Morphologic variants of focal segmental glomerulosclerosis and their significance.

Focal segmental glomerulosclerosis (FSGS) comprises a group of clinical-pathologic syndromes characterized by heavy proteinuria and segmental obliteration of glomerular capillaries by extracellular matrix. FSGS lesions display morphologic heterogeneity with respect to their relationship to the glomerular vascular and tubular poles, the presence of capillary collapse, and endocapillary and extracapillary hypercellularity. A working proposal, commonly referred to as the Columbia Classification, distinguishes 5 mutually exclusive morphologic variants: collapsing, tip, cellular, perihilar, and not otherwise specified (NOS), which can be applied to primary and secondary forms of FSGS. Several studies have documented significant differences in baseline clinical characteristics and outcomes between morphologic variants of primary FSGS, supporting that this classification may provide useful prognostic information. The association of certain variants with particular secondary causes of FSGS suggests pathogenetic relevance.