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ORGAN SYSTEMS Renal System

Renal cyst

Renal cysts are composed of enclosed liquid/semisolid fluid and are commonly identified on abdominal imaging.

Renal cysts are composed of enclosed liquid/semisolid fluid and are commonly identified on abdominal imaging.

  • M/C lesion of the kidney (present in 40% population)
Prevalence of Stage I renal cysts diagnosed on ultrasound in a healthy ageing population in Taiwan. | Chang CC, Kuo JY, Chan WL, et al. Prevalence and clinical characteristics of simple renal cyst. J Chin Med Assoc. 2007;70:486–491.

Classification

Bosniak renal cyst classification system:

Consists of four categories based on triphasic CT findings, ranging from simple to complex cysts
Israel and Bosniak 2005

Sonographic criteria:

  • Simple renal cysts (SRC): When all of the criteria are met, the cyst is benign and no follow-up is required.
    1. Absence of internal echoes
    2. Posterior enhancement
    3. Round/oval shape
    4. Sharp, thin posterior walls
  • Complex renal cysts: When cysts do not meet the rigid characteristics of the “simple” definition

Clinical features

Simple renal cysts (SRCs):

2-4% may become symptomatic
  • Abdominal pain or hematuria (owing to increasing size or complications like infection, hemorrhage, or rupture)

Management

  • Category I and II renal cysts: No further imaging or follow-up required
  • Category IIF (~5% malignant risk): Follow-up by imaging
  • Category III (50% malignant risk) and category IV (75-90% malignant risk): Surgical excision recommended
  • Large, SRCs:
    • Aspiration & sclerotherapy
    • Laparoscopic surgery

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