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Urogenital Imaging

Radiation nephritis

the result of the kidneys being included within a therapeutic field of radiation beyond a certain dose. Other sources of radiation, such as radioactive isotopes, diagnostic X-rays, and atomic explosions have not been shown to produce this abnormality in humans. Pathologically, all elements of renal tissue are affected. Interstitial fibrosis, tubule atrophy, glomerular sclerosis, sclerosis of arteries of all sizes, hyalinization of afferent arterioles and thickening of the renal capsule are present in varying degrees. The radiation field determines the amount of tissue involved. Radiation nephritis is usually limited to one kidney; however both may be involved under appropriate conditions. The threshold dose for the induction of nephritis appears to be 2300 rads administered over a 5-week period.

Clinically, both acute and chronic forms have been described. The chronic form may follow a period of clinically apparent acute disease or may appear de novo without any prior evidence of radiation-induced renal disease. This often occurs at a later time, perhaps 2 years or more after the initial exposure to radiation. Radiation nephritis is associated with anaemia, proteinuria, hypothermia and azotemia. Granular epithelial and hyaline casts are seen in the urinary sediment. Moderate to malignant hypertension is present in half of the patients; this may be due to reninangiotensin factors. In many respects the clinical picture is similar to that of chronic glomerulonephritis. However, radiation nephritis may be compatible with long life, even in the presence of a progressive reduction in renal size. Deterioration of renal function and clinical findings are most likely related to glomerular damage. The basic mediating factor in the pathogenesis of this disease is radiation-induced damage to the small vessels of the kidney.

There is nothing specific about the intravenous urography (IVU), ultrasound and CT appearance of the kidney in radiation nephritis. IVU may show decreased excretion of contrast, atrophy of the portion of kidney in the radiation portal. In unilateral disease, the same radiological abnormalities of ischaemia seen in renal artery stenosis may also be present (see renal artery stenosis). The contralateral kidney is likely to undergo compensatory hypertrophy particularly when radiation nephritis develops in younger patients. Depending on the size and shape of the radiation field, both kidneys may be involved. In some patients, renal size remains normal, in others the kidney becomes extremely small. A smooth contour and normal pelvicalyceal system is seen. Atrophy is limited to those portions of the kidney involved in the radiation field.

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