What is infected hydronephrosis in nephrolithiasis and how is it managed?

Updated: Sep 16, 2021
  • Author: Chirag N Dave, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Infected hydronephrosis, defined as urinary tract infection (UTI) proximal to an obstructing stone, mandates hospital admission for antibiotics and prompt drainage. Midstream urine culture and sensitivity was a poor predictor of infected hydronephrosis in one series, being positive in only 30% of cases. [45]

The clinical presentation of infected hydronephrosis is variable. Pyuria (>5 white blood cells [WBCs] per high-power field [hpf]) is almost always present but is not diagnostic of proximal infection. In one small series of 23 patients with infected hydronephrosis, the temperature was higher than 38°C in 15 patients, the peripheral WBC count was more than 10 × 109/L in 13 patients, and the creatinine level was greater than 1.3 mg/dL in 12 patients. [46]

Renal ultrasonography or CT may distinguish pyonephrosis from simple hydronephrosis by demonstrating a fluid-fluid level in the renal pelvis (urine on top of purulent debris). In two small studies, ultrasonographic sensitivity for pyonephrosis was found to be 62-67%. CT sensitivity for pyonephrosis has not been reliably determined. [47, 48] The emergency physician must maintain a high index of suspicion. [49]

Antibiotics should cover Escherichia coli and Staphylococcus, Enterobacter, Proteus, and Klebsiella species. In another small study of 38 patients with hydronephrosis, 16 had infected hydronephrosis and 22 had sterile hydronephrosis. Ultrasonography alone detected 6 of 16 cases of pyonephrosis, a sensitivity of 38%. Using a cutoff value of 3 mg/dL for C-reactive protein and 100 mm/h for erythrocyte sedimentation rate, the diagnostic accuracy of detecting infected hydronephrosis and pyonephrosis increased to 97%. [50]

Relative indications to consider for a possible admission include comorbid conditions (eg, diabetes), dehydration requiring prolonged IV fluid therapy, renal failure, or any immunocompromised state. Patients with complete obstruction, perinephric urine extravasation, a solitary kidney, or pregnancy, and those with a poor social support system, also should be considered for admission, especially if rapid urologic follow-up is not reliably available.

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