CT Versus Ultrasound for Kidney Stones

 Author: Stephen Alerhand, MD (EM Resident Physician, Icahn School of Medicine at Mount Sinai) // Edited by: Alex Koyfman, MD (@EMHighAK, EM Attending Physician, UTSW / Parkland Memorial Hospital)

Case History

27 year-old female presents to the ED with her husband on an extremely busy overnight shift. She complains of new left flank pain that began earlier that afternoon. It is sharp, intermittent, worse with movement, and radiates to her groin. On exam, she is sitting up in the stretcher, clutching her left flank, and squirming uncomfortably in pain.

You suspect a kidney stone. Upon hearing this, the patient states that she does not want to be exposed to any radiation, as she is trying to get pregnant. After treating the patient’s pain, how will you proceed in confirming your diagnosis?

Background

Classically, kidney stones are diagnosed by abdominal CT scan. However, this test makes the patient wait her turn for the CT scan, sends her down the hall to Radiology and thus away from physicians/nurses, and exposes her abdomen to the side effects of ionizing radiation.

So what now?

US vs. CT for Kidney Stones

Smith-Bindman, R et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med. 2014 Sept 18;371(12):1100-10.

Type of Study

  • Multi-center, comparative effectiveness trial

Methods

  • Randomly assigned 2,759 patients (18-76 years old) to three separate treatment groups:
    1. Point-of-care ultrasound (POCUS)
    2. Formal radiology US
    3. CT scan
  • Subsequent management at the discretion of the physician

Outcomes Measures

  • 30-day incidence of high-risk diagnoses
  • 6-month cumulative radiation exposure
  • Secondary measures: serious adverse events, pain, return ED visits, hospitalizations, diagnostic accuracy

Results

  • Incidence of high-risk diagnoses in first 30 days was 0.4% and did not vary by imaging method.
  • Mean 6-month cumulative radiation exposure was significantly lower in US groups than in CT group.
  • Serious adverse events: 12.4% in POCUS group, 10.8% in US group, 11.2% in CT group. No statistical significance.
  • By 7 days, average pain score was similar in each group, with no statistically significant difference.
  • No statistical difference in return ED visits, hospitalizations, and diagnostic accuracy.

Conclusions

  • Initial US associated with lower cumulative radiation exposure than CT, without significant differences in high-risk diagnoses, serious adverse events, pain scores, return ED visits, or hospitalizations.
  • Patient work-up should at least start with a POCUS, and progress further based on physician discretion.
  • Less inclination for ordering a CT on patients with past history of stones (higher sensitivity but not necessarily improved outcomes).
  • Shorter length of stay with POCUS compared with both CT scan and formal US groups.

POCUS of the Kidneys

  • Stones appear hyperechoic, vary from 1-10 mm, and cast a prominent shadow.
  • However, one must usually rely on finding unilateral hydronephrosis on the side of pain.
    • Urine back-up into the renal pelvis 2/2 to obstruction of the ureter, bladder, or urethra
    • More pronounced after administering IVF
    • Degree of hydronephrosis associated with proportional increase in stone size and likelihood of stone passage
    • Hyperechoic: renal parenchyma. Hypoechoic: dilated renal pelvis.
us1
Normal
us2
Mild-to-moderate
Moderate
Moderate
Severe
Severe
Hydronephrosis with stones
Hydronephrosis with stones

4 thoughts on “CT Versus Ultrasound for Kidney Stones”

  1. no doubt ultrasound has its utility in diagnosis of kidney stone. i find i’ll use it in patients with a known history of kidney stones, who say this feels just like prior stones, and they’ve had a number of CTs in their past. in those patients, if I can get a u/s that shows no severe hydronephrosis, a normal WBC, a normal Cr, and a urine with blood but no infection, then i’m a happy man. the patient then has a high likelihood of having a stone, and its a stone that will likely pass on its own, even if I can’t usually identify the actual stone, its size, or its location within the ureter.

    in younger, low risk populations it works. in older, comorbid, higher risk patients, I don’t find the u/s to be useful. in patients where kidney stone is in the differential, but there also other very viable alternative diagnoses like appendicitis, AAA, diverticulitis, etc, then I don’t find the renal specific u/s is going to help me. I concede that I could find a AAA or appendicits with ultrasound (AAA >> than appendicits) but in general, these patients are going to get a CT. you also need to take into context if they are febrile or toxic looking. an obstructing septic stone is something I’m going to want radiographic evidence of. an ultrasound is unlikely to give me that.

    radiation exposure needs to be considered in all patients. a non-contrast renal stone protocol CT does have the advantage of eliminating allergic reaction and renal toxicity from the equation. it will show other potential pathologies.

    from my standpoint, i think its important for physicians to have a good handle of all the tools at their disposal, and when its most appropriate to use each tool. its important to know that ultrasound can help you in a very select population of renal stone patients. but at this stage of the game, I’m still more likely to get a CT over ultrasound in possible kidney stone patients.

  2. no doubt ultrasound has its utility in diagnosis of kidney stone. i find i’ll use it in patients with a known history of kidney stones, who say this feels just like prior stones, and they’ve had a number of CTs in their past. in those patients, if I can get a u/s that shows no severe hydronephrosis, a normal WBC, a normal Cr, and a urine with blood but no infection, then i’m a happy man. the patient then has a high likelihood of having a stone, and its a stone that will likely pass on its own, even if I can’t usually identify the actual stone, its size, or its location within the ureter.

    in younger, low risk populations it works. in older, comorbid, higher risk patients, I don’t find the u/s to be useful. in patients where kidney stone is in the differential, but there also other very viable alternative diagnoses like appendicitis, AAA, diverticulitis, etc, then I don’t find the renal specific u/s is going to help me. I concede that I could find a AAA or appendicits with ultrasound (AAA >> than appendicits) but in general, these patients are going to get a CT. you also need to take into context if they are febrile or toxic looking. an obstructing septic stone is something I’m going to want radiographic evidence of. an ultrasound is unlikely to give me that.

    radiation exposure needs to be considered in all patients. a non-contrast renal stone protocol CT does have the advantage of eliminating allergic reaction and renal toxicity from the equation. it will show other potential pathologies.

    from my standpoint, i think its important for physicians to have a good handle of all the tools at their disposal, and when its most appropriate to use each tool. its important to know that ultrasound can help you in a very select population of renal stone patients. but at this stage of the game, I’m still more likely to get a CT over ultrasound in possible kidney stone patients.

  3. All outstanding points–thank you for the comments.

    To add, once you do in fact get the CT…Stones beyond 5 mm in size have shown a progressively longer time for passage, as well as a progressively decreased likelihood of spontaneous passage without intervention. Same goes for those located proximally in the ureter.

    Miller OF, Kane, KJ. Time to stone passage for observed ureteral calculi: a guide for patient education. J Urol. 1999 Sep;162(3 Pt 1):688-90; discussion 690-1.

    Coll DM, Varanelli MJ, Smith RC. Relationship of spontaneous passage of ureteral calculi to stone size and location as revealed by unenhanced helical CT. AJR Am J Roentgenol. 2002 Jan;178(1):101-3.

  4. All outstanding points–thank you for the comments.

    To add, once you do in fact get the CT…Stones beyond 5 mm in size have shown a progressively longer time for passage, as well as a progressively decreased likelihood of spontaneous passage without intervention. Same goes for those located proximally in the ureter.

    Miller OF, Kane, KJ. Time to stone passage for observed ureteral calculi: a guide for patient education. J Urol. 1999 Sep;162(3 Pt 1):688-90; discussion 690-1.

    Coll DM, Varanelli MJ, Smith RC. Relationship of spontaneous passage of ureteral calculi to stone size and location as revealed by unenhanced helical CT. AJR Am J Roentgenol. 2002 Jan;178(1):101-3.

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