Table 4.

Definitions of glomerular lesions derived from the Oxford classification of IgA nephropathy1,64 and patterns of GN derived from the ISN/RPS lupus classification22

Glomerular lesions
 Mesangial hypercellularity>3 Mesangial cells per mesangial area
 Cellular crescentExtracapillary cell proliferation of more than two cell layers with >50% of the lesion occupied by cells
 Fibrocellular crescentAn extracapillary lesion comprising cells and extracellular matrix, with <50% cells and <90% matrix
 Fibrous crescentExtracapillary crescents with >90% matrix
 Endocapillary hypercellularityHypercellularity caused by an increased no. of cells within glomerular capillary lumina, causing narrowing of the lumina
 Fibrinoid necrosisDisruption of the GBM with fibrin exudation
 SclerosisObliteration of the capillary lumen by increased extracellular matrix with or without hyalinosis or foam cells
Patterns of GN
 Minimal mesangial GNaNormal glomeruli by LM but mesangial immune deposits by IF
 Mesangial proliferative GNaPurely mesangial hypercellularity
 Active (proliferative) GNaAny or all of the following glomerular lesions: endocapillary hypercellularity, karyorrhexis, fibrinoid necrosis, rupture of GBMs, cellular or fibrocellular crescents, subendothelial deposits identifiable by LM, and intraluminal immune aggregates
 Necrotizing GNSegmental or global fibrinoid necrosis
 Crescentic GN≥50% Glomeruli with cellular, fibrocellular, or fibrous crescents (with percentage of crescents always noted in the diagnostic line, even when <50%)b
 Membranoproliferative GNMesangial and/or endocapillary hypercellularity and thickening of capillary walls caused by subendothelial Ig and/or complement factors
 Exudative GNNeutrophils accounting for >50% of glomerular hypercellularity
 Sclerosing GNaAny or all of the following glomerular lesions: glomerular sclerosis, fibrous adhesions, and fibrous crescents
  • ISN/RPS, International Society of Nephrology/Renal Pathology Society.

  • a Except for the first two patterns, multiple patterns can occur together in a single specimen (derived from the ISN/RPS lupus classification22).

  • b The term crescentic GN is used when crescents are present in at least 50% of glomeruli, and applies to immune-complex GN/C3 glomerulopathy. This does not apply to ANCA GN and anti-GBM GN, where less than 50% of the glomeruli may be involved by crescents.