This is a basic article for medical students and other non-radiologists
The term renal tract calculi, or, more correctly, urinary tract calculi or urolithiasis, refers to the presence of stones in the kidneys, ureters, bladder or urethra.
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Reference article
This is a summary article; read more in our article on urolithiasis.
Summary
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epidemiology
presentation between 30 and 60 years
incidence 5% (female), 12% (male)
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presentation
pain
hematuria (absent in ~15%)
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pathophysiology
composition varies (calcium oxalate/phosphate 75%)
size varies (gravel to staghorn)
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risk factors
congenital, e.g. urinary tract malformation
metabolic, e.g. hypercalciuria
acquired, e.g. dehydration, UIT
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investigation
US used to assess whether there is upper tract dilatation
CT (non-contrast) accurately depicts size and location of stones
AXR may be used for follow-up
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treatment
depends on location and size
if a stone is smaller than 4 mm, 90% will pass spontaneously
analgesia and hydration
Role of imaging
identify renal tract calculi
identify and grade renal tract obstruction
identify any secondary complications of obstruction
Radiographic features
In the context of hematuria, renal colic and suspicion of renal tract stone, the decision about any investigation will depend on local protocol. The dose associated with CT may mean that ultrasound examination to exclude hydronephrosis is a preferred option.
Ultrasound
Ultrasound may be used in the acute setting to determine whether there is any evidence of hydronephrosis. If there is no hydronephrosis in a patient who is symptomatic, it is unlikely that there is a calculus that will not pass spontaneously.
Ultrasound is a good tool for ruling out hydronephrosis. However, assessment of the renal tract in more detail (the ability to assess the ureter along its length) is very dependent on patient body habitus.
CT (non-contrast)
Non-contrast CT of the kidneys, ureters and bladder is a quick and simple test that can be used to identify and locate calculi within the renal tract. The problem with using CT (especially in young patients and those of child-bearing potential) is the radiation dose associated with the test.