Beyond Hydronephrosis: Perirenal Fluid on Screening Ultrasound in Patients With Renal Colic at a Basic Emergency Service

Screening ultrasound has been progressively integrated into the evaluation of renal colic in emergency settings, enabling rapid identification of indirect signs of urinary obstruction, such as hydronephrosis, and supporting clinical triage when laboratory testing is limited. This article reports a case of recurrent severe renal colic refractory to analgesia, in which screening ultrasound demonstrated moderate unilateral hydronephrosis associated with perinephric/perirenal fluid. We discuss the clinical significance of this combined finding in light of the available evidence, acknowledging that the literature remains inconclusive: some studies link perinephric fluid to more severe presentations, whereas others do not show a consistent impact on hard outcomes such as hospitalization, emergency department length of stay, or the need for urologic intervention. In a Basic Emergency Service (BES) setting without immediate access to detailed renal function analysis, the coexistence of moderate hydronephrosis and perinephric fluid, particularly in the context of persistent pain, should be interpreted as a contextual marker of potentially clinically significant obstruction and/or urinary extravasation, warranting a lower threshold for referral for complementary evaluation and specialist decision-making. Finally, we propose a BES-specific decision-support table integrating key clinical, limited laboratory, and ultrasound variables to guide management pathways for renal colic in our local setting.