Neurovascular Contact Research Articles

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.

30 oral Radiosurgery for the treatment of idiopathic trigeminal neuralgia: influence on outcome ofsome anatomical characteristics of neurovascular contact

30 oral Radiosurgery for the treatment of idiopathic trigeminal neuralgia: influence on outcome ofsome anatomical characteristics of neurovascular contact

Demonstration of neurovascular compression in trigeminal neuralgia and hemifacial spasm with magnetic resonance imaging: Comparison with surgical findings in 60 consecutive cases

Background Until recently, it has been impossible to demonstrate vascular compression at the root entry or exit zone (REZ) of the trigeminal nerve and facial nerve in patients with trigeminal neuralgia (TN) and hemifacial spasm (HFS) preoperatively, although surgical findings have revealed apparent neurovascular compression and its correction has resulted in a good outcome in most cases. Revealing the anatomic correlation between nerves and vessels at the REZ preoperatively would be useful to predict operative findings. Methods To assess whether the vascular contact of the nerve at the REZ could be demonstrated preoperatively, high-resolution magnetic resonance tomographic angiography (MRTA) was performed in 21 patients with TN and 39 with HFS. Neuroradiological findings were compared with the operative findings in all patients. Contralateral asymptomatic nerves were evaluated as a control. Results MRTA correctly identified offending vessels in 14 (67%) of the 21 TN and 34 (87%) of the 39 HFS patients. Failure to identify neurovascular contact was noted in the cases with compression by veins or small arteries, thickened arachnoid, or distal compression. Neurovascular contact was also observed in 15% of the asymptomatic nerves. The deformity of the nerve seemed to be a more important factor for determining operative indication. Conclusions MRTA could demonstrate offending vessels in TN and HFS at a high rate and was useful to predict operative findings. MRTA gave supportive evidence of surgical indications in patients with TN and HFS, although attention should be paid to the fact that MRTA did not necessarily detect all of the offending vessels.

Vertebro-basilar syndromes causing oculo-motor disorders

All functional classes of eye movements require exquisite coordination between cortical, basal ganglia and brainstem centers involved in ocular motor control. Vertebrobasilar stroke may produce a wide spectum of isolated or combined eye-movement disorders. The intent of this article is to summarize the curent knowledge of eye-movement disorders occurring in infarcts involving the different arterial territories of the vertebrobasilar circulation.In the last few years there has been an improvement in our understanding of pathophysiological mechanisms that are related mainly to abnormal vergence disorders due to thalamic-subthalamic infarcts, as well as of the peculiar symptoms resulting from otolith pathway involvement occurring in lateral medullary infarcts. Moreover, progress in neuroimaging technology has implicated neurovascular contact of the trochlear nerve in instances of superior oblique myokimia.Eye-movement disorders commonly occur in vertebrobasilar stroke, although they are often unappreciated. They may make it possible to establish specific anatomical correlates, as well as the probable nature of the underlying pathology.

A Case of Trigeminal Neuralgia and Neurogenic Hypertension Due to Megadolichobasilar Artery Anomaly.

We report neuroradiological findings in a unique case with mega-dolichobasilar artery and trigeminal neuralgia and neurogenic hypertension. A 39-year-old man with hypertension and trigeminal neuralgia received the first physical check-up in PL Tokyo Health Care Center.Physical check-up suggested moderate degree of obesity, severe degree of hypertension, hyperlipidemia and hyperuricemia. Neurological examination showed paresthesia in the right lower face, auditory disturbance in the right side and horizontal nystagmus to the right direction. Magnetic resonance imaging showed the dilated and tortuous basilar artery compressing the pons and the left ventrolateral medulla oblongata. Magnetic resonance angiography (MRA) demonstrated megadolichobasilar artery anomaly. The resource images of MRA revealed compression to the root entry zone of the right trigeminal nerve by the ectatic basilar artery and the neurovascular contact of the right vestibulocochlear nerve.Megadolichobasilar artery anomaly causes dysfunction of the cranial nerves, cerebral ischemia and hemorrhage. Our neuroimages indicate that the megadolichobasilar artery compresses the root entry zone of the ipsilateral trigeminal nerve, the vestibulocochlear nerve and the left ventrolateral medulla, leading to trigeminal neuralgia, vestibulocochlear deficits and marked hypertension in our patient. Thus, the resource images of MRA have benefits for pathognomonic evaluation of the neurovascular structure.

Superior oblique myokymia: magnetic resonance imaging support for the neurovascular compression hypothesis. Yousry I, Dieterich M, Naidich TP, Schmid UD, Yousry TA. Ann Neurol 2002;51:361–368

Superior oblique myokymia (SOM) is a rare recurring disorder of ocular motility characterized by unilateral paroxysmal oscillopsia and microtremor. Visible structural lesions on conventional magnetic resonance imaging (MRI) are rarely demonstrated as causal of SOM. It has been hypothesized that vascular compression of the trochlear nerve may be a common cause of SOM. Direct display of such neurovascular compression by MRI has been lacking. The goal of this study was to assess the presence of neurovascular contacts in patients with SOM, using a specific MRI protocol. A total of six patients with right SOM underwent detailed neuroophthalmological examination, which showed tonic or phasic eye movements diagnostic of SOM. All patients underwent MRI using a MRI Fourier transform constructive interference in steady-state sequence in combination with MRI time of flight magnetic resonance angiography, both before and after the administration of gadolinium. With this protocol, the trochlear nerve could be visualized on 11 of 12 sides (92%). Arterial contact was detected at the root exit zone of the symptomatic right trochlear nerve in all six patients (100%). No arterial contact was identified at the root exit zone of the asymptomatic left trochlear nerve in any of the five left nerves visualized. The authors conclude that SOM can result from neurovascular contact at the root exit zone of the trochlear nerve and that SOM should therefore be considered among the neurovascular compression syndromes. This may have implications regarding possible surgical intervention for microvascular decompression.—Nancy J. Newman

Detailed anatomy of the intracranial segment of the hypoglossal nerve: neurovascular relationships and landmarks on magnetic resonance imaging sequences.

The thin hypoglossal nerve can be very difficult to distinguish on magnetic resonance (MR) images. The authors used a combination of sequences to increase the reliability of MR imaging in its demonstration of the 12th cranial nerve as well as to assess the course of the nerve, display its relationships to adjacent vessels, and provide landmarks for evaluating the nerve in daily practice. The study group consisted of 34 volunteers (68 nerves) in whom a three-dimensional (3D) Fourier-transformation constructive interference in steady-state (CISS) sequence and a 3D T1-weighted contrast-enhanced magnetization-prepared rapid-acquisition gradient-echo (MPRAGE) sequence were applied. Two trained neuroradiologists collaboratively identified the hypoglossal trigone, preolivary sulcus, 12th cranial nerve, posterior inferior cerebellar artery, vertebral artery, 12th nerve root sleeve, and the hypoglossal canal on each side. The 3D CISS sequence successfully demonstrated the hypoglossal trigone (100% of images), 12th nerve root bundles (100% of images), and 12th nerve sleeves (88.2% of images). The canalicular segment was exhibited with the aid of plain 3D CISS sequences in 74% of images and by using contrast-enhanced 3D CISS sequences and contrast-enhanced MPRAGE sequences in 100% of images. The landmarks that proved useful to identify the cisternal segment of the 12th cranial nerve included the hypoglossal trigone, preolivary sulcus, and 12th nerve root sleeve. Neurovascular contact was identified in 61% of root bundles. The roots were distorted in 44% of these contacts. The contrast-enhanced 3D CISS sequence consistently displayed the cisternal segment as well as the canalicular segments of the hypoglossal nerve and is, therefore, the best sequence to visualize the complete cranial course of this nerve. Landmarks such as the 12th nerve sleeves can assist in the identification of this nerve.

Heterogeneity of autonomic regulation in hypertension and neurovascular contact.

Brainstem neurovascular contact (NVC) may interfere with central autonomic regulation and contribute to essential hypertension. We have previously shown that patients with autosomal-dominant hypertension, brachydactyly, and NVC feature extreme phenylephrine hypersensitivity due to impaired baroreflex buffering. We tested the hypothesis that similar abnormalities are present in patients with essential hypertension who have NVC. Six patients with NVC and essential hypertension and five patients with NVC and monogenic hypertension and brachydactyly were studied. Responses to incremental phenylephrine doses were assessed before and during ganglionic blockade with trimethaphan. Supine blood pressure was 172 +/- 8.8/89 +/- 6.1 mmHg before ganglionic blockade. Blood pressure decreased 47 +/- 5/18 +/- 3 mmHg with trimethaphan (16 +/- 4.4/4 +/- 4.0 mmHg in autosomal-dominant hypertension, P < 0.05). Before ganglionic blockade, 25 microg phenylephrine increased systolic blood pressure 17 +/- 4 mmHg in patients with essential hypertension and 30 +/- 3 mmHg in patients with autosomal-dominant hypertension (P < 0.05). During ganglionic blockade, the same dose increased systolic blood pressure 32 +/- 1 and 33 +/- 4 mmHg in patients with essential and with autosomal-dominant hypertension, respectively (NS). Phenylephrine hypersensitivity due to baroreflex dysfunction is uncommon in patients with essential hypertension and NVC. This finding may suggest that the effect of NVC on autonomic regulation is heterogeneous. An alternative explanation is that radiological NVC is not necessarily functionally relevant.

MR anatomy of the proximal cisternal segment of the trochlear nerve: neurovascular relationships and landmarks.

To assess the anatomic features and vascular relationships of the proximal portion of the cisternal segment of the trochlear nerve. In 30 subjects (60 nerves) and in one patient with right superior oblique myokymia (SOM), the anatomy of the trochlear nerve was depicted with three-dimensional (3D) Fourier transformation constructive interference in steady state (CISS) magnetic resonance (MR) imaging, whereas the adjacent vessels were detected with 3D time-of-flight (TOF) MR imaging before and after gadopentetate dimeglumine administration. The images were evaluated with respect to the identification of the trochlear nerve, the distance between the point of exit (PE) and the midline, the visualized length, the vascular relationships, and the distance between the PE and the point of neurovascular contact. 3D CISS MR imaging depicted the proximal cisternal segment of the trochlear nerve in the transverse, sagittal, and coronal planes in 57 (95%), 51 (85%), and 48 (80%) of 60 nerves, respectively. The distance from the midline to the PE was 3-9 mm, and the maximum visualized length of the trochlear nerve was 1-14 mm. An arterial-trochlear neurovascular contact was seen at the root exit zone (REZ) in eight (14%) nerves and at a mean distance of 3.4 mm distal to the PE in 29 nerves (51%). The patient with SOM had arterial-trochlear neurovascular contact at the REZ. Use of 3D CISS sequences and 3D TOF sequences with or without gadopentetate dimeglumine enables accurate identification of the proximal cisternal segment of the trochlear nerve and its neurovascular relationships.

Choice of open or percutaneous procedures in the surgical treatment of trigeminal neuralgia

The aim of this study was to define criteria for the selection of patients for percutaneous or open operations for the cure of drug-resistant trigeminal neuralgia (TN). Trigeminal percutaneous radiofrequency thermorhizotomy (TPRT) has an established place because of its safety in elderly patients, while microvascular decompression (MVD) has appeal in younger patients beause of its non-destructive nature and because it attacks what is believed to be the primary etiology of tic douloureux.Nevertheless, MVD is a successful operation only when true neurovascular conflict (NVC) is ascertained, rather than a simple arterial loop and neurovascular contract. Probably, many immediate failures and early relapses are the consequence of the inadequate patient selection for MVD on the presumption that this operation is in any case the ideal cure. The inadequate selection can be explained by the difficult preoperative diagnosis of NVC in the past. Indeed, angiography and computed tomography showed the neurovascular contact but not the size of compression. Fortunately, today magnetic resonance imaging is a reliable instrument to ascertain NVC. So, the diatribe between the supporters of percutaneous techniques and MVD can be concluded with the following: (1) percutaenous techniques are indicated for patients without demonstrated NVC (including patients with TN in multiple sclerosis) and in those with NVC if MVD is contraindicated by ill-health or refused by the informed patient; and (2) MVD is incated for patients with ascertained NVC who are in good health and who, informed of the surgical risk, favor this operation desiring no sensory deficit.

Neurovascular contact and blood pressure response in young, healthy, normotensive men

Background Neurovascular contact (NVC) of the left rostral ventrolateral medulla has been implicated in the pathogenesis of “essential” hypertension, and recent studies suggest that this anomaly may be genetically determined. We therefore assessed the prevalence of this vascular anomaly in young normotensive volunteers. We also studied blood pressure, heart rate reactivity, and changes in baroreflex sensitivity in response to mental and physical stress in a subset of subjects with positive and negative brainstem findings. Methods Magnetic resonance imaging of the brainstem was performed in 113 young (aged 25 ± 8 years), normotensive male volunteers. Baroreflex sensitivity was then assessed in 13 subjects with positive brainstem findings and 20 subjects with negative findings. Results Left-sided NVC was found in 19 subjects. Blood pressure levels, heart rate, and baroreflex sensitivity were similar in all groups. However, modulation of baroreflex sensitivity was reduced under mental and physical stress in subjects with a positive finding for NVC. Subjects with a positive finding also had a significantly lower body mass index than those with a negative finding. Conclusions Left-sided NVC is present in approximately one-fifth of young normotensive men, and may modulate the baroreceptor reflex under stress in these individuals.

Oxytocin-Secreting Neurons: A Physiological Model of Morphological Neuronal and Glial Plasticity in the Adult Hypothalamus

Oxytocin-secreting neurons of the hypothalamoneurohypophysial system undergo reversible morphological changes whenever they are strongly stimulated. In the hypothalamus, such structural plasticity is represented by modifications in the size and shape of their somata and dendrites, in the extent to which their surfaces are covered by glia, and in the density of their synapses. In the neurohypophysis, there is a parallel reduction in glial (pituicyte) coverage of their axons together, with retraction of pituicyte processes from the perivascular basal lamina and an increase in the number and size of their terminals. These changes occur rapidly, within a few hours. On the other hand, the system returns to its prestimulated condition on arrest of stimulation at a rate that depends on the length of time it has remained activated. Such neuronal–glial changes have several functional consequences. In the hypothalamic nuclei, reduction in astrocytic coverage of oxytocinergic neurons and their synapses modifies extracellular ionic homeostasis and glutamate clearance and, therefore, their overall excitability. Since it results in extensive dendritic bundling, it may also lead to ephaptic interactions and may facilitate dendritic electrotonic coupling. A most important indirect effect may be to permit synaptic remodeling that occurs concomitantly and that results in significant increases in the number of excitatory and inhibitory synapses driving their activity. In the stimulated neurohypophysis, glial retraction results in increased levels of extracellular K+ which can enhance neurohormone release while an enlarged neurovascular contact zone may facilitate diffusion of neurohormone into the circulation.Ongoing work aims to unravel the cell mechanisms and factors underlying such plasticity and has revealed that neurons and glia of the hypothalamoneurohypophysial system continue to express juvenile molecular features associated with similar neuron–glial interactions and synaptic events during development and regeneration. They include strong expression of cell surface adhesion molecules like F3/contactin and polysialylated neural cell adhesion molecule, extracellular matrix glycoproteins like tenascin C, and cytoskeletal proteins like vimentin and microtubule-associated protein 1D. Some of these molecules reach the cell surface constitutively while others follow the activity-dependent regulated pathway. We consider many of these molecular features permissive, allowing oxytocin neurons and their glia to undergo morphological remodeling throughout life, provided the proper stimulus intervenes. In the hypothalamic nuclei, one such stimulus is centrally released oxytocin; in the neurohypophysis, an adrenergic, cAMP-mediated mechanism appears responsible.

Three-dimensional time-of-flight MR angiography in trigeminal neuralgia on a 0.5-T system.

The goal of this study was to analyze the diagnostic value of three-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA), performed on a 0.5-T system in the detection of neurovascular compression in patients with trigeminal neuralgia (TN). One hundred seventy-two TN patients were examined using plain and contrast-enhanced 3D TOF MRA on a 0.5-T system. Maximum intensity projection (MIP) reconstruction was performed in three standard planes. Both the original and the reconstructed images were studied to search for vascular compression shown by close neurovascular contact and/or dislocation of the trigeminal nerve. Forty-two TN patients underwent surgical exploration of the posterior fossa. Results of MRA were compared with clinical data in all cases and to result of surgery in the surgically treated cases. Neurovascular contact at the root entry zone of the trigeminal nerve was detected on the symptomatic side in 94 patients, and on the asymptomatic side in 12 patients. Sensitivity, specificity, accuracy, as well as positive and negative predictive value of 3D TOF MRA in the detection of neurovascular compression in the patient group undergoing surgery, were 97.6, 92.5, 95.0, 93.0, and 97.4%, respectively. Three-dimensional TOF MRA performed on a 0.5-T system appears to be not less effective than similar examinations by higher field strength devices in the detection of neurovascular contact. This sequence accurately demonstrates the presence of neurovascular compression, and in this way valuable information may be achieved for the planning of surgical therapy of patients with trigeminal neuralgia.

Neurovascular Contact of Cranial Nerve IX and X Root-Entry Zone in Hypertensive Patients.

-Neurovascular contact of the left rostral ventrolateral medulla has been implicated in the pathogenesis of "essential" hypertension, and recent intervention studies suggest that surgical decompression of the ventrolateral medulla lowers blood pressure in these patients. We assessed the prevalence of this vascular anomaly in patients with essential hypertension by using an advanced MRI technique. We performed MRI of the brain stem in 125 hypertensive patients and in 105 age-matched, sex-matched, and body mass index-matched normotensive control subjects. Imaging of the root-entry zone of cranial nerves IX and X was performed by combining a high-resolution 3D constructive interference in steady-state sequence with a flow-sensitive time-of-flight technique, and images were independently assessed by 4 readers using predefined criteria. Left-sided neurovascular contact was found in 23% of the hypertensive patients and in 16% of the normotensive individuals (P:=0.12). Blood pressure level, heart rate, and number of antihypertensive medications in treated hypertensive patients were similar among patients with positive, borderline, and negative brain stem findings. Our findings cast doubt on the importance of left-sided neurovascular contact as a frequent cause of essential hypertension or as a major factor determining the severity of hypertension in patients with this anomaly.

Complex Abnormalities in Baroreflex Function in Patients with Monogenic Hypertension and Neurovascular Contact

P53 We have shown that autosomal-dominant hypertension with brachydactyly regularly features brainstem neurovascular compression (NVC). To seek mechanisms by which NVC could influence blood pressure, we conducted extensive autonomic tests in 5 affected persons (18-34 yrs.). Cold pressor testing, hand-grip testing, and upright posture all increased BP excessively. Baseline muscle sympathetic nerve activity was 15±4.6 bursts/min in patients, 12±6 bursts/min in normotensive controls, and 14±9 bursts/min in borderline hypertensive controls (ns). The increase in nerve traffic during cold pressor testing was not excessive. Urinary norepinephrine excretion was 19±4.0 μg/24 hours (normal range 23-105 μg/ 24 hours). Blood pressure during ganglionic blockade was134±4.9/ 82±4.1 mmHg in patients and 90±6/49±2.4 mmHg in controls (p&lt;0.05). In patients, plasma vasopressin concentration changed from 0.47±0.03 pg/ml at baseline to 0.84±0.23 pg/ml during ganglionic blockade. In contrast, in control subjects, plasma vasopressin concentration increased profoundly from 1.6±0.17 pg/ml at baseline to 39±13 pg/ml during ganglionic blockade. The phenylephrine dose that increased SBP 12.5 mmHg was 8.0±2.0 μg in patients and 135±35 μg in control subjects before ganglionic blockade (p&lt;0.01). During ganglionic blockade, the dose of phenylephrine that increased SBP 12.5 mmHg was 5.4±0.4 μg in patients and 13±4.8 μg in control subjects. The baroreflex slope was 9.4±1.6 msec/mmHg. We conclude that in these patients, basal BP was increased even during interruption of sympathetic and parasympathetic nerve traffic. However, sympathetic stimuli caused an excessive increase in BP. This excessive response cannot be explained by increased sympathetic nerve traffic or increased vascular sensitivity. Instead, we suggest that the ability of the baroreflex to buffer changes in blood pressure is severely impaired despite retained heart rate control.

A case-controlled MRI/MRA study of neurovascular contact in hemifacial spasm.

Neurovascular contact (NVC) with the root exit zone (REZ) of the ipsilateral facial nerve is associated with hemifacial spasm (HFS), but unresolved issues remain. To 1) determine the frequency of symptomatic and nonsymptomatic NVC, 2) determine the features of NVC associated with HFS, and 3) correlate severity of HFS to these features. Two independent, blinded, prospective assessments of high-resolution MR and MR angiography (MRA) images were performed on Chinese cases (HFS: n = 44; age-matched control subjects: n = 20). Over 88% of 44 symptomatic sides in patients with HFS had NVC of the ipsilateral facial nerve. At least 80% of symptomatic sides involved NVC at the anterior aspect of the REZ [REZ(ant.)]. Although NVC was observed in approximately half of nonsymptomatic sides, at least 70% of them were not at REZ(ant.). NVC at the cisternal and intracanalicular portions of the facial nerve were not associated with HFS. Half of our patients with HFS had bilateral NVC, but none had bilateral symptoms. Most of our MR/MRA images showed that the size and position of the arterial branches of the vertebrobasilar system were markedly asymmetric. Of patients with bilateral NVC, over 83% had asymmetric NVC sites. The anterior inferior cerebellar artery was the most common vessel involved in NVC, but was not significantly associated with HFS. Most of the NVC involved one vessel at one contact point with no indentation. The development of HFS was significantly associated with nerve indentation in NVC. The development and severity of HFS were not associated with multiple contact points in NVC. No significant interobserver variability existed between the blinded assessments. MRI/MR angiography are accurate, fast, and safe in characterizing neurovascular contact (NVC) at the brainstem. The site of NVC and ipsilateral facial nerve indentation in NVC are significant determinants for the development of hemifacial spasm (HFS). The lack of bilateral NVC at the anterior aspect of the root exit zone of the facial nerve could explain in part the lack of bilateral symptoms. The development and severity of HFS are not associated with a specific blood vessel or multiple contact points in NVC.

In vivo anatomical analysis of arterial contact with trigeminal nerve: detection with three-dimensional spoiled grass imaging.

The purpose of this study was to review the normal in vivo neurovascular relationship between the trigeminal nerve and surrounding arteries without the use of volunteers. 290 nerves in 145 cases were reviewed during a 1-year period. Axial source images and multiplanar reconstructed (MPR) images were used to determine the neurovascular contact and direction of contact. Multiplanar volume reformation (MPVR) was used to identify the contact vessels and to demonstrate the relationship between the nerve and arteries. Vascular contact was found in 29% of the 290 nerves (83 nerves). The arteries involved were the superior cerebellar artery (SCA) or the anterior inferior cerebellar artery (AICA). Vascular contact with two arteries was found in 3%. Of the 286 asymptomatic nerves, the nerve was located between the two vessels in 3% and compression was seen in 1%. Three points of vascular contact by the two arteries were identified in one asymptomatic nerve. The direction of contact between the SCA and the nerve was superior (38%), superomedial (32%) or medial (15%) in most cases. The direction of contact between the AICA and the nerve was inferior, inferolateral or lateral in all cases. Vascular contact at the root entry zone (REZ) was noted in 90%. Four nerves were affected by trigeminal neuralgia, one of which touched an artery and two were compressed. It was concluded that arterial contact can be assessed without difficulty but evaluation of vascular compression is not easy.

Recovery of nerve conduction following microvascular decompression for trigeminal neuralgia

To assess the function of trigeminal nerve before and after microvascular decompression for trigeminal neuralgia. To date there is no direct evidence that microvascular decompression of the trigeminal root restores normal conduction in the nerve. The authors examined 10 patients with trigeminal neuralgia in whom preoperative MRI and MR angiography demonstrated neurovascular contact. During microvascular decompression, the trigeminal nerve was monitored by recording early scalp trigeminal evoked potentials immediately before, during, and after decompression. Direct recordings from the root entry zone were also performed. In all patients preoperative scalp evoked potentials showed impaired conduction of the trigeminal root. Microvascular decompression was associated with immediate recovery of conduction in seven patients, demonstrated by both scalp evoked potentials and direct root recordings. All 10 patients were pain free postoperatively. Improvement in trigeminal neuralgia following microvascular decompression is often associated with normalization of neurophysiologic data, suggesting recovery of nerve function. Rapid electrophysiologic recovery and pain relief following microvascular decompression argue that neither phenomenon is linked to remyelination. It is possible that the trigeminal evoked potentials might predict an effective microvascular decompression.

The significance of three-dimensional MR-defined neurovascular compression for the pathogenesis of trigeminal neuralgia

Three-dimensional MR tomography was used to examine the relationship between symptoms of trigeminal neuralgia and neurovascular compression of the nerve in 18 patients. The intensity of neurovascular interaction was classified according to neuroradiological criteria. We found that a radiologically defined compression or dislocation of the nerve by an artery was always associated with symptoms of trigeminal neuralgia. A simple contact between vessel and nerve, however, was also observed on the asymptomatic sides of 10 out of 18 patients. In 6 of 18 patients, in contrast, trigeminal neuralgia was present in spite of the absence of neurovascular contact. In accordance with a cited study based on autopsy and intraoperative findings, our findings indicate that, in a certain proportion of cases, trigeminal neuralgia may be caused by neurovascular compression alone, whereas in other cases, other pathogenetic factors may be involved to a varying degree or be even exclusively responsible for the development of trigeminal neuralgia. The possible significance of the method for a preoperative estimation of the success of microvascular decompression of the trigeminal nerve is discussed.