title: Renal oncocytoma revisited: a clinicopathological study of 109 cases with emphasis on problematic diagnostic features.
abstract: OBJECTIVE
  To evaluate problematic diagnostic features in renal oncocytoma.
  
  
  RESULTS
  One hundred and nine cases of oncocytoma were reviewed and the problematic gross and microscopic features recorded. Multifocal and bilateral neoplasms were found in 12 (11%) and five (4.6%) cases, respectively. Haemorrhage was seen grossly in 30 (27.5%) neoplasms and a central scar was identified in 35 (32.1%). On microscopy, perinephric fat extension was present in 17 (15.6%) neoplasms and vascular extension was identified in four (3.7%) oncocytomas. Rare mitoses and focal coagulative necrosis were identified in two (1.8%) cases each. Focal clear cell changes were found in 16 (14.7%) oncocytomas, typically within hyalinized areas. Limited foci with chromophobe-like histology (not exceeding 5% of the neoplasm) were found in 13 (11.9%) oncocytomas. In 12 (11%) oncocytomas, rare papillary formations were noted in the lumina of microcysts. Significant nuclear atypia, oncoblasts and entrapped tubules were identified in 27 (24.8%), 41 (37.6%) and 40 (36.7%) neoplasms, respectively. After a median follow-up of 52 months (range 1-113 months), there was no disease recurrence, progression or death attributed to oncocytoma.
  
  
  CONCLUSIONS
  The recognition of the spectrum of morphological changes observed in renal oncocytoma should help pathologists establish a diagnosis of oncocytoma in problematic cases.
authors.affiliation: Department of Pathology and Laboratory Medicine, Calgary Laboratory Services and University of Calgary, Calgary, Alberta, Canada. kiril.trpkov@cls.ab.ca
authors.forename: Kiril
authors.initials: K
authors.lastname: Trpkov
authors.forename: Asli
authors.initials: A
authors.lastname: Yilmaz
authors.forename: Dina
authors.initials: D
authors.lastname: Uzer
authors.forename: Kristin M
authors.initials: KM
authors.lastname: Dishongh
authors.forename: Charles M
authors.initials: CM
authors.lastname: Quick
authors.forename: Tarek A
authors.initials: TA
authors.lastname: Bismar
authors.forename: Neriman
authors.initials: N
authors.lastname: Gokden
mesh_terms: D018249:Adenoma, Oxyphilic / Q000378:metabolism / Q000473:pathology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002292:Carcinoma, Renal Cell / Q000378:metabolism / Q000473:pathology; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007668:Kidney / Q000378:metabolism / Q000473:pathology*; D007680:Kidney Neoplasms / Q000378:metabolism / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D009336:Necrosis; D012189:Retrospective Studies