II. Epidemiology

  1. Renal Cysts are present in one third of older adults (Incidence increases with age)

III. Classification: Bosniak Classification

  1. Category I: Benign Simple Cyst
    1. No monitoring needed
  2. Category II: Benign cystic lesion with some complex features
    1. No monitoring needed
  3. Category IIF: Nonenhancing complex cysts >3 cm
    1. Malignancy risk: 5-10%
    2. Follow with serial imaging
  4. Category III: Enhancing complex cysts
    1. Malignancy risk: 50%
    2. Surgical resection
  5. Category IV: Malignant cystic mass
    1. Surgical resection

IV. Evaluation

  1. Simple Renal Cysts
    1. Benign in most cases
  2. Complex cysts
    1. Complex cysts (especially with enhancement on imaging) have increased malignant potential
    2. Surgical resection for Category III and Category IV lesions

V. Labs: Biopsy indications

  1. Suspected abscess
  2. Suspected Lymphoma
  3. Suspected metastatic lesions

VI. Management

  1. Simple cysts (Category I and II) require no additional evaluation
  2. Fat containing solid lesions consistent with benign angiomyolipoma may be followed or biopsied
  3. Category IIF lesions should be followed
  4. Suspicious Renal Masses are resected surgically instead of biopsied (due to biopsy sampling error risk)

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