Editing Benign Kidney Tumours (section)

== Oncocytoma ==

=== Epidemiology ===
* '''More common in younger females and older patients''' with a small incidentally discovered renal mass

=== Pathology ===
* '''Derived from the collecting duct/distal renal tubules, similar to chromophobe and collecting duct RCC'''
** '''Recall that clear cell and papillary RCC are derived from the proximal tubules'''
* '''Cells demonstrate an abundance of mitochondria'''
* Hemorrhage, extension into perinephric fat, vascular invasion, cellular atypia, prominent nucleoli, and pleomorphism may be seen in up to 1/3rd of patients, yet the clinical behavior in these cases is benign
[[File:Stellate scar in right renal mass.jpg|alt=Stellate scar in right renal mass. Source: Wikipedia|thumb|500x500px|Stellate scar in right renal mass. Source: [[commons:File:Onkozytom_der_Niere.jpg|Wikipedia]]]]
=== Diagnosis and Evaluation ===
* '''Imaging'''
** '''Clinically and radiographically indistinguishable from RCC'''
*** '''Classic findings of spoke-wheel pattern seen on angiography or stellate scar on cross-sectional imaging''' '''have a poor predictive value'''

* '''Scroll through CT of oncycytoma on Radiopaedia'''
** '''Other'''
*** '''Biopsy'''
**** '''Can provide diagnosis'''
***** '''Histologically, difficult to distinguish oncocytoma from chromophobe and clear cell RCC, either with eosinophilic characteristics'''
**** '''Frozen section is unreliable''' and should not be used to guide treatment

=== Management ===
* '''Options include observation, thermal ablation, or surgery'''
** If surgery, partial nephrectomy preferred given benign nature and very low probability of recurrence
** If observation, should be followed with the same imaging protocols used for untreated, low risk (cT1, NO, Nx) renal cancer patients.
*** Benign tumors can exhibit substantial growth patterns over time that may threaten destruction of the renal unit by compression/invasion of surrounding parenchyma and vascular structures
*** Although the accuracy of percutaneous biopsy has improved substantially in the past several years, the pathologic differentiation between oncocytoma and oncocytic neoplasms (e.g., chromophobe renal cell carcinoma) and renal cell carcinoma can at times be difficult, with the true pathology of the mass only coming to attention by rapid tumor growth.
*** The purpose of routine imaging of these benign neoplasms is, therefore, to capture undue tumor growth and allowing for expedient surgical/ablative intervention and avoidance of radical nephrectomy.
*** AUA Guidelines for the follow-up of renal cancers and untreated low-risk tumors, including oncocytoma, include:
**** History and physical examination
**** Basic laboratory testing to include blood urea nitrogen (BUN)/creatinine, urine analysis (UA), and estimated glomerular filtration rate (eGFR)
**** Continued renal imaging (US, CT or MRI scan) at least annually, and annual chest X-ray (CXR) to assess for pulmonary metastases.