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Keywords:

  • complicated cyst;
  • cystic degeneration;
  • kidney;
  • oncocytoma;
  • renal neoplasm

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Case report
  5. Discussion
  6. References

Abstract  A case of a small renal oncocytoma with central cystic degeneration, 15 mm in diameter, is reported. Contrast-enhanced computed tomography showed the tumor contained a central hypoattenuating region and had an irregular, heterogeneously enhanced wall. Magnetic resonance images showed a well-circumscribed lesion and the T1-weighted image indicated medium signal intensity, whereas the T2-weighted image indicated slight hypointensity. Both T1- and T2-weighted images showed central hyperintensity. Our preoperative diagnosis was renal cell carcinoma originating in a renal cyst wall or cystic renal cell carcinoma. Nephrectomy was performed because frozen-section examination did not completely rule out malignancy. The final pathological diagnosis of the entire surgical specimen was renal oncocytoma with cystic degeneration. To our knowledge, this is the 14th case of renal oncocytoma with central cystic degeneration reported in the published works. We discuss herein the variant forms of oncocytoma and difficulties with their preoperative diagnosis, especially when the tumor is small.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Case report
  5. Discussion
  6. References

Small cystic renal masses often pose difficult clinical and radiological management issues. Renal oncocytoma is a benign tumor that accounts for 4.3% of all solid renal tumors.1 Pathologically, a typical oncocytoma does not present evidence of necrosis or hemorrhage. Herein, we report a case of small renal oncocytoma with central cystic degeneration.

Case report

  1. Top of page
  2. Abstract
  3. Introduction
  4. Case report
  5. Discussion
  6. References

A 67-year-old man with a history of gastric ulcer was admitted to our hospital because of a right renal mass incidentally detected by computed tomography (CT) during a general checkup. Plain abdominal CT showed two cystic lesions, one on the anterior and another on the posterior side of the lower portion of the right kidney (Fig. 1a). Contrast-enhanced CT demonstrated that the anterior mass was 15 × 15 mm in diameter, with irregular and heterogeneously enhanced walls (Fig. 1b). Contrast-enhanced CT showed that the posterior mass had nearly imperceptibly thin walls and lacked contrast enhancement, which was believed to represent a simple cyst. Ultrasonography showed a cystic mass on the anterior side with irregular and thick walls. Transverse magnetic resonance (MR) images showed a well-circumscribed lesion and the T1-weighted image indicated medium signal intensity (Fig. 2a), whereas the T2-weighted image indicated slight hypointensity (Fig. 2b). Both T1- and T2-weighted images showed central hyperintensity. Renal angiography did not indicate any abnormal findings.

image

Figure 1. (a) Plain abdominal computed tomography (CT) shows two cystic lesions, one on the anterior and another on the posterior side of the lower portion of the right kidney. (b) Contrast-enhanced CT of the anterior mass with irregular and heterogeneously enhanced walls. In contrast, the posterior mass has nearly imperceptibly thin walls and lacks contrast enhancement. Bar, 1 cm.

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image

Figure 2. Transverse magnetic resonance images show a well-circumscribed lesion with central hyperintensity. A simple renal cyst can also be seen on the posterior side in the ipsilateral kidney. (a) T1- and (b) T2-weighted images. Bar, 1 cm.

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These results suggested a diagnosis of renal cell carcinoma originating in a renal cyst wall or cystic renal cell carcinoma. The examination of a frozen section suggested the possibility of a high-grade granular cell carcinoma or renal oncocytoma. Although the location and size of the tumor seemed suitable for local resection, we performed nephrectomy, which the patient selected if malignancy could not be ruled out completely.

The cystic tumor had a brownish color (Fig. 3a) and contained 2 mL of a dark brown fluid. There was no cytological evidence of malignant cells. Pathological examination revealed a solid lesion consisting of sheets of uniform polygonal cells with central nuclei and abundant pink cytoplasm (Fig. 3b). The cyst wall was lined with tumor cells, but not with epithelial cells. Because no nuclear pleomorphism or mitosis in either the solid or the cystic lesion was seen, a diagnosis of renal oncocytoma with central cystic degeneration was made.

image

Figure 3. (a) Gross pathology. The cystic tumor has a brownish color. (b) Photomicrograph of the nephrectomy specimen shows tumor cells with central nuclei and abundant pink cytoplasm (hematoxylin and eosin; original magnificaton ×200).

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Case report
  5. Discussion
  6. References

Pathologically, a typical oncocytoma does not present evidence of necrosis or hemorrhage. However, variant forms of oncocytoma (i.e. with cystic degeneration [6.1%] and hemorrhage [at least 5.6%]) have been reported.2 Therefore, the case presented herein was considered a variant form of oncocytoma. There have been 13 cases of renal oncocytoma with central cystic degeneration reported in the published works (Table 1).

Table 1.  Reported cases of renal oncocytoma accompanied by central cystic degeneration
Case no.Age (years)SexTumor size (cm)Reference
 175F 14
 274M8 × 7.5 × 715
 356F5 × 5 × 416
 469M19 × 18 × 1117
 563F8 × 7 × 618
 663F 19
 767M6.5 × 4.7 × 4.220
 851F 21
 961M4.5 × 4.0 × 3.522
1071M6 × 423
1149M3 × 3 9
1260M6 × 6 × 524
1345M3 × 3 × 325
1467M1.5 × 1.5 × 1.5Present case

With advances in diagnostic imaging, small renal masses are being detected earlier and with increased frequency. The differential diagnosis of a small renal mass is extensive and includes a cyst, infarction, focal infection, angiomyolipoma, lymphoma, metastatic neoplasm, oncocytoma, renal carcinoma and pseudotumor.3 According to data available from a number of case series, approximately 85–90% of small solid renal tumors (1–3 cm in size) are renal cell carcinomas (or renal adenomas).4 These small tumors are usually treated as if they are renal cell carcinomas because adenomas, carcinomas and oncocytomas cannot be distinguished by imaging techniques.5

Furthermore, it is difficult to establish a critical differentiation between atypical benign cysts and cystic tumors. Between 5 and 10% of renal cell carcinomas have a cystic appearance related to four patterns of presentation: (i) intrinsic multilocular growth; (ii) cystic necrotic tumor; (iii) unilocular cystadenocarcinom; and (iv) a tumor found within a cyst wall.6 Although simple, uncomplicated cystic renal lesions are usually readily diagnosed with ultrasonography or CT, more complicated cystic renal masses often lead to diagnostic dilemmas and differences in opinion regarding management. Imaging characteristics of typical cystic renal cell carcinoma include nodularity and irregular thickening of the walls, large dystrophic calcifications and heterogeneous signal intensity on both T1- and T2-weighted images. Cystic renal cell carcinoma can have foci of internal necrosis and hemorrhage, so the presence of hemorrhage within a cystic renal mass cannot be used to discriminate between a complicated renal cyst and a cystic malignant tumor. In addition, various combinations of signal intensity may be seen on MR images of hemorrhagic cysts depending on the amount of hemorrhage, the type of hemoglobin-degeneration products present, the degree of red blood cell lysis and protein content. Consequently, the overlapping, variable signal intensities of hemorrhagic cysts and tumors with hemorrhage tend to blur the distinction between benign and malignant cystic masses.

Some have reported potential advantages of fine needle aspiration to identify renal oncocytoma.7,8 Sampling of fluid from a cystic renal lesion is readily accomplished percutaneously with ultrasound or CT guidance. Sekido et al.9 reported a case of a cystic oncocytoma with a high level of carcinoembryonic antigen and carbohydrate antigen 19-9 in the cyst fluid. In our case, sampling of fluid could not be performed, because the cystic lesion was small and was located on the anterior portion of the kidney.

Frozen section examination could not completely rule out malignancy in the present case. On light microscopic examination, the morphologically overlapping features of granular eosinophilic cytoplasma in renal oncocytoma and the eosinophilic variants of chromophobe renal cell carcinoma and conventional (clear cell) renal cell carcinoma may make diagnosis difficult. Wiatrowska et al.10 reported that careful attention to cytoplasmic and nuclear features thus makes it possible to distinguish chromophobe renal cell carcinoma from renal oncocytoma in cytologic preparations.

Nephron-sparing surgery should have been indicated in the present case of small renal cystic lesion. Nephron-sparing surgery is effective for localized renal cell carcinoma, providing long-term tumor control with preservation of renal function.11 Laparoscopic and retroperitoneoscopic surgery offers certain advantages over traditional open surgery for patients with renal tumor, such as malignancy. Ono et al.12 reported that laparoscopy did not reduce disease-free and overall survival of patients with small renal cell carcinoma. Moreover, laparoscopic techniques for partial nephrectomy through retroperitoneal or transperitoneal approaches have been developed and may expand the indication of partial nephrectomy.13

In conclusion, a preoperative diagnosis with some certainty of renal oncocytoma is sometimes possible but, more often, specific diagnosis is not possible, especially when the tumor is small. Improvements in the quality of diagnostic imaging studies and additional research on the accuracy of fine needle aspiration and frozen section examination may reduce the need for surgical exploration in cases of benign disease, such as renal oncocytoma.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Case report
  5. Discussion
  6. References
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