Segmental Collapsing Capillary Tufts (SCCT) in Diabetic Glomeruli.
L Clarke Stout. University of Texas Medical Branch, Galveston
Background: Capillary obliteration is obvious in large Kimmelstiel-Wilson nodules, but its mechanism is unknown in the far more prevalent diffuse lesion, where expanding mesangium just seems to fill the glomerulus until it becomes obsolescent. This report describes novel segmental collapsing capillary tufts (SCCT) in 2 of 25 diabetics, 1 with Type 1 (T1DM) and 1 with Type 2 (T2DM) diabetes.
Design: SCCT were found by chance in a study of glomerular changes in 74 diabetics (end stage renal disease excluded) and 59 matched controls from consecutive autopsies at our hospital. The present study group consisted of 25 of the diabetics that had any degree of diabetic glomerulopathy and 12 matched controls. All 37 cases had 18 variously stained paraffin embedded 4 µm serial sections. One hundred glomeruli from each case were reviewed in section 9 (PAS). Nine to 15 glomeruli were completely traced in each of 2 diabetics and 2 controls that had PolyBed 812 embedded toluidine blue stained 1µm serial sections.
Results: SCCT were first seen in 1 μm serial sections in the T1DM case that had 16 SCCT in 8 of 9 complete and 4 partial glomeruli (5 gomeruli had 1, 1 had 2, 1 had 3 and 1 had 6 SCCT). Six SCCT in 5 glomeruli were large. No definite SCCT were found in the 4 µm sections from the same case. SCCT were called early [mild decrease in capillary lumen size and glomerular capillary basement membrane (GBM) width], mid (moderately decreased lumen size and GBM width), and late (collapsed autolyzed masses of barely recognizable capillaries and mesangium). SCCT were called small (in-situ capillary segments) or large (detached capillaries and mesangium up to 35 x 60 x >55µm in size. Three large SCCT were attached to the tuft by a single capillary, the GBMs of which were contiguous but abruptly thinned in the SCCT. Mesangium occupied the intracapillary space in the tuft at the junction. One T2DM case had 1 probable and 1 possible large SCCT in paraffin sections.
Conclusions: The decreased intraluminal volume and thin GBMs of SCCT suggested decreased perfusion. This and their seemingly autolytic demise suggested a gradual rather than a sudden decrease in flow, possibly due to diabetic mesangial expansion and/or disordered mesangial contraction. Inter or intralobular small anastomotic capillary loops would seem likely candidates for SCCT. Their obliteration could account for the glomerular lobulation and simplification typically seen in advanced diabetic glomerulopathy. The frequency of SCCT in 1µm plastic sections and their absence in 4µm paraffin sections in the same case suggest that SCCT may be underrecognized.
Category: Kidney (does not include tumors)
Wednesday, March 2, 2011 1:00 PM
Poster Session VI # 242, Wednesday Afternoon