Cystic Disease of the Kidney

A renal cyst is a fluid-filled sac or segment of a dilated nephron. The cysts may be single or multiple and can vary in size from microscopic to several centimeters in diameter. Although all types of cysts are not inherited, they are discussed here for convenience.

Renal cystic disease is thought to result from tubular obstructions that increase intratubular pressure or from changes in the basement membrane of the renal tubules that predispose to cystic dilatation. After the cyst begins to form, continued fluid accumulation contributes to its persistent growth. Renal cystic diseases probably exert their effects by compressing renal blood vessels, producing degeneration of functional renal tissue and obstructing tubular flow. There are essentially four types of renal cystic disease: polycystic kidney disease, medullary sponge kidney, acquired cystic disease, and simple kidney cysts.

Simple and Acquired Renal Cysts

Simple cysts are the most common cystic disease of the kidney. These can be single or multiple, unilateral or bilateral, and usually are less than 1 cm in diameter, although they may grow larger. Most simple cysts do not produce signs or symptoms or compromise renal function. When symptomatic, they may cause flank pain, hematuria, infection, and hypertension related to ischemia-produced stimulation of the renin-angiotensin system. They are most common in older persons.

Although the cysts are benign, they may be confused clinically with renal cell carcinoma. Acquired renal cystic disease occurs in persons with end-stage renal failure who have undergone pro longed dialysis treatment. They probably form as a result of tubular obstruction. The cysts may bleed causing hematuria. Tumors, usually adenomas but occasionally adenosarcomas, may develop in the walls of these cysts.

Medullary Cystic Disease

There are two major types of medullary cystic disease: medullary sponge kidney and nephronophthisis medullary cystic disease complex.6.7 Medullary sponge kidney is characterized by small (<5 mm in diameter), multiple cystic dilations of the collecting ducts of the medulla. The disorder does not cause progressive renal failure; it does, however, produce urinary stasis and pre disposes to kidney infections and kidney stones. Symptoms may develop between 30 and 60 years of age when calcification develops in the dilated tubules.

Nephronophthisis-medullary cystic disease complex is a group of related diseases characterized by renal medullary cysts, sclerotic kidneys, and renal failure. About 85% of cases have a hereditary basis. Symptoms usually develop during childhood, and the disorder accounts for 10% to 20% of renal failure in children. Polyuria, polydipsia, and enuresis (bed wetting), which are early manifestations of the disorder, reflect impaired ability of the kidneys to concentrate urine?

Polycystic Kidney Disease 

The most common form of renal cystic disease is polycystic kidney disease, which is the result of a here ditary trait. It is one of the most common hereditary diseases in the United States, affecting more than 500,000 Americans.8 There are two types of inherited polycystic disease: autosomal recessive and autosomal dominant.