENERAL Epithelial proliferations form rounded, discrete nodules unassociated with native kidney
Review of metanephric adenoma of the kidney with focus on clinical and pathobiological aspects.
Kuroda N, Tol M, Hiroi M, Enzan H.
First Department of Pathology, Kochi Medical School, Kohasu, Oko-cho, Nankoku city, Kochi 783-8505, Japan.
Histol Histopathol. 2003 Jan;18(1):253-7 Abstract quote.
The concept of metanephric adenoma has become established in recent years. Metanephric adenoma is a rare neoplasm. Macroscopically, the cut surface of the tumor displays a tan to gray or yellow color, and tumors generally form well-circumscribed masses.
Histologically, tumors are composed of small epithelial cells that form small acini. Glomeruloid bodies, which are composed of lobulated papillary projections, are occasionally seen. Although there have been few studies using chromosomal analysis, two recent studies have shown partial monosomy or LOH of 2p. On the other hand, the concept of metanephric tumors has recently become broadened. These tumors include metanephric adenomas, adenofibromas and stromal tumors, and they compose a continuous histological spectrum.
Therefore, further studies on various aspects are needed to identify the gene responsible for the occurrence of metanephric tumors and, furthermore, to clarify the association among the three types of metanephric tumors.The Spectrum of Metanephric Adenofibroma and Related Lesions Clinicopathologic Study of 25 Cases
From the National Wilms Tumor Study Group Pathology Center
May R. Arroyo, etal.
Am J Surg Pathol 2001;25:433-444 Abstract quote
The authors report nine new metanephric adenofibroma (MAFs; previously termed nephrogenic adenofibroma) and 16 related tumors from the files of the National Wilms Tumor Study Group Pathology Center (NWTSGPC).
All tumors contained a variable amount of a bland spindle cell stroma, which is essentially identical to the recently described metanephric stromal tumor (MST).
Features that distinguish this stroma from congenital mesoblastic nephroma (CMN) include intratumoral angiodysplasia, concentric cuffing of entrapped tubules (``onion skinning''), and heterologous differentiation. The epithelial components of these lesions spanned a wide range of appearances. All tumors contained at least focally an inactive embryonal epithelium identical morphologically to metanephric adenoma (MA), and hence each case could be classified as containing MAF. The epithelium of nine tumors had this appearance throughout, and hence these were considered usual MAFs. The epithelium of four tumors demonstrated increased mitotic activity but was otherwise similar to MA. The epithelial component of seven tumors spanned a morphologic spectrum from inactive MA to malignant epithelial predominant Wilms tumor (WT), with gradual transitions noted in several cases. Five other tumors contained a carcinomatous component distinct from these lesions but identical morphologically to papillary renal cell carcinoma (PRCC). In one of these cases, this component had metastasized to the regional lymph nodes at the time of diagnosis. No tumor recurred during follow-up, although almost all patients received adjuvant therapy for WT regardless of their tumor's histology and NWTSGPC diagnosis.
In conclusion, MAF is a biphasic tumor that spans the morphologic spectrum between benign pure stromal (MST) and pure epithelial (MA) lesions, and can merge with the morphology of WT, supporting the concept that these are all related lesions. A relationship to PRCC is also evident.
Metanephric Adenoma, Nephrogenic Rests, and Wilms' Tumor A Histologic and Immunophenotypic Comparison
Trudie E. Muir, M.D.; John C. Cheville, M.D.; Donna J. Lager, M.D.
From the Department of Laboratory Medicine and Pathology, Mayo Foundation, Rochester, Minnesota, U.S.A.
Am J Surg Pathol 2001;25:1290-1296 Abstract quote
Metanephric adenoma (MA) is a renal tumor that is generally detected in adults and occasionally in children. These tumors usually behave in a benign fashion. Although the histogenesis of MA is unclear, a morphologic similarity to Wilms' tumor (WT) complex exists.
Six cases of MA, five cases of childhood WT (CWT), two cases of adult WT (AWT), and four cases of treated MWT and/or nephrogenic rests (MWT/NR), with paraffin blocks available for use, were retrieved from the surgical pathology files of the Mayo Clinic. Clinical information was extracted from the medical record. Immunoperoxidase stains for WT1, AE1, CK7, CD57, CD56, and desmin were performed on paraffin sections from all cases. All six cases of MA were strongly and diffusely positive with antibodies to WT1 and CD57 and focally positive with antibodies to CK7. Three cases showed focal faint staining in <5% of the cells with keratin AE1. Stains for CD56 and desmin were negative. All seven cases of WT, including five CWT and two AWT, were strongly and diffusely positive with WT1 in the blastema and epithelium but showed only weak focal positivity in stromal cells. Six cases were diffusely positive for CD56 and one case showed focal positivity. Keratin AE1 was positive in one case of AWT and focally positive in the other AWT. The blastema of all cases of WT were negative for desmin, CK7, and CD57, although staining for keratin AE1, CD56, and CD57 was seen in maturing tubules of CWT cases. Of the five CWT cases, two had associated NR and two showed maturing WT after treatment. The areas of NR and maturing WT were histologically similar to MA and were composed of small tubules with uniform nuclei with no mitotic activity, scant cytoplasm, and focal calcifications. All four cases of maturing WT/NR were positive for WT1 and focally positive for CD57, CK7, and AE1. Stains for CD56 and desmin were negative except in foci of residual blastema, which stained for CD56 but lacked CD57 and CK7 staining. Five cases each of renal cell carcinoma, papillary renal cell carcinoma, and oncocytoma were negative for WT1. Two of five cases of chromophobe carcinoma showed very weak staining present in <10% of tumor nuclei.
Metanephric adenoma is histogenetically related to WT and is morphologically and immunophenotypically identical to maturing WT and nephrogenic rests.
Metanephric adenoma: histology, immunophenotype, cytogenetics, ultrastructure.
Gatalica Z, Grujic S, Kovatich A, Petersen RO.
Department of Pathology and Cell Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Mod Pathol. 1996 Mar;9(3):329-33 Abstract quote.
Metanephric adenoma is a rare renal neoplasm that is histologically and clinically unique.We found this neoplasm in a 54-year-old woman. This large, well-circumscribed, solid, tan tumor showed histologic similarity to developing metanephric tubular epithelium. It is composed of uniformly small epithelial cells forming tubules. Immunohistochemical evaluation showed that the tumor cells express proximal tubule marker URO-2 and wt1 gene protein product, commonly expressed in Wilms' tumors.
Ultrastructurally, the epithelial cells were characterized by the presence of cilia on the luminal side and were resting on an abundant basement membrane. Cytogenetic analysis showed normal female karyotype. The unique features of metanephric adenoma should be clinically and pathologically recognized because of its invariably benign course.
Metanephric adenoma of the kidney. A clinicopathological, immunohistochemical, flow cytometric, cytogenetic, and electron microscopic study of seven cases.
Jones EC, Pins M, Dickersin GR, Young RH.
Department of Pathology, Vancouver Hospital and Health Sciences Center, British Columbia, Canada.
Am J Surg Pathol. 1995 Jun;19(6):615-26 Abstract quote.
We report seven examples of a distinctive adenomatous tubular cortical neoplasm of the adult kidney. The average age of the patients (six women and one man) was 48.6 years (range, 38-64 years). In six patients the tumor was discovered during investigation of unrelated conditions, and all were treated with total nephrectomy. One tumor was found at autopsy. The tumors were well-circumscribed, nodular, tan-pink masses localized to the kidney, ranging in size from 0.6 to 8 cm.Histological examination demonstrated orderly, closely packed, small round tubules lined by bland, darkly staining oval cells with little cytoplasm, merging with rounded nests of similar cells. Occasional branching, elongated tubules, and papillary infoldings of glomeruloid-like bodies were present but blastema was absent. The tumor cells were immunoreactive for Leu 7 (three of five cases) and vimentin (four of six cases), and a few tumors were immunoreactive for cytokeratin (two of six cases), epithelial membrane antigen (one of six cases), and muscle-specific antigen (one of six cases). Ultrastructural examination of two tumors revealed tubular and solid nests of epithelial cells surrounded by basal lamina, with prominent cell junctions, microvilli, and apical secretory granules. DNA content analysis by flow cytometry yielded diploid histograms (four of four cases). Cytogenetic analysis of one case revealed a normal male karyotype. Clinical follow-up, available for six patients, revealed no evidence of recurrence (mean follow-up, 60.8 months).
We believe this is a benign tumor, best classified as a metanephric adenoma because of its embryonic architectural and cytological appearance, that can be recognized by its very characteristic pathological features.
ADENOSARCOMA Metanephric Adenosarcoma in a Young Adult: Morphologic, Immunophenotypic, Ultrastructural, and Fluorescence In Situ Hybridization Analyses A Case Report and Review of the Literature
Maria M. Picken, M.D. , Ph.D. ; Jonathan L. Curry, M.D. ; Valerie Lindgren, Ph.D. ; Joseph I. Clark, M.D. ; John N. Eble, M.D.
From the Departments of Pathology (M.M.P., J.L.C., V.L.) and Medicine (J.I.C.), Loyola University Medical Center, Chicago, Illinois; and Department of Pathology (J.N.E.), Indiana University and Roudebush VA Medical Center, Indianapolis, Indiana, U.S.A.
Am J Surg Pathol 2001;25:1451-1457 Abstract quote
Metanephric neoplasms are uncommon renal tumors that arise in both children and adults. They may be composed of small epithelial cells or benign stroma, or both, and are termed metanephric adenoma, metanephric stromal tumor, or metanephric adenofibroma, respectively. Thus far, these tumors have been known for their benign behavior.
We present the case of a 21-year-old woman who developed a neoplasm composed of a renal epithelial component identical to metanephric adenoma combined with a malignant spindle cell sarcoma. The epithelial component was positive for pankeratin AE1/3, whereas the sarcomatous component was negative for epithelial markers and positive for vimentin, CD34, and CD117. No smooth muscle differentiation was apparent in the sarcoma by immunohistochemistry or ultrastructural analysis. By fluorescent in situ hybridization analysis of the sarcomatous component there was monosomy of the X chromosome, but no apparent variation from the normal diploid pattern for chromosomes 3, 7, 12, and 17.
We conclude that the spectrum of metanephric neoplasia should be expanded to include malignant stromal variants, and we propose the term “metanephric adenosarcoma” for the present case.
DIFFERENTIAL DIAGNOSIS KEY DIFFERENTIATING FEATURES GENERAL
Metanephric adenoma-like tumors of the kidney: report of 3 malignancies with emphasis on discriminating features.
Pins MR, Jones EC, Martul EV, Kamat BR, Umlas J, Renshaw AA.
Department of Pathology, Northwestern Memorial Hospital, Northwestern University Medical School, Chicago, Ill 60611-3053, USA.
Arch Pathol Lab Med. 1999 May;123(5):415-20. Abstract quote
BACKGROUND: Metanephric adenoma is a very rare benign renal tumor; only 80 well-documented cases have been reported to date. We have seen several renal tumors that were originally incorrectly diagnosed as metanephric adenoma.DESIGN: We present 3 unusual renal tumors (2 primary and 1 metastatic), each of which illustrates important pathologic features useful in discriminating metanephric adenoma from malignant mimics.
RESULTS: Case 1 involved a 46-year-old man with multiple small, cortical, solid, papillary (chromophil) renal cell carcinomas in his right kidney; the patient developed multiple, histologically identical, solid, papillary (chromophil) carcinomas in the opposite kidney 17 months later. Case 2 involved a 32-year-old woman with a 14-cm right renal tumor who developed soft tissue and bone metastases over a 17-year period. Case 3 involved a 52-year-old woman who presented with a 1.8-cm corticomedullary renal nodule, which eventually proved to represent a metastasis from a poorly differentiated (insular) carcinoma of the thyroid. All 3 tumors superficially resembled metanephric adenoma and consisted of primitive, dark-staining cells arranged in tubules or sheets. Each tumor, however, also had features inconsistent with the diagnosis of metanephric adenoma, including multifocal lesions with a variable nuclear-cytoplasmic ratio and diffuse cytokeratin 7 and epithelial membrane antigen immunopositivity in case 1, a 14-cm-diameter tumor with occasional mitoses in case 2, and a distinct fibrous capsule with capsular and vascular invasion in case 3. In addition, all 3 tumors lacked the cytologic features of bland overlapping nuclei with imperceptible cytoplasm consistently seen in metanephric adenoma.
CONCLUSION: Adherence to strict histopathologic criteria will discourage misdiagnosis of a malignant or potentially malignant renal neoplasm as the rare and always benign metanephric adenoma.
PROGNOSIS CHARACTERIZATION METASTASIS
Metastatic metanephric adenoma with foci of papillary carcinoma in a child: a combined histologic, immunohistochemical, and FISH study.
Drut R, Drut RM, Ortolani C.
Servicio de Patologia, Hospital de Ninos Superiora Sor Maria Ludovica, La Plata, Argentina.
Int J Surg Pathol. 2001 Jul;9(3):241-7 Abstract quote.
We report an example of metastatic metanephric adenoma containing foci of papillary carcinoma in the primitive tumor arising in the left kidney of an 11-year-old girl.Histology revealed a monomorphous population of small cells with bland cytology arranged in pseudoglandular, tubular, papillary, and glomeruloid structures with frequent psammoma bodies. Intermixed there were foci of and small cavities lined by larger cells with eosinophilic cytoplasm and larger nuclei with small nucleoli. A regional lymph node contained metastatic deposits with the former histologic pattern. By immunohistochemistry the small cells were negative for carcinoembryonic antigen (CEA) and keratin 7 while these antibodies reacted positively in the larger cells. A fluorescent in-situ hybridization (FISH) study for chromosome 17 in imprints from the primitive tumor revealed 3 signals in about 10% of the nuclei while the rest was disomic. Disaggregated cells from the metastatic lymph node consistently revealed 2 signals for chromosomes 7, 16, and l7.
Histology of the primitive tumor resembled the epithelial component of the so-called metanephric adenofibroma while the metastatic lymph node exhibited histologic and FISH genomic features of metanephic adenoma.
Metastatic metanephric adenoma in a child.
Renshaw AA, Freyer DR, Hammers YA.
Department of Pathology, Baptist Hospital of Miami, FL 33176, USA.
Am J Surg Pathol. 2000 Apr;24(4):570-4 .
Metanephric adenoma is a recently characterized renal tumor that generally occurs in adults and has an excellent prognosis. To date, only one atypical metanephric adenoma has been reported to metastasize.The authors report a case of typical metanephric adenoma that arose in the left kidney of a 7-year-old girl that was associated with metastases to the para-aortic, hilar, and aortic bifurcation lymph nodes. The tumor was 9.5 cm and was composed entirely of epithelial elements arranged in tubules, short papillae, and glomeruloid bodies with scattered psammoma bodies. No atypia and only rare mitotic activity were present. Immunohistochemically, the tumor was negative for epithelial membrane antigen, negative for keratin AE1, and focally positive for both keratin CAM5.2 and cytokeratin 7. Tumor cytogenetics revealed a normal diploid karyotype, and disomy of chromosomes 7 and 17 was confirmed by fluorescence in situ hybridization.
The authors conclude that tumors with histologic, immunohistochemical, and genetic features characteristic of typical metanephric adenoma can present with metastatic disease.
TREATMENT CHARACTERIZATION GENERAL SURGICAL Removal Henry JB. Clinical Diagnosis and Management by Laboratory Methods. Twentieth Edition. WB Saunders. 2001.
Rosai J. Ackerman's Surgical Pathology. Eight Edition. Mosby 1996.
Sternberg S. Diagnostic Surgical Pathology. Third Edition. Lipincott Williams and Wilkins 1999.
Robbins Pathologic Basis of Disease. Sixth Edition. WB Saunders 1999.
DeMay RM. The Art and Science of Cytopathology. Volume 1 and 2. ASCP Press. 1996.
Weedon D. Weedon's Skin Pathology Second Edition. Churchill Livingstone. 2002
Fitzpatrick's Dermatology in General Medicine. 5th Edition. McGraw-Hill. 1999.
Weiss SW and Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors. Fourth Edition. Mosby 2001.
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