Aberrant regeneration of motor axons into the pia mater after ventral root neuroma formation

Abstract

The spinal pia mater receives a rich innervation of small sensory and autonomic axons via the ventral roots. In the present study this pathway was interrupted by the transection of the L7 ventral root in young kittens. The animals were killed 12-18 months postoperatively. It was observed that the pia mater adjacent to the divided ventral root contained large numbers of myelinated axons. We suggest that these axons represent sprouts which had reached the pia mater by retrograde growth from the neuroma on the ventral root. Some of these aberrant pial axons ended blindly in the pia mater. Abnormal terminal-like swellings were observed along pial blood vessels. Fibers with diameters exceeding 11 microns were observed. Many fibers had an internodal spacing below 100 microns and the maximum value was only about 300 microns. Thus, motor axons which are forced to grow into a foreign territory show a maldevelopment which is more obvious with regard to nodal spacing than to fiber diameter.