Left-right asymmetry in the thoracic spinal cord.

Evidence of left-right asymmetry in the spinal cord has been accumulating for some time. This report adds an anatomical example. For thoracic segments in the cat, the dorsal root entries of a given segment, at least for T5 to T9, were shown to have a tendency to be located more rostrally on the right than on the left. Measurements of the root positions have been brought together from notes in experimental protocols over nine years (36 animals). The rostral-most root of a segment on the right was found to lie up to 4.5 mm more rostrally than that on the left (mean 0.93 ± 1.05 mm, n = 86), while the caudal-most root was similarly asymmetric by up to 5.5 mm (mean 0.98 ± 1.72 mm, n = 30). These results are supported by very similar measurements made from the undamaged regions of spinal cords in a further 36 animals that had spinal cord lesions. Implications of the asymmetry are discussed.