Snapshot A 48-year-old woman presents to the emergency department due to severe back pain. Her symptoms began approximately 3 hours ago and says the pain is in her left mid-back. She describes the pain as sharp and 9/10. The pain radiates to her left groin. On physical exam, there is left-sided costovertebral angle tenderness. A non-contrast computerized tomography (CT) scan of the abdomen demonstrates left-sided urolithiasis and hydronephrosis. She is started on a nonsteroidal antiinflammatory drug (NSAID) and intravenous normal saline. (Nephrolithiasis resulting in hydronephrosis) Introduction Clinical definition renal calyx and pelvis distension secondary to an obstruction in urine flow distal to the renal pelvis dilation of the ureter describes hydroureter Epidemiology demographics age calculi is the most common cause of hydronephrosis and hydroureter in young adults sex pregnancy and gynecologic causes are more common causes in women prostatic hyperplasia and cancer are a major cause of hydronephrosis in men Etiology pregnancy normal finding there may be a more prominent dilation on the right ureter and renal pelvis than the left benign prostatic hyperplasia calculi ureteral narrowing secondary to surgery malignancy e.g., ureteral, cervical, and prostate e.g., transitional cell carcinoma of the bladder can cause uni- or bi-lateral ureteral obstruction congenital defects between the kidney, ureter, and bladder junction ureteropelvic junction obstruction retroperitoneal fibrosis Pathogenesis pathologic or anatomic processes interupt urine flow which leads to an increase in the hydrostatic pressure in Bowman's space decline in glomerular filtration rate impaired ability to concentrate, dilute, and transport sodium, potassium, and hydrogen ions chronic hydronephrosis results in gross changes to the kidney such as renal papillae compression renal septa and calyx coalescence peri-calyx renal parenchymal thinning Prognosis variable as it is dependent on the underlying cause Presentation Symptoms depends on whether the obstruction is acute or chronic asymptomatic pain secondary to bladder, collecting system, or renal capsule distention anuria Physical exam palpable kidney in severe cases costovertebral angle tenderness distended bladder in lower urinary tract obstruction (e.g., benign prostatic hyperplasia) Imaging Renal ultrasonography indication imaging test of choice for evaluating urinary tract obstruction Computerized tomography (CT) scan of the abdomen indication used when results are equivocal on renal ultrasound Studies Labs urinalysis to evaluate for infection, stone, or tumor serum chemistry ↑ BUN and creatinine In cases of unilateral ureteral obstruction, the contralateral kidney usually compensates to maintain a normal GFR and serum creatinine; if the contralateral kidney is diseased or if the obstruction is bilateral, then GFR decreases and serum creatinine rises Differential Pyelonephritis Peripelvic cyst Calyceal diverticula Treatment Conservative bladder catheterization indication performed initially if the clinical presentation is suggestive of a bladder neck obstruction such as suprapubic pain palpable bladder Treatment ultimately depends on the underlying cause of hydronephrosis e.g., oral alkalinization therapy for patients with uric acid stones Complications Postobstructive diuresis