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Diagnostic Value of Attenuation Measurements of the Kidney on Unenhanced Helical CT of Obstructive Ureterolithiasis

¹ Department of Radiology, Federal University of São Paulo School of Medicine, Rua Napoleão de Barros 800, São Paulo CEP 04024-002, Brazil.
² Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave., Boston, MA 02215.
³ Department of Radiology, Hospital do Rim e Hipertensão UNIFESP, Rua Borges Lagoa 960, São Paulo CEP 04038-002, Brazil.
⁴ Department of Urology, Federal University of São Paulo School of Medicine, Rua Napoleão de Barros 715/2, São Paulo CEP 04024-002, Brazil.
⁵ Department of Radiology, University of Alabama at Birmingham, 619 S 19th St., Birmingham, AL 35233.

OBJECTIVE. The objective of this study was to assess the diagnostic value of attenuation measurements of the kidney on unenhanced helical CT in patients with obstructive ureterolithiasis.

MATERIALS AND METHODS. Consecutive unenhanced helical CT scans of patients referred for acute unilateral renal colic were retrospectively reviewed. Patients with CT evidence of other urinary system diseases were excluded. Included scans (n = 145) were assessed for ureteral stone and secondary signs of obstruction such as unilateral collecting system or ureteral dilatation, perinephric stranding, and periureteral edema. Renal attenuation in Hounsfield units was measured in the upper, middle, and lower portions of the parenchyma, and a mean value was determined for each kidney.

RESULTS. Ureteral stones were present in 76 patients. Renal attenuation on the side with lithiasis was lower than on the opposite kidney: 27.2 ± 3.9 H vs 32.6 ± 3.4 H (p < 0.001). Attenuation differences between kidneys were higher for patients with ureterolithiasis: 5.4 ± 3.2 H (range, –3.3 to 13.0 H) versus 1.2 ± 1.0 H (range, 0–4.7 H) (p < 0.001). An attenuation difference between kidneys greater than or equal to 5.0 H had 61% sensitivity, 100% specificity, 100% positive predictive value, 69% negative predictive value, and 79% accuracy for diagnosis of ureteral lithiasis.

CONCLUSION. Attenuation difference between kidneys greater than or equal to 5.0 H was a valuable sign and had diagnostic performance similar to other secondary signs of obstructive ureterolithiasis. Furthermore, attenuation difference had the advantage of being an objective, measurement-based indicator.

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