Diagnostic Modality Efficacy for Kidney Stone Presentation
Fig. 1 (left): Ultrasound showing calculi at left ureterovesical junction
Fig. 2 (right): CT scan showing the same stone at left UVJ junction
CASE
The patient is a 70-year-old male with a past medical history of prostate cancer, esophageal cancer, and recurrent urolithiasis who is complaining of lower abdominal/pelvic pain that came on gradually in the middle of the night. The pain has been constant for the past few hours, ranked as greater than 10/10, and is described as a strong, knife-like pain. The pain started in the middle of his suprapubic area and has radiated slightly to the right. The patient tried taking oxycodone during the night to help alleviate the pain, but his pain persisted.
The patient deferred right-sided ultrasound due to an upcoming outpatient appointment with his urologist. Instead, CT scan of the abdomen without contrast was performed due to his upcoming urology appointment. The results of the CT scan showed multiple stones, each less than 10 mm in diameter, causing bilateral obstruction of the ureters and bilateral hydronephrosis. The patient’s pain was managed with oxycodone and morphine. After speaking with the urology consult in the ED, the patient declined ureteral stents and planned to follow-up with his urologist at his upcoming appointment.
Clinical Question: In a patient presenting with abdominal pain and a history of recurrent urolithiasis, is Ultrasonography the most efficacious modality to rule out urolithiasis in the setting of acute abdominal pain or is Computed Tomography (CT) indicated despite increased radiation exposure?
SUMMARY OF EVIDENCE
Patients with a history of urolithiasis undergo more CT scans than patients without a similar history. As a result, these patients are exposed to increased levels of radiation, thus increasing their risk for cancer.(4)
In a retrospective study conducted at the University of Pennsylvania, a total of 5,564 unenhanced CT examinations were performed on 4,562 patients with suspected renal colic over a 6-year period.
176 patients (4%) had three or more CT scans, 19 had six or more, and 1 patient had eighteen CT scans over this period.
All the patients with three or more CT scans had a history of nephrolithiasis as indicated at their first examination.
These statistics do not include the number of CT scans done outside the 6-year period, the number of CT scans performed for purposes other than renal colic, or the number of CT scans performed at institutions other than the testing institution.
A CT scan is the gold standard in identifying nephrolithiasis in patients. In acute management of hydronephrosis, ultrasonography is acceptable, but is not adequate for planning and determining management.(1)
Table 1. Appropriateness Criteria for Recurrent Stone Disease
A CT scan can better identify the size and location of the stone, allowing the clinician to better predict the likelihood the stone will pass on its own. Other imaging modalities such as ultrasonography, can miss smaller stones.(6)
As described in a meta-analysis in the Annals of Emergency Medicine, point-of-care ultrasound was moderately sensitive and specific in diagnosing urolithiasis when hydronephrosis was present, but much more specific when severe hydronephrosis was present.(3)
Limitations:
The individual skill and training of providers as point-of-care ultrasonography is a user-dependent skill.
Less experienced sonographers may have had difficulty in differentiating between mild and moderate hydronephrosis.
Some of the studies included in the meta-analysis had small sample sizes thus decreasing the power of the studies.
Table 2. Point-of-Care Ultrasound int he Use of Diagnosing Urolithiasis
The use of an ultrasound-first approach in the emergency department can help physicians identify hydronephrosis without the use of a CT scan. However, a lack of hydronephrosis does not rule out a ureteral stone; it simply makes a large stone (>5 mm) less likely.(5)
A prospective observational study of 302 patients suspected of renal colic underwent emergency physician (EP) ultrasound.
A finding of hydronephrosis on EP ultrasound was predictive of a ureteral stone on CT scan (PPV = 88%, LR+ 2.91)
Lack of hydronephrosis did not rule out ureteral stone (NPV = 65%)
Lack of hydronephrosis made larger stone size (>5 mm) less likely (NPV = 89%; LR- 0.39)
In a prospective study in Valencia, Spain, the use of abdominal x-rays and ultrasonography to detect stones and obstruction produced similar results to a CT scan.(7)
66 patients with acute flank pain were studied for a 4-month period. The x-rays were used only as a guide for ultrasonography.
56 of the 66 patients had confirmed renal colic.
Plain x-ray and ultrasound successfully detected calculi in 44 patients (sensitivity = 79%). CT successfully detected calculi in 52 patients (sensitivity = 93%).
Specificity for both imaging modalities was 100%.
When lithiasis was combined with obstruction, the sensitivity of both imaging techniques increased to 100%.
Table 3. Diagnostic Accuracy of Plain Film with US and CT
RECOMMENDATIONS
When presented with patients complaining of lower abdominal pain and/or renal colic, the presence of a history of urolithiasis should be determined. If the patient has a positive history, ultrasound should be used first to limit their exposure to radiation while looking for hydronephrosis.
If hydronephrosis is found on ultrasound, a CT scan can be done to identify the exact size and location of the stone. Management can then be determined.
If hydronephrosis is found on ultrasound, there is an increased chance of a large ureteral stone. Therefore, the stone is less likely to pass on its own and warrants a urology consultation.
If hydronephrosis is not found on ultrasound, a CT scan is not needed, and a small stone (<5 mm) is more likely. A small stone is more likely to pass on its own; therefore, the patient should be treated with fluids and pain management.
If hydronephrosis is not found and a stone is not seen on ultrasound, urolithiasis can be moved lower on the differential diagnoses for the patient’s lower abdominal pain.
REFERENCES
1. acr.org [Internet]. American College of Radiology ACR Appropriateness Criteria®; 2022 [cited 2022 Sep 7]. Available from: https://acsearch.acr.org/docs/69362/Narrative/.
2. Foundation ABIM. ACEP - CT of abdomen and pelvis for ED patients under 50: Choosing wisely [Internet]. Choosing Wisely | Promoting conversations between providers and patients. 2015 [cited 2022Sep22]. Available from: https://www.choosingwisely.org/clinician-lists/acep-ct-of-abdomen-and-pelvis-for-ed-patients-under-50/
3. Gottlieb, MD M, Hill, MD ED, Arno, MD, MFA K. Annals of Emergency Medicine [Internet]. Is Point-of-Care Ultrasonography Effective for the Diagnosis of Urolithiasis?; 2018 Aug 13 [cited 2022 Sep 7]. Available from: https://www.annemergmed.com/article/S0196-0644(18)30561-4/fulltext#relatedArticles
4. Katz SI, Saluja S, Brink JA, Forman HP. Radiation dose associated with unenhanced CT for suspected renal colic: impact of repetitive studies. AJR Am J Roentgenol. 2006 Apr;186(4):1120-4. doi: 10.2214/AJR.04.1838. PMID: 16554590.
5. Leo MM, Langlois BK, Pare JR, Mitchell P, Linden J, Nelson KP, Amanti C, Carmody KA. Ultrasound vs. Computed Tomography for Severity of Hydronephrosis and Its Importance in Renal Colic. West J Emerg Med. 2017 Jun;18(4):559-568. doi: 0.5811/westjem.2017.04.33119. Epub 2017 May 15. PMID: 28611874; PMCID: PMC5468059.
6. Meibom, PhD S. Home Page: Journal of the American College of Radiology [Internet]. Patient-Friendly Summary of the ACR Appropriateness Criteria Acute Onset Flank Pain—Suspicion of Stone Disease (Urolithiasis); 2018 [cited 2022 Sep 7]. Available from: https://www.jacr.org/article/S1546-1440(18)30008-5/pdf
7. Ripollés T, Agramunt M, Errando J, Martínez MJ, Coronel B, Morales M. Suspected ureteral colic: plain film and sonography vs unenhanced helical CT. A prospective study in 66 patients. Eur Radiol. 2004 Jan;14(1):129-36. doi: 10.1007/s00330-003-1924-6. Epub 2003 Jun 19. PMID: 12819916.
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