Renal Mass




  • Epidemiology: account for 75% of benign renal rumors
  • Oncocytoma typically appears on computed tomography (CT) or magnetic resonance imaging (MRI) as a homogeneous, well-circumscribed solid mass containing a central scar [28]. However, these features are not sufficiently specific to exclude renal cell carcinoma.


  • Epidemiology: account for 11% of benign renal tumors
  • Angiomyolipomas can be reliably distinguished on imaging as an enhancing mass that contains macroscopic fat and no calcifications (image 3). Renal cell carcinoma, particularly the clear cell subtype, can contain microscopic fat, but this can reliably be distinguished from macroscopic fat on imaging. Small angiomyolipomas with minimal fat are difficult to characterize on imaging and generally require further evaluation [29,30].
  • When renal angiomyolipomas are bilateral, patients have an 80 to 90 percent chance of having tuberous sclerosis. Patients with tuberous sclerosis also have an increased frequency of RCC, although malignancies are less common than with other hereditary syndromes such as von Hippel-Lindau disease [31]. (See “Renal manifestations of tuberous sclerosis complex” and “Tuberous sclerosis complex: Genetics, clinical features, and diagnosis” and “Clinical features, diagnosis, and management of von Hippel-Lindau disease” and “Hereditary kidney cancer syndromes”.)

Metanephric Adenoma<

  • Epidemiology: account for 3% of benign renal tumors
  • Metanephric adenomas are rare benign lesions that are more common in women than men [32,33]. Although many cases are initially identified incidentally, some patients present with pain, hematuria, or a palpable mass. Metanephric adenomas are defined by a characteristic histology but may be difficult to distinguish from chromophilic (papillary) RCC or epithelial predominant Wilms tumor [34].

Renal Cyst

  • Bosniak Classification
    • I
    • II
    • IIf
    • III
    • IV

Primary Renal Malignancy (see Renal Cancer, [[Renal Cancer]])

  • Renal Cell Carcinoma
  • Urothelial Cell Carcinoma (Transitional Cell Carcinoma) of the Renal Pelvis

Metastatic Malignancy to Kidney

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  • Xanthogranulomatous Pyelonephritis: Xanthogranulomatous pyelonephritis is an unusual variant of chronic pyelonephritis
    • In two-thirds of cases, it is a complication of urinary obstruction from infected renal stones
    • Clues to the presence of xanthogranulomatous pyelonephritis include a history of urinary tract infections and the presence of pyuria and bacteriuria at presentation
    • CT can suggest this diagnosis by demonstrating an obstructing kidney stone and several rounded, low density areas corresponding to dilated calyces lined with necrotic xanthomatous tissue extending into the renal parenchyma.



  • Abdominal/Pelvic CT With/Without Contrast: preferred study
    • Study is done with/without contrast to determine enhancement of the tumor
  • CT Urogram: preferred study when the suspected pathology is urothelial cell carcinoma
    • Intraluminal filling defects are better detected with this study than with conventional CT

Fine Needle Aspiration (FNA)

  • May Be Required


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