Hiroshi Ryu

Neurovascular Compression Syndrome of the Eighth Cranial Nerve. What are the Most Reliable Diagnostic Signs

Summary Forty-three surgical cases were retrospectively analyzed to establish diagnostic criteria and operative indications for vertigo and tinnitus due to neurovascular compression (NVC) of the eighth cranial nerve (8th N). Many NVC syndromes were mistakenly diagnosed as Ménières disease or benign paroxysmal positional vertigo. NVC was confirmed in 31 of the 43 patients. Neurovascular decompression (NVD) resulted in complete recovery or marked improvement of subjective symptoms in all 19 cases with vertigo (100%), and in 19 of 29 patients with tinnitus (65.5%). Multiple factor analysis revealed that abnormal caloric responses have high diagnostic value for vertigo due to NVC. Vertigo due to NVC is of short duration (a few sec to a few min.) in the early phase of the disease, which becomes longer and hearing becomes impaired as the history of NVC lengthens. Low pitch pulsatile and high pitch continuous tinnitus are probably due to NVC and are cured by NVD if hearing is still preserved. Tinnitus associated with hemifacial spasm is strongly indicative of NVD. Decompression of the 8th N should be performed in the early phase of disease, since cochlear and vestibular functions are irreversibly impaired if NVC continues for a long period of time.

Functional anatomy of the human cochlear nerve and its role in microvascular decompressions for tinnitus.

OBJECTIVEThe functional anatomy (i.e., tonotopy) of the human cochlear nerve is unknown. A better understanding of the tonotopy of the central nervous system segment of the cochlear nerve and of the pathophysiology of tinnitus might help to ameliorate the disappointing results obtained with microvascular decompressions in patients with tinnitus. METHODSWe assume that vascular compression of the cochlear nerve can induce a frequency-specific form of hearing loss and that when the nerve is successfully decompressed, this hearing loss can recuperate. Thirty-one patients underwent a microvascular decompression of the vestibulocochlear nerve for vertigo or tinnitus. Preoperative audiograms were subtracted from postoperative audiograms, regardless of the surgical result with regard to the tinnitus and vertigo, because the hearing improvement could be the only sign of the vascular compression. The frequency of maximal improvement was then correlated to the site of vascular compression. A tonotopy of the cochlear nerve was thus obtained. RESULTSA total of 18 correlations can be made between the site of compression and postoperative maximal hearing improvement frequency when 5-dB hearing improvement is used as threshold, 13 when 10-dB improvement is used as threshold. A clear distribution can be seen, with clustering of low frequencies at the posterior and inferior side of the cochlear nerve, close to the brainstem, and close to the root exit zone of the facial nerve. High frequencies are distributed closer to the internal acoustic meatus and more superiorly along the posterior aspect of the cochlear nerve. CONCLUSIONThe tonotopic organization of the cisternal segment of the cochlear nerve has an oblique rotatory structure as a result of the rotatory course of the cochlear nerve in the posterior fossa. Knowledge of this tonotopic organization of the auditory nerve in its cisternal course might benefit surgeons who perform microvascular decompression operations for the vestibulocochlear compression syndrome, especially in the treatment of unilateral severe tinnitus.

Stereotactic Interstitial Laser-Hyperthermia Using Nd-YAG Laser

Laser hyperthermia using Nd-YAG laser was studied experimentally and clinically to treat deep-seated brain tumors. Histological changes, temperature profile, and modification of the blood-brain barrier were studied using cat and rat brains. In a clinical study 5 patients with brain tumors were treated with laser hyperthermia using this computed tomography-stereotactic technique. All tumors of these patients disappeared on computed tomography, and 3 of the 5 patients are still alive without recurrence. It was possible to make optimal lesion and to have accurate peripheral temperature control by using the combination of the Komai stereotactic method and the SLT Nd-YAG laser system. Interstitial laser hyperthermia using this method is easy and safe to use, and it is beneficial to treat deep-seated brain tumors.

Chronological Changes of Arterial Diameter, cGMP, and Protein Kinase C in the Development of Vasospasm

BACKGROUND AND PURPOSE We hypothesized that nitric oxide exerts a negative feedback control on protein kinase C (PKC) activation, and the disturbance of the feedback control after subarachnoid hemorrhage results in vasospasm due to PKC activation. This study was undertaken to verify this hypothesis. METHODS Different dogs were prepared for three separate experiments: measurement of the angiographic diameter of the basilar artery and determination of cGMP and PKC activity in vascular smooth muscle cells. In each experiment, two models were used: the single-hemorrhage model for mild vasospasm and the two-hemorrhage model for severe vasospasm. In both models, chronological changes of these three parameters were examined from day 1 until day 7. RESULTS In the single-hemorrhage model, mild vasospasm and a slight decrease of the cGMP level were noted on day 4, then both returned to the baseline levels on day 7. PKC activity was slightly enhanced throughout the study period. In the two-hemorrhage model, severe vasospasm and a significant decrease of the cGMP level were observed on day 5 and persisted until day 7. PKC activity was remarkably enhanced from day 5 until day 7. The differences between the two models with regard to the three parameters were statistically significant. CONCLUSIONS The decrease of cGMP level and the enhancement of PKC activity were obviously associated with the development of severe vasospasm. We conclude that subarachnoid hemorrhage disturbed the feedback control exerted by nitric oxide on PKC activation, leading to PKC-dependent vasospasm.

Neurovascular compression syndrome of the eighth cranial nerve. Can the site of compression explain the symptoms

Summary Considerable skepticism still exists concerning the concept of neurovascular compression (NVC) syndromes of the eighth cranial nerve (8th N). If such syndromes exist, the sites of compression of the nerve must explain the symptoms encountered. We recorded compound action potentials of the cochlear nerve (CCAPs) during neurovascular decompression (NVD) to examine the topography of the three components of the 8th N. The sites of compression of the 8th N in cases of NVC syndrome confirmed at surgery were superimposed on the topography of the CN and vestibular nerve (VN) in order to determine the relationship between the sites of compression and the symptoms. CCAPs were clearly and consistently recorded on the caudal surface of the 8th N along the midline. In patients with vertigo and tinnitus there was vascular compression of the rostro-ventral (VN) and caudal surface (CN) of the nerve, respectively. In patients with both vertigo and tinnitus, there was compression of both VN and CN. Our findings clearly demonstrate that the symptoms of NVC of the 8th N depend on the part of the nerve that is compressed by blood vessels, and they support the concept of NVC syndrome of the 8th N.

Cerebral blood flow autoregulation following subarachnoid hemorrhage in rats: Chronic vasospasm shifts the upper and lower limits of the autoregulatory range toward higher blood pressures

We sought to determine whether chronic vasospasm following subarachnoid hemorrhage (SAH) would abolish the cerebral blood flow (CBF) autoregulation in anesthetized Sprague-Dawley rats. SAH was induced by intracisternal injection of autologous blood; in control animals saline was injected instead. CBF was measured 48 h after SAH, that is during chronic vasospasm, by laser-Doppler flowmetry over the frontal cortex under condition of hypertension (SAH, n = 6; control, n = 8) or hypotension (SAH, n = 6; control, n = 6). Hyper- and hypotension were induced by increasing mean arterial blood pressure (MABP) stepwise from 90 to 180 mmHg with phenylephrine (0.1-10 micrograms/min i.v.), or by decreasing it from 90 to 40 mmHg by controlled hemorrhage. An autoregulatory index (AI) expressed as delta CBF (%) per 10 mmHg increase or decrease in MABP was employed to analyze CBF response. CBF remained constant (-7 < AI < 7) at MABPs ranging from 60 to 130 mmHg in the control group and from 70 to 140 mmHg in the SAH group, showing CBF autoregulation. In the SAH group, that is, the upper and the lower limits of autoregulatory range were increased by 10 mmHg (p < 0.05). SAH did not increase intracranial pressure significantly (control 9.2 +/- 0.67 vs. SAH 10.0 +/- 1.05 mmHg, n = 5) 48 h after SAH was induced. These results indicate that, during chronic vasospasm, SAH does not abolish the autoregulation process but raises its lower and upper blood pressure limits. The capacity of spastic cerebral arteries to dilate in case of hypotension decreased, while their tolerance to hypertension increased.

Myelopathy Caused by Retro-odontoid Disc Hernia: Case Report

OBJECTIVE AND IMPORTANCE Among masses in the craniovertebral junction causing severe compression of the medulla and upper cervical cord, cases of retro-odontoid disc hernia are extremely rare. We report a case of retro-odontoid disc hernia resulting in severe myelopathy. CLINICAL PRESENTATION An 82-year-old man suffered from progressive tetraparesis. Although cervical radiological studies showed marked spondylotic change, no congenital malformations or traumatic lesions were identified. Magnetic resonance imaging disclosed a retro-odontoid soft tissue mass with peripheral enhancement compressing the medulla and the upper cervical cord posteriorly. INTERVENTION The patient underwent surgery through the posterior approach. The histopathological examination of the surgical specimen revealed fibrocartilage accompanied by reactive vascular tissue; the mass was diagnosed as a retro-odontoid disc hernia. CONCLUSION In the differential diagnosis of mass lesions compressing the neural structures in the craniovertebral junction, retro-odontoid disc hernia, although extremely rare, should be considered to be one possibility. The posterior approach with wide laminectomies provides a good operative field from which to remove the retro-odontoid mass and is especially adequate for elderly patients, because it is less invasive than other procedures.

Frequency specific hearing improvement in microvascular decompression of the cochlear nerve

SummaryBackground. Microvascular compressions of the cochlear nerve can lead to hearing loss. Due to the tonotopic organization of the cochlear nerve any focal compression of the cochlear nerve will result in a frequency specific hearing loss. Decompressing the cochlear nerve could result in a frequency specific hearing improvement, without improving overall hearing.Method. Thirty one patients underwent microvascular decompression operations of the vestibulocochlear nerve for vertigo or tinnitus. Preoperative audiograms were substracted from postoperative audiograms obtained 2 years after microvascular decompression. The frequencies of maximal hearing improvement postoperatively were determined.Findings. Of the 31 patients studied, 19 had improvements of 5 dB or more at one or more frequencies postoperatively, and 15 patients had improvements of 10 dB or more. Three patients had improvements of 25 dB or more postoperatively. The postoperative hearing improvement was frequency-specific and related to the anatomical location of the vascular contact on the auditory nerve. The improvement of hearing becomes diluted when the difference between pre- and postoperative hearing thresholds are averaged over all audiometric frequencies. We therefore present results for each frequency that was tested.Conclusions. Microvascular decompression of the cochlear nerve can improve hearing in selected patients. The improvement seems too small to justify decompressive surgery for the sole purpose of hearing improvement, but it could be considered if associated short vertigo spells, ipsilateral tinnitus, otalgia and cryptogenic hemifacial spasm are present. Decompression should be performed early, before BAEP changes become noticeable. 3D-MRI could become a valuable tool for selecting good surgical candidates.

Atypical Hemifacial Spasm

Summary Among 155 cases of hemifacial spasm (HFS), the authors found two cases of atypical HFS (1.3%) in which spasm started with the orbicularis oris and buccinator muscles, and gradually spread upward to involve the orbicularis occuli muscle, whereas the reverse process is usually seen in cases of typical HFS. The compression site in cases of atypical HFS is the posterior/rostral aspect of the facial nerve (FN), whereas it was the anterior/caudal aspect of the FN in all cases of typical HFS except for one. The meatal loop of the anterior inferior cerebellar artery (AICA) compressed the FN when the vessel passed between the FN and the eighth cranial nerve (8th N). These findings suggest that the topographical organization in the FN in the cerebellopontine cistern may be reversed to a peripheral distribution: the fibres on the posterior/rostral side of the FN innervate the lower part of the facial muscles, and those in the anterior/caudal side of the nerve innervate the upper part of the facial muscles. When examining patients with HFS, we must very carefully determine whether patients have typical or atypical HFS, to determine whether blood vessels (usually the meatal loop of the AICA) between the FN and the 8th N as well as at the root exit zone of the FN are to be decompressed.

Facial nerve monitoring by monopolar low constant current stimulation during acoustic neurinoma surgery

Electrophysiological characteristics of monopolar low constant current stimulation, and evoked facial muscle responses to such stimulation, were evaluated in 34 cases of acoustic neurinoma. Our study, using stimulus parameters of 0.1-ms-duration pulse wave with 0.5-0.6 mA intensity, revealed that extent of spreading current depends on the current intensity, being about 1 mm from the electrode with 0.5-0.6 mA, and insulation of the electrode prevented the current from spreading through the cerebrospinal fluid, giving a reliable amount of current to the tissue. Evoked facial muscle responses to facial nerve stimulation in the internal auditory meatus and over the pons were analyzed and revealed the following: (1) The responses to stimulation in the internal auditory meatus showed no amplitude attenuation throughout the operation. (2) The responses to stimulation over the pons gradually decreased in amplitude as tumor dissection from the nerve proceeded, especially in large tumors. (3) Anatomical continuity of the nerve was obtained in 100% of small, 91.7% of medium, and 88.2% of large tumors. Our data show that monopolar low constant current stimulation is effective in obtaining the precise anatomical orientation of the facial nerve during tumor removal.