Prominent parietal epithelium: a common sign of renal glomerular injury

Reported abnormalities of the normally inconspicuous renal glomerular parietal epithelium include tubular metaplasia, adenomatoid transformation, columnar metaplasia, and embryonal hyperplasia of Bowman's capsular epithelium. In this study, glomerular parietal epithelium was analyzed in 77 consecutive renal biopsy specimens representing a spectrum of renal diseases. In 57 biopsy specimens, prominent parietal epithelium (PPE) (ten or more enlarged parietal cells with hyperchromatic or vesicular nuclei and discernable vacuolated cytoplasm in at least two glomeruli) was identified and graded according to its severity in the specimen. Extensive PPE was present in all five cases of diabetic nephropathy and was common in membranoproliferative glomerulonephritis, acute glomerulonephritis, focal sclerosing glomerulopathy, and diffuse proliferative lupus nephritis. In most disease categories, however, PPE varied in grade from case to case. Interstitial fibrosis and tubular atrophy (39 of 57 biopsy specimens) and vascular thickening (43 or 57 biopsy specimens) were common in specimens containing PPE. On electron microscopy, normal parietal cells appeared to be mature and relatively inactive. PPE cells, in contrast, had features compatible with actively proliferating cells and damaged cells. It is proposed that PPE may be the result of acute or chronic glomerular injury. Possible pathogenetic mechanisms are discussed, as is the probable relationship between PPE and crescents.