Feline Obstructive Ureterolithiasis: Utility Of Computed Tomography And Ultrasound In Clinical Decision Making

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Carr AH, Wisner ER, Westropp JL, et al.

American College of Veterinary Radiologists 2012:87.

Introduction/Purpose: The clinical utility of ultrasound (US), unenhanced computed tomography (U-CT) and contrast-enhanced CT (CE-CT) were evaluated to assess diagnostic accuracy for detection of feline ureterolithiasis and ureteral obstruction.

Methods: Medical records were reviewed for feline patients with a diagnosis of ureteral disease. Inclusion criteria were an abdominal US examination followed by a contemporaneous abdominal CT study and either surgical or necropsy confirmation of diagnosis. US, U-CT and CE-CT images were evaluated for evidence of ureteral obstruction, presence of ureteroliths, and renal lesions including pylectasia/hydronephrosis.

Results: U-CT had the highest accuracy for detection of ureteroliths (78%) and ureteral obstruction (79%). The combination of U-CT and US had the highest sensitivity (96.5%) and negative predictive value (NPV, 96%) for the detection of ureteroliths; however, U- CT alone had the highest specificity (85.5%) and positive predictive value (PPV, 86%). The combination of U-CT and US had the highest sensitivity (96%) and NPV (96.5%) for the detection of obstruction, but was only slightly higher than U-CT alone (sensitivity 92.5%, NPV 93.5%). US alone had the highest specificity (76.5%) and PPV (65.5%) for obstruction, but had the same accuracy for obstruction as U-CT (79% for both). For obstruction detection, the addition of CE-CT did not improve the sensitivity or NPV, and diminished the specificity, PPV and accuracy of detection of obstruction.

Discussion/Conclusion: U-CT had the greatest accuracy for detection of ureteroliths and ureteral obstruction. CE-CT did not improve the diagnostic accuracy for the detection of ureteroliths or ureteral obstruction in cats. With the increased risk of intravenous iodinated contrast administration in an azotemic patient, the inclusion of CE-CT is not indicated for detection of collecting system obstruction from ureterolithiasis.