The significance of focal glomerular sclerosis in children who have nephrotic syndrome

This study was undertaken to learn the significance of focal glomerular sclerosis in children who have nephrotic syndrome. Tissue obtained by percutaneous renal biopsy 10-15 years previously was re-examined. Initially, two of the 29 biopsy specimens contained focal segmental hyalinosis or sclerosis and five of the 29 had focal glomerular obsolescence. The paraffin blocks were serially sectioned and examined. Following this procedure, seven of the 29 biopsies had focal segmented hyalinosis and 16 of the 29 had focal glomerular obsolescence. The percentages of focal segmental hyalinosis and focal glomerular obsolescence were recorded. Only those patients whose focal segmental hyalinosis exceeded 2% progressed to renal failure. Age-matched autopsy material from patients dying without renal dysfunction was used as a control. Focal glomerular sclerosis was seen in 75.8% of the control specimens, although few glomeruli within each specimen were involved. Focal glomerular sclerosis may be found normally; it may be found in nephrotic children who do not develop renal failure. The quantification of sclerotic lesions may be of prognostic significance in childhood nephrosis.     

De novo collapsing glomerulopathy in renal allografts

BACKGROUND: Collapsing glomerulopathy is a recently described form of glomerular injury characterized by capillary collapse and visceral epithelial hypercellularity associated with nephrotic range proteinuria and a rapid, progressive decline in renal function. The lesion has rarely been described in allografts. METHODS: We reviewed 892 allograft biopsies from a population of 1079 recipients who received renal transplants between 1978 and 1996. RESULTS: Five cases of de novo collapsing glomerulopathy were identified (0.6% of biopsies; 3.2% since 1993). None occurred before 1993. The patients were 31 to 66 years of age and they presented 6 to 25 months after transplantation. The 24-hr urinary protein ranged from 1.8 to 11.8 g. All patients and donors were negative for the human immunodeficiency virus and had no risk factors for human immunodeficiency virus infection. Diffuse or focal, global or segmental collapse of glomerular capillaries, swelling and hypercellularity of the visceral epithelium, hyaline arteriolosclerosis, and interstitial fibrosis were characteristic histologic features. Two cases had concomitant glomerular immune complex deposits. Progressive decline in allograft function occurred within 2-24 months after diagnosis, culminating in return to dialysis in all patients. CONCLUSION: Collapsing glomerulopathy can arise in renal allografts as a de novo disease. Although its pathogenesis remains to be clarified, it is important to distinguish this lesion in allografts as it can be associated with rapidly progressive graft failure.     

Temporal trends in Canadian birth defects birth prevalences, 1979-1993

Syrian hamsters of the APA strain (APA hamsters) develop spontaneous mesangial thickening in the renal glomeruli from an early age. They also develop focal and segmental glomerulosclerosis (FSG) at and after 6 months of age. In this study, histopathological, immunohistochemical and lectin histochemical examinations were conducted to clarify the modification of the spontaneous renal lesions of APA hamsters by streptozotocin(SZ)-induced diabetes. Histopathological analysis revealed that the expansion of the mesangial region was more prominent and the thickening of the glomerular basement membrane (GBM) was weaker in SZ-treated animals than in non-treated ones. Immunohistochemical analysis suggested that type IV collagen and laminin were involved in the expansion of the mesangial region and thickening of the GBM. In lectin histochemical analysis, podocytes, capillary endothelial cells, GBM and a part of mesangial region of SZ-treated animals were positive for RCA120 and GSL-I with neuraminidase-pretreatment although they were negative for these lectins in non-treated animals. These results suggest that the spontaneous glomerular lesion of APA hamsters is modified qualitatively and quantitatively by SZ-induced diabetes.     

The transducing pathway of Ca2+ influx during progesterone-initiated acrosome reaction of guinea pig sperm

Although idiopathic membranous nephropathy (IMN) is thought to represent a diffuse glomerulopathy, it was found that three of 31 children histologically diagnosed as IMN showed focal and segmental deposition of immunoglobulin G (IgG) and C3 on the glomerular capillary walls. The present study attempted to comparatively investigate clinical and pathological features of the diffuse group and the focal segmental group in 31 IMN children. Immunofluorescence study revealed that 28 of 31 IMN exhibited diffuse granular deposition of IgG along glomerular capillary walls. In contrast, focal and segmental deposition of IgG and C3 was noted in three children with IMN. In addition, focal and segmental electron-dense deposits were identified in these cases. In two children of the focal segmental group, immunofluorescent patterns of IgG deposition were unchanged even at the second biopsy. The focal segmental form of IMN tended to occur in younger children than diffuse IMN. However, other clinical parameters such as the range of proteinuria, hematuria, serum albumin and prognosis did not show any significant differences between both groups. Electrophoretic profiles of urinary proteins on sodium dodecylsulfate-polyacrylamide gel electrophoresis were not different between both groups. It is proposed that the focal segmental form of IMN may have a distinctive glomerulopathy from the typical form of IMN.     

Renal pathology of human immunodeficiency virus infection

Renal complications of HIV infection are clinically and morphologically diverse. These may affect the glomerular, tubulointerstitial, and vascular compartments. Tubulointerstitial injury predominates in most autopsy-based studies, whereas glomerular disease is most frequently identified in biopsy-based studies. The most common glomerular lesion is HIV-associated focal segmental glomerulosclerosis and related mesangiopathies (collectively termed HIV-associated nephropathy). Increasingly, a variety of immune complex-mediated glomerular diseases such as membranoproliferative glomerulonephritis, IgA nephropathy and lupus-like nephritis, as well as hemolytic uremic syndrome/thrombotic thrombocytopenic purpura have been reported. The spectrum of tubulointerstitial lesions includes acute tubular necrosis, interstitial nephritis, diffuse infiltrative lymphocytosis syndrome, renal infection, and neoplasms including lymphoma and Kaposi's sarcoma. The pathological features of these conditions are reviewed with emphasis on clinical-pathological correlations and pathogenesis.     

Kidney in Galloway-Mowat syndrome: clinical spectrum with description of pathology

The Galloway-Mowat syndrome, a rare inherited disorder, is characterized by congenital microcephaly with hypotonia and developmental delay, often hiatus hernia, and nephrotic syndrome manifested in infancy or in early childhood. The glomerular lesion has been poorly characterized in the few previous reports of this syndrome. We studied three siblings with microcephaly and nephrotic syndrome occurring during the first two weeks of life. Hematuria, glycosuria and renal failure were also present. Renal biopsy and postmortem specimens of two patients were studied. Glomerular structure was disorganized; capillary lumina were of varying calibers, capillary walls were adherent to one another, and mesangial zones were poorly demarcated. Glomerular basement membrane ultrastructure was markedly altered. The normal trilaminar structure was obscured or replaced by flocculent material; furthermore, 6 to 8 nm fibrils of unknown nature permeated the space between endothelial and epithelial cells. Non-glomerular basement membranes were unaltered in appearance. This syndrome apparently represents, in part, a new disorder of glomerular basement membrane formation and function.     

Secondary collapsing glomerulopathy associated with Loa loa filariasis

This is the first case of nonprimary collapsing focal segmental glomerulosclerosis (FSGS) associated with Loa loa filariasis. Loa loa micofilariae were detected on a blood smear after a patient presented with nephrotic syndrome (NS), microhematuria, and renal failure. The renal biopsy showed a collapsing glomerulopathy variant of FSGS. Microfilariae also were identified in renal microvasculature, including the afferent arterioles and the glomerular and peritubular capillaries.     

Statistical methods for dependent competing risks

In this study, the kinetics of glomerular endothelial cells during the repair process following glomerular injury was investigated in a model of mesangial proliferative glomerulonephritis induced by Habu-snake venom (HSV) in rats. Intravenous injection of HSV led to a cystic ballooning type lesion at day 1. Subsequently a marked segmental proliferative lesion was observed in the cystic areas at day 5. Thereafter cellularity decreased and reconstruction of the glomerular tuft was gradually observed with time. The histological structure of the glomeruli had almost returned to normal 21 days following HSV injection. After prominent depletion at day 1, the number of endothelial cells increased rapidly and reached a plateau at day 7, not significantly different from that of the control group. Morphologically endothelial cell elongation from the vascular pole into the cystic lesion was seen together with premature capillary formation in the proliferative lesion. Accompanying the reduction of mesangial expansion, the endothelial cells gradually formed definite capillary lumens. We conclude that the mesangial proliferative glomerulonephritis induced by HSV recovers to its original structural state and that the migration and proliferation of endothelial cells with accompanying capillary formation are essential for the repair process, in addition to mesangial cell proliferation.     

Modulation of glomerular hypertension defines susceptibility to progressive glomerular injury

The fawn-hooded rat constitutes a spontaneous model for chronic renal failure with early systemic and glomerular hypertension, proteinuria (UpV) and high susceptibility to development of focal and segmental glomerular sclerosis (FGS). It has been argued that uninephrectomy (UNX) accelerates the development of glomerular injury by aggravation of glomerular hypertension and by an independent effect to promote glomerular enlargement. The present study was performed to further delineate the importance of these parameters for the development of FGS. At the age of eight weeks male rats were UNX and randomly assigned to either control (CON), enalapril (ENA) or Nw-nitro L-arginine methyl ester (NAME) treatment. In all groups glomerular hemodynamic studies were performed four weeks post-UNX. Systemic blood pressure and UpV were monitored for 4 to 12 weeks post-UNX. Kidneys were then prepared for morphologic study. ENA treatment achieved control of both systemic and glomerular hypertension, maintenance of glomerular hyperfiltration and hyperperfusion, increased ultrafiltration coefficient(Kf), and long-term protection against UpV and FGS. NAME rats showed aggravation of both systemic and glomerular hypertension, decreased renal perfusion and filtration with reduced Kf, and high filtration fraction. The incidence of FGS in NAME and CON groups was similar at 8 and 12 weeks post-UNX, respectively. Glomerular enlargement was present in CON and ENA rats, but did not correlate with injury, while glomerular tuft size was lowest in NAME rats, which displayed prominent glomerular injury. Systemic blood pressure correlated strongly with glomerular capillary pressure. We conclude that systemic and glomerular hypertension govern the development of UpV and FGS.(ABSTRACT TRUNCATED AT 250 WORDS)     

Contractile cells of the kidney in primary glomerular disorders: an immunohistochemical study using an anti-alpha-smooth muscle actin monoclonal antibody

Mesangial cells of the renal glomerulus are thought to have contractile properties, resembling those of smooth muscle cells. Since actin synthesis in mesangial cells is increased in selected animal models of glomerulonephritis, we evaluated the expression of alpha-smooth muscle actin (ASMA), the principal actin isoform found in smooth muscle cells, in biopsy specimens from patients with primary glomerular disorders and in control tissues. Normal glomeruli and glomeruli in acute tubulointerstitial disorders showed few or no ASMA-positive cells in the glomeruli. In contrast, ASMA expression in mesangial cells was increased in minimal change disease, focal segmental glomerulosclerosis, mesangial proliferative glomerulonephritis, membranous glomerulonephritis, and immunoglobulin A nephropathy. In membranoproliferative glomerulonephritis and cryoglobulinemic glomerulonephritis both mesangial and capillary loop ASMA-positive cells were observed with a segmental distribution. In addition, ASMA-positive interstitial cells were seen in many biopsy specimens and often were increased in number in biopsy specimens showing early interstitial fibrosis and tubular atrophy. We conclude that ASMA synthesis in mesangial cells is upregulated in a variety of glomerular disorders, frequently associated with increased cell proliferation and mesangial matrix production. This phenotypic change may be an indicator of mesangial cell activation after injury and may have important pathophysiologic consequences.     

Clinical and morphological predictors of renal outcome in adult patients with focal and segmental glomerulosclerosis (FSGS)

In this retrospective study, we examined 35 adult patients with biopsy-proven, primary focal and segmental glomerulosclerosis (FSGS) and nephrotic syndrome to determine whether any of the clinical and morphological features of FSGS were associated with a higher risk of a poor renal outcome. Clinical factors assessed were the age, sex, amount of urinary protein, and presence of microscopic hematuria, hypertension and renal dysfunction at onset in each patient. Morphological parameters included the number of segmental sclerosis and global sclerosis, sclerosis score, location of segmental sclerosis, mean glomerular diameter, grade of tubulo-interstitial changes, and presence of vascular lesions. Twenty-three patients (66%) were in complete or incomplete (partial) remission, and 12 (34%) were non-responders at the end of follow-up. On univariate analysis, the age at onset, sclerosis score, mean glomerular diameter, and grade of tubulo-interstitial changes in no response were significantly greater than those parameters in remission. Multivariate logistic regression analysis revealed that the degree of tubulo-interstitial changes and mean glomerular diameter were independent risk factors for a poor renal outcome. These findings suggest that the estimation of these latter two parameters allows the nephrologist to predict the probable course and prognosis of an adult with FSGS. Intensive and prolonged therapy is recommended for patients without these two morphological features.     

Preliminary description of focal segmental glomerulosclerosis in patients with renovascular disease

BACKGROUND: Primary and secondary forms of focal segmental glomerulosclerosis (FSGS) are common causes of glomerular proteinuria. Secondary forms of FSGS seem to be the result of adaptive changes that follow a reduction in renal mass. We saw an elderly patient with severe bilateral renal vascular disease (RVD) who had FSGS on percutaneous biopsy. To find out whether elderly patients with atherosclerotic RVD are predisposed to the development of FSGS, we reviewed all cases of FSGS at our institution between 1990 and 1995. METHODS: We identified 59 cases of biopsy-proven FSGS and examined clinical, histological, and radiographic records. FINDINGS: Of the 59 patients, 24 were older than 50 years; eight of these had RVD. No patient under the age of 50 had RVD. Seven of the eight patients with RVD and FSGS had substantial proteinuria at presentation. All had typical glomerular lesions with focal segmental tuft collapse and synechiae; other glomeruli were hypertrophic. All patients showed further decline in renal function on follow-up. INTERPRETATION: The association of FSGS and RVD may represent an under-recognised aetiology of significant proteinuria in elderly patients.     

Approach of cellular mechanisms of glomerulosclerosis in a model of accelerated aging the obese Zucker rat

With age, the morphological changes which occur in renal glomeruli in the absence of any added pathology are an expansion of the extracellular matrices (ECM)--glomerular basement membrane (GBM) and mesangial matrix--and lesions of focal and segmental glomerular hyalinosis (FSGH). Although the mechanisms involved in these glomerular changes are still unknown, an inflammatory step seems to precede the expansion of the extracellular matrices, but the nature of the cytokines and adhesion molecules has yet to be explored. In order to understand the cellular and molecular events of the FSGH, we used the genetically obese Zucker rat (fa/fa) which develops several early FSGH lesions. We observed that FSGH is the result of a modification of the podocyte: 1) bulging of the podocyte with endocytotic vesicles rich in albumin; 2) detachment from the GBM, collapsing of the capillary loops with a progressive disappearance of capillary cells and formation of hyalin and lipid deposits, synthesis of new ECM components; 3) focal adherence of the GBM and the basement lamina of Bowman's capsule and synthesis of new matrix. The detachment of the podocytes from the GBM appeared to be linked to the disappearance of the alpha 3 beta 1 integrin, major molecule which anchors the epithelial cells to the GBM. By immuno-gold techniques, we showed that the density of alpha 3 moieties significantly diminished when podocytes are spreaded over the GBM. This integrin is probably bound to the laminin in the GBM.     

Feasibility of an emergency department-based, risk-targeted voluntary HIV screening program

Renal biopsies from 19 boys and 11 girls, most with moderate or severe forms of hemolytic uremic syndrome (HUS) of the classic diarrhea-associated type, were analyzed as part of their long-term follow-up. Patients were biopsied because of late or persistent proteinuria, hypertension, and prolonged renal failure. The median length of follow-up was 11.2 years (range 0.9-22.0 years). Four histological groups were identified: focal segmental glomerulosclerosis and hyalinosis (FSGSH) (17 patients), diffuse mesangial proliferative glomerulonephritis (DMPGN) (9 patients), diffuse glomerulosclerosis (2 patients), and minimal glomerular changes (2 patients). The median interval between the onset of disease and renal biopsy was significantly shorter in DMPGN than in FSGSH (P < 0.001). The pathological findings may be the expression of two different stages of the same dynamic process: a regular sequence of glomerular lesions consisting of early DMPGN, followed by FSGSH. This lesion would ultimately lead to the final stage of global glomerulosclerosis. At the last examination, only a quarter of the patients had normal renal function. These observations also confirm that prolonged oligoanuria during the acute stage of HUS frequently results in an unfavorable long-term prognosis.     

Lipoprotein glomerulopathy: first case in a white European

Since 1988, 11 cases of a new entity, 'Lipoprotein glomerulopathy' (LG), were described in Japan. Some of these reports suggested that this glomerular lipid storage is due to excess apo E associated with heterozygous E2/3 apo E isoform. We report the first case of LG in a white European with no such lipid abnormalities. Proteinuria was discovered in 1967 when he was 42. Blood pressure and renal function were normal. Family history was negative. Renal biopsy disclosed lesions which were only understood at the time of the Japanese publications. They were composed of endocapillary glomerular deposits. Staining for lipids disclosed capillary loop obstruction with lipid droplets. Electron microscopy showed confluent droplets of various sizes obstructing capillary loops. Proteinuria progressively increased. In 1974 repeat renal biopsy showed the same lipid deposits, now associated with focal-segmental glomerulosclerosis (FSGS). Several serum lipoprotein and apolipoprotein studies ruled out any specific lipid derangement. This suggested a local glomerular disorder, presumably affecting the glomerular endocapillary disposal of lipids. A third biopsy showed progressive glomerular destruction by FSGS with persistence of the lipid droplets. Renal insufficiency progressed and haemodialysis was started in 1992. This observation suggests that LG is a local glomerular, not a general lipid disorder and indicates that this disease is not restricted to Asian patients.     

Analysis of the expression of two thiolprotease genes from daylily (Hemerocallis spp.) during flower senescence

Rats treated with two injections of adriamycin (week 0 and week 12) developed glomerusclerosis and severe tubulointerstitial lesions as described in the literature. In addition, a number of glomerular alterations were present. These included capillary loop dilation, insudation of eosinophilic material, necrosis, duplication of the glomerular basement membrane, severe mesangiolysis with disruption of the mesangial matrix and segmental double-contours. The renal arterioles and interlobular arteries showed endothelial cell swelling. The subendothelial space was infiltrated by fibrinoid material and there was intensive fibrinoid necrosis of the wall of both arteries and arterioles extending into the glomerular tuft. These alterations were very similar to those observed in the hemolytic uremic syndrome. This observation suggests that the two injections of adriamycin, with a long interval in between them, might induce renal lesions similar to those observed in the hemolytic uremic syndrome.     

Glomerular morphology in nephrotic heroin addicts

Renal biopsies of 23 heroin addicts who presented with the nephrotic syndrome were examined by light and electron microscopy. The majority of patients (14) showed focal segmental glomerular sclerosis on light microscopy, four patients showed "minimal change", and two were classified as "focal global sclerosis." In one case focal mesangial proliferation was the outstanding feature; one patient had diabetic glomerulosclerosis; and one had mesangiocapillary glomerulonephritis and dysproteinemia. Visceral epithelial swelling and proliferation were present in 14 patients on light on light microscopy. Electron microscopy showed distinct podocyte changes consisting of loss of foot processes, vacuolization, and cytoplasmic degeneration; focal separation of podocytes from basement membranes was found in 11 of 18 cases. In some instances a few electron-dense deposits were present in the mesangium. Membranous nephropathy was not encountered, although it occurs in 30 to 40% of unselected adult nephrotic individuals. Of 15 patients followed for 2 months to 5 years, one died of heroin overdose, eight went into renal failure, two improved, and four continued to have proteinuria. It is concluded that nephrotic syndrome of heroin addicts is most often associated with focal segmental glomerular sclerosis and occasionally with minimal change disease or focal global sclerosis. Conceivably these three conditions represent different phases of one disease process, although different reactions to heroin or its various vehicles and contaminants cannot be excluded. The morphologic resemblance to experimental aminonucleoside and N,N'-diacetylbenzidine-induced nephrosis suggests a possible toxic origin.     

Primary Sj?gren's syndrome and glomerulonephritis

HISTORY AND CLINICAL FINDINGS: An 82-year-old woman with hypertension for 20 years developed a nephrotic syndrome with severe oedema followed by acute oliguric renal failure after a bout of bronchitis and a gastrointestinal infection. She also complained of xerostomia and dry eyes of recent onset. INVESTIGATIONS: Biochemical tests showed a serum creatinine level of 6.1 mg/dl, a 1:5120 antinuclear antibody (ANA) titre, and positive values for Ro(SS-A) and La(SS-B) antibodies. HLA-DR typing demonstrated HLA-DR3 (HLA-DRB1*0301) and DR13 (HLA-DRB1*13) antigens. Renal biopsy revealed minimal glomerular lesions with focal and segmental glomerulo-sclerosis as well as (hypertension-induced) benign nephrosclerosis and focal tubular atrophy with interstitial fibrosis. TREATMENT AND COURSE: After two hemofiltrations and concomitant administration of 100 mg prednisone renal function quickly improved and the proteinuria fell to 1 g/dl. At the same time the xerostomia improved. The nephrotic syndrome recurred 7 months later after the prednisone dose had been reduced to 10 mg/d, but after the dose had been raised to 50 mg/d and cyclosporin A (150 mg/d) had been added a lasting remission occurred and renal function became stable though impaired. CONCLUSION: The relatively rare association of glomerular disease (here focal segmental glomerulosclerosis) with Sj?gren's syndrome can, as in this case, be triggered by a viral infection. A genetic predisposition for Sj?gren's syndrome is suggested by the demonstration of HLA-DR3 alleles. Administration of steroids is indicated for the treatment of the nephrotic syndrome and, in case of recurrence, can be combined with cyclosporin A. Both drugs also influence the symptoms of Sj?gren's syndrome.     

Cyclosporine in glomerular disease

Cyclosporine was introduced in 1981 as an immunosuppressive agent in renal transplantation. Its use was soon extended to the treatment of various glomerular disorders. In light of its known immunomodulating effects, the use of cyclosporine has been most prominent in those glomerular diseases thought to have an immune basis. The most careful studies of cyclosporine in glomerular diseases have been performed in the pediatric population with idiopathic nephrotic syndrome (i.e., minimal change disease and focal segmental glomerulosclerosis), although data are accumulating regarding efficacy and safety in adults with idiopathic nephrotic syndrome. In patients who are steroid-dependent, cyclosporine therapy can induce complete or partial remission in a significant proportion of cases; success rates in patients with steroid-resistant nephrotic syndrome are less encouraging. Treatment with cyclosporine allows for dose reduction or elimination of corticosteroids, and the consequent salutary effect on growth in the child and glucose and bone metabolism in all patients. Studies that suggest a potential benefit of cyclosporine in recurrent nephrotic syndrome in renal allografts and in other glomerular diseases are also discussed.     

From segmental glomerulosclerosis to total nephron degeneration and interstitial fibrosis: a histopathological study in rat models and human glomerulopathies

BACKGROUND: Focal segmental glomerulosclerosis (FSGS) is consistently associated with tubular degeneration and interstitial fibrosis, altogether, accounting for the progressive decline in renal function. The mechanisms which link glomerular injury to tubulo-interstitial fibrosis are controversial. The present study describes the step-by-step sequence of histopathological events, i.e. the evolution of the injury from the initial lesion in the glomerulus to total nephron destruction. METHODS: The investigation was performed in male hypertensive Fawn-hooded rats (6-, 9-, and 12-month-old) and 14-month-old Milan normotensive rats. The kidneys were fixed by in vivo perfusion and processed for structural investigation. Autopsy materials from human cases of focal segmental glomerulosclerosis and diabetic nephropathy were also examined. RESULTS: FSGS as seen in rat models consists of collapsed and hyalinized capillaries and mesangial portions which are included within a synechia between the glomerular tuft and Bowman's capsule. In addition, a synechia generally contains glomerular capillaries which are perfused and continue to filter with the filtrate being delivered into the interstitium rather than into Bowman's capsular space. Such filtration creates a paraglomerular space on the outer aspect of the parietal epithelium. This space becomes separated from the interstitium by a dense layer of sheet-like fibroblast processes. Associated with the progression to global sclerosis, this space spreads around the entire circumference of a glomerulus; all 'sclerotic' tuft portions are eventually contained in this space. Starting from the urinary pole this process also involves the proximal tubule, initially by expanding the tubular basement membrane (TBM) and later, by separating the TBM from its epithelium, thus creating a peritubular space by misdirected filtrate spreading. Similar to the situation observed at the glomerulus this space becomes separated from the interstitium by a layer of fibroblast processes. The final degeneration of the nephron occurs via two pathways. Pathway I whereby development to global sclerosis is dominant or develops concurrently with tubular degeneration, eventually terminating in global and cylindrical remnants of extracellular matrix surrounded by abundant fibrous tissue. Pathway II where the degeneration of the tubule is ahead of damage progression in the glomerulus leading to atubular glomerular cysts. CONCLUSION: The present study suggests that severely injured glomeruli may continue to filter with the filtrate spreading along interstitial routes. Fluid added locally to the interstitium from such 'extraterritorial' glomerular capillaries probably is quite different in quantity and composition compared to that from interstitial capillaries. We propose that this kind of abnormal addition of fluid to the interstitium is the essential mechanism accounting for interstitial progression of the disease. Similar histopathological phenomena in human kidneys with focal segmental glomerulosclerosis suggest that the pathogenetic pathways defined in the rat models operate in human disease as well.