Experimental observation of particulate flow along cranial nerves

The purpose of this study was to investigate the communicative routes via the cranial nerves among the middle ear, the auditory tube, the inner ear, and the subarachnoid space under nearly physiological conditions. Various volumes of Indian ink were slowly injected into the facial nerve trunk of rabbits at the stylomastoid foramen, then serial sections of the heads were observed under the light microscope. This study yielded the following results: (i) Indian ink penetrated into the subarachnoid space through the internal auditory canal and/or the jugular foramen along the nerve sheaths of the VIIth, IXth, and/or Xth cranial nerves. (ii) Indian ink penetrated through the nerve sheaths of the cochlear, superior vestibular, and inferior vestibular nerves to the fundus of the internal auditory canal. (iii) Indian ink reached the scala tympani and the scala vestibuli via the cochlear aqueduct. (iv) Indian ink penetrated to the nerve sheaths of the tensor tympani and/or tensor palati nerves from the subarachnoid space of the trigeminal ganglion. In conclusion, it was shown that certain small particles are able to penetrate from the facial nerve sheath at the entrance of the stylomastoid foramen to the VIIIth, IXth, and Xth nerve trunks, the middle ear, the area around the auditory tube, the inner ear, and the subarachnoid space.