CT Versus Ultrasound for Kidney Stones
- Oct 2nd, 2014
- Stephen Alerhand
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)
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?
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
- Randomly assigned 2,759 patients (18-76 years old) to three separate treatment groups:
- Point-of-care ultrasound (POCUS)
- Formal radiology US
- CT scan
- Subsequent management at the discretion of the physician
- 30-day incidence of high-risk diagnoses
- 6-month cumulative radiation exposure
- Secondary measures: serious adverse events, pain, return ED visits, hospitalizations, diagnostic accuracy
- 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.
- 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.