The trigeminal nerve

Effects of visual input on changes in the bioelectrical activity of the cervical and masticatory muscles in myopic subjects

The study aimed to analyze the changes within the bioelectrical activity of the cervical spine and masticatory muscles during the change of visual stimulus—open and closed eyes test. After applying the inclusion criteria, 50 subjects were included in the study, with visual impairment ranging from −0.5 to −5.75 Diopters. Four muscle pairs were analyzed: the anterior part of the temporalis muscle (TA), the superficial part of the masseter muscle (MM), the anterior belly of the digastric muscle (DA), and the middle part of the sternocleidomastoid muscle (SCM) belly during rest, teeth clenching, teeth clenching on dental cotton rollers, and active mouth opening. Statistical analysis showed a significant decrease in the bioelectrical activity during teeth clenching of all analyzed muscles during the closed eyes test. Significant decreases of electromyographic values were also observed during resting activity within TA muscles, during teeth clenching with dental cotton rollers within SCM and DA muscles, and during active mouth opening within the right masseter. Changing the visual stimulus from open eyes to closed eyes in people with myopia affects the bioelectrical activity of the masticatory and cervical spine muscles.

Masticatory Muscle Thickness and Activity Correlates to Eyeball Length, Intraocular Pressure, Retinal and Choroidal Thickness in Healthy Women versus Women with Myopia

This study aims to examine the correlations between masticatory and neck muscle thickness and activity versus eyeball length, retinal thickness, choroidal thickness, and intraocular pressure in healthy women versus women with myopia. The study group consisted of 21 women aged 24 years and a control group of 19 women (mean age 23 years). For bioelectrical activity analysis within the temporalis anterior, the superficial part of the masseter muscle, the middle part of the sternocleidomastoid muscle, and the anterior belly of the digastric muscle, an eight-channel BioEMG III electromyograph were used. An M-Turbo ultrasound machine was used to analyze masticatory and neck muscle thickness. The eyeball length was examined by IOL Master 500; choroidal and retinal thickness by Optovue Angiovue; and intraocular pressure by Tono-Pen XL. Refractive errors are related to differences in muscle thickness and electromyographic activity. Bioelectrical activity within the temporalis anterior seems to be associated with ocular length, retinal thickness, and choroidal thickness in women with myopia.

The Influence of Visual Input on Electromyographic Patterns of Masticatory and Cervical Spine Muscles in Subjects with Myopia

This study aimed to analyze the change of visual input on electromyographic patterns of masticatory and cervical spine muscles in subjects with myopia. After applying the inclusion criteria, 50 subjects (18 males and 32 females) with myopia ranging from −0.5 to −5.75 Diopters (D), were included in the study. Four muscle pairs were analyzed: the anterior part of the temporalis muscle (TA), the superficial part of the masseter muscle (MM), the anterior belly of the digastric muscle (DA), and the middle part of the sternocleidomastoid muscle belly (SCM) during resting and functional activity. Statistical analysis showed a significant decrease within functional indices (FCI) for the sternocleidomastoid muscle (FCI SCM R, FCI SCM L, FCI SCM total) during clenching in the intercuspal position with eyes closed compared to eyes open. During maximum mouth opening, a statistically significant increase of functional opening index for the left temporalis muscle (FOI TA L) was observed. Within the activity index (AcI), there was a statistically significant decrease during clenching on dental cotton rollers with eyes closed compared to eyes open.

Creation of a novel trigeminal tractography atlas for automated trigeminal nerve identification

Diffusion MRI (dMRI) tractography has been successfully used to study the trigeminal nerves (TGNs) in many clinical and research applications. Currently, identification of the TGN in tractography data requires expert nerve selection using manually drawn regions of interest (ROIs), which is prone to inter-observer variability, time-consuming and carries high clinical and labor costs. To overcome these issues, we propose to create a novel anatomically curated TGN tractography atlas that enables automated identification of the TGN from dMRI tractography. In this paper, we first illustrate the creation of a trigeminal tractography atlas. Leveraging a well-established computational pipeline and expert neuroanatomical knowledge, we generate a data-driven TGN fiber clustering atlas using tractography data from 50 subjects from the Human Connectome Project. Then, we demonstrate the application of the proposed atlas for automated TGN identification in new subjects, without relying on expert ROI placement. Quantitative and visual experiments are performed with comparison to expert TGN identification using dMRI data from two different acquisition sites. We show highly comparable results between the automatically and manually identified TGNs in terms of spatial overlap and visualization, while our proposed method has several advantages. First, our method performs automated TGN identification, and thus it provides an efficient tool to reduce expert labor costs and inter-operator bias relative to expert manual selection. Second, our method is robust to potential imaging artifacts and/or noise that can prevent successful manual ROI placement for TGN selection and hence yields a higher successful TGN identification rate.

Anatomical assessment of trigeminal nerve tractography using diffusion MRI: A comparison of acquisition b-values and single- and multi-fiber tracking strategies

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Investigation of the performance of multiple dMRI acquisitions and fiber models for trigeminal nerve (TGN) identification.

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Expert rating study of over 1000 TGN visualizations using seven proposed expert rating anatomical criteria.

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The two-tensor tractography method had better performance on identifying true positive structures, while generating more false positive streamlines in comparison to the single-tensor tractography method.

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TGN tracking performance was significantly different across the three b-values for almost all structures studied.

Background

The trigeminal nerve (TGN) is the largest cranial nerve and can be involved in multiple inflammatory, compressive, ischemic or other pathologies. Currently, imaging-based approaches to identify the TGN mostly rely on T2-weighted magnetic resonance imaging (MRI), which provides localization of the cisternal portion of the TGN where the contrast between nerve and cerebrospinal fluid (CSF) is high enough to allow differentiation. The course of the TGN within the brainstem as well as anterior to the cisternal portion, however, is more difficult to display on traditional imaging sequences. An advanced imaging technique, diffusion MRI (dMRI), enables tracking of the trajectory of TGN fibers and has the potential to visualize anatomical regions of the TGN not seen on T2-weighted imaging. This may allow a more comprehensive assessment of the nerve in the context of pathology. To date, most work in TGN tracking has used clinical dMRI acquisitions with a b-value of 1000 s/mm² and conventional diffusion tensor MRI (DTI) tractography methods. Though higher b-value acquisitions and multi-tensor tractography methods are known to be beneficial for tracking brain white matter fiber tracts, there have been no studies conducted to evaluate the performance of these advanced approaches on nerve tracking of the TGN, in particular on tracking different anatomical regions of the TGN.

Objective

We compare TGN tracking performance using dMRI data with different b-values, in combination with both single- and multi-tensor tractography methods. Our goal is to assess the advantages and limitations of these different strategies for identifying the anatomical regions of the TGN.

Methods

We proposed seven anatomical rating criteria including true and false positive structures, and we performed an expert rating study of over 1000 TGN visualizations, as follows. We tracked the TGN using high-quality dMRI data from 100 healthy adult subjects from the Human Connectome Project (HCP). TGN tracking performance was compared across dMRI acquisitions with b = 1000 s/mm², b = 2000 s/mm² and b = 3000 s/mm², using single-tensor (1T) and two-tensor (2T) unscented Kalman filter (UKF) tractography. This resulted in a total of six tracking strategies. The TGN was identified using an anatomical region-of-interest (ROI) selection approach. First, in a subset of the dataset we identified ROIs that provided good TGN tracking performance across all tracking strategies. Using these ROIs, the TGN was then tracked in all subjects using the six tracking strategies. An expert rater (GX) visually assessed and scored each TGN based on seven anatomical judgment criteria. These criteria included the presence of multiple expected anatomical segments of the TGN (true positive structures), specifically branch-like structures, cisternal portion, mesencephalic trigeminal tract, and spinal cord tract of the TGN. False positive criteria included the presence of any fibers entering the temporal lobe, the inferior cerebellar peduncle, or the middle cerebellar peduncle. Expert rating scores were analyzed to compare TGN tracking performance across the six tracking strategies. Intra- and inter-rater validation was performed to assess the reliability of the expert TGN rating result.

Results

The TGN was selected using two anatomical ROIs (Meckel's Cave and cisternal portion of the TGN). The two-tensor tractography method had significantly better performance on identifying true positive structures, while generating more false positive streamlines in comparison to the single-tensor tractography method. TGN tracking performance was significantly different across the three b-values for almost all structures studied. Tracking performance was reported in terms of the percentage of subjects achieving each anatomical rating criterion. Tracking of the cisternal portion and branching structure of the TGN was generally successful, with the highest performance of over 98% using two-tensor tractography and b = 1000 or b = 2000. However, tracking the smaller mesencephalic and spinal cord tracts of the TGN was quite challenging (highest performance of 37.5% and 57.07%, using two-tensor tractography with b = 1000 and b = 2000, respectively). False positive connections to the temporal lobe (over 38% of subjects for all strategies) and cerebellar peduncles (100% of subjects for all strategies) were prevalent. High joint probability of agreement was obtained in the inter-rater (on average 83%) and intra-rater validation (on average 90%), showing a highly reliable expert rating result.

Conclusions

Overall, the results of the study suggest that researchers and clinicians may benefit from tailoring their acquisition and tracking methodology to the specific anatomical portion of the TGN that is of the greatest interest. For example, tracking of branching structures and TGN-T2 overlap can be best achieved with a two-tensor model and an acquisition using b = 1000 or b = 2000. In general, b = 1000 and b = 2000 acquisitions provided the best-rated tracking results. Further research is needed to improve both sensitivity and specificity of the depiction of the TGN anatomy using dMRI.

Guidelines for radiographic imaging of cranial neuropathies

Disruption of the complex pathways of the 12 cranial nerves can occur at any site along their course, and many, varied pathologic processes may initially manifest as dysfunction and neuropathy. Radiographic imaging (computed topography or magnetic resonance imaging) is frequently used to evaluate cranial neuropathies; however, indications for imaging and imaging method of choice vary considerably between the cranial nerves. The purpose of this review is to provide an analysis of the diagnostic yield and the most clinically appropriate means to evaluate cranial neuropathies using radiographic imaging. Using the PubMed MEDLINE NCBI database, a total of 49,079 articles' results were retrieved on September 20, 2014. Scholarly articles that discuss the etiology, incidence, and use of imaging in the context of evaluation and diagnostic yield of the 12 cranial nerves were evaluated for the purposes of this review. We combined primary research, guidelines, and best practice recommendations to create a practical framework for the radiographic evaluation of cranial neuropathies.

End-organ radiographic manifestations of cranial neuropathies: A concise review

BACKGROUND

Cranial neuropathies are a spectrum of disorders associated with dysfunction of one or more of the twelve cranial nerves and the subsequent anatomic structures they innervate.

OBJECTIVE

The purpose of this article is to review radiographic imaging findings of end-organ aberrations secondary to cranial neuropathies.

METHOD

All articles related to cranial neuropathies were retrieved through the PubMed MEDLINE NCBI database from January 1, 1991 to August 31, 2014. These manuscripts were analyzed for their relation to cranial nerve end-organ disease pathogenesis and radiographic imaging.

RESULTS

The present review reveals detectable end-organ changes on CT and/or MRI for the following cranial nerves: olfactory nerve, optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, accessory nerve, and hypoglossal nerve.

CONCLUSION

Radiographic imaging can assist in the detailed evaluation of end-organ involvement, often revealing a corresponding cranial nerve injury with high sensitivity and diagnostic accuracy. A thorough understanding of the distal manifestations of cranial nerve disease can optimize early pathologic detection as well as dictate further clinical management.

New Insights in Trigeminal Anatomy: A Double Orofacial Tract for Nociceptive Input

Orofacial pain in patients relies on the anatomical pathways that conduct nociceptive information, originating from the periphery towards the trigeminal sensory nucleus complex (TSNC) and finally, to the thalami and the somatosensorical cortical regions. The anatomy and function of the so-called trigeminothalamic tracts have been investigated before. In these animal-based studies from the previous century, the intracerebral pathways were mapped using different retro- and anterograde tracing methods. We review the literature on the trigeminothalamic tracts focusing on these animal tracer studies. Subsequently, we related the observations of these studies to clinical findings using fMRI trials. The intracerebral trigeminal pathways can be subdivided into three pathways: a ventral (contralateral) and dorsal (mainly ipsilateral) trigeminothalamic tract and the intranuclear pathway. Based on the reviewed evidence we hypothesize the co-existence of an ipsilateral nociceptive conduction tract to the cerebral cortex and we translate evidence from animal-based research to the human anatomy. Our hypothesis differs from the classical idea that orofacial pain arises only from nociceptive information via the contralateral, ventral trigeminothalamic pathway. Better understanding of the histology, anatomy and connectivity of the trigeminal fibers could contribute to the discovery of a more effective pain treatment in patients suffering from various orofacial pain syndromes.

Lung cancer presenting with trigeminal neuropathy

The purpose of this case report is to describe MR imaging and CT findings of a patient in whom the first clinical and neuroradiological manifestation of a metastatic lung adenocarcinoma was unilateral trigeminal neuropathy caused by a presumed metastasis involving cisternal and Meckel's cave segments of ipsilateral trigeminal nerve. MR imaging and CT scan differential diagnosis of expansive lesions of the intracranial trigeminal nerve must include metastases. Physicians and neuroradiologists must be aware of metastases as an uncommon cause of trigeminal neuropathy, even as the presenting condition of cancer.

Intraosseous trigeminal schwannoma of mandible with intracranial extension

Objective:

There have been few previous reports of intraosseous schwannomas within the mandible with extension into the cranium. We report two such cases and discuss the relevant clinical features, radiological manifestations and treatment protocols.

Method:

Two case reports of trigeminal schwannoma of the mandible with intracranial extension, including analysis of clinical, radiological and pathological aspects.

Results:

Panoramic radiographs showed both tumours as multilocular radiolucencies. Solid and cystic components were seen on computed tomography and magnetic resonance imaging. The two tumours extended into the cranium through the pterygomandibular space and an obviously expanded foramen ovale.

Conclusion:

Trigeminal schwannoma of the mandible can develop to involve intracranial extension. Radiological identification of an expanded foramen ovale may facilitate pre-operative identification.

Evaluation of a magnetic resonance-compatible dentoalveolar tactile stimulus device

Abstract

Background

The organization of the trigeminal system is unique as it provides somatosensory innervation to the face, masticatory and oral structures, the majority of the intracranial contents [1] and to specialized structures (tongue, nasal mucosa, auricle, tympanic membrane, cornea and part of the conjunctiva) [2]. Somatic sensory information transmitted by the trigeminal nerve is crucial for normal orofacial function; however, the mechanisms of many chronic pain conditions affecting areas innervated by this sensory system are not well understood [3-5]. The clinical presentation of chronic intraoral pain in the area of a tooth or in a site formally occupied by a tooth with no clinical or radiological signs of pathology, referred to as atypical odontalgia (AO) [6,7], is one such chronic pain condition of particular interest to dentists that is difficult to diagnose and manage. Recent research suggests both peripheral and central nervous system mechanisms being involved in AO pathophysiology [8-10], but the majority of mechanism-based research of patients with AO has focused on the "peripheral aspect" [7].

Functional magnetic resonance imaging (fMRI) is an established research technique to study the central aspects of pain [11]. Of existing neuroimaging techniques, fMRI provides good spatial resolution of cortical and subcortical structures critical in the processing of nociception, acceptable temporal resolution, does not involve ionizing radiation, and can be performed using most MRI systems that already exist in research centers and the community. For these reasons, we sought to develop a protocol that allows us to use this tool to investigate the central mechanisms involved in the processes of intraoral pain arising from the dentoalveolar region. Using this device, our long-term objective is to improve our understanding of the underlying mechanisms of persistent dentoalveolar pain.

In the past few years several studies used fMRI to investigate the human trigeminal system [12,13], with a limited subset focusing on intraoral stimulation - specifically on the dentoalveolar processes, such as lip, tongue and teeth stimulation [14] or only teeth [15-17]. Some reasons for scarce literature on this topic may be the technical challenges involved in delivering facial/intraoral stimulation inside a MR scanner [17,18]: possibility of magnetic interference, detriment of image quality, subject discomfort and reduced working space between the subject's head and the radiofrequency coil. As a consequence a MR-compatible device would need to not only overcome these challenges but also be capable of delivering a controlled and reproducible stimuli [19], as reliability/reproducibility is a necessary feature of sensory testing [20].

Existing MR-compatible methods of dentoalveolar stimulation are limited and do not adequately deliver stimuli across a range of non-painful to painful intensities and/or cannot be adjusted to reach posterior aspects of the dentoalveolar region. Therefore our goal was to develop and test the feasibility of a device able to: 1) provide reliable and valid dentoalveolar stimuli, 2) deliver such stimulation within the restricted space of an MR head coil, 3) be compatible for use within an MR environment, and 4) produce brain activation in painfree controls consistent to those observed by others using fMRI.

The Hypothalamic Orexinergic System: Pain and Primary Headaches

The primary headaches are a group of distinct individually characterized attack forms, which although varying in presentation, share some common anatomical basis responsible for the pain component of the attack. The hypothalamus is known to modulate a multitude of functions and has been shown to be involved in the pathophysiology of a variety of primary headaches including cluster headache and chronic migraine. It seems likely that it may be involved in other primary headache disorders due to their episodic nature and may underlie many of their diverse symptoms. We discuss the hypothalamic involvement in the modulation of trigeminovascular processing and examine the involvement of the hypothalamic orexinergic system as a key regulator of this function.

Imaging the cranial nerves: part II: primary and secondary neoplastic conditions and neurovascular conflicts

There have been unprecedented improvements in cross-sectional imaging in the last decades. The emergence of volumetric CT, higher field MR scanners and higher resolution MR sequences is largely responsible for the increasing diagnostic yield of imaging in patients presenting with cranial nerve deficits. The introduction of parallel MR imaging in combination with small surface coils allows the depiction of submillimetric nerves and nerve branches, and volumetric CT and MR imaging is able to provide high quality multiplanar and curved reconstructions that can follow the often complex course of cranial nerves. Seeking the cause of a cranial nerve deficit is a common indication for imaging, and it is not uncommon that radiologists are the first specialists to see a patient with a cranial neuropathy. To increase the diagnostic yield of imaging, high-resolution studies with smaller fields of view are required. To keep imaging studies within a reasonable time frame, it is mandatory to tailor the study according to neuro-topographic testing. This review article focuses on the contribution of current imaging techniques in the depiction of primary and secondary neoplastic conditions affecting the cranial nerves as well as on neurovascular conflicts, an increasingly recognized cause of cranial neuralgias.

Imaging of muscular denervation secondary to motor cranial nerve dysfunction

The effects of motor cranial nerve dysfunction on the computed tomography (CT) and magnetic resonance imaging (MRI) appearances of head and neck muscles are reviewed. Patterns of denervation changes are described and illustrated for V, VII, X, XI and XII cranial nerves. Recognition of the range of imaging manifestations, including the temporal changes in muscular appearances and associated muscular grafting or compensatory hypertrophy, will avoid misinterpretation as local disease. It will also prompt the radiologist to search for underlying cranial nerve pathology, which may be clinically occult. The relevant cranial nerve motor division anatomy will be described to enable a focussed search for such a structural abnormality.

Trigeminal neuralgia and facial nerve paralysis

The trigeminal nerve is the largest of the cranial nerves. It provides sensory input from the face and motor innervation to the muscles of mastication. The facial nerve is the cranial nerve with the longest extracranial course, and its main functions include motor innervation to the muscles of facial expression, sensory control of lacrimation and salivation, control of the stapedial reflex and to carry taste sensation from the anterior two-thirds of the tongue. In order to be able adequately to image and follow the course of these cranial nerves and their main branches, a detailed knowledge of neuroanatomy is required. As we are dealing with very small anatomic structures, high resolution dedicated imaging studies are required to pick up normal and pathologic nerves. Whereas CT is best suited to demonstrate bony neurovascular foramina and canals, MRI is preferred to directly visualize the nerve. It is also the single technique able to detect pathologic processes afflicting the nerve without causing considerable expansion such as is usually the case in certain inflammatory/infectious conditions, perineural spread of malignancies and in very small intrinsic tumours. Because a long course from the brainstem nuclei to the peripheral branches is seen, it is useful to subdivide the nerve in several segments and then tailor the imaging modality and the imaging study to that specific segment. This is particularly true in cases where topographic diagnosis can be used to locate a lesion in the course of these nerves.