Computed tomographic and angiographic findings in renal oncocytoma

Low grade oncocytic tumors of the kidney: a clinically relevant approach for the workup and accurate diagnosis

Renal oncocytoma and chromophobe renal cell carcinoma were accepted as unique renal tumors in the late 1990s. Since their formal description, criteria for diagnosis have evolved and additional distinct tumor subtypes originally considered as one these two entities are now recognized. The last two decades have witnessed unprecedented interest in the spectrum of low grade oncocytic renal neoplasms in three specific areas: (1) histologic characterization of tumors with overlapping morphologic features between oncocytoma and chromophobe renal cell carcinoma; (2) description of potentially unique entities within this spectrum, such as eosinophilic vacuolated tumor and low-grade oncocytic tumor; and (3) better appreciation of the association between a subset of low grade oncocytic tumors and hereditary renal neoplasia. While this important work has been academically rewarding, the proposal of several histologic entities with overlapping morphologic and immunophenotypic features (which may require esoteric adjunctive immunohistochemical and/or molecular techniques for confirmation) has created frustration in the diagnostic pathology and urology community as information evolves regarding classification within this spectrum of renal neoplasia. Pathologists, including genitourinary subspecialists, are often uncertain as to the "best practice" diagnostic approach to such tumors. In this review, we present a practical clinically relevant algorithmic approach to classifying tumors within the low grade oncocytic family of renal neoplasia, including a proposal for compressing terminology for evolving categories where appropriate without sacrificing prognostic relevance.

Radiologic Findings in Renal Oncocytoma

The imaging findings of 36 renal oncocytomas in 32 patients were evaluated retrospectively. Twenty-two patients underwent ultrasound (US), 16 CT, 25 angiography, 19 urography, and 6 fine-needle biopsy. At US 8 of the oncocytomas were isoechoic, 7 hyperechoic, and 7 hypoechoic. The structure was homogeneous in 59% and nonhomogeneous in 41 %. At plain CT 12 oncocytomas were homogeneously hypodense, 3 isodense, and one hyperdense. Contrast enhancement was homogeneous in 10 and inhomogeneous in 4 cases. A stellate scar was detected in one case, and in one case a contrast study was not performed. At angiography the oncocytomas were hypervascular in 21, hypovascular in 3 cases, and one was not detected. Nineteen of the tumors were well delineated. A spoke-wheel arterial pattern was detected in 3 tumors. The cytologic diagnosis was benign renal oncocytoma in 4 cases and highly suggestive of oncocytoma in 2 cases. We conclude that the homogeneity of a renal tumor at US and at CT may suggest the possibility of oncocytoma. US-guided fine-needle biopsy is a useful diagnostic tool in patients who need a precise presurgical diagnosis.

Small renal oncocytomas: differentiation with multiphase CT

OBJECTIVES

To evaluate characteristic imaging findings of tumor attenuation in multiphase computed tomography (CT) between renal oncocytomas and clear-cell renal cell carcinoma (ccRCC) of small tumor size (≤5 cm).

METHODS

We retrospectively identified 20 patients with complete four-phase CT with either histologically confirmed small renal oncocytoma (N=10) or ccRCC (N=10) who underwent subsequent total or partial nephrectomy. Exclusion criteria for RCC were non-clear-cell components in histology and a tumor diameter>5 cm. The relative attenuation of solid renal lesions and normal renal cortex was determined in the unenhanced, corticomedullary, nephrographic and excretory phase. Statistical comparison was carried out by Wilcoxon Rank Sum Test.

RESULTS

Mean tumor size of renal oncocytomas was 2.8±0.4 cm (1.2-5) and of ccRCC 2.5±0.2 cm (1.7-4.4; p=0.57). All lesions were homogenous without extended areas of necroses. In the nephrographic phase, the difference of attenuation between renal cortex and tumor lesion was highest in both entities (oncocytoma, 48.1±5.2 HU; ccRCC, 67.5±12.1) but not between entities (p=0.30). In the corticomedullary phase, renal oncocytomas showed greater isodensity to the normal renal cortex (13.9±4.3 HU) compared to clear-cell RCC (51.5±5.0 HU; p=0.003). No further significant differences were found for the unenhanced and excretory phase.

CONCLUSIONS

In this study, the maximum tumor-to-kidney contrast coincided with the nephrographic phase which was thus the most reliable for the detection of a renal lesion<5 cm. For lesion characterization, the corticomedullary phase was most useful for differentiating both entities. This finding is particularly important for the preoperative planning of a partial nephrectomy.

Spoke-wheel pattern in renal oncocytoma seen on double-phase helical CT

Renal oncocytomas are benign, solid tumours of the kidney. An angiographic spoke-wheel pattern is known to be associated with oncocytomas, although it is not pathognomonic. On review of the literature, we found two reports of sonographic spoke-wheel appearance in oncocytomas. These were sufficiently characteristic to enable a confident preoperative diagnosis of oncocytoma. We present a case of a surgically proven oncocytoma with a distinct helical CT appearance, -commensurate with the angiographic and sonographic spoke-wheel appearance from which the diagnosis was suspected preoperatively.

Renal oncocytoma: a reappraisal of morphologic features with clinicopathologic findings in 80 cases

Renal oncocytoma has several features that overlap with other renal neoplasms with a preponderance of granular cytoplasm, such as chromophobe, granular, and papillary renal cell carcinomas. Lack of knowledge of this entire spectrum of eosinophilic renal cell neoplasms has led to several misconceptions in the literature regarding renal oncocytoma. These include the "grading of oncocytomas," "metastatic oncocytomas," and the impression that renal oncocytoma is usually low grade and lacks prominent nucleoli. In order to further characterize the histologic features and embelLish diagnostic criteria, we evaluated 93 tumors from 80 patients. Four tumors were bilateral and two were multifocal. The mean age was 67.2 years (32-89 years), men were more commonly affected (3.1:1), and 82.7% tumors were incidental findings. Grossly, the tumors were mahogany brown, lacked necrosis, and averaged 4.4 cm in size (range 0.6-15 cm). Histologically, renal oncocytoma was composed of an exclusive or predominant component of acidophilic cells with three architectural patterns of disposition: (a) The "classic" pattern (57.5%), composed of a characteristic nested or organoid arrangement of cells, each surrounded by a distinct reticulin framework; (b) a "tubulocystic pattern" (6.3%) with numerous closely packed cystically dilated tubular structures; and (c) "mixed pattern" (36.2%), which had both the organoid and tubulocystic patterns. A gross or microscopic scar was noted in 53.8% cases, and histologically a distinctive myxoid and/or hyalinized stroma separated nests of cells. Generally, the nuclei of renal oncocytoma were round with uniform nuclear contours. Nearly half of the tumors had prominent nucleoli (42.5% had prominent nucleoli equivalent to Fuhrman's grade III or IV). Pleomorphism was absent in 50% of cases but was conspicuous in 12.5% of cases including foci of bizarre cells. Other atypical features included perinephric fat involvement (11.3%), renal parenchymal invasion not associated with desmoplasia (10%), and hemorrhage (31.3%). Renal oncocytoma by definition lacks areas of clear cell carcinoma, significant lesional necrosis, or conspicuous papillary formations. Ancillary features noted included normal-appearing renal tubules within the lesion (15%), intranuclear holes (20%), psammoma bodies (7.5%), and foam cells (7.5%). 15% of tumors were locally excised, and 85% resulted in radical nephrectomy. Mean follow-up of 7.6 years (range 15-200 months) showed no evidence of recurrence, metastasis, or death due to tumor. In conclusion, renal oncocytoma, herein described, is a benign neoplasm and therefore does not merit a nuclear grading scheme. It has unique histologic features including an organoid and tubulocystic architecture, myxoid or hyalinized stroma, and occasionally some atypical findings including nuclear pleomorphism, prominent nucleoli, and adjacent renal parenchymal and perinephric fat involvement.

Renal oncocytoma: magnetic resonance imaging characteristics

PURPOSE

We investigated the magnetic resonance imaging (MRI) appearance of renal oncocytomas.

MATERIALS AND METHODS

Between 1985 and 1993, 11 patients at our institution underwent MRI of the kidneys and were subsequently diagnosed with renal oncocytoma. Patient charts and MRI were reviewed.

RESULTS

Of 11 T1-weighted images 8 showed a mass with decreased signal intensity compared to renal cortex and 3 of 6 T2-weighted images revealed masses with increased intensity. In addition, 5 tumors were surrounded by a well defined capsule, 3 demonstrated a central stellate architecture and 1 contained an area of central decreased signal, all of which corresponded pathologically to scar. These MRI findings differ somewhat from those of renal cell carcinoma, which typically show intermediate to high signal intensity compared to renal cortex on T1 and T2-weighted pulse sequences and usually contain evidence of either hemorrhage or necrosis.

CONCLUSIONS

A low intensity homogeneous mass on T1-weighted images, which appears as increased intensity on T2-weighted images, the presence of a capsule, central scar or stellate pattern and the absence of either hemorrhage or necrosis suggest oncocytoma. It is in the evaluation of patients with a solitary kidney, poor renal function, advanced age or a small easily resectable renal mass when MRI may help diagnose an oncocytoma and, thus, allow renal sparing surgery. The optimal MRI to evaluate renal masses should include T1-weighted spin echo images and without gadolinium, T2-weighted images and gradient recalled echo images.

Kidney preserving surgery in renal cell tumors: indications, techniques and results in 152 patients

Between 1975 and 1991, 142 patients with renal cell carcinoma and 10 with oncocytoma underwent a total of 164 kidney preserving operations. The indication for surgery was imperative (group 1, 47 patients) among those with a solitary kidney (9), renal insufficiency (17) or bilateral tumors (21). Of the patients with small or peripheral tumors and a healthy contralateral kidney 105 were selected for elective surgery (group 2). Most procedures were done either without ischemia (24%) or with warm ischemia (69%). In some patients from the imperative indication group hypothermia was achieved by in situ perfusion (5%) or ex vivo work bench surgery and autotransplantation (2%). Complication rates were 15% for group 1 and 9.5% for group 2. In group 1, 3 patients died of cancer, 5 lived with metastases and 2 had local tumor recurrence. No patient in group 2 had recurrences or metastases. The tumor-specific survival rate of patients with kidney preservation for renal cell carcinoma was comparable to that of a control group undergoing radical nephrectomy. Due to the high reliability and efficacy, kidney preserving surgery for renal cell carcinoma should be done more often, even in patients with a normally functioning contralateral kidney.

Bilateral renal oncocytomas: management and nuclear analysis

Only 16 cases of bilateral renal oncocytomas have been previously reported in the English language literature, 9 of which were treated with bilateral surgical resections. We report a case treated with bilateral partial nephrectomy. Although pathological examination revealed grade I oncocytomas on both sides, flow cytometry demonstrated tumor DNA content to be aneuploid on one side and diploid on the other, the first cellular differences reported in a case of bilateral renal oncocytomas. The management of suspected renal oncocytomas is discussed, with emphasis on the need for complete excision in most patients. The results of nuclear studies of these tumors, including DNA flow cytometry, cytogenetics, and molecular analysis of both nuclear and mitochondrial DNA, are reviewed.

Case report: characteristic ultrasonographic appearance of a large renal oncocytoma

The sonographic appearance of a large renal oncocytoma is described. The 'spoke-wheel' of hypoechoic radiating bands within the tumour was found to correlate closely with other imaging modalities and the histopathological appearance of the surgical specimen. This characteristic sonographic picture, which appears to be a feature of size, enabled a confident pre-operative diagnosis to be made.

Massive thyroid oncocytoma

A patient with a massive thyroid oncocytoma is presented. The symptoms of hoarseness and dysphagia were due to compression and were relieved by surgical excision of the tumour.

Renal oncocytoma: long-term follow-up and flow cytometric DNA analysis

We report a retrospective study on the clinicopathologic features and flow cytometric DNA analysis of ten renal oncocytomas compared with a control group of ten randomly selected renal cell carcinomas. Among the oncocytoma patients, no recurrences or metastases were noted over an average follow-up of 6.7 years (range = 6 months to 16 years). Reproducible, high-quality DNA histograms were obtained on the paraffin-embedded specimens by using our modified flow cytometric procedure. One aneuploid (10%) and two hyperdiploid tumors (20%) were found in the oncocytoma group. There was no correlation between these abnormal DNA histographic patterns and survival or tumor stages. On the contrary, a good correlation was found between tumor grades and DNA ploidy in the controls. We conclude that renal oncocytoma is a clinically benign tumor, yet it may exhibit varying degrees of flow cytometric DNA abnormalities, which have no predictive value on survival and probably reflect the characteristics of oncocytes rather than its malignant potential.

Renal oncocytoma: report of a case with bilateral multifocal oncocytomas

Renal oncocytomas are uncommon, benign tumors that classically are treated by local excision or heminephrectomy. Preoperative differentiation from renal cell carcinoma is invaluable in the planning of treatment. Cases of renal oncocytoma treated conservatively have been reported. This is a case report of bilateral multifocal renal oncocytomas of which only three previous cases have been reported. Diagnosis was made from multiple fine needle biopsies and present treatment consists only of conservative observation.

Problematic renal masses in ultrasonography and computed tomography

The diagnosis of renal masses is based upon the contribution of ultrasonography (US) and computed tomography (CT), which enable the recognition of these lesions with high diagnostic accuracy. However, a number of diagnostic difficulties exist in the definition of the nature of the mass, both for cystic and solid lesions, and to a lesser extent in the identification of the mass. "Complicated" cystic masses, such as calcified cysts, hemorrhagic cysts, inflammatory cysts, abscesses, and cystic tumors may be difficult to diagnose with US and sometimes with CT. CT is helpful in most of these cases because it enables the evaluation of the calcifications and the density of the fluid content. CT is also helpful in cases of cystic tumors because it shows the enhancement of septae within the masses. Problems with solid masses are the identification of small renal tumors and the definition of the benign or malignant nature of the mass. Although both techniques enable the recognition of most tumors, even if small in diameter, they are still limited in defining the pathological structure of the tumor.