Tubular luminal dilatation Dilatation (expansion beyond the normal dimension) of the cavity (lumen) of tubules of the kidney. The tubular cross section displays an attenuated brush border (apical PAS positivity greater than 10 percent of the normal expected height, but unequivocally less than normal expected height), resulting in an apparent increase in the size of lumen. Tubular ectasia By definition, ,tubular luminal dilatation excludes simplifcation, which is defined as a tubular cross-section with flattened tubular cell cytoplasm (height unequivocally less than width), with complete loss of brush borderinvolving over 50 percent of the tubular cells in cross-section, resulting in an apparent increase in the size of lumen, without presence of casts. Abnormal renal tubular lumen morphology dilated renal tubule