ACQUIRED RENAL CYSTIC DISEASE

Acquired renal cystic disease (ARCD)
Cystic degenerative disease of the kidney with cysts visualized on CT scan. By definition this is an acquired condition, as opposed to adult polycystic kidney disease (ADPKD) which is inherited (in an autosomal dominant fashion). It is predominantly associated with chronic and end-stage renal failure (originally, it was thought to specifically affect patients on haemodialysis). Clinically important because it may cause pain or haematuria and is associated with the development of benign and malignant renal tumours. ~one third of patients develop ARCD after 3 years of dialysis. Male:female ratio is 2:1.

Pathology
Usually multiple, bilateral cysts found mainly within the cortex of small, contracted kidneys. Cysts vary in size (average 0.5 - 1cm) and are filled with a clear fluid, which may contain oxalate crystals. They usually have cuboidal and columnar epithelial linings, and are in continuity with renal tubules (and therefore cannot be defined as simple cysts). Atypical cysts have a hyperplastic lining of epithelial cells, which may represent a precursor for tumour formation. Renal transplantation can cause regression of cysts in the native kidneys.

Aetiology
The exact pathogenesis is unknown, but several theories have been proposed. Obstruction or ischaemia of renal tubules may induce cyst formation. Renal failure may predispose to the accumulation of toxic endogenous substances or metabolites, alter the release of growth factors and result in changes in sex steroid production, or cause cell proliferation (secondary to immunosuppressive effects) which result in cyst formation.

Associated disorders
There is an increased risk of benign and malignant renal tumours. The chance of developing renal cell carcinoma is 3 - 6 times greater than the general population (males > females). ARCD may also be associated with tubulo-interstitial nephritis and membranoproliferative glomerulonephritis.

Presentation
Flank pain; UTI; macroscopic haematuria; renal colic (stone disease); hypertension.

Investigation
This depends on the presenting symptoms.
- For suspected UTI culture urine.
- For haematuria urine cytology, flexible cystoscopy, and renal ultrasound. On ultrasound the kidneys are small and hyperechoic, with multiple cysts of varying size, many of which show calcification. If the nature of the cysts cannot be determined with certainty on ultrasound, arrange a renal CT.

Treatment
Persistent macroscopic haematuria can become problematic, exacerbated by heparinization (required for haemodialysis). Options include transferring to peritoneal dialysis, renal embolisation, or nephrectomy. Infected cysts which develop into abscesses require percutaneous or surgical drainage. Radical nephrectomy is indicated for renal masses with features suspicious of malignancy. Smaller asymptomatic masses require surveillance.