Glomerular morphometry I: nephrotic syndrome in childhood

Glomerular number and size: facts and artefacts

This review article is concerned with clinical and experimental data on glomerular number and size and includes a critical discussion of the relevant stereological methods. There is considerable evidence supporting the view that the size of the glomerular filter, in toto, is related to the inception and development of glomerular disease. Major divergences from the filter size are incompatible with normal structure and function. Furthermore, the hypothesis has been put forward that there exists a subset of individuals with minor divergences from the norm that is more susceptible to glomerular disease than the general population. Stereological methods for estimating glomerular number and mean glomerular size could be applied to set standard values. In addition, if the above hypothesis is confirmed, then they could identify on biopsy specimens the patients that belong to cohorts at risk of developing glomerular disease. Unfortunately, despite the development of new, robust methods for particle counting and size determination, such as the fractionator and the dissector, no universal standards of glomerular number and size have been agreed on to date. The major difficulties depend on 1) establishing a standard protocol of tissue acquisition and processing and 2) defining possible variations across age, sex, and ethnic subgroups. The considerable effort required to overcome these difficulties should be rewarded, however, by important advances in the understanding of the morphogenesis of glomerular disease and in the diagnostic and prognostic yield of renal biopsy.

Glomerular morphometry in childhood reflux nephropathy, emphasizing the capillary changes

As a consequence of nephron loss, reflux nephropathy (RN) causes considerable glomerular hypertrophy. To examine the relative contributions of capillary dilatation and growth in producing hypertrophy, glomeruli contained in unscarred areas of renal biopsies from 19 children with RN were compared with those in 16 children with minimal change nephrotic syndrome and 16 with recurrent hematuria, who were used as controls representing normal childhood growth. Using computerized digitometry we measured the mean glomerular tuft area (GTA) in all complete, undistorted, nonsclerotic glomeruli in periodic acid-Schiff (PAS) stains. Measurements were repeated in four glomeruli of uniform size in periodic acid-silver methenamine stains, the results (GTA4) correlating significantly with GTA. In the same four glomeruli we measured the mean individual capillary luminal area (CLA) and counted the mean number of lumens per glomerulus (N). Mean mesangial area (MA) was calculated as GTA4 - (CLA x N). Cells per distal mesangial region were counted in PAS stains. GTA, GTA4, N, MA and mesangial cell counts were significantly greater in RN than controls, but CLA and fractional MA (MA/GTA%) did not differ. N correlated highly significantly with GTA4 in both RN and controls, but CLA did not do so. These findings are consistent with capillary growth by subdivision being the main mechanism of glomerular hypertrophy when nephron loss occurs during childhood, and the identity of the regressions of N versus GTA4 in RN and controls suggests that compensatory hypertrophy resembles the normal glomerular growth pattern in this age group.

Human glomerular growth during childhood: a morphometric study

Morphometric measurements of glomerular size were made on renal biopsy specimens obtained from 16 children with minimal change nephrotic syndrome (MCNS) and 16 with isolated recurrent haematuria (RH), whose ages ranged from 1.8 to 15.2 years. Glomeruli were normal on light and electron microscopy, and immunofluorescence was essentially negative. Tracings were made of the outlines of glomerular capsules, tufts, and individual capillary lumens; using computerized digitometry, the mean areas of each item were determined. The number of capillary lumens per glomerulus was counted automatically. From these data, the mean mesangial area was also calculated. Mesangial cells were counted in at least 100 distal mesangial areas per biopsy. The mean glomerular capsular area (GCA) correlated well with the mean glomerular tuft area (GTA) but frequent capsular artefacts rendered the former measurement less suitable for comparison with diseased glomeruli. The mean GTA correlated significantly with age and body surface area in both MCNS and RH, as did the number of capillary lumens per glomerulus, but the mean capillary lumina area showed no such correlations. The mean mesangial area increased with age in proportion to GTA, whereas mesangial cell counts remained normal. These findings indicate that glomerular growth during childhood is proportional to body growth, and are consistent with capillary subdivision as the mechanism of enlargement.

Glomerular volume and renal function in children with different types of the nephrotic syndrome

Glomerular hypertrophy has been suggested to be an important factor in the pathogenesis of focal glomerular sclerosis. The aim of the present study was to analyse retrospectively the renal biopsies of 58 children (0.2-16.1 years of age) with different types of the nephrotic syndrome, minimal change nephrotic syndrome (MCNS), diffuse mesangial proliferation (DMP) and focal segmental glomerulosclerosis (FSGS). Glomerular surface area was measured and glomerular volume was calculated and related to steroid responsiveness and to renal function, measured by clearances of inulin and para-aminohippuric acid. Glomerular volume correlated with body surface area (BSA) and age. Because of this, patients with FSGS and DMP were matched according to BSA and age, with corresponding MCNS patients. Glomerular volumes of FSGS and DMP patients were significantly larger than those of MCNS patients. In the MCNS patients, significant correlations were found between glomerular volumes and glomerular filtration rate and effective renal plasma flow. Steroid-dependent and steroid-resistant patients showed larger glomeruli than the steroid-responsive children. We suggest that hyperfiltration and hyperperfusion, among other factors, may contribute to glomerular hypertrophy, mesangial proliferation and glomerulosclerosis.

Segmental sclerosing glomerular lesions

Segmental sclerosing glomerular lesions are usually all grouped together and called focal segmental glomerulosclerosis. This has meant that the term that was originally used for a defined clinical entity is now applied to a variety of conditions in man and experimental animals, with the assumption that the morphological changes are the same in all conditions. Studies of the position of segmental lesions within glomeruli, the size of glomeruli and the proportion of glomeruli affected have shown that this assumption is wrong. Such studies have identified a disease that corresponds to the original clinical concept of focal segmental glomerulosclerosis. This begins with the nephrotic syndrome in patients whose renal biopsies show large glomeruli with mesangial hypercellularity and segmental lesions at every tubular origin. Later the biopsies have segmental lesions throughout the glomerular tuft. This disease differs clinically and pathologically from other conditions that have segmental sclerosing lesions, such as in patients with reduced renal mass or patients with hypertension and proteinuria. The term focal segmental glomerulosclerosis is now too ambiguous and unsatisfactory to be used without qualification.

Glomerular morphometry in reflux nephropathy: functional and radiological correlations

Using computerized digitometry, we investigated the relationships between renal size, glomerular filtration rate (GFR), proteinuria, incidence of segmental and global glomerulosclerosis, glomerular size, hilar arteriolar wall thickness and hyaline deposition in renal biopsies obtained from 24 children and adolescents with reflux nephropathy, of whom only 4 were hypertensive. Age-matched controls comprised minimal-change nephrotic syndrome (6) and recurrent haematuria with normal biopsy (13). The mean sectional area of patients' glomeruli was double that of controls. Glomerular size correlated with the amount of proteinuria (measured as protein/creatinine ratios in early morning urine) and inversely with renal size and GFR. Segmental sclerosis, invariably of hilar origin, was observed in 8 patients and the percentage of glomeruli affected correlated strongly with glomerular size and proteinuria. Global sclerosis was found equally in patients and controls, and showed no similar correlations. Compared with controls, patients' hilar arterioles showed increased wall thickness, more intramural hyaline deposits and decreased luminal diameter when related to glomerular size. The proteinuria and glomerular changes are consistent with hyperfiltration, while the previously undescribed hilar vascular changes, which both precede and accompany sclerosis, resemble abnormalities reported experimentally following renal ablation.

Assessment of glomerular size in renal biopsies including minimal change nephropathy and single kidneys

A method of assessing glomerular size on sections of post-mortem kidney was adapted for use on needle biopsies of kidney. A semi-automatic image analyser was used to measure the cross-sectional area of the outline of Bowman's capsule on all glomeruli in renal biopsies. The mean of approximately the largest 25 per cent of areas was calculated. The method was used to compare glomeruli in 13 control patients without obvious structural abnormalities with those in 10 patients with a single kidney, 22 with minimal change nephropathy, and 20 with membranous nephropathy. Patients were at least 14 years old. Glomeruli in minimal change nephropathy were significantly smaller than those in all other groups. Glomeruli in single kidneys were significantly larger than those in all other groups. Glomeruli in membranous nephropathy were the same size as controls. Any differences between groups could not be explained by differences in body build. It is possible that in adults glomeruli in minimal change nephropathy are abnormally small. The method of assessing glomerular size can be used on renal biopsies as well as on sections of whole kidney.

Focal segmental glomerulosclerosis with and without nephrotic syndrome in children

The clinical presentation, initial laboratory and renal biopsy findings, and course of focal segmental glomerulosclerosis (FSGS) were studied retrospectively in 57 children in order to compare findings in those with and without nephrotic syndrome and to establish factors of prognostic significance. All patients had proteinuria. Eleven patients were otherwise asymptomatic, and nephrotic syndrome did not develop (group 1); 14 patients had asymptomatic proteinuria, but nephrotic syndrome subsequently developed (group 2); 32 patients had nephrotic syndrome (group 3). There were no differences between these three groups with regard to sex, age, initial renal function, incidence of hypertension and hematuria, and pathologic findings. At the latest follow-up, five group 1 patients, six in group 2, and 14 in group 3 had chronic renal failure; the incidence was similar for those with asymptomatic proteinuria and those with nephrotic syndrome. The location of the sclerosis within the glomerulus proved to have prognostic significance. All 12 patients with peripheral FSGS maintained normal renal function, whereas in 25 of the 44 with hilar FSGS chronic renal failure developed.

An electron microscopy method for studying full cross-sections of the human renal glomerulus

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Mesangial alterations in steroid-responsive minimal change nephrotic syndrome

Renal biopsies from 25 children with steroid-sensitive minimal change nephrotic syndrome were evaluated retrospectively to determine whether there is any relation between the morphological changes and the frequency of relapses. Biopsy material was examined by light-, immunofluorescence-, and electron microscopy, and by morphometric methods. The patients were divided in a group of 15 children with frequent relapses (FR) and another group of 10 children with an absence of, or only infrequent, relapses (NR/IR). Semiquantitative evaluation of biopsy specimens disclosed no significant differences between groups, but morphometric measurements performed on toluidine stained semi-thin sections showed a significant increase of mesangial nuclei in FR compared with NR/IR (P less than 0.01). Furthermore, the mean area of mesangial nuclei was decreased and the relative frequency of smaller nuclear profiles was higher in patients with FR compared to NR/IR (p less than 0.01). These findings suggest mesangial cell activation in FR which may be related to a longer course of the disease prior to renal biopsy (mean 4.0 years in FR vs. 1.4 years in NR/IR). In our opinion, morphometric assessment of discrete mesangial alterations is a promising method for exploring clinicopathological correlations in minimal change nephrotic syndrome.

Glomerular morphometry II: familial and nonfamilial haematuria

Differential glomerular cell counts and measurements of glomerular diameter were made in 13 children with Alport's syndrome (AS), four with benign familial haematuria (BFH) and 15 with nonfamilial haematuria (NFH). Mesangial cellularity was increased in the six cases of NFH with diffuse mesangial deposits of IgA (IgA +). In AS, IgA + and -NFH, epithelial cellularity decreased with age while glomerular diameter increased. In AS mesangial and endothelial cellularity also decreased with age. These findings support the view that AS, IgA + and -NFH are three distinct entities. BFH, although similar in several respects to IgA -NFH, should nevertheless be retained as a separate category by virtue of its familial incidence of haematuria.