Detected Renal Cysts Are Tips of the Iceberg in Adults with ADPKD

Abstract

In autosomal dominant polycystic kidney disease, progressive renal enlargement secondary to expanding cysts is a hallmark. The total cyst load and range of cyst diameters are unknown. The purpose of this study was to quantify the total number and range of diameters of individual cysts in adults with preserved GFR. A retrospective, morphometric analysis of renal cyst number and diameter using magnetic resonance images from eight adult autosomal dominant polycystic kidney disease patients was performed at baseline and after 6.9 years. Cyst number and diameter were measured in microscopic sections of nephrectomy specimens from five different adults. The diameters of 1010 cysts ranged from 0.9 to 77.1 mm in baseline T2 magnetic resonance images, and the mean total number of cysts increased from 682 to 1002 in 6.9 years. However, magnetic resonance imaging detects only cysts above the lower limit of detection. In 405 cysts measured in nephrectomy specimens, 70% had diameters <0.9 mm. Cyst counts by magnetic resonance in eight subjects compared with histology revealed approximately 62 times more cysts below the limit of magnetic resonance imaging detection than above it. This study presents quantitative data indicating that renal cysts develop in a minority of renal tubules. Increased numbers detected by magnetic resonance imaging are caused primarily by cysts below detection at baseline enlarging to a detectable diameter over time. The broad range of diameters, with a heavy concentration of microscopic cysts, may be most appropriately explained by a formation process that operates continuously throughout life.