SEARCH

SEARCH BY CITATION

Keywords:

  • biopsy;
  • image diagnosis;
  • solid renal mass;
  • surgery

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

Background:  Solid renal masses are found increasingly. Further analysis of the characteristics of solid renal masses is useful for optimal treatment.

Methods:  A retrospective analysis of all solid renal masses was conducted from December 1998 to May 2003 at the Urology Department, Central University Hospital of Saint-Etienne, France. A total of 162 solid renal masses were treated. The preoperative imaging diagnosis of ultrasound and computed tomography, and final pathological results were reviewed.

Results:  One hundred and forty-five tumors were pathologically confirmed to be renal cell carcinomas (RCC); 17 tumors (10.5%) were benign. There were eight renal oncocytomas, eight renal angiomyolipomas and one benign mixed epithelial/stroma tumor. Three oncocytomas and five angiomyolipomas were strongly suspected before surgery. The majority of the benign tumors were ≤4 cm. The percentage of small benign tumors (≤4 cm) was significantly higher than large benign tumors (>4 cm). Although it is possible to use imaging to detect some benign tumors, the majority of benign tumors cannot be diagnosed definitively by imaging before surgery.

Conclusions:  Malignancy in solid renal masses is tumor-size related. Benign solid renal tumors appear mainly as small-sized tumors. The preoperative differentiation between an RCC and a benign tumor can be difficult. Our data suggest that a biopsy is necessary in selected patients to achieve the maximum accuracy in order to provide optimal treatment.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

Renal cell carcinoma (RCC) is a major tumor of the adult kidney. The wide use of ultrasound and computed tomography (CT) has been successful in detecting RCC. As a result, many small renal tumors without symptoms are found.1–4 Advances in biomedical imaging have been considered a major clinical breakthrough in the past 25 years.5 It enables a timely diagnosis of many cancers such as those in the breast, liver or kidney.6–8 A radical nephrectomy performed on a small RCC found early is considered a medical success because it provides the patient with a strong chance of being cured.

Accompanied by the advances in imaging diagnosis, the treatment of RCC is rapidly changing. The ipsilateral sparing of the adrenal gland and partial nephrectomy have become alternatives to the standard radical nephrectomy.1,9 Recently, minimally invasive surgery by laparoscopy as well as by percutaneous ablation of renal tumors has also been introduced.10–12

Solid renal mass refers to a tumor of renal cellular origin with radiological detection of tissue and vascular signals. It does not predominantly contain liquid although necrosis or hemorrhage may occur. Solid renal mass is primarily regarded to be malignant. However, the percentage of benign solid renal masses is on the rise. The frequent use of renal imaging and the increased proportion of incidental tumors have posed a dilemma to urologists: Is the renal mass malignant or benign? A radical nephrectomy performed on a benign tumor is considered a medical failure. Because more solid renal masses are being found and several treatment modalities are available, urologists are facing a critical question: What is the optimal method to treat a specific solid renal mass? Further analysis of the characteristics of the solid renal mass is necessary to answer this question. In the present study, we evaluate a contemporary series of solid renal masses to provide some useful information.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

We undertook a retrospective analysis of solid renal masses from December 1998 to May 2003. Data were collected from patient files. Cystic renal masses were excluded for the purpose of the study. We limited our analysis to a single question: How can we optimize the treatment of solid renal masses?

A total of 162 patients with a solid renal tumor entered into this study. All of these patients undertook ultrasound and conventional CT examinations as recommended by the European Society of Urology.4 CT was performed according to standard procedure with intravenous contrast enhancement. If the imaging examination was not verified, the same imaging examination was repeated. Diagnosis of solid renal mass was based on the results of ultrasound and CT. Angiography and magnetic resonance imaging (MRI) were performed when it was considered necessary to confirm the ultrasound and CT results or to plan the surgical strategy. The imaging results were reviewed by radiologists and urologists. There were 113 men and 49 women in the study group. The age of the patients ranged from 31 to 87 years with a mean age of 66 years.

Our emphasis was on CT study, as CT is a gold standard for evaluating a solid renal mass. We set the CT criteria to diagnose an RCC or a benign tumor. A typical RCC was usually well-limited, heterogenous and could be calcified, necrotic or hemorrhagic. It had tissue and hypervascular compositions. After an injection of contrast, the tumor intensity increased and the necrotic or hemorrhagic areas formed hypodense plages. A typical angiomyolipoma contained a fat signal with a negative intensity. A typical oncocytoma usually presented as a well-defined, homogenous, low-density tumor image, and postcontrast enhancement exhibited coefficients less than those of enhanced normal renal tissue. The central stellar scar was usually present in large oncocytomas.

Tumor size was measured from its largest diameter. To demonstrate the distribution of benign tumors, we divided all the tumors into three categories by size: small-sized (≤4 cm), middle-sized (4–7 cm) and large-sized tumors (≥7 cm). Statistical analysis was performed using the Mann-Whitney U-test to compare the percentages of benign tumors in each category of tumor size.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

One hundred and forty-five renal tumors were pathologically confirmed to be RCC. There were 127 conventional carcinomas, 12 papillary carcinomas and 6 chromophobe carcinomas. The percentages of pathological subtypes are shown in Fig. 1. The positive predictive rate of RCC by imaging was 89.5%.

image

Figure 1. Percentages of tumor subtypes. BT, benign tumors; CC, chromophobe carcinomas; Con C, conventional carcinomas; PC, papillary carcinomas.

Download figure to PowerPoint

Seventeen renal tumors were benign lesions. There were eight renal oncocytomas, eight renal angiomyolipomas and one benign mixed epithelial/stroma tumor. The distribution of benign tumors by tumor size is shown in Table 1. The percentage of benign small-sized tumors was significantly higher than benign middle- or large-sized tumors (P < 0.05 and P < 0.01, respectively).

Table 1.  Percentage of benign tumors according to tumor size
 Tumor sizeTotal
≤4 cm4–7 cm≥7 cm
  1. RCC, renal cell carcinoma.

Benign tumors (n)13 2 2 17
Benign tumors + RCC (n)654651162
Benign tumors (%)20.0 4.3 3.9 10.5
Positive predictive rate (%)80.095.796.1 89.5

The characteristics of the benign tumors are shown in Table 2. Three large oncocytomas were preoperatively suspected as they had a typical central stellar scar, whereas no small oncocytomas were preoperatively realized. Five angiomyolipomas were radiologically typical in fat composition. The other three angiomyolipomas were atypical on CT with a heterogenous image. One benign mixed epithelial/stroma tumor was heterogenous on CT imaging.

Table 2.  Analysis of benign solid renal tumors
Case no.Sex/age (years)Tumor size (cm)ImageTreatmentPathology
  1. F, female patient; M, male patient; partial, partial nephrectomy.

 1F/66 3.0Homogenous, low-densityNephrectomyOncocytoma
 2F/55 3.8Homogenous, low-densityNephrectomyOncocytoma
 3F/77 4.0Homogenous, low-densityNephrectomyOncocytoma
 4F/4512.0Homogenous, central scarNephrectomyOncocytoma
 5F/63 8.5Homogenous, central scarNephrectomyOncocytoma
 6M/56 4.0Homogenous, central scarNephrectomyOncocytoma
 7F/78 3.3Homogenous, low-densityNephrectomyOncocytoma
 8F/57 6.0Homogenous, central scarPartialOncocytoma
 9F/61 2.8Fat-densityPartialAngiomyolipoma
10F/53 3.2High-densityPartialAngiomyolipoma
11F/55 1.7Fat-densityPartialAngiomyolipoma
12F/43 4.0Fat-densityPartialAngiomyolipoma
13F/46 6.3High-densityPartialAngiomyolipoma
14M/46 3.0HeterogenousTumorectomyAngiomyolipoma
15F/53 4.0Fat-densityTumorectomyAngiomyolipoma
16F/66 3.0Fat-densitySurveillanceAngiomyolipoma
17F/55 1.8HeterogenousPartialMixed epithelial/stroma tumor

Of the eight oncocytomas, seven nephrectomies and one partial nephrectomy were performed. There were no nephrectomies performed on angiomyolipomas. The benign mixed epithelial/stroma tumor was treated by a partial nephrectomy. Of the 16 surgical operations, 10 were carried out using laparoscopy.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

The evaluation of renal tumors has changed with the widespread use of ultrasound and the introduction of CT. Imaging possesses a high accuracy for renal tumors.13,14 However, the characterizations of these tumors by imaging remains a challenge. In the present study, 145 of the 162 solid renal tumors were RCC. Radical nephrectomies were successfully performed on these RCC. The study shows a positive predictive rate of 89.5% for RCC by imaging diagnosis.

In the present study, 10.5% of solid renal tumors were benign, which is a similar result to that reported by Silver et al.15 This information is important for preoperative counseling and surgical planning when choosing the optimal treatment. If these benign tumors can be distinguished by imaging, the choice of surgical method can be made easily. Unfortunately, this is not the case. However, imaging has evolved so that it can provide some strong hints of the presence of benign renal tumors. Current imaging examinations for RCC mainly consist of ultrasound and CT, as proposed by the European Society of Urology.4 Renal oncocytoma and angiomyolipma were the most frequently detected benign renal tumors in the present study. Our understanding of the biology and clinical behavior of oncocytoma and angiomyoliopoma has recently been augmented and renal oncocytoma has been separated from RCC. The treatment for renal oncocytoma is different from the treatment for RCC.16Renal oncocytoma can sometimes be diagnosed as a big tumor. Previous data and that of the present study indicate that this type of image has characteristics of renal oncocytomas.17 The characteristics of these images and increased awareness can lead to the preoperative detection of some renal oncocytomas. In the present study, three large oncocytomas were preoperatively suspected and operated on as benign tumors. However, small oncocytomas were difficult to delineate by imaging. Renal angiomyolipomas were another frequently detected benign tumor in the present study. In our experience, angiomyolipoma is usually found as a small tumor. Imaging can strongly suggest a typical angiomyolipoma with predominant fat composition.18 MRI can help determine the presence of fat in a renal tumor, independent of the presence of hemorrhage, and can often help to differentiate an RCC from an angiomyolipoma.19 However, the CT image cannot diagnose an atypical angiomyolipoma with little fat content. The remaining problem is benign tumors of rare types. We had one mixed epithelial/stromal tumor. The radiological features of this benign tumor were not specific.

Not surprisingly, the choice of treatment for benign renal tumors of small size in the present study was not 100% correct. Nephrectomy was avoided in most of the patients with a benign tumor. In fact, this is attributed to recent acceptance of partial nephrectomy or tumorectomy and to laparoscopic technology.10–12 We performed these operations to remove the small tumors under laparoscopy, and these patients benefited from the minimally invasive surgery. These surgical interventions were more a final pathological diagnosis rather than a therapeutic purpose. However, several nephrectomies for benign tumors could have been avoided if the diagnoses had been definite in the present series.

Renal cell carcinoma lacks an efficient serum marker and therefore diagnosis depends solely on imaging with an emphasis on CT. The recent imaging techniques of spiral acquisition CT or multiarray CT can increase the sensitivity of detection or better localize a renal tumor, but the characterization remains impossible. Imaging has greatly advanced the detection of breast and prostate cancer, where advances in biopsy are considered state of the art diagnosis.20 However, a biopsy of a renal mass is performed much less often than on other tumors such as those of the breast, prostate or liver.6,7,20 Many centers have used the biopsy technique to complement imaging of a renal mass. The results of biopsy in renal tumors are controversial, with some disappointing results reported.21–23 Renshaw et al. reviewed the role of fine needle aspiration (FNA) in the adult kidney.24 They concluded that FNA provides important information that can affect the management of patients with renal masses. Recent reports advocate the preoperative biopsy of a renal mass as a safe and accurate diagnostic procedure with an impact on tumor management.25–30 Wood et al. showed that clinical management was altered because of results in 32 of 79 biopsies (41%) by avoiding nephrectomy or other surgical options.25 At present, the image can be impossible to use to differentiate a benign tumor from an RCC. We think that a biopsy may be the only appropriate technique for some patients with a solid renal mass.

We can demonstrate the relationship between the tumor size and malignancy in solid renal masses as the percentage of benign small-sized tumors was significantly higher than benign large-sized tumors. Based on the data in the present study, we suggest two major indications for biopsy of a solid renal mass discovered by imaging. First, the biopsy is performed to discover renal oncocytoma in large tumors. If imaging studies suggest an oncocytoma, a preoperative or intraoperative biopsy should be carried out to make a final diagnosis so that unnecessary radical nephrectomy can be avoided. Second, if a radical nephrectomy is to be performed for a small tumor, special attention should be paid to rule out the possibility of a benign tumor. The data in the present study indicated the majority of the benign tumors were of a small size. One characteristic of the solid renal masses was that two out of 10 small-sized tumors discovered by imaging were benign. We suggest a biopsy for these types of small tumors before radical nephrectomy if imaging cannot confirm an RCC. This is a practical strategy that will benefit patients in whom a solid renal mass is found by imaging. Recent data have demonstrated that patients undergoing radical nephrectomy are at a greater risk of developing chronic renal insufficiency than patients undergoing partial nephrectomy.31,32

In conclusion, malignancy in solid renal masses is tumor-size related. Benign solid renal tumors appear mainly in small-sized tumors. A preoperative biopsy is suggested in some patients to achieve the maximum accuracy for optimal treatment.

Acknowledgment

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References

Dr G Li is supported by le Comité de la Loire de la Ligue Nationale Contre le Cancer, France.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgment
  8. References