Ureteral calculi are highly prevalent worldwide. Due to the high probability of spontaneous passage for stones smaller than 10 mm, conservative treatment is widely recommended by physicians and preferred by patients. Medications such as alpha-adrenergic receptor blockers can alleviate ureteral colic, expedite ureteric stone passage, and prevent ureteral obstruction [7]. However, spontaneous stone passage can be time-consuming.Moreover, in populations affected by ureteral calculi, the proportion of middle-aged and elderly individuals is as high as 76.2%, with a higher prevalence of comorbidities such as hypertension, diabetes, and cardiovascular diseases [1]. The conservative treatment process for stones is associated with a decreased quality of life, an increased risk of infection, and an elevated risk of cardiovascular emergencies [8]. Therefore, relying solely on stone size is insufficient to determine the safety of conservative treatment.

There is an urgent need in clinical practice for accurate methods to assess the risk of spontaneous stone passage, thereby reducing the risk of complications associated with ureteral stones. Non-contrast computed tomography (NCCT) is considered the gold standard for diagnosing urolithiasis [11]. Although CT provides accurate diagnoses, it is worth noting that in the United States, approximately one-third of CT scans are performed without medical necessity. The ionizing radiation generated by CT scans is increasingly recognized as a public health concern [9].

In recent years, ultrasonography has gained widespread use as a simple, repeatable, and non-invasive imaging technique in the diagnosis of urological conditions. By utilizing grayscale imaging and techniques such as the visualization of stone “twinkling artifacts,” ultrasonography can provide ureteral stone-related information that exhibits a high degree of consistency with CT and other imaging modalities [4, 5]. In this retrospective cohort study, the ultrasonographic measurements of ureteral stone longitudinal diameter and location showed good consistency with CT parameters. The ultrasonographic measurements of ureteral stone longitudinal diameter, stone location, and UJF on the affected side are identified as independent risk factors for the spontaneous passage outcome of ureteral stones. Constructing a predictive model based on these three ultrasound variables can accurately assess the risk of failed spontaneous stone passage.

Currently, clinical decisions regarding ureteral stones primarily rely on size, with stones larger than 10 mm typically requiring invasive interventions such as extracorporeal shock wave lithotripsy or surgery, while stones smaller than 10 mm are often manageable through conservative treatment [10, 11]. Stone size significantly influences the likelihood of spontaneous passage, with stones smaller than 5 mm demonstrating a spontaneous passage rate of 75-89% [12]. This study demonstrates that patients in the failed spontaneous stone passage group had significantly larger ultrasonographically measured stone longitudinal diameters compared to the successful group, indicating it as an independent risk factor for failed spontaneous passage. Similarly, stone location plays a significant role in spontaneous passage outcomes [13, 14], with stones located in the lower ureter having a higher likelihood of passing spontaneously. The successful spontaneous passage group in this study had a significantly higher proportion of lower ureteral stones compared to the failed group.

Previous studies have shown that a history of ureteral stone disease is unfavorable for spontaneous passage due to the increased risk of ureteral injury [15]. Additionally, the maximum thickness of the adjacent ureteral wall is significantly associated with stone impaction [16, 17], highlighting the impact of structural and functional changes in the affected ureter on stone passage prognosis. Acquiring accurate structural information of the ureter through ultrasonography poses challenges. However, by continuously monitoring the ureterovesical junction for the ureteral jet phenomenon, changes in ureteral function can be accurately assessed using parameters such as UJF and peak flow velocity. Structural and functional impairments of the ureter, caused by factors such as congenital obstruction, stone presence, or inflammation, lead to increased pressure in the renal pelvis and ureter, reduced peristaltic function, and a decrease in the ureteral jet phenomenon. In cases of complete obstruction, the ureteral jet phenomenon may be completely absent [18, 19]. Jandaghi et al. [20] found that a UJF of less than 1.5 jets per minute can serve as a reasonable cutoff point for suspected ureteral obstruction in patients with urinary tract stones (with a sensitivity of 97.8% and specificity of 87%). Consistent with their findings, this study identifies an affected side UJF of less than 1.5 jets per minute as an independent risk factor for failed spontaneous passage of ureteral stones. A lower UJF indicates severe ureteral dysfunction, an increased risk of stone impaction, and diminishes the likelihood of spontaneous stone passage.

Unlike the existing risk models that primarily utilize CT variables, such as maximum ureteral wall thickness, to predict the spontaneous passage and risk of impaction of ureteral stones [16, 17], this study employed ultrasound-related variables to construct a nomogram. By incorporating stone longitudinal diameter, stone location, and UJF as ultrasound parameters, this predictive model utilizes information from both the stone itself and the affected ureteral function, enabling an accurate assessment of the risk of spontaneous stone passage. The model demonstrates good clinical utility and strong interpretability of the ultrasound-related parameters. Although CT is considered the gold standard for diagnosing urolithiasis [11], ultrasound information regarding ureteral stones is more easily accessible for primary healthcare facilities and remote areas. For the primary healthcare institutions, doctors can preliminarily assess patients’ stone conditions quickly and affordably through ultrasound examinations, enabling them to devise rational and personalized treatment plans, thereby reducing unnecessary referrals and medical costs. For patients with low risk of failed spontaneous passage, they can be encouraged to adopt conservative treatment to facilitate the natural excretion of stones. The predictive model proposed in this study can provide feasible alternative solutions for remote areas with relatively scarce medical resources. Local healthcare providers can analyze ultrasound parameters based on the study’s findings to conduct initial assessments of patients’ conditions. Additionally, through remote ultrasound image transmission technology, experts can offer consultations based on this study’s conclusions, providing remote healthcare advice to patients in remote areas, thereby reducing the inconvenience and burden of travel for medical treatment. Moreover, ultrasound is radiation-free, cost-effective, easily obtainable, suitable for follow-up, and more applicable to populations such as pregnant women and children. Furthermore, the nomogram presents the predictive results in an intuitive manner, making it easily applicable in clinical practice. Therefore, it serves as an indispensable tool for clinical decision-making, allowing surgeons and patients to make better treatment choices based on this readily available scoring tool. However, this study has certain limitations. It is a retrospective cohort study conducted in a single center, and the conclusions need to be validated and optimized through multicenter prospective cohort studies.

In summary, this retrospective cohort study demonstrates that constructing a predictive model based on ultrasound measurements of ureteral stone longitudinal diameter, stone location, and UJF enables an accurate assessment of the risk of spontaneous passage of ureteral stones. The ultrasound parameters included in the model are highly interpretable and clinically accessible, providing a basis for precise clinical decision-making and reducing the risk of stone-related complications in the management of ureteral stones.