Renal tract calculi (summary)
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This is a basic article for medical students and other non-radiologists
Renal tract calculi, also known as urolithiasis, refer to renal stone formation at any point along the renal tract (from kidneys to bladder and urethra).
- presentation between 30 and 60 years
- incidence 5% (female), 12% (male)
- hematuria (absent in ~15%)
- composition varies (calcium oxalate/phosphate 75%)
- size varies (gravel to staghorn)
- risk factors
- congenital, e.g. urinary tract malformation
- metabolic, e.g. hypercalciuria
- acquired, e.g. dehydration, UIT
- 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
- 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
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 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.
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.