Central Journal of Urology and Research

Cite this article: Khoo CCK, Khetrapal P, Roux J, Bates AW, Mumtaz F (2014) Metanephric Adenoma: A Case Report with a Discussion of Pathology and Follow-Up Duration. J Urol Res 1(3): 1012.

*Corresponding authorP Khetrapal, Pilgrim Hospital, United Lincolnshire Hospitals NHS Trust, UK, E-mail:

Submitted: 22 October 2014

Accepted: 17 September 2014

Published: 21 September 2014

Copyright© 2014 Khetrapal et al.

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Keywords•Metanephric•Adenoma•Follow-Up•Renal tumour

Case Report

Metanephric Adenoma: A Case Report with a Discussion of Pathology and Follow-Up DurationCCK Khoo1, P Khetrapal2*, J Roux3, AW Bates4 and F Mumtaz5

1Department of Urology, Royal Free Hospital, UK2Pilgrim Hospital, United Lincolnshire Hospitals NHS Trust, UK3Department of Urology, Watford General Hospital, UK4Department of Cellular Pathology, Royal Free Hospital, UK5Department of Urology, Royal Free Hospital, UK

Abstract

Background: Metanephric adenomas are extremely rare, and often present as a mass or incidental scan finding. Differentiating them from Wilms’ tumours is important, but histology and immunohistochemistry have key similarities and some differences. From a clinical perspective, there is little guidance on post-operative management and follow-up duration.

Case: a 52-year old lady had a 16 mm mass identified as an incidental finding on a CT scan with no evidence of metastasis. She underwent a laparoscopic retroperitoneal partial nephrectomy. The tumors were solid, firm and white on macroscopic appearance. The immunophenotype was WT1, vimentin and CK7 positive and negative for CD10 and CD56. This was initially thought to be a metanephric adenoma but the diagnosis was later revised taking patient age and histochemical appearance into account. The patient is disease free at 6 months post-surgery, with a planned follow-up for a total of 24 months. No adjuvant or neoadjuvant treatment was used for her treatment.

Conclusion: Histological differentiation of metanephric adenomas and Wilmstumours remains a diagnostic challenge, but immunohistochemistry techniques are helpful in this endeavour. 24 months of post-operative follow-up is appropriate for metanephric adenomas of similar clinical and radiological presentations.

INTRODUCTIONWhilst, metanephric adenoma’s are extremely rare and

usually benign tumours with an incidence of 0.2% of all adult epithelial neoplasms, they can present a diagnostic challenge as they may be difficult to distinguish from Wilm’s tumours. Both can present as small incidental renal masses and have similar radiological and histological appearances, with the latter exhibiting abundant mitotic figures with distinct cellular atypia.

For adult Wilms’, International treatment guidelines advocate radical nephrectomy and lymph node dissection followed by chemotherapy with or without radiotherapy within 30 days of surgery. With such management, reported 5-year survival rates have reached 82.6% [1-3]. In contrast, for a metanephric adenoma a local excision of the lesion would be considered adequate. A biopsy may be able to distinguish between the two but could remain inconclusive [2]. The following case highlights the potential difficulties in diagnosis and management of these tumours.

CASE REPORTA 52-year old lady presented with an incidental small renal

lesion with no significant urological history. A renal protocol CT scan showed a 16mm enhancing mass in the left lower pole of the kidney with no evidence of metastases. (Figure 1) After MDT discussion, the patient underwent laparoscopic retroperitoneal partial nephrectomy.

The macroscopic appearance of the specimen showed a solid, firm, whitish 15 x 15 x 12mm tumour. On microscopy the lesion was a well-circumscribed nodule formed of tubules lined by cells with moderately pleomorphic, vesicular nuclei with small nucleoli, sharply defined from surrounding renal parenchyma. The immunophenotype was positive for WT1, vimentin, and CK7 focally, and negative for CD10 and CD56. This was initially suggested to be a nephroblastoma (adult Wilms’ tumour). A supplementary specialist report favoured a cellular metanephric adenoma based on histochemical appearance and patient age. As the tumour was low-grade with low metastatic potential, post-

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operative chemotherapy was felt to be unnecessary, and she was reviewed in clinic in 6 months, with a plan to followup for 24 months total.

DISCUSSIONBoth metanephric adenomas and Wilms’ tumours are thought

to derive from nephrogenic rests (persisting clusters of embryonal cells). However, unlike Wilms’ tumours, metanephric adenomas usually present in adulthood. Histologically, metanephric adenomas usually have no or a sparse fibrous capsule (Figure 2), whereas Wilms’ tumours tend to be encapsulated. Additionally, Wilms’ tumours have areas of larger cells with more mitoses and hyperchromatic nuclei.The immunohistochemical staining profiles of Wilms’ tumours and metanephric adenomas have some key differences and similarities. Both display strong nuclear staining for WT1 so it is unhelpful in differentiating the two tumour types. Metanephric adenoma stains for CD57 and focally for CK7, but not for CD56 and desmin [4] whereas Wilms’ tumours stain for CD56, but not for CD57. It is important to remember that mixed tumours have also been reported in the literature, [5] further complicating the differentiation of these tumours.

Despite their histological relationship, metanephric adenoma and adult Wilms’ tumours have a vastly divergent clinical course. Early identification of these rare tumours enables best possible treatment. A localised excision with clear margins is an acceptable treatment for metanephric adenoma but inadequate for Wilms’ tumour. A pre-operative biopsy may enable best treatment decisions [2] but in cases of histological uncertainty, partial nephrectomy allows confirmation of the diagnosis.

Another interesting point of discussion was follow-up after surgical treatment. Various case reports have been published looking into the histopathology of metanephric adenomas, but to our knowledge there is no review discussing follow-up duration and imaging modalities. For this discussion, we went through all cases reported on Pubmed in the last 10 years in English and a summary is as follows (Table 1).

13 publications were identified using the above criteria and all of them included, in which 24 patients were discussed. Of these 24 cases, 2 patients did not report follow up durations, 2 patients had ongoing follow-up for an unlisted time and 3 had ongoing

Figure 1 A 16mm enhancing mass is visible in lower pole of left kidney.

Figure 2 Unencapsulated and hypercellular metanephric adenoma pushing against normal renal parenchyma. H&E stain.

Figure 3 Metanephric adenoma tumor cells with uniform, oval nuclei, pale cytoplasm and indistinct nucleoli H&E stain.

Reference Follow-up duration Age Adjuvant Procedure

[6] CT 3 months, USS 18 months 4 18 weeks

chemo RN

[7] 12 months 5 chemo+radio RN

[8] 24 months 35 not listed RN

[8] 18 months 46 not listed PN

[9] 24 months 70 not listed PN

[9] 24 months 23 not listed PN

[10] 60 months teenage not listed not listed

[10] 60 months 40s not listed not listed

[11] 6 months* 47 not listed

[12] 27 months 50 not listed PN

[12] 59 months 19 not listed PN

[12] not available 59 not listed PN

[12] 30 months 50 not listed PN

[12] 13 months 79 not listed PN

[12] not available 36 not listed PN

Table 1: cases reported on Pubmed in the last 10 years in English and a summary.

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follow-up with follow-up at the time of writing the publication stated. Of the remaining 15 cases, the mean follow-up time was 36 months, with a range of 12-179 months. Bastide et al [12] looked at 9 cases, and only one of them was followed up for more than 5 years and this case has significantly increased our mean follow-up duration. The mean follow-up duration if this case is excluded is 27.5 months, which is closer to the modal follow-up duration of 24 months. Only 2 of the cases reported had adjuvant treatment, 1 due to bilateral disease who had a single radical nephrectomy with close monitoring of the remaining kidney, and the other for lymph node metastases.

Of the 24 cases reviewed, all patients were free of disease at the time of respective publication. Metanephric adenomas are most often benign lesions, and this data suggests that post-operative outcome is good even without adjuvant treatment if no metastases are identified at the time of definitive surgical management. Exceptions need to be made for longer follow-up durations if other associated features such as polycythaemia are identified, as is discussed by Le Nue et al.

In our case, we chose a follow-up duration of 24 months. No evidence of metastases was identified on the initial CT scan prior to surgery, and the patient was disease free on follow-up CT scan at 6 months.

While only partial nephrectomy, nephroureterectomy and radical nephrectomy are discussed in this case reports as treatment options, novel approaches such as radiofrequency ablation and radiofrequency-assisted partial nephrectomy are being used for treatment, which may offer better outcomes and shorter follow-up once there is sufficient data available.

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* Follow-up not complete

PN = Partial nephrectomy, NU = nephroureterectomy, RN = radical nephrectomy, chemo = Chemotherapy, radio = Radiotherapy

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Khoo CCK, Khetrapal P, Roux J, Bates AW, Mumtaz F (2014) Metanephric Adenoma: A Case Report with a Discussion of Pathology and Follow-Up Duration. J Urol Res 1(3): 1012.

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