A new computer-assisted three-dimensional reconstruction method provides accurate measurement of glomerular mesangial volume.

Many glomerulopathies are characterized by progressive mesangial (interstitial) expansion which can be quantitated by morphometric analysis. The purpose of this study was to analyze mesangial and glomerular volumes using a new computer-assisted reconstruction (CAR) method. CAR was compared to two standard planar methods, point-counting and linear integration, for accuracy and time efficiency. In Phase I of the study, a computer-based model of the mesangial space was created by placing spherical and ellipsoidal objects of known volume into an enclosing volume mimicking the glomerulus. The simulated mesangium occupied approximately 10 percent of the glomerular volume. The model glomerulus was sectioned serially into ten sections of equal thickness and the three morphometric methods applied to determine the mesangial/glomerular volume. The complexity of the mesangial model was varied by increasing the number of mesangial regions from one to ten to 100. The CAR method estimated the model mesangial volume more accurately (1-9 percent error) through each level of complexity compared to point-counting (3-17 percent error) and linear integration (3-18 percent error). The point-counting method consistently overestimated (P less than 0.05) the fractional mesangial volume for the ten- and 100-region mesangium models. In Phase II of the study, a normal rat glomerulus was sectioned serially (215 sections) and a transmission electron micrograph (TEM) of every fifth section (n = 43) was obtained. Each TEM image (2% of glomerular surface) was digitized for analysis by CAR. Point-counting and linear integration were also performed on the whole glomerular TEMs (n = 10, randomly chosen). The estimated relative mesangial/glomerular volume was 6.6 +/- 0.1 percent by CAR (mean +/- SD), 9.7 +/- 1.5 by linear integration, and 14.9 +/- 3.4 by point-counting. The point-counting method was most efficient, requiring 40 +/- 8 sec/section, followed by CAR at 85 +/- 24 sec/section. Linear integration was least efficient (93 +/- 23 sec/section). We conclude that CAR is the most accurate morphometric method of the three compared for estimating mesangial and glomerular methods, although it is more time consuming than the point-counting method and requires more complex instrumentation. CAR is the only method that will analyze the shape and three-dimensional complexity of glomerular structures using TEMs.