Root Exit Zone Research Articles

Botulinum toxin therapy of hemifacial spasm: comparing different therapeutic preparations

Hemifacial spasm (HFS) is characterized by involuntary irregular clonic or tonic movements of the muscles innervated by cranial nerve VII on one side of the face, and is most often a result of vascular compression of the facial nerve at the root exit zone (Muscle and Nerve 1998;21:1740). Disability associated with this disorder ranges from social embarrassment to interference with vision resulting from involuntary eye closure. Treatment of HFS most often involves botulinum toxin injections, but may also include medications and surgery. We describe treatment with the three types of botulinum toxin currently commercially available--Botox, Dysport and Myobloc/NeuroBloc.

Tic convulsivo doloroso y toxina botulínica

Painful tic convulsif is a rare disorder that associates trigeminal neuralgia (TN) and ipsilateral hemifacial spasm (HFS). These two disorders are the most common examples of hyperactive cranial rhizopathy and are frequently caused by vascular compression of these cranial nerves at the nerve root entry and exit zone in the brain stem, which leads to paroxysmal ephaptic transmission.We report the cases of four patients with combined TN and HFS out of a total of 247 patients with HFS who were treated with botulinum toxin. One patient had TN that was contralateral to the HFS, while the other three were ipsilateral, and one of these had bilateral HFS. In all four cases both the HFS and the TN improved with botulinum toxin treatment.These four patients with TN and HFS suggest a common aetiology for the two disorders, due either to central neuronal hyperactivity or to vascular compression of several cranial nerves. The beneficial effect of botulinum toxin in both disorders supports the idea of this toxin having a central mechanism of action that acts by controlling neuronal hyperactivity in the brain stem, as well as its peripheral action.

Dissecting Aneurysm of the Vertebral Artery Developed after Microvascular Decompression for Hemifacial Spasm

We report a rare case of a ruptured de novo dissecting aneurysm induced by ethyl 2-cyanoacrylate. A 39-year-old woman underwent microvascular decompression for left hemifacial spasm. The offending vessel was left posterior inferior cerebellar artery (PICA). Left vertebral artery (VA) was mobilized and affixed to the dura mater with cyanoacrylate to remove pressure of PICA to the root exit zone of the facial nerve. The left VA was found to be intact at the time of the operation. One year later, the patient sufferd subarachnoid haemorrhage (SAH) caused by rupture of a newly-developed dissecting aneurysm of the left VA. Endovascular occlusion of the dissecting site was performed using Guglielmi detachable coils. We suppose mechanical injury and chemical reaction of ethyl 2-cyanoacrylate induced dissecting aneurysm.

Hemifacial spasm associated with otitis media with effusion: A first reported case

Hemifacial spasm is a condition consisting of unilateral paroxysmal involuntary contractions of the muscles innervated by the facial nerve. The most common etiology is a vascular loop compression at the root exit zone of the nerve. We present here a first reported case of hemifacial spasm associated with otitis media with effusion, in a 6-year-old girl, which was relieved immediately following ventilation tubes insertion. A proposed mechanism is described.

Microvascular decompression for primary hemifacial spasm. Importance of intraoperative neurophysiological monitoring

There is considerable evidence that primary Hemi-Facial Spasm (HFS) is in almost all cases related to a vascular compression of the facial nerve at its Root Exit Zone (REZ) from brainstem, and that Micro-Vascular Decompression (MVD) constitutes its curative treatment. Clinical as well as electrophysiological features plead for mechanisms of the disease in structural lesions at the neural fibers (putatively: focal demyelination at origin of ephapses) and functional changes in the nuclear cells (hyperactivity of the facial nucleus). Lateral Spread Responses (LSRs) elicited by stimulation of the facial nerve branches testify of these electrophysiological perturbations. Monitoring LSRs during surgery is feasible; however the practical value of their intraoperative disappearance as control-test of an effective decompression remains controversial.MVD allows cure of the disease in most cases. Because the VIIIth nerve is at risk during surgery, intraoperative monitoring of Brainstem Auditory Evoked Potentials (BEAPs) is of value to reduce occurrence of hearing loss. Increase in latency of Peak V and decrease in amplitude of Peak I are warning-signals of an excessive stretching of the the cochlear nerve and impairment of the cochlear vascular supply, respectively.

Hemifacial spasm caused by pontine glioma: case report and review of the literature

Hemifacial spasm (HFS) is an involuntary paroxysmal contractions of the facial musculature, caused generally by vascular compression of the seventh cranial nerve at its root exit zone from the brain stem. The case of an adult man harbouring brain stem glioma (BSG) whose only neurological signs were left HFS and mild facial weakness is reported. Radiological and neurophysiological findings are described. No responsible vessel could be identified during surgery, but the causative lesion was found to be an astrocytic tumour encasing the facial nerve at its root exit zone from the brain stem. The rarity of such a condition prompted us to review the literature. Nine cases, including our patient presenting with HFS caused by BSG, are reviewed.

Sixth Cranial Nerve Palsy Caused by Compression From a Dolichoectatic Vertebral Artery

A 68-year-old man had an unremitting left sixth cranial nerve palsy immediately after completing a long bicycle trip. High-resolution (3 Tesla) magnetic resonance imaging disclosed a dolichoectatic vertebral artery that compressed the left sixth cranial nerve against the belly of the pons at its root exit zone. It was postulated that increased blood flow in the vessel during the unusually prolonged aerobic exercise precipitated the palsy. Compressive palsies of cranial nerves caused by a dolichoectatic basilar artery have often been documented; compressive palsy caused by a dolichoectatic vertebral artery is less well-recognized.

Cryptic cerebellopontine angle neuroglial cyst presenting with hemifacial spasm

Hemifacial spasm (HFS) is commonly caused by a vascular loop compressing the Root Exit Zone (REZ) of the facial nerve. We report a case of HFS caused by a vascular loop that was abnormally displaced by a neuroglial cyst not seen in Magnetic Resonance Imaging (MRI). Microvascular decompression (MVD) was planned and the patient underwent a key-hole retromastoid posterior fossa exposure. A cystic lesion was found in the cerebellopontine angle (CPA), located around the seventh and eighth cranial nerves extending from the porous acousticus to the brainstem REZ of the facial nerve. The cyst wall was partially excised revealing the region of the neurovascular conflict. MVD of the facial nerve was performed with immediate postoperative complete resolution of the patient's symptoms.

Glycerol rhizotomy versus gamma knife radiosurgery for the treatment of trigeminal neuralgia: An analysis of patients treated at one institution

Medically refractory trigeminal neuralgia (TN) has been treated with a variety of minimally invasive techniques, all of which have been compared with microvascular decompression. For patients not considered good surgical candidates, percutaneous retrogasserian glycerol rhizotomy (GR) and gamma knife (GK) radiosurgery are two minimally invasive techniques in common practice worldwide and used routinely at Jefferson Hospital for Neuroscience. Using a common pain scale outcomes questionnaire, we sought to analyze efficacies and morbidities of both treatments. Between June 1994 and December 2002, 79 patients were treated with GR and 109 patients underwent GK for the treatment of TN. GR was performed with fluoroscopic guidance as an overnight inpatient procedure. GK was performed using a single 4-mm shot positioned at the root exit zone of the trigeminal nerve. Radiation doses of 70-90 Gy prescribed to the 100% isodose line were used. Treatment outcomes including pain response, pain recurrence, treatment failure, treatment-related side effects, and overall patient satisfaction with GK and GR were compared using a common outcomes scale. Using the Barrow Neurologic Institute pain scale, patients were asked to define their level of pain both before and after treatment: I, no pain and no pain medication required; I, occasional pain not requiring medication; IIIa, no pain and pain medication used; IIIb, some pain adequately controlled with medication; IV, some pain not adequately controlled with medication; and V, severe pain with no relief with medication. We used posttreatment scores of I, II, IIIa, and IIIb to identify treatment success, whereas scores of IV and V were considered treatment failure. Results were compiled from respondents and analyzed using SAS software. Statistical comparisons used log-rank test, univariate and multivariate logistic regression, Fisher's exact test, and Wilcoxon test with significance established at p < 0.05. There were 63 evaluable GK patients and 36 evaluable GR patients. The median follow-up time was 34 and 29 months for the GR and GK groups, respectively. The median age was 69 and 70 years and the median number of years with TN pain was 6 and 7 years in the GR and GK groups, respectively. Thirty-one GR (86%) and 58 GK (92%) patients achieved a successful treatment outcome (p = 0.49). The median time to pain relief was < or = 24 h in the GR group and 3 weeks in the GK group (p < 0.001, ordinal logistic regression). Nineteen GR and 26 GK patients experienced pain recurrence or pain never relieved (p = 0.30). The median time to pain recurrence was 5 and 8 months in the GR and GK groups, respectively (p = 0.22). At last follow-up, however, a statistically significant greater number of GR vs. GK patients had failed treatment. Twelve or 33% of GR patients, whereas 8 or 13% of GK patients, had BNI scores of 4 or 5 (p = 0.019, Fisher's exact test). When both initial and late treatment failures were combined, the overall rate of treatment failures was 39% in the GR group and 24% in the GK group (p = 0.023, log-rank). More GR patients developed facial numbness and facial numbness morbidity than GK patients: 19 GR (54%) and 17 GK patients (30%) developed new facial numbness and 12 GR and 7 GK patients reported either somewhat or very bothersome facial numbness (p = 0.018). On multivariate analysis, only treatment with GK and severity of pain before treatment significantly predicted treatment response. GK patients were more likely to have a lower pain score at last follow-up than were GR patients (p = 0.005, OR = 4.3), and patients with pretreatment pain scores of 5 were more likely to have lower posttreatment pain scores than patients with pretreatment pain scores of 4 and lower (p = 0.003, OR = 4.0). Despite greater facial numbness morbidity and a higher failure rate, GR provided more immediate pain relief than GK. GR therefore should be considered in patients with disabling trigeminal pain requiring urgent pain relief. For all other patients, GK provides better long-term pain relief with less treatment-related morbidity, and should therefore be considered the preferred treatment for patients with medically refractory trigeminal neuralgia who are not suitable candidates for microvascular nerve decompression.

Radiological and Electrophysiological Detection of Nerve Roots Avulsion in Patients with Birth-Related Brachial Plexus Paralysis

Obstetrical trauma is one of the most common causes of traction injuries of the brachial plexus, with incidence varying between one and two per 1000 live births. This incidence remains stable despite improvement in obstetrical care because of increasing mean birth weight. The majority of the patients with obstetrical brachial plexus palsy recover spontaneously after conservative treatment, without any or with minor functional deficit. The rest of the children require microsurgical treatment, which recently, with the introduction of interposition nerve grafting and neurotization techniques, has significantly improved the prognosis of these patients. Outcomes of surgical treatment depend on the severity and localization of the brachial plexus lesion and also on the timing of surgery. The results of early microsurgical brachial plexus interventions are superior to late brachial plexus reconstructions or following secondary procedures dealing with established joint contractures and bone deformities. Root avulsion is the most severe type of obstetrical brachial plexus lesion, usually found following use of extreme force during a complicated delivery. Presence of an avulsion lesion implies devastating paralysis without possibility for spontaneous recovery, as well as associated spread of the traction force to neighboring spinal nerves or trunks. Therefore, clinical signs of root avulsion such as Horner sign and phrenic nerve palsy are considered strong indicators for brachial plexus exploration and reconstruction. However, the absence of these signs does not rule out root avulsion. Thus, poor spontaneous recovery necessitates accurate diagnostic between preganglionic and postganglionic lesions of the brachial plexus. Postganglionic lesions occur distally to the dorsal root ganglion at the level of the spinal nerve, trunks, or cords. Continuity usually can be restored with nerve repair or interposition nerve grafting. Preganglionic lesions occur proximal to the dorsal root ganglion, with irreversible loss of the original source of nerve fibers. Preganglionic lesions were once considered inoperable, but the use of neurotization procedures from other plexus donors or the use of extraplexus donor nerves has allowed the return of rewarding degree of function.1,2,3,4 Radiological studies such as cervical myelography, computed tomography myelography (CTM) and preoperative electrophysiological testing are commonly used in an effort to correctly pinpoint the brachial plexus lesion. However, there are some controversies regarding the place of all these methods in diagnostic of obstetrical brachial plexus lesions. Cervical myelography can indicate a sign that has a strong association with root avulsions; however, the signs can exist without root avulsion. Furthermore, large, contrast-enhancing pseudomeningoceles expanding along the cervical spine can overlap adjacent normal roots. The CTM allows more accurate assessment of the root and rootlets, but delineation of a level of avulsion on axial slides can be difficult because of discrepancy between the location of root exit zones from spinal cord segments and that of respective intervertebral foramina. The electrophysiology in obstetric brachial plexus lesions differs essentially from one in older patients. The electromyelography (EMG) in obstetric palsy is far too optimistic compared with the clinical picture.5 Others consider EMG unreliable and excluded it from their protocol for examination of the children with obstetrical brachial plexus paralysis, but some still use it with the condition that studies must be done by experienced electromyographer, and results must be interpreted expertly.6 This study was undertaken to determine the diagnostic value of plain myelography, CTM, and preoperative electrophysiology in patients with obstetrical brachial plexus paralysis. Data obtained from these studies will be correlated with intraoperative diagnosis on the basis of operative findings following exploration of these lesions, intraoperative electrostimulation, and histological studies of nerve biopsies.

Espasmo hemifacial como presentación clínica de meningiomas intracraneales. Presentación de 3 casos y revisión de la literatura

Hemifacial spasm (HFS) is a clinical entity consisting of brief clonic jerking movements of the facial musculature, beginning in the orbicularis oculi with downward spreading to other facial muscles. Apart from vascular loop compression at the root exit zone of the facial nerve, other causes of HFS are rare. It is exceptional as a form of presentation of intracranial meningiomas We report three cases of patients with meningiomas who presented with HFS, either as an isolated sign or associated with symptoms of rise intracranial pressure or focal deficit. We review the literature and discuss the possible physiopathological mechanisms responsible for this association.

Monitoring of the lateral spread response in the endovascular treatment of a hemifacial spasm caused by an unruptured vertebral artery aneurysm

The lateral spread response (LSR) is used in the electrophysiological diagnosis of a hemifacial spasm or for monitoring during microvascular decompression. The authors used LSRs for intraoperative monitoring during endovascular surgery in a rare case of vertebral artery (VA) aneurysm that caused intractable hemifacial spasm. A 49-year-old woman presented with a right hemifacial spasm that had persisted for 9 months. No other clinical symptom was observed. Vertebral artery angiography revealed a saccular aneurysm of the right VA. Magnetic resonance (MR) imaging demonstrated that the aneurysm was compressing the root exit zone of the right facial nerve. Endovascular treatment of the VA aneurysm was performed while monitoring the patient's LSRs. During occlusion of the VA at sites distal and proximal to the aneurysm, the LSRs temporarily disappeared and then reappeared with a higher amplitude than those measured preceding their disappearance. The hemifacial spasm alleviated gradually and disappeared completely 6 months after treatment. The LSRs changed in parallel with the improvement in the patient's hemifacial spasms and eventually disappeared. No recurrence of symptoms has been noticed as of 18 months postoperatively. This is the first report of the use of LSR monitoring during endovascular surgery for an intracranial aneurysm that causes hemifacial spasm. Intraoperative and postoperative changes in the LSRs provided useful information regarding the pathophysiology of hemifacial spasm.

Superior Oblique Myokymia Caused by Vascular Compression

A 49-year-old man had left superior oblique myokymia for eight years. Magnetic resonance images with enhanced spoiled gradient recalled acquisition in the steady state (SPGR) and flow imaging using steady acquisition (FIESTA) disclosed a branch of the superior cerebellar artery lying on the root exit zone of the left trochlear nerve. Posterior fossa craniotomy confirmed the imaging findings. A Teflon pad was placed between the compressing artery and the trochlear nerve. The patient's superior oblique myokymia has completely resolved with a one-year follow-up. Only one such case has been previously reported. This is the first report to display the imaging findings.

Hemifacial Spasm.

Hemifacial spasm (HFS) is a peripheral movement disorder caused by direct or indirect compression or distortion of the root exit zone of the seventh cranial nerve, which is most commonly compressed by an arterial loop, but also may be compressed by a tumor, cyst, or aneurysm. All patients with HFS should undergo magnetic resonance imaging, with particular attention to the seventh cranial nerve. For patients with HFS who want treatment, there are three options. Oral medications, particularly anticonvulsants, may be useful, but the response rate is low and evidence is almost exclusively anecdotal. Local injection of botulinum toxin into the overactive muscles has a very high rate of success and virtually no serious side effects. Backed by controlled clinical trials, the authors consider it the treatment of choice. Microvascular surgical decompression has the advantage of being potentially curative, and obviates the need for chronic injections with botulinum toxin. However, surgery carries much greater risk than botulinum toxin and the spasm may recur. It is important that surgery is carried out by an experienced neurosurgeon to reduce the risk.

Clinico-radiologic correlation in unilateral and bilateral hemifacial spasm

Introduction: Bilateral hemifacial spasm (HFS) is rare. Clinico-radiologic correlates utilizing advanced imaging techniques have not been systematically examined in bilateral HFS. The prevalence of bilateral HFS in an Asian population has not been clarified. Objectives: We examined the prevalence and clinico-radiologic correlates of bilateral HFS in a clinic-based cohort and compared the clinical characteristics of unilateral HFS patients with and without contralateral neurovascular contact (NVC) in HFS. Methods: Patients clinically diagnosed with HFS were examined for bilateral symptoms. Imaging analysis involved the utilization of reformatted, multi-planar three-dimensional time-of-flight magnetic resonance angiography (3D-TOF MRA), and constructive interference at steady state (CISS-MR) sequences. The clinical and imaging data was compared between HFS with and without NVC. Results: Amongst 162 consecutive HFS patients, 2 (1.6%) had bilateral symptoms. Both patients had unilateral onset followed by bilateral and asynchronous facial contractions. The contralateral side of the face began to twitch at a mean of 1.5 years later. MRI/A revealed significant NVC of the root exit zone (REZ) of the facial nerve on the ipsilateral side with mild NVC contralaterally. The degree of NVC correlated with the clinical severity of the patients' symptoms. MRI/A analysis of 40 HFS patients with unilateral symptoms demonstrated NVC on the contralateral side in six patients (15%). The mean age and duration of symptoms were not different between HFS patients with and without contralateral NVC. Conclusions: We demonstrated clinico-radiologic correlation between the clinical severity and the degree of NVC at the REZ of the facial nerve in bilateral HFS. Amongst unilateral HFS, there was no significant difference clinically between those with and without contralateral NVC. The low 1.6% prevalence of bilateral HFS in our Asian cohort was compatible with the rare prevalence in other ethnic populations.

Clinico-radiologic correlation in unilateral and bilateral hemifacial spasm

Introduction: Bilateral hemifacial spasm (HFS) is rare. Clinico-radiologic correlates utilizing advanced imaging techniques have not been systematically examined in bilateral HFS. The prevalence of bilateral HFS in an Asian population has not been clarified. Objectives: We examined the prevalence and clinico-radiologic correlates of bilateral HFS in a clinic-based cohort and compared the clinical characteristics of unilateral HFS patients with and without contralateral neurovascular contact (NVC) in HFS. Methods: Patients clinically diagnosed with HFS were examined for bilateral symptoms. Imaging analysis involved the utilization of reformatted, multi-planar three-dimensional time-of-flight magnetic resonance angiography (3D-TOF MRA), and constructive interference at steady state (CISS-MR) sequences. The clinical and imaging data was compared between HFS with and without NVC. Results: Amongst 162 consecutive HFS patients, 2 (1.6%) had bilateral symptoms. Both patients had unilateral onset followed by bilateral and asynchronous facial contractions. The contralateral side of the face began to twitch at a mean of 1.5 years later. MRI/A revealed significant NVC of the root exit zone (REZ) of the facial nerve on the ipsilateral side with mild NVC contralaterally. The degree of NVC correlated with the clinical severity of the patients' symptoms. MRI/A analysis of 40 HFS patients with unilateral symptoms demonstrated NVC on the contralateral side in six patients (15%). The mean age and duration of symptoms were not different between HFS patients with and without contralateral NVC. Conclusions: We demonstrated clinico-radiologic correlation between the clinical severity and the degree of NVC at the REZ of the facial nerve in bilateral HFS. Amongst unilateral HFS, there was no significant difference clinically between those with and without contralateral NVC. The low 1.6% prevalence of bilateral HFS in our Asian cohort was compatible with the rare prevalence in other ethnic populations.

Microvascular decompression for hemifacial spasm caused by the vertebral artery: a simple and effective transposition method using surgical glue

Background Microvascular decompression for the treatment of trigeminal neuralgia and hemifacial spasm (HFS) has been established and has brought about excellent results. However, recurrence or lack of relief from the symptoms was experienced in some cases in which the nerve root or root exit zone were compressed by the vertebral (VA) and basilar arteries. We experienced a severe HFS case, mainly caused by a compression with the tortuous VA. A more simple transposition technique of the offending VA using surgical glue is reported. Methods A 64-year-old male had been suffering from HFS for six years. The tortuous right VA with anterior inferior cerebellar arteries (AICA) was considered to be responsible for his vascular compression syndrome. The VA was carefully and slowly dislocated away from the pontomedullary junction toward the cranial base. Then the arteriosclerotic portion of the VA wall was chosen, where a small piece of Surgicel (ETHICON, Inc., Somerville, NJ) is placed beforehand so as to use a minimum amount of glue (Biobond; Mitsubishi Pharma Corp., Osaka, Japan). Until the glue is hardened, the VA is held away from the brain stem. After this procedure, the ordinary transposition of AICA branches was added. Results The annoying HFS completely disappeared immediately after the operation. Conclusion The advantage of our method is the simplicity of the procedure. It requires less space and time while the other methods using tapes, strips, and clips need a greater working space and more time.

Functional Anatomy of the Human Cochlear Nerve and Its Role in Microvascular Decompressions for Tinnitus

The 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. We 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. A 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. The 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.

Microvascular decompression for treatment of trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia: three surgical approach variations: technical note.

We have used three different approaches, namely, the infratentorial lateral supracerebellar approach, the lateral suboccipital infrafloccular approach, and the transcondylar fossa approach, for microvascular decompression for treatment of trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia, respectively. Each approach is a variation of the lateral suboccipital approach to the cerebellopontine angle (CPA); however, each has a different site of bony opening, a different surgical direction, and a different route along the cerebellar surface. The infratentorial lateral supracerebellar approach is used to access the trigeminal nerve in the superior portion of the CPA through the lateral aspect of the cerebellar tentorial surface. The lateral suboccipital infrafloccular approach is directed through the inferior part of the cerebellar petrosal surface to reach the root exit zone of the facial nerve below the flocculus. The transcondylar fossa approach is used to access the glossopharyngeal nerve in the inferior portion of the CPA through the cerebellar suboccipital surface, after extradural removal of the jugular tubercle as necessary. In all three approaches, the cerebellar petrosal surface is never retracted transversely, that is, the cerebellar retraction is never directed parallel to the longitudinal axis of the VIIIth cranial nerve, dramatically reducing the risk of postoperative hearing loss. The greatest advantage of the differential selection of the surgical approach is increased ability to reach the destination in the CPA accurately, with minimal risk of postoperative cranial nerve palsy.

Microscopic measurement of the facial nerve root exit zone from central glial myelin to peripheral Schwann cell myelin.

The authors have attempted to define the exact borders of the root exit zone (RExZ) of the facial nerve, measure the distribution of myelin histologically, and examine the relationship between contact vessels and the RExZ. Seventy-five facial nerves were obtained from brainstems excised from 44 adult patients at autopsy. The arteries and veins associated with the facial nerve were counted and measured. The facial nerves, associated vasculature, and adjoining portions of the brainstem were then removed en bloc. These tissues were serially sectioned and stained, and a photomicrograph of each section was obtained. The distribution of myelin on each section was measured from the upper edge of the supraolivary fossette, and the relationship between contact vessels and the RExZ examined. The lateral transitional zone of the facial nerve began 8 mm distal to the upper edge of the supraolivary fossette (root exit point [RExP]) and had a mean length of 1.9 mm. The root detachment point (RDP) of the facial nerve at the medial side was located very close to the beginning of the medial transitional zone. In more than 80% of the nerves that were examined, vascular structures compressed the central glial myelin of the nerve. The authors propose the use of the terms "RExP," "RDP," and "transitional zone," instead of RExZ, which cannot be well defined. The RDP appears to be a good landmark for use during microvascular decompression.