Renal Oncocytoma
Definition
- Benign neoplasm of the kidney composed of cells with mitochondria rich eosinophilic cytoplasm
Diagnostic Criteria
- Strictly defined, oncocytoma is benign
- In the past, some cases of clear cell carcinoma and chromophobe carcinoma have been included in series of oncocytomas
- Such cases probably explain the rare examples of metastatic oncocytoma
- In the past, some cases of clear cell carcinoma and chromophobe carcinoma have been included in series of oncocytomas
- Pathologic findings must fall within the following range of criteria
- Grossly circumscribed but not encapsulated
- Usually dark (mahogany) brown
- Frequent central scar
- No gross necrosis
- Usually dark (mahogany) brown
- Tight nests and alveoli surrounded by myxoid or hyalinized hypocellular stroma
- Round balls of cells appearing to float in the stroma
- Nests may form central lumen or multiple lumens
- Nests may show central hyalinization
- This pattern is nearly always present and usually predominates
- Tubulocystic areas may also be present
- Closely packed tubules and cysts with scant stroma
- Usually mixed with nest pattern (above)
- Exclusively or pronounced cystic growth suggests tubulocystic carcinoma, which is composed of cells reminiscent of oncocytoma
- Solid areas may be formed by densely packed tight nests and alveoli
- Nests retain their circumscribed pattern
- Individually surrounded by reticulin, even in areas of collapse
- Invariably merge with floating nests as above
- Nests retain their circumscribed pattern
- Nearly all cells have prominent granular eosinophilic cytoplasm
- Due to presence of numerous mitochondria
- Foci of smaller cells with scant eosinophilic cytoplasm, hyperchromatic nuclei and high N:C ratio may be present
- Should merge with conventional eosinophilic cells
- Have been termed "oncoblasts"
- Rare cases have been described in which these small cell predominate (Hes 2001, Petersson 2011)
- Diagnosis should be made with great caution in such cases
- Clear cytoplasm seen only in rare cells trapped in hyaline scarred areas
- No peripheral ballooning of clear cells
- No perinuclear clearing in eosinophilic cells
- Extracellular eosinophilic round hyaline bodies may be seen within the nests (Guarino)
- Round regular nuclei throughout
- Frequently have dispersed chromatin and prominent central nucleolus
- Mitotic figures are infrequent and never atypical
- Intranuclear vacuoles may be seen
- Foci of degenerative atypia may be present
- Pleomorphic, hyperchromatic nuclei with smudged chromatin
- Occasionally multinucleated or polylobated
- Not associated with mitotic activity
- Typically clustered, not diffuse
- Pleomorphic, hyperchromatic nuclei with smudged chromatin
- Grossly circumscribed but not encapsulated
- Must not have any of the following features
- Grossly visible or substantial microscopic necrosis
- Focal microscopic necrosis is permitted
- Sheet-like growth pattern
- Prominent or well-developed papillary architecture, even if focal
- Minimal short, degenerate appearing papillae are permitted
- Significant clear cell population
- Only focal clear cells in hyalinized scar area are permitted
- Spindled/sarcomatoid change
- Easily found mitotic activity
- Any atypical mitotic figures
- Grossly visible or substantial microscopic necrosis
- Following features are permitted if above criteria (positive and negative) are fulfilled
- Minimal microscopic necrosis
- Infrequent mitotic figures
- Rare, focal psammoma bodies and foam cells
- Invasion of renal parenchyma (surrounded normal tubules)
- Must not have desmoplastic response
- Invasion of perirenal fat
- Must not have desmoplastic response
- Microscopic vascular and/or gross renal vein invasion (Hes 2008)
- Pseudorosettes with PASd positive globule in center (Petersson 2011)
- Extensive sampling is required to confirm this diagnosis
- At least 1 section per cm diameter
John P Higgins MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/updates: 1/24/11, 11/27/11
