NE-AUA 2006 Annual Meeting, September 28 - 30, 2006, The Westin Hotel & Rhode Island Convention Center Providence, Rhode Island
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Renal Parenchymal Thickness on Computed Tomography May Predict Renal Function in Obstructed Renal Units: Is a Nuclear Renogram Necessary?
Daniel M. Kaplon, MD, Gyan Pareek, MD, David Bae, MD.
Brown University, Providence, RI,

Background: Clinical decision making often involves assessing renal function in order to decide between nephrectomy and renal salvage therapy. Our purpose is to define the relationship between relative renal parenchymal thickness (RPT) on computed tomography and function on Mag-3 Lasix renogram in obstructed renal units (ORUs) and to define a minimal thickness ratio associated with adequate function.
Methods: The records of 28 patients who underwent Lasix renogram and computed tomography for evaluation of unilateral obstruction were reviewed (2004 to 2006). RPT was measured at the mid-portion of each renal unit on helical CT scan. All patients had a unilateral abnormality and presumed normal contralateral renal unit. For contrast CT scans, the measurement included the visible cortex and excluded the medulla. For non-contrast scans, the measurement included the cortex and medulla but excluded the collecting system. The ratio of thicknesses between the obstructed and non-obstructed renal unit (NORUs) was calculated and this was compared to the observed function on Mag-3 Lasix Renogram.
Results: A total of 28 patients were evaluated. Mean patient age was 49 (range 13-90 years). Obstruction was secondary to UPJ obstruction (n=12), calculus disease (n=5), malignancy (n=2), stricture (n=1), ureterocele (n=1), and non-specified hydronephrosis (n=7). Mean serum creatinine was .96.
Mean paranchymal thickness was 1.68 cm and 2.05 cm in ORUs and and NORUs, respectively. The mean renal function of ORUs was 39%. Linear regression analysis comparing renogram function to ratio of thicknesses between the ORUs and NORUs revealed a correlation coefficient of 0.74 (p<.001). The linear regression equation was computed as: FUNCTION =0.1241239 + 0.3118374 * RATIO. A thickness ratio of 0.24 correlated with 20% renal function.
Conclusion: RPT on computed tomography appears to be a powerful predictor renal function in ORUs. A RPT ratio of less than 0.24 defines a non-functioning kidney. We recommend assessing RPT when making a treatment decision (renal salvage therapy versus nephrectomy) in patients with ORUs.


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