What are cysts?

Cystic kidneyA cyst in the kidney begins as an outpouching of the nephron, similar to a blister, and can occur any where along the length of the nephron. The fluid inside the cysts often reflects the area in the nephron that the cyst began.

Approximately 70 percent of cysts detach from the nephron once they reach 2 mm (1/8 inch) in diameter. Over time, the cysts enlarge and can become filled with clear fluid or blood. Cysts can also form in other organs, with the liver being the most common site. Liver cysts are derived from the bile ducts or tubules.

What causes cysts to form?

Mutations of the PKD1 or PKD2 gene reduce the normal level of polycystins, which regulate many important tubular cell functions. Recent research has highlighted a central defect in PKD related to dysregulation of calcium levels and a signalling molecule called cyclic AMP (cAMP) within the cells that form tubules in the kidneys and other target organs. These abnormalities in turn can lead to cyst formation through at least three important mechanisms:

  • Cell proliferation (growth) – the cells lining a cyst reproduce themselves more than normal kidney cells do, making them grow in size. This process is essential to growth and replacement of the old cells.
  • Fluid secretion – the lining cells secret fluid into the empty sac which expands the cyst. Without fluid secretion a cyst would collapse like a deflated balloon.

Kidney cyst formation

How do cysts cause problems?

In general, cysts cause problems because of their size and the space they occupy. Many of the symptoms you may have are dependent on how large your kidneys are, detailed below:

  • Kidneys over 15 cm (6 inches) are more likely to cause pain than smaller kidneys.
  • Patients with bigger kidneys are more likely to experience high blood pressure than those with smaller kidneys.
  • Patients with bigger kidneys are more likely to have bleeding into their urine than those with smaller kidneys.
  • Patients with bigger kidneys are more likely to experience more rapid loss of renal function than those with smaller kidneys.

Kidney disease progression in ADPKD