Giant mitochondria in the epithelial cells of the proximal convoluted tubules of diseased human kidneys.

Electron microscopy of 100 renal biopsies obtained at random from patients with various renal disorders revealed gigantic mitochondria in the cytoplasm of the epithelial cells of the proximal tubules in 36 cases (36 per cent). These giant mitochondria are usually round, ovoid, spindle-shaped or rod-shaped often reaching the size of the cell nucleus, and appear singularly and sporadically in the epithelial cell lining of the tubules. Once recognized by electron microscopy they are easily identified in routine histologic preparations and show the same staining characteristics as other mitochondria. In electron microscopy, giant mitochondria have a double limiting membrane, abundant matrical substance, and few remnants or cristae. In addition, they are characterized by (1) intramatrical irregularly branching fibrils approximately 35 A thick, (2) intramatrical bundles of straight filaments approximately 60 to 70 A thick, (3) intramatrical electron-opaque globules up to 0.6 mum., and (4) helical filaments in focally dilated spaces of the outer compartment. The significance of such a remarkable morphologic change of tubular mitochondria and the nature of the unusual components are at present unknown, but an abnormal metabolic condition is considered in its pathogenesis. Nothing specific has yet been found in the relationship between the positive appearance of giant mitochondria and types of renal disorders or clinical and laboratory data. It may be postulated from the present study that "giant mitochondrial tubulopathy" is a rather common, characteristic, and noteworthy change in the histopathology of renal tubule.