Yoshiaki Nakao

Prediction of facial nerve outcome using electromyographic responses in acoustic neuroma surgery.

Objective To determine whether early and late postoperative facial nerve function can be predicted on the basis of electromyographic responses in acoustic neuroma surgery. Setting Prospective blinded study. Design Tertiary referral center. Patients and Methods Burst and train electromyographic responses were recorded intraoperatively during the last step of vestibular schwannoma removal. The responses were classified and compared with early and late postoperative facial function in 49 patients who underwent enlarged translabyrinthine acoustic neuroma surgery. Results In the early postoperative period, 20 of 22 patients with an irritable pattern and 10 of 13 patients with an ordinary pattern had Grade III or better facial nerve function, whereas all 3 patients with a stray pattern and 9 of 11 patients with a silent pattern had Grade V or VI. In the late postoperative period, on the other hand, Grade III or better facial nerve function was achieved in 37 of 38 patients with an irritable, stray, or ordinary pattern, but the facial nerve function remained at Grade V or VI in 2 patients with the silent pattern. Conclusion Patients with mechanically evoked facial electromyographic responses to the last step of tumor dissection may not experience severe facial nerve dysfunction or show a remarkable improvement. However, patients with silent electromyographic responses during this step tend to experience severe facial nerve dysfunction early in the postoperative course, and some patients may not show any functional improvement.

Vascular permeability to sodium fluorescein in the rabbit cranial nerve root: possible correlation with normal cranial nerve enhancement on gadolinium-enhanced magnetic resonance imaging

Vascular permeability in cranial nerve roots was examined after intravenous injection of sodium fluorescein in the adult rabbit. Fluorescence was observed in the distal nerves through the following portions: intracavernous portion of the oculomotor nerve, distal internal auditory camal segment of the facial nerve, and ganglionic portions of the trigeminal, glossopharyngeal and vagus nerves. In the acoustic nerve, the vestibular ganglion showed fluorescence. No fluorescence was observed in the olfactory or optic nerves. During in vivo gadolinium-enhanced magnetic resonance imaging (Gd-MRI) of two separate animals, trigeminal nerve enhancement was observed in the region showing fluorescence. Histologically, intense fluorescence was observed in ganglia and external nerve sheaths of the cranial nerves showing macroscopic fluorescence. A slight fluorescence was also seen in endoneurial connective tissue but not observed within the nerve fibers. The results of this study suggest that the physiological enhancement of human cranial nerves seen on Gd-MRI may correlate with vascular permeability.

Vascular permeability changes associated with experimentally induced facial nerve lesions in the rabbit

Changes in vascular permeability to sodium fluorescein following experimentally induced nerve lesions were examined in the rabbit facial nerve. Sodium fluorescein was injected intravenously as a permeability tracer and then localized by fluorescence microscopy. In control nerves, endoneurium showed only slight fluorescence while intense fluorescence was observed in the epineurium and perineurium. In nerves demonstrating edema and Wallerian degeneration, endoneurium was found to have an increased accumulation of tracer. This increased endoneurial vascular permeability in facial nerve lesions may explain nerve enhancement seen in gadolinium-enhanced magnetic resonance imaging in patients with facial nerve paralysis.

Altered Distribution of Motor Neurons in Experimental Facial Nerve Paralysis

The alteration of motor neurons in the brainstem after recovery from experimental facial nerve paralysis was examined by the retrograde horseradish peroxidase (HRP) technique in the rabbit. Six months after nerve crush injury at the center of the vertical portion, HRP was injected into the zygomatic muscle on the recovered side. The distribution of labelled neurons in the brainstem was compared with that in the normal rabbit. In control animals, motor neurons in the facial nucleus were somatotopically organized, and there were no labelled neurons in other nuclei in the brainstem. In recovered animals, on the contrary, the somatotopic organization of the facial nucleus was obscure and multipolar neurons of varying size were labelled bilaterally in the reticular formation from the pons to the medulla.

Mesenchymal chondrosarocoma of the temporal bone

A 64-year-old patient with mesenchymal chondrosarcoma of the temporal bone is described. CT and MRI showed an extensive mass with calcification involving the temporal bone and extending into the middle cranial fossa and nasopharynx. The tumor was ill-defined from surrounding normal bone, and a subtotal petrosectomy was carried out. The nasopharyngeal extension was removed secondarily using an endoscope. The clinical and diagnostic aspects and management of this rare lesion are discussed.

Extracellular Fluid Pathway inside the Facial Nerve Fascicles

The extracellular fluid pathway in the facial nerve and the diffusion of a tracer from the facial nerve to other cranial nerves was examined in the rabbit. Sodium fluorescein solution was injected into either the facial nerve fascicles or the epineurial connective tissue as a tracer at the stylomastoid foramen and then localized by fluorescence microscopy. In the facial nerve, fluorescence was observed in the endoneurium and external nerve sheath (epineurium and perineurium) through the geniculate ganglion following injection into the nerve fascicles. The vestibular, trigeminal, and glossopharyngeal ganglia also showed fluorescence on the injection side in ganglion cells and intercellular connective tissues. The results suggested that the endoneurial connective tissue constitutes a diffusion pathway inside the facial nerve fascicles and that the extracellular fluid pathway from the facial nerve to these cranial ganglia may be related to the neural spread of inflammation or neoplastic metastasis.

Vascular permeability to fluorescent substance in human cranial nerves.

It has recently been reported that in the facial canal, the facial nerve shows enhancement on gadolinium-enhanced magnetic resonance imaging in patients with clinically normal facial nerves. However, the mechanism of this enhancement has not yet been sufficiently clarified. The present study investigated the permeability of blood vessels in human cranial nerves that were obtained from surgically treated patients. The patients received an intravenous injection of sodium fluorescein 45 minutes before nerve resection. For histologic observation, the nerves were removed and frozen at −70°C, and the sections were then cut at 4-μm thickness with a freezing microtome. The localization of the tracers was examined with a fluorescence microscope. Fluorescence was observed in the external nerve sheath and slightly in the endoneurium of these nerves, but was not observed within nerve fibers. These findings indicate that the vascular barrier in human peripheral nerves is incomplete.

Fluorescence Findings of the Facial Nerve at Decompression Operation

Decompression operation was performed on patients with Bells palsy and facial nerve palsy due to temporal bone fracture or otitis media, and a study was made on the relation between the fluorescence findings of the nerve and prognosis. The fluorescence of nerve was visible in 4 cases of Bells palsy but none of the patients was completely cured, though the degree of cure tended to be proportional to the intensity of fluorescence. On the other hand, cure was seen even in cases of facial nerve palsy due to temporal bone fracture or otitis media that showed no fluorescence or any response in the maximal stimulation test (MST). It is suggested that Bells palsy and facial nerve palsy due to trauma or otitis media do not share the same pathophysiology.

Gadolinium-Enhanced Magnetic Resonance Imaging in Experimental Facial Nerve Paralysis

Recently, it has been reported that the facial nerve shows enhancement on gadolinium-enhanced magnetic resonance imaging (Gd-MRI) in patients with such conditions as Bell’s palsy or traumatic facial nerve paralysis. The site of involvement in Bell’s palsy remains unknown, and accurate lesion-site information is useful for surgical planning in cases of facial nerve paralysis. The importance of this technique in detecting the lesion site has been discussed, but the mechanism of facial nerve enhancement is unknown. In the present study, in order to elucidate the correlation between facial nerve enhancement and lesion site, Gd-MRI study was performed in the rabbit.

Observation of motoneurons after recovery from experimental facial nerve paralysis.

In Bell’s palsy and in Ramsay Hunt’s syndrome, sequelae such as synkinesis, facial spasm, or contracture occur during recovery from facial nerve palsy. The mechanism of these sequelae has not yet been sufficiently clarified. The misdirection of regenerating nerve fibers at the site of injury may result in synkinesis. However, other possible mechanisms of synkinesis, including rearrangement of synaptic vesicles in the facial nucleus, have been suggested [1]. In the present study, the alteration of motoneurons in the brainstem after recovery from experimental facial nerve paralysis was examined by the retrograde horseradish peroxidase (HRP) technique in rabbits.