The fine structure of lipofuscin in the human inner ear.

Lipofuscin inclusions in the human membranous labyrinth were studied by electron microscopy. Lipofuscin is morphologically an irregularly shaped, membrane-bound inclusion consisting of an electron-dense structure. The most common component was a fine, granular, osmiophilic substance which was always associated with a homogenous, spherical structure resembling a lipid droplet. The combination of these two components was frequently observed in the human inner ear. Distended inclusions containing lipofuscin components were also observed within the supporting cells, saccular, utricular and ampullar wall, the epithelial cells of the transitional zone and in the dark cells. Lipofuscin is closely associated with lysosome and is known to accumulate in the tissue as a result of aging. The high lysosomal activity possibly may result in lipofuscin formation in the human inner ears. Also some other unknown metabolic conditions may provide the deposits of lipofuscin.