Sexual dimorphism of the human spinal cord in the aging process.

There have been few morphometric studies on age-related changes in the human spinal cord. The purpose of the present study was to determine the existence of sexual dimorphism of the spinal cord between males and females during the aging process. Spinal cords were removed from cadaver specimens, 26 males and 22 females for anatomic practice, the age at death ranged from 41 to 97 years for males (average, 71.5 years) and from 59 to 92 years for females (average, 76.6 years). Spinal cord segments were embedded in celloidin after secondary fixation and dehydration. Sections were stained with the Luxol fast blue-periodic acid-Schiff-hematoxylin and Klüver-Barrera methods. Morphometric analysis was performed with an electronic optical planimeter and a computer. Each section was enlarged 13.5 times to take a picture. The areas of the transverse section white matter and gray matter of the spinal cord at segments C5 and L3 were measured. Although there was no correlation between the total transverse area of the spinal cord and age either in males or females, we noticed that the area of the gray matter decreased faster in males than in females; while the area of the white matter decreased faster in females than in males. The area ratio of the white matter to the whole segment area of the spinal cord (W/T) at level C5 is larger in males than that in females. Our results suggest that there could be a difference between males and females in changes in the white and gray matters of the spinal cord due to aging.