There are several cystic diseases of the kidney, some of which produce renal failure by
causing disturbance of renal structure. Importantly, some conditions are heritable.
Adult polycystic disease is inherited in an autosomal dominant trait, generally
becoming clinically manifest in adult life.
Increasingly, disease is detected in childhood, with family screening and ultrasound
examination.
Cysts develop and progressively enlarge over a number of years, but remain asymptomatic
until the number and size of the cysts is so great that the patient becomes aware of
abdominal masses.
At about the same time, the replacement and compression of functioning
renal parenchyma by the cysts leads to slowly progressive impairment of renal function,
and patients develop chronic renal failure and hypertension.
Patients with adult-type polycystic renal disease may also develop cysts in the liver,
lung and pancreas.
There is an association with berry aneurysms of the cerebral arteries.
which, with development of hypertension, predisposes to intracranial haemorrhage.
There are two genes associated with this condition:
90% of cases are associated with PKD1, which is located on chromosome 16,
5-10% with PKD2,located on chromosome 2.
As yet, the gene sequences and functions are unknown.
Nephronophthisis complex describes two diseases:
familial juvenile nephronophthisis (NPH) and medullary cystic disease (MCD).
Both are inherited causes of cysts at the corticomedullary junction of the kidney,
and are associated with interstitial fibrosis leading to early-onset chronic
renal failure.
The conditions account for 10-25% of cases of end-stage renal failure in
the first three decades. Although virtually identical clinically and pathologically,
NPH presents around the age of 11 years as an autosomal recessive disease, and MCD
around the age of 20 years as an autosomal dominant trait.
Medullary sponge kidney is a condition in which multiple cysts develop in renal
papillae.
Renal function is not impaired and the main clinical problem is development of
renal stones,which predispose to renal colic and infection.
Infantile polycystic disease is uncommon and is encountered at birth.
Children develop severe renal failure, with compression of the lungs due to massive
enlargement of the kidneys.
Simple renal cysts are the most common form of renal cystic disease and must be
distinguished from the congenital types discussed above.
They are widely held to be acquired abnormalities, incidence increasing with age.
They contain clear, watery fluid and have a smooth lining.
Simple cysts may be single or multiple and vary in size, generally being no larger
than 5-6 cm.
They have no effect on renal function,but may rarely become infected or develop
haemorrhage.
Acquired cystic disease is seen in kidneys left in situ while patients are treated
by dialysis or transplantation for chronic renal failure.
