Renal cystic disease is a term that represents a wide spectrum of diseases that may be hereditary, developmental, or acquired; these diseases share the feature of renal cysts. These cysts can occur in the cortex, the corticomedullary junction, and/or the medulla, depending on the underlying disease process. Acquired cysts can be simple or part of acquired cystic kidney disease (ACKD), also called acquired renal cystic disease (ARCD).
Acquired renal cystic disease is characterized by the development of numerous fluid-filled cysts in the kidneys in individuals who have no history of hereditary cystic disease. Acquired renal cystic disease is a bilateral condition. It can antedate the clinical recognition of end-stage renal failure. In the early stages, acquired renal cystic disease does not produce symptoms and is usually discovered incidentally in the course of abdominal imaging procedures.
For patient education information, see Renal Cell Cancer.
Acquired renal cystic disease was previously thought to be a consequence of hemodialysis. Studies have shown that, although the association of dialysis and acquired renal cystic disease is indisputable, it is the uremic state that promotes the development of acquired renal cystic disease. Dialysis prolongs the patient's survival to allow more time for acquired renal cystic disease to occur.
The exact mechanism is not known. The postulates are as follows:
Tubule block: The development of cysts is due to tubular abnormalities; tubular obstruction due to oxalate crystals, fibrosis, or micropolyps; and tubular fluid accumulation due to glomerular filtrate and tubular fluid excretion.
Compensatory growth: The profound loss of renal tissue in end-stage kidney disease promotes tubular cell hypertrophy and hyperplasia. Hypertrophy and hyperplasia, together with transepithelial secretion of fluid by the tubular epithelium, result in the development of cysts. Many factors may influence the process, but most important among them are growth factors and activation of oncogenes.
Ischemia  : Kidney atrophy is a recognized consequence of ischemia that may be caused either by primary renal arterial occlusion or by the secondary arterial occlusions that develop after dialysis is begun. Parenchymal acidosis may result from chronic progressive occlusion and, if sustained just short of causing cell death, might result in renal cyst formation.
Research into the cystic fluid and epithelium suggests that the cysts arise from proliferation of renal tubules. [2, 3] Cystic fluid derives from the ultrafiltrate, transepithelial solute and fluid secretion, and resembles plasma in its composition.  Additionally, microdissection studies have shown that most cysts present a low cuboidal or columnar epithelium, while some of the cells that line cysts show an apical brush border configuration, suggesting that they stem from proximal tubules. 
Progressive destruction of the renal parenchyma triggers several mitogenic signals (eg, azotemic products, altered concentration of sodium and potassium, activation of the renin-angiotensin-system, inflammation, local growth factors), ultimately leading to hypertrophy and hyperplasia of renal tubules. [2, 5] In addition, restricted tubular fluid flow and net fluid secretion are contributory factors to form cysts.  Over a period of time, the activation of proto-oncogenes combined with additional risk factors may result in malignant transformation. [2, 6, 7] The image below illustrates the proposed pathophysiology of the progression of acquired renal cystic disease to renal malignancy.
The rates of occurrence of acquired renal cystic disease are 7-22% in the predialysis population, 44% within 3 years after beginning dialysis, 79% more than 3 years after beginning dialysis, and 90% longer than 10 years after beginning dialysis. The rate of progression appears to slow after 10-15 years of dialysis.
Renal transplant recipients
The prevalence of acquired renal cystic disease is lower in renal transplant recipients than in patients on dialysis. In a cohort of 561 renal transplant recipients, the prevalence of acquired renal cystic disease was 23%, whereas in patients with end-stage renal disease, the prevalence may vary from 30-90%.  However, renal cell carcinoma develops more often in transplant recipients with acquired cystic kidney disease than in those without (19% vs. 0.5%). 
Acquired renal cystic disease gives rise to many significant complications, the most serious of which is the development of renal cell neoplasms, ranging from adenoma to metastatic renal cell carcinoma. Other complications include the following:
Cystic hemorrhage 
Cyst infection, abscess formation, and/or sepsis
Calcification in or around cysts
The incidence of renal cell carcinoma (RCC) is 0.18% per year in patients with acquired renal cystic disease, compared with 0.005% in the general population.  Most patients are asymptomatic, but about 15% of patients present with hematuria and flank pain; patients with metastasis may present with lumbar pain. Risk factors include the following:
Male sex (male-to-female ratio is 7:1)
Long duration of dialysis
Severe acquired renal cystic disease with marked organomegaly
Renal cancers from acquired renal cystic disease are multicentric in at least 50% of cases and bilateral in about 10% of cases. They are predominantly of the clear cell or papillary subtype.  The International Society of Urological Pathology Vancouver Classification of Renal Neoplasia recognizes acquired cystic disease–associated RCC as a distinct entity within the classification system. 
Hemorrhage is sometimes associated with hematuria. Bleeding may evolve into cyst rupture, with subsequent retroperitoneal or perinephric hemorrhage (Wunderlich syndrome). Rarely, bleeding can be severe enough to cause hypovolemic shock.
Race-, Sex-, and Age-related Demographics
Acquired renal cystic disease is relatively more common in blacks. Blacks account for 53% of cases of acquired renal cystic disease; however, in the United States, only 25% of patients on dialysis are black.
Acquired renal cystic disease occurs more frequently in men than in women. Acquired renal cystic disease-associated renal cell carcinoma is found predominantly in men; the male-to-female ratio is 7:1 compared with 2:1 in the general population.
Acquired renal cystic disease occurs with equal frequency in children and adults.  Renal cell carcinoma occurs approximately 20 years earlier in people with acquired renal cystic disease than in the general population. In children, acquired renal cystic disease-associated renal cell carcinoma is rare.
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