Interrupted eccentric longitudinal muscle fibers of the kidney and adrenal veins

A large number of sections were taken from adrenals and kidneys of human subjects of various age groups. The sections were stained by hematoxylin and trichrome methods, and they were examined for presence or absence of interrupted eccentric longitudinal muscle fibers along the course of the veins. It is noted that these muscle fibers are absent in newborns and infants; they are present in small amounts in children and they increase with age. The fibrous tissue particularly is noted to increase as age advances. These are more easily found in the adrenals than they are in the kidneys. In older people, focal hypertrophy and fibrosis of these muscle bundles could form a nodular pattern occluding the lumen of the veins. It appears to us that hypertrophy and fibrosis of these muscle fibers are related to old age and stress rather than to a particular disease process such as hypertension. Examination of the adrenals and kidneys of rats showed no evidence of longitudinal muscle fibers.