Morphometric changes in the spinal cord during prenatal life: a stereological study in sheep.

This study describes the volumetric changes in the spinal cord during prenatal life in sheep using quantitative stereological methods. Twenty healthy sheep fetuses were included in the present study, divided into four groups representing 9-11, 12-14, 15-17, and 18-20 weeks of gestation. In each group, the spinal cord was dissected out and sampled according to the unbiased systematic random sampling method then used for stereological estimations. The total volume of spinal cord, volume of gray matter (GM), volume of white matter (WM), ratio of GM volume to WM volume, and volume of central canal (CC) were estimated in the whole spinal cord and its various regions using Cavalieri's principle. The total volume of the spinal cord increased 8 times from week 9 to week 20. The cervical region showed the greatest (9.7 times) and the sacral region the least (6.3 times) volumetric change. The CC volume of the whole spinal cord increased 5.8 times from week 9 to week 20. The cervical region developed faster (8.2 times) and the thoracic region slower (4.4 times) than the total spinal cord. During development, the volume ratio of GM to WM decreased from lower toward upper regions. The greatest volume changes occurred mostly in weeks 9-11 and 12-14. The cervical region showed the greatest volume changes in comparison with other regions of the spinal cord.