Evidence of extraordinary growth in the progressive enlargement of renal cysts

Abstract

Background and objectives: In autosomal dominant polycystic kidney disease, cysts derived from tubules are detected at birth by ultrasound (threshold for detection >7.0 mm); thus, fetal cyst growth rates must exceed 2300%/yr. In adults, the combined renal cyst component enlarges at approximately 12%/yr by growth of individual cysts. To explore this discrepancy, the growth rates of individual cysts were determined in adult polycystic kidneys.

Design, setting, participants, & measurements: Diameter, volume, and growth rates of individual cysts were measured by magnetic resonance in 30 individual cysts in three adult patients over a span of 3 years. Results were confirmed in 22 cysts measured in five patients by computed tomography over a span of 11 years.

Results: Mean cyst diameters were 20.4 +/- 9.9 mm (range 7.1 to 40.5 mm) at baseline and 25.8 +/- 15.6 mm (range 7.8 to 49.6 mm) after 3 years. Mean cyst volumes, determined by manual segmentation and summation of magnetic resonance cross sections, were 8.7 +/- 12.9 cm(3) (0.3 to 43.3 cm(3)) and 24.2 +/- 66.3 cm(3) (0.3 to 364.8 cm(3)) after 3 years. Mean cyst growth rates ranged from 6.9 to 23.9%/yr; the maximum growth rate was 71.1%/yr, far less than required to develop a 7-mm diameter cyst in utero. Results were similar in 22 cysts examined by computed tomography.

Conclusions: It was concluded that renal cysts detected by ultrasound in newborns must have grown at exuberant rates in utero; thereafter, expansion appears to proceed at much slower rates.

Figure 1.

Histograms of cyst diameter, volume, and growth rate distribution. (A) Baseline cyst diameter determined from the average maximal diameter. (B) Baseline cyst volume determined by the segmentation method. (C) Cyst growth rate determined by the segmentation measurement method.

Figure 2.

Validation of methods. The relation between cyst volumes determined by segmentation and diameter methods. R² = 0.959. Thirty cysts measured at baseline and after 3 years.

Figure 3.

Volume change in 52 single cysts. (A) Volume determined from MR scans by stereology method over 3 years. Relative change was 1.94 ± 1.43; P < 0.001. (B) Volume determined from contrast-enhanced CT scans by maximal diameter method over 3 to 11 years. Relative change was 8.82 ± 12.94; P < 0.001.

Figure 4.

Duration of postpartum growth required to generate a cyst 10 mm in diameter. Horizontal dotted line shows the maximal growth rate (71.1%/yr) observed in a single cyst in the study presented here. The dashed line shows the mean rate of cyst growth (17%/yr) in the stereology study presented here. Regression lines signifying starting cyst diameters at birth of 0.5, 1.0, and 5.0 mm are shown.

Figure 5.

Influence of in utero accelerated growth on the enlargement of individual cysts postpartum. Cyst originating in 100-μm collecting duct in utero grows at a rate of 2347%/yr for 6 months, then at a rate of 17%/yr thereafter. Dashed line at bottom indicates grow of cyst at 17%/yr after formation in utero. Vertical dashed line indicates birth.