Incidental healed postinfectious glomerulonephritis: A study of 1012 renal biopsy specimens examined by electron microscopy

Histologic, IF, and EM findings in 3 biopsies showing incidental largely healed postinfectious GN. (A, B, and C) Biopsy specimen with primary diagnosis of ANCA-associated necrotizing and crescentic GN. (A) The glomerulus exhibits a cellular crescent but no more than very mild and segmental mesangial hypercellularity. (B) IF shows C3 staining (3+ on a scale of 0 to 4+) in the mesangium and capillary loops of a glomerular tuft compressed by a large crescent; there is also staining of Bowman's capsule. (C) EM shows 2 subepithelial deposits in “notch” regions underlying the mesangium (arrows). (D, E, and F) Biopsy specimen with a primary diagnosis of drug-induced interstitial nephritis. (D) By LM, the glomeruli contain occasional mononuclear leukocytes but are otherwise normocellular. (E) IF shows 1+ granular mesangial C3 staining. (F) EM shows 2 partially resorbed intramembranous deposits (arrows), again underlying a mesangial area. (G, H, and I) Biopsy specimen with primary diagnosis of diabetic nephropathy (diffuse glomerulosclerosis). (G) Histologically, there is a moderate increase in mesangial matrix and a mild, segmental increase in mesangial cellularity (arrowheads). Hyaline change is seen in both afferent and efferent arterioles (arrows). (H) IF shows granular mesangial and capillary loop staining for C3 (2+). (I) EM shows 2 extensively resorbed intramembranous deposits (arrows); the deposit within the lower basement membrane is interpreted as showing striated membrane structures or possibly cellular elements, as have been described by Tornroth¹⁰ within foci of resorbed deposits in resolving postinfectious GN. The glomerular basement membranes are thickened. Compare this with (C), which is of the same magnification. [(A and G) Periodic acid-Schiff stain, original magnification ×400; (D) periodic acid-Schiff stain, original magnification ×200; (B, E, and H) direct immunofluorescence with fluorescein isothiocyanate-conjugated goat anti-human C3, original magnification ×400; (C and I) uranyl acetate and lead citrate stain, original magnification ×6300; (F) uranyl acetate and lead citrate, originaol magnification ×8000.].