Renal cystic disease comprises a wide range of disease entities. They can be classified as either (1) hereditary or acquired or (2) systemic or renal confined diseases that have the common feature of multiple renal cysts. Each disease entity differs in its presentation, prognosis, and management.
Renal cysts are smooth-walled, fluid-filled circular structures formed by focal outpouching of renal tubules. The pathogenesis of cyst formation has not been entirely elucidated. However, tremendous strides have been made in recent years. For autosomal dominant and autosomal recessive polycystic kidney diseases (ADPKD and ARPKD), a picture is starting to emerge. Defects in the primary ciliary sensing mechanisms, intracellular calcium regulation, and cellular cyclic AMP (cAMP) accumulation all seem to play a role in the altered cellular phenotype and functions.
Today, treatment includes risk modification, management of complications, and renal transplant or dialysis. There is no definitive therapy to eliminate or to retard cyst growth. A better understanding of its pathogenesis offers hope in the near future for correcting the underlying abnormalities in cystic pathways.
- Two renal cysts unilaterally or bilaterally before age 30 years by renal ultrasound in patients with a family history of ADPKD.
- Two cysts in each kidney between the ages of 30 and 59 years by renal ultrasound in patients with a family history of ADPKD.
- Four or more cysts in each kidney after age ≥60 years by renal ultrasound in patients with a family history of ADPKD.
ADPKD is the most common life-threatening monogenic disease. It occurs worldwide and in all races, affecting 1 in 400–1000 individuals. In the United States, approximately 500,000 people are affected and about 2000 begin hemodialysis each year.
ADPKD is an autosomal dominantly transmitted disease. It is composed of two types: ADPKD1, caused by mutations in the PKD1 gene and responsible for 85% of the clinical cases of ADPKD, and ADPKD2, caused by mutations in the PKD2 gene and accounting for approximately 15% of cases. A very small percentage of ADPKD patients, with a milder form of disease not linked to mutations in either PKD1 or PKD2, might have mutation(s) in a yet to be identified third PKD gene.
In addition to its renal manifestations, ADPKD is a multisystemic disorder with prominent extrarenal cystic and noncystic manifestations including polycystic liver disease and cysts in diverse organ systems (pancreas, arachnoid membrane, pineal gland, and seminal vesicles), intracranial saccular aneurysms, thoracic aortic aneurysms and dissections, coronary artery aneurysms, mitral and/or tricuspid valve prolapse, aortic valve insufficiency, aortic root dilation, and possibly colonic diverticula.
The severity of cystic renal dysfunctions is highly heterogeneous with significant interfamilial and intrafamilial variations. In general, ADPKD1 is more severe and is marked by an early onset of end-stage renal failure (mean age of 54 years) versus that of ADPKD2 (mean age of 74 ...