Point-of-care ultrasound by emergency physicians for direct ureteral stone detection: a case series and review of the literature

Nadav Granat; Evan Avraham Alpert

doi:10.15441/ceem.23.096

Clin Exp Emerg Med > Volume 11(2); 2024 > Article

Granat and Alpert: Point-of-care ultrasound by emergency physicians for direct ureteral stone detection: a case series and review of the literature

Case Report

Clin Exp Emerg Med 2024; 11(2): 218-223.

Published online: January 29, 2024

DOI: https://doi.org/10.15441/ceem.23.096

Point-of-care ultrasound by emergency physicians for direct ureteral stone detection: a case series and review of the literature

Nadav Granat^1,²

, Evan Avraham Alpert^3,⁴

¹Department of Emergency Medicine, Rabin Medical Center, Petah Tikva, Israel

²Department of Diagnostic Ultrasound, Hasharon Hospital, Rabin Medical Center, Petah Tikva, Israel

³Department of Emergency Medicine, Hadassah Medical Center-Ein Kerem, Jerusalem, Israel

⁴Faculty of Medicine, Hebrew University of Jerusalem, Israel

Correspondence to: Evan Avraham Alpert Department of Emergency Medicine, Hadassah Medical Center-Ein Kerem, Kalman Ya'akov Man St, Jerusalem 91120, Israel Email: Evanavrahamalpert@gmail.com

Received: July 24, 2023 Revised: September 12, 2023 Accepted: September 23, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/).

Abstract

Symptomatic urolithiasis is a common cause of emergency department visits, with noncontrast computed tomography considered the imaging gold standard. According to the current guidelines, point-of-care ultrasound (POCUS) is limited to evaluating hydronephrosis as a secondary sign of acute ureteral stones. However, the use of POCUS to detect ureteral stones may lead to decreased radiation to the patient and a more rapid diagnosis. This case series describes 10 patients with suspected symptomatic urolithiasis who were diagnosed accurately by emergency physicians using POCUS to detect obstructive ureteral stones. In three of the cases, POCUS significantly changed the patient's management. This article also describes the proper techniques for the emergency physician to learn to master POCUS for ureteral stone detection.

Keywords: Ultrasonography; Point-of-care ultrasound; Emergency departments; Kidney calculi; Case reports

Capsule Summary

What is already known

Symptomatic urolithiasis is a common cause of emergency department (ED) visits, with noncontrast computed tomography considered the imaging gold standard. POCUS is limited to evaluating hydronephrosis as a secondary sign of acute ureteral stones. However, this is not very sensitive or specific for accurate direct identification of ureteral stones.

What is new in the current study

An emergency physician with a strong background in POCUS can easily learn how to detect ureteral stones, which may lead to a more rapid diagnosis, decreased ED length of stay, and reduced exposure to radiation. When performing POCUS for urolithiasis, the emergency physician should focus on the sites with the highest possibility of ureteral stones: the ureterovesical junction, proximal-mid ureter, ureteropelvic junction, and distal ureter. To identify stones, one should look for a round or oval hyperechoic structure located within the ureter that exhibits an acoustic shadow or a twinkling artifact. Color Doppler should be used to improve the sensitivity of stone detection.

INTRODUCTION

Symptomatic urolithiasis is one of the most common causes of emergency department (ED) visits in the United States [1]. Noncontrast computed tomography (NCCT) scanning has been considered the imaging gold standard [2]. Performing NCCT in the workup for suspected urolithiasis has increased significantly in the last decades (up to 85%–90% of patients with a new diagnosis of urolithiasis in the United States in 2007–2015) [3]. However, it has several disadvantages including exposure to ionizing radiation [4] and an association with a high rate of incidental findings [5]. Moreover, the increase in CT use was not found to be associated with improved patient outcomes [6].

Point-of-care ultrasound (POCUS) is also well-investigated in the workup for suspected urolithiasis in the ED. Like other POCUS applications, it can potentially shorten ED length of stay and decrease radiation exposure [7]. Nevertheless, it has one major disadvantage. According to the current guidelines, POCUS, as opposed to radiology-performed ultrasonography, is limited to evaluating hydronephrosis as a secondary sign of acute ureteral stone obstruction [8]. Unfortunately, a comprehensive meta-analysis showed that hydronephrosis is neither sensitive nor specific as an indicator for nephrolithiasis [9]. There is a paucity of literature on the use of POCUS by emergency physicians (EPs) to directly identify obstructive ureteral stones [10].

The following is a case series of 10 patients with suspected symptomatic urolithiasis who were diagnosed accurately by EPs using POCUS to detect obstructive ureteral stones (Table 1). All cases (except one involving a pregnant woman) were eventually confirmed by NCCT or radiology-performed ultrasonography. Three of the cases in which POCUS significantly changed the patient's management are described in detail. The POCUS technique used to detect ureteral stones is described and the relevant literature is reviewed.

This was a descriptive retrospective case series of ED patients with ureteral stones reporting to Rabin Medical Center (Petah Tikva, Israel), a tertiary care medical center that sees more than 100,000 adults annually. The images were obtained from the LOGIQ e (GE Healthcare) and CX50 (Philips) using a curvilinear probe. All POCUS images were either obtained or supervised by the first author (NG), who is an EP.

CASE REPORTS

Case 1

A 67-year-old female patient with a past medical history (PMH) of diabetes mellitus, hypertension, and morbid obesity presented to the ED with 3 days of right lower quadrant (RLQ) pain that radiated to the groin, rigors, vomiting, and constipation. Physical examination revealed RLQ and right flank tenderness. Her laboratory tests revealed leukocytosis (18,000 white blood cells/µL), elevated C-reactive protein (12 mg/dL), and elevated creatinine (1.2 mg/dL compared to a baseline of 0.7 mg/dL).

POCUS performed by an EP demonstrated a large hyperechoic stone (10 mm) at the ureteropelvic junction (UPJ) with moderate secondary hydronephrosis (Fig. 1A). Based on the POCUS findings and clinical evidence of sepsis, the patient urgently received intravenous (IV) antibiotic treatment, urologic consultation, and an NCCT (Fig. 1B), which confirmed the diagnosis. The patient underwent a right nephrostomy that drained infected urine. After 5 days of hospitalization for IV antibiotics, the patient was discharged for ambulatory stone removal.

Case 2

A 27-year-old healthy female patient, with no PMH, presented to the ED with a complaint of 2 weeks of intermittent RLQ pain radiating to the groin, worsening with flexion of the thigh. Laboratory tests were normal. The ultrasound performed by an experienced radiologist did not reveal hydronephrosis or ureteral stones. After improvement due to analgesia, the patient was released.

Twenty hours later, the patient returned to the ED for worsening pain. Physical examination revealed right flank tenderness. POCUS performed by an EP demonstrated moderate hydronephrosis and a right distal ureteral stone (8 mm) with twinkling artifact (Fig. 2). This prompted the second ultrasound performed by the same experienced radiologist, which confirmed the POCUS findings. After analgesia and repeated normal laboratory tests, the patient was released for ambulatory urologic follow-up. An unnecessary NCCT was avoided.

Case 3

A 31-year-old female patient in her 29th week of gestation, with a PMH of diabetes mellitus, hypertension, and recurrent urinary tract infection, presented to the ED with left flank pain and dysuria for 2 days. Symptoms resolved after analgesics administration. Her physical examination was absent for flank tenderness. Laboratory tests were unremarkable, except for urinalysis with 75 leukocytes per high-power field. Ultrasound performed by a radiologist revealed moderate left hydronephrosis but did not detect a ureteral stone. One hour later, POCUS demonstrated hydronephrosis and a mid-size (6 mm) left distal ureteral stone with twinkling artifact (Fig. 3). Based on the POCUS findings, the patient was admitted for observation and IV antibiotics. After hospitalization for 2 days, her pain resolved, and she was released for ambulatory urologic follow-up.

Ethics statement

The study was approved by the Institutional Review Board of the Rabin Medical Center (No.0211-19-RMC). Informed consent was waived due to the retrospective nature of the study.

DISCUSSION

This article describes 10 cases of ureteral stones identified by EPs using POCUS. The variety of cases depicts stone detection in different levels of the ureter. In some of these cases, early identification of renal stones in septic patients enabled a more rapid urgent treatment, such as IV antibiotics and nephrostomy insertion (cases 1 and 5), whereas in other cases radiation was avoided (cases 2 and 3).

When performing POCUS for direct detection of ureteral stones, the EP should focus on the sites with the highest possibility of ureteral stones. The ureterovesical junction (UVJ) contains 30% to 60%, whereas the proximal-mid ureter contains 30% to 40% of ureteral stones. Less commonly, stones are found at the distal ureter (5%–15%), UPJ (3%–10%), and ureter-external iliac vessels (1%–2%) [11–14]. Additionally, the EP must recognize several features that identify ureteral stones. Classically they are a round or oval hyperechoic structure located within the ureter that exhibits an acoustic shadow. A twinkling artifact is essentially machine noise seen with color Doppler. A stone appears as a focus of alternating colors on Doppler signal behind a hyperechoic object (such as calculi), which gives the appearance of turbulent blood flow. A color comet-tail artifact may be associated with this finding [15].

Several tips are essential for the EP to successfully identify ureteral stones. First, a curvilinear transducer should be used. One should decrease the gain to make the stones more prominent. One should use the color Doppler even when there is not a clear sign of a stone in the grayscale to improve stone detection sensitivity [16,17].

Our method to identify ureteral stones is to first obtain the bladder view to detect stones located in the UVJ. Moderate bladder volume (100–150 mL) is ideal for optimizing stone detection rate, especially at the UVJ, as was demonstrated in NCCT [18].

The second step involves sliding the probe at an oblique angle along the distal ureter, as much as possible (this is the most challenging part because of air shadowing from distal ileum bowel loops). Then one moves the probe proximal to the kidney looking for UPJ stones. For the last step, the user must slide the probe along the proximal-mid ureter along the psoas muscle by a frontal or lateral approach. To improve the stone detection rate in this step, a graded compression method should be used, as for appendicitis detection, to reduce the distance between the transducer and ureter [19].

In the radiology literature, ultrasound for identification of ureteral stones is very specific (≤95%). Sensitivity is variable depending on the study. In a meta-analysis from 2010 [20], the average sensitivity was 45%, but more recent studies [16,17] using color Doppler to identify a twinkling artifact showed sensitivities greater than 90%. Abdel-Gawad et al. [19] in a large prospective study, demonstrated a sensitivity of 97% compared to NCCT.

To our knowledge, only one small, prospective, recently published study investigated the use of POCUS by EPs to directly identify obstructive ureteral stones. Bourcier et al. [10] demonstrated in a group of 103 patients that, while EPs had an accuracy of POCUS of 91% for detecting urinary tract dilatation, they had only a 54% accuracy for directly detecting kidney stones. Along with study strengths, such as the methodologic design, there are a few limitations, including a relatively small population from a single small emergency unit (19,000 visits per year) as well as highly demanding criteria for POCUS performers, including a 5-day theoretical and practical training course at a certified center along with 18 months of follow-up e-learning.

This study has several limitations. As with all POCUS applications, the accuracy is operator dependent. There is also a learning curve for any new ultrasound technique. In addition, ultrasound may overestimate stone size (≤2 mm), a finding that may have implications for nonemergent stone management [20]. Some stones may not be localized by ultrasound and a NCCT will need to be performed even in the hands of an expert emergency medicine sonographer. Of the 10 patients with ureteral stones identified via POCUS, seven underwent NCCT scans. A comparison between the two imaging modalities was not feasible since neither the ED length of stay, nor the ultrasound scan duration for each patient was assessed.

In conclusion, POCUS in the hands of the EP has the potential to directly identify ureteral stones. While this may lead to a more rapid and accurate diagnosis, which can be time-critical in unstable patients, particularly in crucial situations like sepsis due to an obstructed stone, its full impact on ED length of stay and reducing ionizing radiation from additional NCCT remains to be thoroughly assessed. Further, in-depth prospective studies among EPs would be beneficial to better understand the learning curve, accuracy, and broader clinical context of employing POCUS for the detection of ureteral stones.

NOTES

Author contributions

Conceptualization: NG; Formal analysis: all authors; Visualization: NG; Writing–original draft: all authors; Writing–review & editing: all authors. All authors read and approved the final manuscript.

Conflicts of interest

The authors have no conflicts of interest to declare.

Funding

The authors received no financial support for this study.

Data availability

Data sharing is not applicable as no new data were created or analyzed in this study.

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Fig. 1.

Images of case 1. (A) Longitudinal sonogram of the right kidney demonstrating moderate hydronephrosis as well as elongated echogenic stone with acoustic shadow in the ureteropelvic junction (arrow). (B) Noncontrast computed tomography axial view demonstrating moderate hydronephrosis with an obstructive hyperdense elongated stone at the ureteropelvic junction (arrow).

Fig. 2.

Images of case 2. (A) Longitudinal sonogram of the right kidney demonstrating moderate hydronephrosis. (B) Transverse sonogram of the bladder demonstrating right distal ureter echogenic stone (arrow) with acoustic shadow. (C) Color Doppler, demonstrating the sonographic twinkling comet-tail artifact around the echogenic stone.

Fig. 3.

Images of case 3. (A) Longitudinal sonogram of the left kidney demonstrating moderate hydronephrosis. (B) Transverse sonogram of the bladder, using low gain, demonstrating left distal ureter echogenic stone (arrow) with acoustic shadow. (C) Color Doppler, demonstrating the sonographic twinkling artifact around the echogenic stone (arrow).

Table 1.

Ten cases of renal stones identified by POCUS performed by an emergency physician

Case no.	Age (yr)	Sex	Medical history	Symptoms, signs and relevant lab tests	Stone location (stone size)	Confirmatory imaging (stone size)	Management
1^a)	67	Female	COPD, obesity, DM, HTN	RLQ pain and tenderness	UPJ (10 mm)	NCCT (10 mm)	Admission for emergent nephrostomy and IV ABX
				Right flank tenderness
				Leukocytosis and elevated CRP
2^a)	27	Female	None	Second ED visit in 24 hr	Distal ureter (8 mm)	Repeated radiology-performed US (8 mm)	Discharged for urology follow-up
				RLQ pain radiate to right groin
				US performed by radiologist in first visit: no hydronephrosis or stones
3^a)	31	Female	29 wk pregnancy (G4P3), DM, HTN, recurrent UTI	Left flank pain and dysuria	Distal ureter (5 mm)	None	Admission for IV ABX in high risk obstetric department
				Leukocytosis			Discharge after clinical and laboratory improvement
				Transient microhematuria
4^a)	44	Male	None	Syncope preceding left back and flank pain radiates to left leg and vomiting	Proximal-mid ureter (5.5 mm)	NCCT (5.5 mm)	Discharged for urology follow-up
5^a)	46	Male	HIV, COPD, sarcoidosis, asymptomatic left nephrolithiasis	RLQ pain radiates to right groin and dysuria	UVJ (6 mm)	NCCT (4.5 mm)	Admission for IV ABX in urology department nephrostomy 24 hr later due to fever 38 °C
5^a)	46	Male	HIV, COPD, sarcoidosis, asymptomatic left nephrolithiasis	Elevated CRP	UVJ (6 mm)	NCCT (4.5 mm)
6^a)	20	Female	None	Left flank pain and vomiting 1 wk after dysuria	Proximal ureter (7 mm)	NCCT 1 day later (6 mm)	Admission for DJ ureteral stent insertion
7	31	Male	Urolithiasis	Right flank pain	Proximal ureter (5 mm)	NCCT 1 day later (4 mm)	Discharged for urology follow-up
8^a)	42	Male	Urolithiasis, status post sleeve gastrectomy	Left flank pain radiate to LLQ	Mid ureter (12 mm)	NCCT (12 mm)	Admission for DJ ureteral stent insertion
9	31	Female	None	Right flank and RLQ pain	UVJ (5 mm)	Radiology-performed US (4 mm)	Discharge for urology follow-up
10	54	Male	Recurrent urolithiasis, DM	Left flank pain, dysuria, and nausea	UVJ (6 mm)	NCCT (7 mm)	Discharge for urology follow-up

POCUS, point-of-care ultrasound; COPD, chronic obstructive pulmonary disease; DM, diabetes mellitus; HTN, hypertension; RLQ, right lower quadrant; CRP, C-reactive protein; UPJ, ureteropelvic junction; NCCT, noncontrast computed tomography; IV, intravenous; ABX, antibiotics; ED, emergency department; US, ultrasound; G, gravidity; P, parity; UTI, urinary tract infection; UVJ, ureterovesical junction; DJ, double J; LLQ, left lower quadrant.

^a) Cases in which POCUS changed the patient management.