Renal Mass

Aka: Renal Mass, Kidney Mass, Kidney Neoplasm, Kidney Tumor, Renal Growth, Kidney Lesion

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II. Epidemiology

  1. Incidental Renal Mass on Autopsy (over age 50): 50%
  2. Incidental Renal Mass on CT Scan (over age 50): 33%

III. Differential Diagnosis

  1. Renal Cyst (Simple, Complex or Multiple)
  2. Malignant Masses
    1. Renal Cell Carcinoma
    2. Lymphoma
    3. Sarcoma
    4. Metastatic cancer
  3. Benign Masses
    1. Renal adenoma
    2. Angiomyolipoma
    3. Oncocytoma
  4. Inflammatory Lesions
    1. Renal infection
    2. Renal Infarction
    3. Renal Trauma (renal Hematoma)

IV. Imaging: Management of Mass on Renal Ultrasound

  1. Efficacy
    1. Test Sensitivity: 79% of renal parenchymal masses
    2. Does not detect Renal Masses less than 5 mm diameter
  2. Simple Renal Cyst Criteria
    1. Spherical or ovoid shaped cysts
    2. No internal echoes
    3. Thin smooth cyst wall separated from renal parenchyma
    4. Posterior cyst wall enhancement
      1. Suggests water-filled cyst
  3. Management
    1. Simple cysts require no further evaluation
    2. Abdominal CT or MRI indicated for other masses

V. Imaging: Management of Mass on Renal CT

  1. Efficacy
    1. Test Sensitivity: 94% of renal parenchymal masses
    2. MRI better distinguishes benign Renal Masses
  2. Absolute Surgery Consultation Indications
    1. Symptomatic Renal Mass
    2. Solid Renal Mass
    3. Bosniak Class III-IV Cystic Mass (see below)

VI. Imaging: Incidental Renal Mass on Abdominal CT

  1. Cystic Mass
    1. See below for Bosniak classification
  2. Fat containing Renal Mass
    1. No calcifications: Angiomyolipoma
      1. Consider urology evaluation
      2. Consider genetic Consultation
    2. Calcifications
      1. Reassess and CT or MRI Abdomen with and without contrast in 12 months
  3. Renal lesion too small to characterize
    1. Enhancement similar to parenchyma
      1. Reassess and CT or MRI Abdomen with and without contrast in 12 months
    2. Non-enhancing
      1. Benign lesion requiring no further workup
  4. Solid Renal Mass
    1. Solid lesion >1 cm
      1. Refer to urology for renal neoplasm
    2. Solid lesion <1 cm
      1. CT or MRI Abdomen with and without contrast every year for 5 years
      2. Refer to urology if growth >3mm per year

VII. Imaging: Cystic Renal Mass Incidental on Abdominal CT (Bosniak Classification)

  1. Bosniak's Class I: Simple Renal Cyst
    1. Criteria
      1. See Renal Ultrasound Criteria above
      2. Hairline thin wall without septa (unilocular), calcification or solid component
      3. Round or oval shape
      4. Uniform water attenuation density within cyst (-10 to 20 HU)
      5. No contrast enhancement
    2. Management
      1. Typically benign, requiring no further workup
  2. Bosniak's Class II Benign, Minimally Complicated Renal Cyst
    1. Criteria
      1. May contain a few hairline thin septa
      2. No measurable enhancement (but may appear subjectively to enhance)
      3. Wall or septa may have fine calcification
      4. May appear as <3 cm, well marginated, hyperdense cyst (density above simple fluid)
    2. Management
      1. Typically benign, requiring no further workup
  3. Bosniak's Class IIF Usually Benign, Complicated Renal Cyst
    1. Criteria
      1. Multiple hairline thin septa
      2. Wall or septa may contain thick or nodular calcifications
      3. No measurable enhancement (but may appear subjectively to enhance)
      4. May appear as >3 cm, well marginated, hyperdense cyst (density above simple fluid)
    2. Management
      1. CT or MRI Abdomen with and without contrast every year for 5 years
      2. Refer to urology if growth >3mm per year
  4. Bosniak's Class III Indeterminate Cystic Renal Mass
    1. Criteria
      1. Thick irregular wall or septa with calcifications
      2. Measurable contrast enhancement
      3. Multilocular
    2. Management
      1. Urology Consultation
  5. Bosniak's Class IV Malignant Cystic Renal Mass (Cystic Renal Cell Carcinoma)
    1. Criteria
      1. Heterogeneous lesions with shaggy appearance
      2. Thickened cyst walls
      3. Contrast enhancing Nodules
    2. Management
      1. Urology Consultation

VIII. References

  1. Curry (1997) Urol Clin North Am 24:493-505 [PubMed]
  2. Gray (2019) Am Fam Physician 99(3): 179-84 [PubMed]
  3. Herts (2018) J Am Coll Radiol 15(2): 264-73 [PubMed]
  4. Higgins (2001) Am Fam Physician 63:288-99 [PubMed]
  5. Wolf (1998) J Urol 159:1120-33 [PubMed]

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