Chronic kidney disease may develop insidiously and be discovered late in its course, because it is often asymptomatic. Frequently, renal disease is first detected by the discovery of proteinuria, hypertension, or azotemia on routine medical examination. Disease-specific findings may precede development of chronic kidney disease. In patients with glomerular disease resulting in nephrotic syndrome, as the glomeruli undergo sclerotic changes and result in nephron loss, the avenue for protein loss is progressively lessened, and the nephrotic syndrome thus becomes less severe with advanced disease. Some degree of proteinuria, however, is present in almost all cases. Hypertension is very common. Although microscopic hematuria is usually present, grossly bloody urine is infrequent at this late stage.
Without treatment, the prognosis is poor; relentless progression to uremia and death is the rule. The rate of progression is extremely variable.
Fig. 14.20 Chronicglomerulonephritis.AMassontrichromepreparationshowscompletereplacementofvirtuallyallglomerulibyblue-stainingcollagen.(Courtesy of Dr. M.A. Venkatachalam, Department of Pathology, University of Texas Health Sciences Center,San Antonio,Texas.)
Cystic diseases of the kidney are a heterogeneous group comprising hereditary, developmental, and acquired disorders. They often present diagnostic problems for clinicians, radiologists, and pathologists and can occasionally be confused with malignant tumors. Some forms, such as adult polycystic disease, constitute major causes of chronic kidney disease.
An emerging theme in the pathophysiology of the hereditary cystic diseases is that the underlying defect is in the cilia-centrosome complex of tubular epithelial cells. Such defects may interfere with fluid absorption or cellular maturation, resulting in cyst formation. A brief overview of simple cysts, the most common form, is presented next, followed by a more detailed discussion of polycystic kidney disease. Renal dysplasia, the most common form of cystic renal disease in childhood, is discussed under congenital and developmental anomalies later in the chapter.
Simple cysts are generally innocuous lesions that occur as multiple or single cystic spaces of variable size. Commonly, they are 1 to 5 cm in diameter; translucent; lined by a gray, glistening, smooth membrane; and filled with clear fluid. On microscopic examination, these membranes are seen to be composed of a single layer of cuboidal or flattened cuboidal epithelium, which in many instances may be completely atrophic. The cysts usually are confined to the cortex. Rarely, massive cysts as large as 10 cm in diameter are encountered.
Simple cysts are a common postmortem finding that has no clinical significance. The main importance of cysts lies in their differentiation from kidney tumors, when they are discovered either incidentally or during evaluation of hemorrhage and pain. Radiographic studies show that in contrast with renal tumors, renal cysts have smooth contours, are almost always avascular, and produce fluid rather than solid tissue signals on ultrasonography.
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Acquired cystic kidney disease occurs in patients with end-stage renal disease who have undergone dialysis for many years. Multiple cysts may be present in both the cortex and the medulla and may bleed, causing hematuria. The risk for renal neoplasms, particularly cystic ones, in this setting is over 100 times greater than in the general population.
Adult polycystic kidney disease is characterized by multiple expanding cysts affecting both kidneys that ultimately destroy the intervening parenchyma. It is seen in approximately 1 in 500 to 1000 individuals and accounts for 10% of cases of chronic kidney disease. This disease is genetically heterogeneous. It can be caused by inheritance of one of at least two autosomal dominant genes of very high penetrance.