Renal Oncocytoma: A Reappraisal of Morphologic Features with Clinicopathologic Findings in 80 Cases

Abstract

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.

Diagnostic criteria for oncocytic renal neoplasms: a survey of urologic pathologists

“…[7][8][9][10] However, some concern persists regarding this finding, with only 59% of participants responding "compatible with oncocytoma diagnosis" and 41% considering it worrisome but not necessarily incompatible with oncocytoma. This decreased slightly to 53% for renal sinus fat involvement, which is well-known as an invasive pathway in clear cell renal cell carcinoma, [26] but has not been thoroughly studied in oncocytoma.…”

Tuberous sclerosis complex: the past and the future

“…Oncocytomas occur more frequently in TSC than in the general population, where they are uncommon benign adenomatous hamartomas accounting for only 3-5 % of renal parenchymal tumors [34]. They arise from the intercalated cells of the cortical portion of the collecting duct [35], and consist of dense eosinophilic cytoplasm with generally uniform nuclei and abundant mitochondria [36,37]. RCC occurs in 3-5 % of patients with TSC at an average age of 28-50 years, with very few reports in childhood [38,39].…”

Radiologic Imaging of Renal Masses

“…[46,44,42,47] Mean tumor size for oncocytomas has ranged from 4 to 6 cm in most series-again, similar to RCC. However, giant oncocytomas (16-18 cm) have been reported.…”

“…Literature review suggests that this benign behaving renal histopathologic type represents approximately 3% to 11% of all solid renal masses [42,43,44,45] Mean age at presentation and male-to-female predominance are similar for oncocytoma and RCC, and although oncocytomas are more likely to be asymptomatic (58% to 83%), most RCCs are now also diagnosed incidentally. [46,44,42,47] Mean tumor size for oncocytomas has ranged from 4 to 6 cm in most series-again, similar to RCC.…”

“…Oncocytomas cells are packed with numerous large mitochondria, which contributes to their distinctive staining characteristics. Hemorrhage is found in 20% to 30% of cases [44,54]. Extension into the perinephric fat has also been reported in 11% to 20% of cases, [46,54] however this is most often not the case in the smaller such lesions that have been resected in recent series.…”