A solitary cyst is usually a clinically insignificant incidental finding at ultrasonography and does not require further follow-up.
In autosomal dominant polycystic kidney disease (ADPKD), cysts increase and the size of kidneys increases with age. Patients with ADPKD may also have cerebrovascular aneurysms, liver cysts, valvular heart disease and hypertension. Family history is important and ultrasonography is diagnostic.
Solitary cysts
Solitary renal cysts are associated with ageing and do not usually have clinical significance when detected as incidental findings on ultrasonography (in as many as 50% of patients above 50 years of age). The cysts may be solitary, multiple and bilateral.
Acquired cysts are associated with chronic renal failure, in which case the kidneys are small or normal in size and the cysts are small.
The sonographic criteria of a benign cyst (picture 1) are:
A solitary cyst may also be malignant. Malignant cysts can usually be differentiated from benign cysts by ultrasonography (see above). Additional investigations include computed tomography or needle biopsy performed by a radiologist.
Polycystic kidney disease
Autosomal dominant polycystic kidney disease
Inherited as an autosomal dominant trait, meaning that the children of a patient have a 50% risk of inheriting the disease.
Its prevalence is 1:400-1:1 000. Its incidence in Finland is 7-8/1 000 000.
Cysts develop in both kidneys, increasing and growing with age. The kidneys grow (may weigh up to several kilogrammes), and renal failure develops.
About 70% of patients require renal dialysis by the age of 40 to 70 years.
The disease is caused by a mutation in either the PKD1 or the PKD2 gene.
A mutation in the PKD2 gene causes a clearly milder disease with dialysis required at an average age of 69 years, whereas those with PKD1 disease need dialysis at an average age of 53 years, already.
85% of patients with polycystic disease have PKD1 disease.
Liver cysts are common in these patients but they have no effect on liver function. Cysts may also occur in the pancreas.
The risk of cerebrovascular aneurysms is increased in patients with a family history of stroke or aneurysm.
These patients should undergo cerebrovascular MRI and if the findings are normal, the examination should be repeated every 5 to 10 years depending on other risk factors.
The patients also have an increased risk of valvular heart disease, particularly mitral regurgitation or prolapse or aortic valve regurgitation.
Colonic diverticula and hernias are also common.
Cysts may be associated with pain from the fibrous capsule of the kidney being stretched. A cyst may rupture causing acute pain and haematuria. A cyst may also become infected.
Hypertension is found in as many as 35% of children with the disease.
Factors worsening the prognosis of kidney disease include
hypertension before the age of 35 years
cyst ruptures/haematuria before the age of 35 years
male sex
mutation in the PKD1 gene
GFR decreased at an early stage
large size of kidneys.
The size of the kidneys can best be measured by MRI. The size can be used to assess the prognosis of the disease.
If parents want it, also children can be investigated by ultrasonography. Gene testing is also possible. If parents do not want diagnostic examinations, at least children's blood pressure should be monitored every 3 years from the age of 5 years on and their urine should be monitored for the possible development of proteinuria.
Chapman AB, Devuyst O, Eckardt KU et al. Autosomal-dominant polycystic kidney disease (ADPKD): executive summary from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference. Kidney Int 2015;88(1):17-27. [PubMed]