Renal parenchymal disease, also termed medical renal disease, includes various disorders of the glomeruli, interstitium, tubules, and small blood vessels of the kidneys. The clinical spectrum encompasses diseases confined to the kidneys and systemic disorders that secondarily affect the kidneys. Renal parenchymal diseases can be primary, secondary, congenital, hereditary, or acquired. There are various classification schemes. Categorization based on the predominantly affected parenchymal structures recognizes 3 major categories of medical renal disease: glomerular, tubulointerstitial, and vascular (Table 46-1). Many parenchymal diseases, however, substantially involve more than 1 of these anatomic divisions.
Table 46–1.Renal Parenchymal Diseases in Children ||Download (.pdf) Table 46–1. Renal Parenchymal Diseases in Children
|Glomerular ||Acute glomerulonephritis |
|Chronic glomerulonephritis |
|Collagen vascular disease |
|Henoch-Schönlein purpura |
|Alport syndrome |
|Tubulointerstitial ||Acute tubular necrosis |
|Tubulointerstitial nephritis |
|Vascular ||Hemolytic uremic syndrome |
|Diffuse cortical necrosis |
|Renal vein thrombosis |
|Sickle cell disease |
Sonography is the primary imaging technique for evaluation of most diseases of the renal parenchyma. Many renal disorders cause alterations in the echogenicity of the kidney parenchyma. Recognition of the normal changes in kidney echogenicity with age is essential for proper interpretation. The high concentration of glomeruli and prominent cellular volume of the neonatal renal cortex result in greater echogenicity than is typical for older children and adults. The echogenicity of the neonatal renal cortex is equal to or greater than that of the parenchyma of the liver and spleen. The medullary pyramids appear prominent and hypoechoic in the neonate, sometimes resembling dilated calyces to the unwary observer. The renal echogenicity assumes the adult pattern by about the age of 6 months, at which time the cortex is hypoechoic relative to the liver and spleen. The echogenicity of the medulla increases slightly during infancy, but remains hypoechoic to the cortex throughout life. Echogenic renal sinus fat tends to increase somewhat with age, and is scant or absent in the newborn.
The definition of acute renal failure is a sudden deterioration in renal function that results in inadequate excretion of nitrogenous wastes. Any insult that produces bilateral renal injury and failure of glomerular filtration can cause acute renal failure. Among these insults are ischemia, toxins, immunological disorders, and obstructive uropathy. In premature infants, dehydration, perinatal asphyxia, and congenital disorders are the most common causes. In older infants, severe dehydration and hemolytic uremic syndrome (HUS) are the most common precipitating events. In older children and adolescents, acute renal failure is most often due to acute glomerulonephritis (GN).1–4
Acute renal failure can be categorized according to the character of the underlying condition. Prerenal azotemia indicates inadequate perfusion of the kidneys. Obstructive uropathy or postrenal azotemia refers to obstruction to the flow of urine. Intrinsic renal failure indicates a process that involves the renal parenchyma itself.