DIFFUSE RENA DISEASE RENAL FAILURE
Category: Diagnostic Radiology
Abstract : DIFFUSE RENAL DISEASE AND RENAL FAILURE Most diffuse medical renal
conditions have non-specific appearances on ultrasound, the kidneys often
appearing normal in the early stages of disease. Renal failure may be acute or
chronic and its causes are numerous. If acute, an increase in overall renal size
may be observed and there may be a diffuse alteration in the renal echogenicity,
howev
DIFFUSE RENAL DISEASE AND RENAL FAILURE
Most diffuse medical renal
conditions have non-specific appearances on ultrasound, the kidneys often
appearing normal in the early stages of disease. Renal failure may be acute or
chronic and its causes are numerous.
If acute, an increase in overall renal size
may be observed and there may be a diffuse alteration in the renal echogenicity,
however this can be either hypo-or hyperechoic compared with normal. Either
increased or decreased corticomedullary differentiation may also be observed.
Although ultrasound is successful in detecting renal parenchymal disease, the
acoustic changes are not specific and the cause must usually be diagnosed
histologically, ultrasound being invaluable in directing the biopsy procedure.
In chronic renal failure the kidneys shrink and the cortex thins. The end-stage
kidney can be quite tiny and hyperechoic and may be difficult to differentiate
from the surrounding tissues. Depending on the cause, either one but generally
both of the kidneys are affected.
Acute tubular necrosis
Acute tubular
necrosis is the result of ischaemia, which destroys the tubules of the kidney,
resulting in acute renal failure. It occurs when there is a sudden decrease in
renal perfusion as a result of a severely hypotensive episode, for example,
cardiac arrest, massive haemorrhage, drug toxicity or septicaemia. Patients are
treated temporarily by dialysis. Tubular damage is capable of regeneration once
the blood supply and perfusion pressure return to normal, reversing the renal
failure. If suspected, it is useful to perform a biopsy to determine the cause
of renal failure, in order to plan further management. On ultrasound the kidneys
are normal in size or slightly enlarged. They may be completely normal in
appearance, a not uncommon finding, although in some cases the echogenicity is
altered, sometimes having a hyperechoic cortex with increased corticomedullary
differentiation. Spectral Doppler can be normal or demonstrate increased
arterial resistance with reduced or even reversed end diastolic
flow.
Glomerulonephritis
Glomerulonephritis is an inflammatory
condition which affects the glomeruli of the kidney. It may be either acute or
chronic, and frequently follows prolonged infection. Patients may present in
acute renal failure, with oliguria or anuria, or with features of nephrotic
syndrome such as oedema, proteinuria and hypoalbuminaemia. Depending upon
aetiology, acute renal failure may be reversible or may progress to chronic
renal failure requiring dialysis.
Glomerulonephritis can be caused by
numerous mechanisms:
● Immunologic mechanisms, for example in systemic lupus
erythematosus (SLE) or acquired immune deficiency syndrome (AIDS)
● Metabolic
disorders, for example diabetes
● Circulatory disturbances, for example
atherosclerosis or disseminated intravascular coagulation (DIC).
As with
acute tubular necrosis, the ultrasound appearances are non-specific. In the
acute stages the kidneys may be slightly enlarged; changes in the echogenicity
of the cortex may be observed. In the chronic stages the kidneys shrink, become
hyperechoic, lose cortical thickness and have increased corticomedullary
differentiation.
Medullary sponge kidney
In medullary sponge kidney
the distal tubules, which lie in the medullary pyramids, dilate. This may be due
to a developmental anomaly but this is not certain. In itself it is usually
asymptomatic and therefore rarely seen on ultrasound. However, the condition is
prone to nephrocalcinosis, particularly at the outer edges of the pyramids, and
stone formation, which may cause pain and haematuria.
Amyloid
In
amyloid disease, excess protein is deposited in the renal parenchyma,
predominantly the cortex. This causes proteinuria and may progress to nephrotic
syndrome (oedema, proteinuria and hypoalbuminaemia). Amyloidosis can cause acute
renal failure and is particularly associated with long-standing rheumatoid
arthritis. As with other diffuse renal diseases, the acute stage may cause renal
enlargement and the parenchyma tends to be diffusely hyperechoic. By the time
the chronic stage of disease has been reached, the kidneys become shrunken and
hyperechoic, in keeping with all end-stage appearances.
The renal
biopsy
Biopsy is rarely merited in endstage renal failure, as the only
treatment is dialysis or renal transplantation. Small kidneys, below 8 cm in
length therefore, are almost never subjected to biopsy. Histology is required
when the kidney is potentially curable, such as in cases of acute disease, or
when a specific knowledge of aetiology is paramount.
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