Neurovascular compression of the abducent nerve causing abducent palsy treated by microvascular decompression

Unveiling the vulnerability of the human abducens nerve: insights from comparative cranial base anatomy in mammals and primates

The topographic anatomy of the abducens nerve has been the subject of research for more than 150 years. Although its vulnerability was initially attributed to its length, this hypothesis has largely lost prominence. Instead, attention has shifted toward its intricate anatomical relations along the cranial base. Contrary to the extensive anatomical and neurosurgical literature on abducens nerve anatomy in humans, its complex anatomy in other species has received less emphasis. The main question addressed here is why the human abducens nerve is predisposed to injury. Specifically, we aim to perform a comparative analysis of the basicranial pathway of the abducens nerve in mammals and primates. Our hypothesis links its vulnerability to cranial base flexion, particularly around the sphenooccipital synchondrosis. We examined the abducens nerve pathway in various mammals, including primates, humans (N = 40; 60% males; 40% females), and human fetuses (N = 5; 60% males; 40% females). The findings are presented at both the macroscopic and histological levels. To associate our findings with basicranial flexion, we measured the cranial base angles in the species included in this study and compared them to data in the available literature. Our findings show that the primitive state of the abducens nerve pathway follows a nearly flat (unflexed) cranial base from the pontomedullary sulcus to the superior orbital fissure. Only the gulfar segment, where the nerve passes through Dorello's canal, demonstrates some degree of variation. We present evidence indicating that the derived state of the abducens pathway, which is most pronounced in humans from an early stage of development, is characterized by following the significantly more flexed basicranium. Overall, the present study elucidates the evolutionary basis for the vulnerability of the abducens nerve, especially within its gulfar and cavernous segments, which are situated at the main synchondroses between the anterior, middle, and posterior cranial fossae-a unique anatomical relation exclusive to the abducens nerve. The principal differences between the pathways of this nerve and those of other cranial nerves are discussed. The findings suggest that the highly flexed human cranial base plays a pivotal role in the intricate anatomical relations and resulting vulnerability of the abducens nerve.

Vertebrobasilar dolichoectasia and other arterial abnormalities leading to abducens nerve palsy

INTRODUCTION

Dolichoectatic vessels can cause cranial nerve dysfunction by either direct compression or ischemia. Abducens nerve palsy due to neurovascular compression by elongated, enlarged, tortuous or dilated arteries is an uncommon but important cause.

AIM

To highlight neurovascular compression as a cause of abducens nerve palsy and discuss various diagnostic techniques.

METHODS

Manuscripts were identified using the National Institutes of Health PubMed literature search system. Search terms included abducens nerve palsy, neurovascular compression, dolichoectasia and arterial compression. Inclusion criteria required that the articles were written in English.

RESULTS

The literature search identified 21 case reports where abducens nerve palsy was due to vascular compression. Out of these 18 patients were male and the mean age was 54 years. Eight patients had unilateral right abducens nerve involvement; eleven patients had unilateral left nerve involvement and two patients had bilateral involvement. The arteries causing the compression were basilar, vertebral and anterior inferior cerebellar arteries. A compressed abducens nerve is not usually clearly detected on CT (Computed Tomography) or MRI (Magnetic Resonance Imaging). MRA (Magnetic Resonance Angiography), Heavy T2- WI (weighted imaging), CISS (constructive interference in steady state) and FIESTA (Fast Imaging Employing Steady-state Acquisition) are essential to demonstrate vascular compression of the abducens nerve. The various treatment options included controlling hypertension, glasses with prisms, muscle resection and microvascular decompression.

The Use of Fusion Images as a Diagnostic and Neurosurgical Planning Tool in Microvascular Decompression

Preoperative assessment of surgery using high-quality images can help surgeons to achieve best result of treatment. With the advances in computer technology, interactive multimodality fusion images have been developed. The use of fusion images as a preoperative planning tool is described with its examples in illustrative cases of trigeminal neuralgia and hemifacial spasm microvascular decompression (MVD). Interactive computer graphics such as multimodality fusion method is a useful tool to preoperatively predict the need of bone exposure and configuration of blood vessels with its correlation to cranial nerves in MVD.

Location of the abducens nerve stretched by a tortuous vertebrobasilar artery in trigeminal neuralgia

BACKGROUND

Trigeminal neuralgia (TGN) caused by the vertebrobasilar artery (VBA) is uncommon. The abducens nerve root is frequently dislocated by a tortuous VBA near the trigeminal nerve root. This unusual location of the root is not well known. This study aimed to investigate the location of the stretched abducens nerve root.

METHODS

The objective is 26 patients with VBA-related TGN who underwent microvascular decompression (MVD). We retrospectively investigated the course of the abducens nerve root with magnetic resonance imaging (MRI) with three-dimensional (3D) imaging and surgical findings. The displacement of the abducens nerve root on the affected side was compared to the contralateral side.

RESULTS

The abducens nerve root was distorted by a tortuous VBA (46.2%) or the anterior inferior cerebellar artery (53.8%). The average length of the cisternal segment was stretched to 23.4 mm versus 12.4 mm on the contralateral side. The peak point of the elevated abducens nerve root was mostly located rostro-medial (65.4%) or caudo-medial (34.6%) to the neurovascular compression site of the trigeminal nerve with a mean distance of 9.1 mm. Contact with the trigeminal nerve root was observed in 7 patients (26.9%). Three-dimensional imaging was consistent with the surgical findings and useful in predicting the location of the abducens nerve root. No abducens nerve palsy was noted in our series.

CONCLUSIONS

The abducens nerve root is located near the trigeminal nerve root in VBA-related TGN. Preoperative understanding of the unusual course of the abducens nerve root contributes to avoiding accidental nerve injury during MVD.

Vertebrobasilar Dolichoectasia as a Rare Cause of Simultaneous Abducens and Vestibulocochlear Nerve Symptoms: A Case Report and Literature Review

Vertebrobasilar dolichoectasia (VBD) can lead to cranial nerve symptoms. However, multiple cranial nerve symptoms associated with VBD in one case remain extremely rare. We here present the case of a 33-year-old male with VBD diagnosed by multimodality imaging, who developed simultaneous abducens and vestibulocochlear nerve symptoms and subsequently improved after blood pressure control treatment. To our knowledge, this is the first report of such a vascular disorder resulting in simultaneous symptoms of the abducens and vestibulocochlear nerves. This study highlights that such a vascular anomaly should be considered when cranial nerve symptom is encountered, especially when multiple cranial nerves involved. Meanwhile, radiological evalurrrrrrrrrrrrrrrrrrration of such neurovascular conflict using three-dimensional constructive interference in steady-state imaging is recommended.

Microvascular decompression for abducens nerve palsy due to neurovascular compression from both the vertebral artery and anterior inferior cerebellar artery: A case report

Background

Neurovascular compression is an extremely rare etiology of isolated abducens nerve palsy. We describe a successfully treated case of isolated abducens nerve palsy due to sandwich-type compression by the vertebral artery (VA) and anterior inferior cerebellar artery (AICA).

Case Description

A 30-year-old man presented with a 6-month history of horizontal diplopia without other symptoms. Magnetic resonance imaging (MRI) demonstrated pinching of the left abducens nerve between the elongated left VA and left AICA. MRI showed no abnormal findings in the brainstem, cavernous sinus, or orbit. Surgery was performed using a standard lateral suboccipital approach. The abducens nerve was found to be severely compressed from both sides by the VA and AICA, with marked indentation. First, the VA was transposed and fixed to the dura mater of the petrous bone using a Teflon sling with the dripping of fibrin glue. Next, because of limited mobilization due to penetration of the AICA into the nerve, the AICA transfixing the nerve was attached to the pons with Teflon felt and fibrin glue to move the AICA away from the main trunk of the abducens nerve. The abducens nerve palsy gradually improved and eventually resolved by 4 months after the operation.

Conclusion

When an elongated vertebrobasilar artery is identified as the offending vessel on high-resolution MRI, microvascular decompression can be carefully considered as a treatment option for patients with isolated abducens nerve palsy.

Magnetic resonance imaging findings of isolated abducent nerve palsy induced by vascular compression of vertebrobasilar dolichoectasia

If the origin of isolated abducent nerve palsy cannot be found on neuroradiological examinations, diabetes mellitus is known as a probable cause; however, some cases show no potential causes of isolated abducent nerve palsy. Here, we report a 74-year-old male who suffered from diplopia due to isolated left abducent nerve palsy. Magnetic resonance angiography and fast imaging employing steady-state acquisition imaging clearly showed a dolichoectasic vertebrobasilar artery compressing the left abducent nerve upward and outward. There were no abnormal lesions in the brain stem, cavernous sinus, or orbital cavity. Laboratory data showed no abnormal findings. We concluded that neurovascular compression of the left abducent nerve might cause isolated left abducent nerve palsy. We observed him without surgical treatment considering his general condition with angina pectoris and old age. His symptom due to the left abducent nerve palsy persisted. From previous reports, conservative treatment could not improve abducent nerve palsy. Microvascular decompression should be considered for abducent nerve palsy due to vascular compression if patients are young, and their general condition is good. We also discuss interesting characteristics with a review of the literature.

Sixth cranial nerve palsy and ipsilateral trigeminal neuralgia caused by vertebrobasilar dolichoectasia

Purpose

To report an unusual case of vertebrobasilar dolichoectasia causing both trigeminal neuralgia and ipsilateral sixth cranial nerve palsy.

Observations

A patient had undergone surgical decompression of trigeminal neuralgia caused by dolichoectatic vertebral and basilar arteries years before presenting with ipsilateral sixth nerve palsy. Brain MRI showed deviant vertebrobasilar arteries that presumably now compressed the sixth cranial nerve. The unaffected left sixth cranial nerve was visible on MRI, but the affected right sixth cranial nerve was not. The central spinal fluid space in Dorello's canal on the affected side was relatively ample, suggesting atrophy of the affected sixth cranial nerve. On follow-up examination one year after presentation, the patient's diplopia was palliated with spectacle prism.

Conclusions and importance

This is the tenth reported case of dolichoectasia causing sixth cranial nerve palsy, but only the second to occur with dolichoectatic trigeminal neuralgia. It provides more detailed imaging that previously reported cases. Review of reported cases of dolichoectatic compression of cranial nerves indicates that vascular decompression may be effective for trigeminal neuralgia, but is not indicated for dolichoectatic sixth nerve palsy, which will resolve spontaneously or can be effectively managed with prism or eye muscle surgery.

Abducent nerve palsy treated by microvascular decompression: a case report and review of the literature

Too few cases of isolated abducent nerve palsy caused by neurovascular compression syndrome have been reported. We here report on a case of abducent nerve palsy caused by neurovascular compression syndrome that was successfully treated by microvascular decompression (MVD). A 46-year-old male presented with a 6-month history of right-sided persistent abducent nerve palsy. High-resolution magnetic resonance imaging revealed a neurovascular contact of the vertebral artery with the right abducent nerve. MVD was performed via a retrosigmoid craniotomy, with remarkable improvement of the palsy. Our report suggests that MVD might be considered as an optional treatment if the symptoms progress or persist.

Hemibody pain relieved by microvascular decompression of the contralateral caudal medulla: case report

Microvascular decompression (MVD) of cranial nerves has become an established treatment for trigeminal and (vago)glossopharyngeal neuralgia and for hemifacial spasm. The authors present the case of a 64-year-old man who had a 3.5-year history of severe, drug-resistant hemibody pain with sensory and autonomic disturbance. The ipsilateral trigeminal, cochlear, and glossopharyngeal function also was affected. The contralateral posterior inferior cerebellar artery was seen on magnetic resonance imaging to be indenting the caudal medulla anterolaterally, causing displacement. After MVD of the medulla, there was an immediate and complete resolution of the pain and almost complete resolution of the sensory and autonomic disturbances. The pain later recurred mildly and transiently. The residual symptoms had resolved by 2 years.

Delayed cranial nerve palsy after microvascular decompression for hemifacial spasm

Objective

Microvascular decompression (MVD) for hemifacial spasm (HFS) is a safe and effective treatment with favorable outcomes. The purpose of this study was to evaluate the incidence of delayed cranirve ( VI, VII, and VIII ) palsy following MVD and its clinical courses.

Methods

Between January 1998 and December 2009, 1354 patients underwent MVD for HFS at our institution. Of them, 100 patients (7.4%) experienced delayed facial palsy (DFP), one developed sixth nerve palsy, and one patient had delayed hearing loss.

Results

DFP occurred between postoperative day number 2 and 23 (average 11 days). Ninety-two patients (92%) completely recovered; however, House-Brackmann grade II facial weakness remained in eight other patients (8%). The time to recovery averaged 64 days (range, 16 days to 9 months). Delayed isolated sixth nerve palsy recovered spontaneously without any medical or surgical treatment after 8 weeks, while delayed hearing loss did not improve.

Conclusion

Delayed cranial nerve (VI, VII, and VIII) palsies can occur following uncomplicated MVD for HFS. DFP is not an unusual complication after MVD, and prognosis is fairly good. Delayed sixth nerve palsy and delayed hearing loss are extremely rare complications after MVD for HFS. We should consider the possibility of development of these complications during the follow up for MVD.

[A 56-year-old woman with adult-onset ophthalmoplegic migraine presenting with recurrent bilateral abducens nerve palsy]

A 56-year-old woman had been experiencing episodic left eye pain followed within 3 days by double vision and adduction of the left eye since the age of 30. The episodes occurred once per month, and her symptoms spontaneously resolved within 3 days. The patient was diagnosed with ophthalmoplegic migraine (OM) with left abducens nerve palsy at the age of 53 years. In May 2011, she developed bilateral retro-orbital pain followed by double vision and limitation of abduction of the right eye. She recalled having a cold and high fever 10 days before the onset of the headache. MRI showed no thickening or enhancement of the right abducens nerve. Constructive interference in steady-state (CISS) MRI showed neurovascular contact between the right abducens nerve and anterior inferior cerebellar artery. Right abducens nerve palsy accompanied by OM was diagnosed after other diseases that can cause ophthalmoplegia were excluded. The patient's eye symptoms gradually improved following steroid treatment. There have been a few similar case reports of adult patients with OM showing left and right abducens nerve palsy at different time points. In this case report, we discuss the possible mechanisms related to OM.

Recurrent isolated abducens nerve paresis associated with persistent trigeminal artery variant

We report a 74-year-old woman who presented with recurrent isolated abducens nerve paresis. Cranial magnetic resonance imaging revealed that the right abducens nerve was sandwiched between the right internal carotid artery and a persistent trigeminal artery (PTA) variant, which might have led to neurovascular compression of the abducens nerve, resulting in abducens nerve damage. Normal variants of PTA, which are cerebellar arteries originating from a precavernous portion of the internal carotid artery, must be carefully observed as such variants can potentially cause a neurovascular compression of the abducens nerve.

Nonaneurysmal cranial nerve compression as cause of neuropathic strabismus: evidence from high-resolution magnetic resonance imaging

PURPOSE

To seek evidence of neurovascular compression of motor cranial nerves (CNs) in otherwise idiopathic neuropathic strabismus using high-resolution magnetic resonance imaging (MRI).

DESIGN

Prospective, observational case series.

METHODS

High-resolution, surface coil orbital MRI was performed in 10 strabismic patients with idiopathic oculomotor (CN III) or abducens (CN VI) palsy. Relationships between CNs and intracranial arteries were demonstrated by 0.8-mm thick, 162-μm resolution, heavily T2-weighted MRI in fast imaging using steady-state acquisition sequences. Images were analyzed digitally to evaluate cross-sectional areas of extraocular muscles.

RESULTS

In one patient with CN III palsy, an ectatic posterior communicating artery markedly flattened and thinned the ipsilateral subarachnoid CN III. Cross-sections of the affected medial, superior, and inferior rectus muscles 10 mm posterior to the globe-optic nerve junction were 17.2 ± 2.5 mm(2), 15.5 ± 1.3 mm(2), and 9.9 ± 0.8 mm(2), significantly smaller than the values of 23.6 ± 1.9 mm(2), 30.4 ± 4.1 mm(2), and 28.8 ± 4.6 mm(2), respectively, of the unaffected side (P < .001). In 2 patients with otherwise unexplained CN VI palsy, ectatic basilar arteries contacted CN VI. Mean cross-sections of affected lateral rectus muscles were 24.0 ± 2.3 mm(2) and 29.8 ± 3.1 mm(2), significantly smaller than the values of 33.5 ± 4.1 mm(2) and 36.9 ± 1.6 mm(2), respectively, in unaffected contralateral eyes (P < .05).

CONCLUSIONS

Nonaneurysmal motor CN compression should be considered as a cause of CN III and CN VI paresis with neurogenic muscle atrophy when MRI demonstrates vascular distortion of the involved CN. Demonstration of a benign vascular cause can terminate continuing diagnostic investigations and can expedite rational management of the strabismus.

Ophthalmic segment aneurysmal subarachnoid hemorrhage presenting with contralateral abducens nerve palsy: a false localizing sign

BACKGROUND

Neuro-ophthalmic manifestations of aneurysmal subarachnoid hemorrhage are commonly linked to a palsy of the cranial nerve in close proximity to the aneurysm or to chronic intracranial hypertension.

CASE REPORT

A patient with subarachnoid hemorrhage secondary to a rupture of an intracranial right ophthalmic segment internal carotid artery aneurysm presented with an acute-onset contralateral abducens nerve palsy. There were no clinical or radiologic features of chronic intracranial hypertension. Magnetic resonance imaging showed a co-existent ectatic basilar artery on the left side of the pons in close relation to the sixth nerve.

CONCLUSION

Abducens weakness in the above-50 age group is most commonly caused by a vascular etiology. The authors discuss the pathogenesis of this rare clinical entity and present pertinent literature review.

Unilateral hypoglossal nerve palsy due to neurovascular conflict in a child

A neurovascular conflict (NC) consists of a pathological contact between a vessel, generally an artery, and the root entry zone of a cranial nerve close to the brainstem. Even if NC of the V, VII and IX cranial nerve have been rarely described, to the best of our knowledge there is no report about the XII cranial nerve NC in the paediatric age. A three-year-old girl presented with right-sided tongue atrophy and fasciculation, of one-year-duration, consistent with a peripheral lesion of the right XII cranial nerve. Brain MRI and MRA documented a marked tortuosity of the vertebrobasilar arteries compressing the brainstem at the emergency of the XII cranial nerve, while the CT disclosed a concomitant osseous malformation of the cranio-cervical junction. The differential diagnosis of a peripheral unilateral cranial nerve palsy should include, even if rare in children, a neurovascular conflict. In this case a complete neuroimaging study is indicated.