[Vascular permeability of fluorescent substance in cranial nerve roots]

Recently, it has been reported that the facial nerve in the facial canal shows enhancement on gadolinium-enhanced magnetic resonance imaging (Gd-MRI) in patients with a clinically normal facial nerve. Enhancement is also observed in the Gasserian ganglion and in the second and third divisions of the trigeminal nerve at the base of the skull. The aim of the present investigation was to study the vascular permeability of cranial nerve roots using the tracer technique. Vascular permeability in the cranial nerve root was examined after intravenous injection of sodium fluorescein (Fluorecite) as a tracer, in the rabbit. Fluorescence was observed in the distal nerves through the following portions: intracavernous portion of the third, distal internal auditory canal segment of the seventh, and ganglionic portions of the fifth, ninth and tenth cranial nerves. No fluorescence was observed in the first, second or eighth cranial nerves. The fluorescence of the other cranial nerves was undetectable because of a slender fasciculus. Histologically, fluorescence was observed in the external nerve sheaths (epineurium and perineurium) and the endoneurium of the cranial nerves showing fluorescence. No fluorescence was observed within the nerve fibers. In the ganglia, fluorescence was also seen in ganglion cells and intercellular connective tissues. Since Fluorecite (mol. wt. 376 and a negative charge) was dispersed in the cranial nerves, it is feasible that Gd-DTPA (mol. wt. 742 and negative charge) may also be distributed in these portions. This distribution may indeed provide an insight into the Gd-MRI enhancement observed in facial and trigeminal nerves.