Clinical Significance of Perinephric Fluid Collection in Patients with Renal Colic and Urolithiasis: A Retrospective Analysis

<b>Background</b>: Perinephric fluid is commonly identified in patients with renal colic and urolithiasis, especially in cases associated with hydronephrosis. However, its clinical relevance, particularly its impact on treatment decisions and prognosis, is not well established. <b>Methods</b>: This retrospective, single-center study included adult patients who presented to the emergency department (ED) with suspected renal colic between January 2021 and October 2023. Patients underwent ultrasound evaluations, which were analyzed for perinephric fluid, hydronephrosis, stone size, and stone location. Data on patient demographics, laboratory results, and clinical outcomes, including the need for urological interventions, were also collected and analyzed. Multivariate logistic regression was used to assess factors associated with perinephric fluid presence. <b>Results</b>: Of the 509 patients included, 200 (39.3%) had perinephric fluid. Hydronephrosis was significantly associated with perinephric fluid (OR: 4.14, <i>p</i> = 0.007), as were stones located in the proximal (OR: 3.06, <i>p</i> = 0.003) and distal ureter (OR: 2.31, <i>p</i> = 0.018). However, sonographic perinephric fluid did not significantly affect the likelihood of urological intervention, in-hospital complications, sepsis, acute kidney injury (AKI), acute kidney disease (AKD), and prolonged hospital stay. <b>Conclusions</b>: Perinephric fluid is a common finding in patients with renal colic and urolithiasis, particularly in cases involving hydronephrosis and ureteral stones. However, despite its prevalence, sonographic perinephric fluid was not significantly associated with the need for urological intervention, longer hospital stays, or worse clinical outcomes. Further prospective studies are required to clarify its clinical implications fully.