Renal cyst
A renal cyst is a fluid collection in the kidney. There are several types based on the Bosniak classification. The majority are benign, simple cysts that can be monitored and not intervened upon. However, some are cancerous or are suspicious for cancer and are commonly removed in a surgical procedure called nephrectomy.
Numerous renal cysts are seen in the cystic kidney diseases, which include polycystic kidney disease and medullary sponge kidney.
Epidemiology
Up to 27% of individuals greater than 50 years of age may have simple renal cysts that cause no symptoms.
Bosniak classification
Renal cysts are classified as either malignant or benign using the Bosniak Classification System. The system was created by Dr. Morton Bosniak, a faculty member at the New York University Langone Medical Center in New York City.
The Bosniak classification categorizes renal cysts into five groups.
Peripelvic versus parapelvic cysts
Parapelvic cysts originate from around the kidney at the adjacent renal parenchyma, and plunge into the renal sinus. Peripelvic cysts are contained entirely within the renal sinus, possibly related to dilated lymphatic channels. When viewed on CT in absence of contrast, they can mimic hydronephrosis. If symptomatic, they can be laparoscopically decorticated.
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