Volumetric determination of progression in autosomal dominant polycystic kidney disease by computed tomography

Abstract

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive renal enlargement and renal failure. We evaluated sequential radiocontrast-enhanced computed tomography (CT) scans to determine the rate of kidney enlargement in patients with ADPKD. Ten adult patients with ADPKD (4 men and 6 women) with initial serum creatinine levels </=1.6 mg/dL had at least two sequential CT scans more than three years apart. The mean patient age at the initial CT study was 33.8 years, and the mean initial serum creatinine concentration was 1.1 mg/dL (range 0.6 to 1.6 mg/dL; range of calculated creatinine clearances 60 to 135 mL/min/1. 73 m2). Total volume (Vt) was determined by manual tracing of renal areas in contiguous 5 to 10 mm thick axial CT slices for each kidney. The area of noncystic parenchyma (Vp) in each slice was determined by differential densitometry segmentation analysis of contrast-enhanced tissue, and total cyst volume (Vc) was the difference between Vt and Vp. The mean diameters of individual cysts were measured sequentially in selected cases. The mean initial Vt, Vp, and Vc values (+/- SEM) were 561 +/- 66, 243 +/- 19, and 317 +/- 57 mL per kidney, respectively. In 10 patients, after a mean of 5.7 years (range 3.3 to 11.9), Vt increased 323 +/- 79 mL (P < 0.01, range -25 to 1182 mL); the rate of volume increase was 53.9 +/- 10.4 mL/year/kidney (P < 0.001). In eight patients with repeat contrast-enhanced scans, Vt, Vp, and Vc increased 211 +/- 58 mL (P < 0.005), 26 +/- 11 mL (P > 0.05), and 185 +/- 52 mL (P < 0.01), respectively. In 19 individual spherical cysts selected in six patients, the mean initial volume was 15.0 +/- 7.2 mL (range 1.1 to 137 mL), and the average rate of volume increase was 0.52 +/- 0.21 mL/month (P < 0.025, range 0.02 to 4.15 mL/month). In five patients who eventually required dialysis, 11.2 years after the initial CT scan, the initial cyst/kidney volume ratio (combined for both kidneys) exceeded 0.43; four patients with lower cyst/kidney volume ratios had serum creatinine levels <1.5 mg/dL, 8.7 years after the initial CT scan. On the basis of this preliminary survey of archival material, we conclude that conventional contrast-enhanced CT scans can be used to quantitate volume components of progression in ADPKD. The rates of individual kidney and cyst enlargement are highly variable within and between patients, but overall, the values increase over time. The volume fraction of kidneys comprised of cysts may be a useful indicator of ADPKD progression.