[Neuroanatomy of the optic, trigeminal, facial, glossopharyngeal, vagus, accessory and hypoglossal nerves (author's transl)]

Morphometric and morphological evaluation of the optic canal in three different parts in MDCT images

PURPOSE

This study aimed to classify the morphometry and variations of optic canal by examining its changes according to gender and body side, and developments according to age.

METHODS

We retrospectively evaluated the orbit and paranasal sinus computerized tomography images of 200 individuals (age range 3 months-90 years;106 female, 94 male). In this study, three different parts of optic canal in evaluated morphometric and morphological.

RESULTS

The intracranial aperture was found to be statistically significantly wide in males than females on both sides (p ˂ 0.05). When optic canal types were evaluated, the most common type among healthy individuals was conical type (right: 68%, left:67.5%), and the least common type was irregular type (right and left:1.5%). According to the type of optic waist, the most common was triangle type.

CONCLUSION

Considering the possible effect of optic canal size on pathologies, it is important to establish a basis for the parameters of this structure in healthy individuals. In this study, both the morphology and morphometry of the canal as well as variations were examined and it was determined that the structure was affected by gender, body side and age group. Knowledge of anatomic morphometry, variations and complexities arising from these are important for clinical diagnosis and management.

Analysis of Failed Microvascular Decompression in Patients with Trigeminal Neuralgia

Background  Microvascular decompression (MVD) has been widely accepted as a definitive therapy for primary trigeminal neuralgia (TN). However, some patients may not experience relief of TN symptoms following surgery. In this study, the findings of redo MVD are discussed. Methods  Between 2015 and 2017, 205 patients with primary TN underwent MVD surgery in Shanghai Tongren Hospital. Among these patients, 187 had immediate complete relief of symptoms, 8 improved apparently, and 10 reported no symptom relief. Of the 10 patients without relief, 6 underwent reoperation within 5 days, 2 underwent reoperation 3 months after the first procedure, and 2 refused to undergo reoperation. Results  The symptoms of those patients who received reoperation disappeared immediately after the surgery. In the second operations, new conflict sites at the motor roots were found in five cases. The real offending vessels were the superior cerebellar artery (SCA) or branch of the SCA in seven cases and the petrosal vein in one case. The nerve was not decompressed completely in either of the two cases. At the 12-month follow-up, no recurrence was found. For the other two patients who did not have reoperation, their symptom persisted. Postoperative complications showed no significant differences between the first and second operations. Conclusion  Compression of the motor roots might be one of the causes of TN. Thorough exploration of both sensory and motor roots of the trigeminal nerve is essential to performing a successful MVD operation. Early reoperation for resistant TN after MVD does not increase the incidence of complications.

Dimensions and position of the Eustachian tube in Humans

Eustachian tube (ET) dysfunction is one of the causes for chronic otitis media. To develop new therapies such as stents to facilitate middle ear ventilation, a better knowledge on dimensions and positions of the ET in individual patients is necessary. Cone beam CT scans of 143 patients were retrospectively investigated. Parameters such as lengths of the ET and its cartilaginous and bony parts, diameters, angles as well as distance of the ostium from the nasal conchae were determined and evaluated for side, gender and age specific differences. The average length of the cartilaginous and bony tubes was smaller in women than men. The average deviation from the horizontal plane was 1.7° larger on the left side (35.4°) compared to the right side (33.7°). Tools to manipulate the ET or to insert stents into the ET should cover angles from at least 42° to 64°. The distance of the pharyngeal orifices from the conchae nasalis inferior increased with age, becoming most prominent above 70 years of age. This investigation provides necessary information to develop stents for human application and tools for safe positioning of the stents.

The Labyrinthine Portion of the Facial Canal

The variational radiographic anatomy of the labyrinthine portion of the facial canal was investigated in 200 plastic and silicone casts of unselected temporal bone specimens by means of multidirectional and computed tomography in different projections. The labyrinthine portion of the canal varied considerably in shape and size; in some specimens the cross-section was circular, but often the canal was crumpled and flattened in its passage above the cochlea. The medial part of the labyrinthine portion was narrowest, the lowest cross-sectional area being 0.5 mm2. In spite of optimal positioning of the specimen it was not always possible to reproduce the entire labyrinthine portion of the canal completely. Most difficult to reproduce were specimens with extremely small vertical diameters and marked caudal sloping of the canal.

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.

Nervus Intermedius Guides Auditory Brainstem Implant Surgery in Children with Cochlear Nerve Deficiency

OBJECTIVE

To investigate the anatomic features of the nervus intermedius and cranial nerve VII in children with cochlear nerve deficiency and to verify whether the nervus intermedius can provide an additional landmark to help guide placement of the auditory brainstem implant electrode.

STUDY DESIGN

Case series with chart review.

SETTING

Tertiary referral center.

SUBJECTS AND METHODS

High-definition video was captured during retrosigmoid surgery in 64 children (mean age, 3.91 ± 2.83 years) undergoing auditory brainstem implant placement. These videos were examined with particular reference to the number and variety of nervus intermedius bundles and any associated facial nerve anomalies.

RESULTS

Absence of cranial nerves VI, VII, and VIII was observed in 3, 6, and all 64 children, respectively. Fifteen children had several abnormalities of the facial nerve in the cerebellopontine angle. Anatomic identification of the facial nerve and the bundles composing the nervus intermedius was possible in 46 children. In 12 children, identification was possible with the assistance of intraoperative monitoring. The number of bundles composing the nervus intermedius varied from 1 to 6. The nervus intermedius and cranial nerve IX were useful landmarks for identifying the foramen of Luschka of the lateral recess.

CONCLUSION

The nervus intermedius provides an additional landmark during auditory brainstem microsurgery since it was identified in all subjects. The nervus intermedius anatomy and its topographic relationship with the neurovascular structures around the foramen of Luschka have been described for the first time in children with cochlear nerve deficiency.

The nervus intermedius as a variable landmark and critical structure in cerebellopontine angle surgery: an anatomical study and classification

BACKGROUND

An understanding of the normal topography during cerebellopontine angle surgery is necessary to obviate the anatomical distortions caused by tumors.

OBJECTIVE

The aim of this study was to analyze the morphological features of the nervus intermedius (NI) and its related structures in the cerebellopontine angle (CPA).

METHODS

Forty-three isolated human brainstems were examined to collect comprehensive morphometric and topographical data of the NI in its course from the brainstem to the ganglion geniculi, and discover its anatomical relationship with the other neurovascular structures in the CPA as well as within the meatus acusticus internus.

RESULTS

A total of 84 NI were analyzed. The number of bundles comprising the NI varied from one to five. The mean length of the cisternal segment of the NI was 11.47 mm. In most cases, a vein between the root entry/exit zones of the facial and the vestibulocochlear nerve (VN) was documented. In all cases the NI joined the facial nerve, typically (85 %) distally to the the porus within the meatus acusticus internus. The entry/exit zone of the NI can be categorized into four types: in type A, they arise directly from the brainstem; in type B, they arise solely from the facial nerve; in type C solely from the VN; and in type D, where the bundle or bundles arise from both the brainstem and the VN or the facial nerve.

CONCLUSION

The anatomical features of the NI can provide an additional variable landmark and critical structure during cerebellopontine microsurgery. Our study of the nerve's anatomy and topographical relations may contribute to preventing intraoperative nerve injuries.

Clinical outcomes of lower cranial nerve palsies caused by vertebral artery-posteroinferior cerebellar artery aneurysms after endovascular embolization

OBJECTIVE

To report clinical outcomes of lower cranial nerve palsy (LCNP) caused by vertebral artery (VA) aneurysms.

METHODS

Seventy-two patients with VA aneurysms, who were treated endovascularly between 2001 and 2008, were retrospectively studied to identify patients presenting LCNP without hemorrhage.

RESULTS

LCNP occurred in 12 patients (16·7%) initially caused by VA aneurysms: four located at vertebral artery-posteroinferior cerebellar artery (PICA) complex, seven at distal to PICA segment and one at proximal to PICA segment. Among these patients, ten patients were diagnosed as having dissecting aneurysms of the intracranial VA, and two were diagnosed having saccular aneurysms. Two patients were treated by sole stent placement, five patients were treated by stent coil embolization and five were treated by vertebral artery occlusion. Nosocomial pneumonia did not occur in our patients. Post-operative LCNP resolved completely within 6 months in nine patients (75%) and within 9 months in ten patients (83%). Two (1·9%) patients died of aneurismal bleeding and brainstem ischemia, respectively.

CONCLUSION

The results of this study can help to identify the effect and natural history of LCNP caused by VA aneurysms. These lesions can be effectively treated by endovascular embolization, even by VA occlusion.

Cisternal segments of the glossopharyngeal, vagus, and accessory nerves: detailed magnetic resonance imaging-demonstrated anatomy and neurovascular relationships

OBJECT

The aim of this study was to determine whether high-resolution MR imaging is suitable for identifying and differentiating among the nerve root bundles of the glossopharyngeal (cranial nerve [CN] IX), vagus (CN X), and accessory nerves (CN XI) as well as any adjacent vessels.

METHODS

Twenty-five patients (50 sides) underwent MR imaging using the 3D constructive interference in steady-state (CISS) sequence, as well as noncontrast and contrast-enhanced 3D time-of-flight (TOF) MR angiography. Two individuals scored these studies by consensus to determine how well these sequences displayed the neurovascular contacts and nerve root bundles of CNs IX and X and the cranial and spinal roots of CN XI. Landmarks useful for identifying each lower CN were specifically sought.

RESULTS

The 3D CISS sequence successfully depicted CNs IX and X in 100% of the sides. Nerve root bundles of the cranial segment of CN XI were identified in 88% of the sides and those of the spinal segment of CN XI were noted in 93% of the sides. Landmarks useful in identifying the lower CNs included the vagal trigone, the choroid plexus of the lateral recess, the glossopharyngeal and vagal meatus, the inferior petrosal sinus, and the vertebral artery. The combined use of 3D CISS and 3D TOF sequences demonstrated neurovascular contacts at the nerve root entry or exit zones in 19% of all nerves visualized.

CONCLUSIONS

The combined use of 3D CISS MR imaging and 3D TOF MR angiography (with or without contrast) successfully displays the detailed anatomy of the lower CNs and adjacent structures in vivo. These imaging sequences have the potential to aid the preoperative diagnosis of and the presurgical planning for pathology in this anatomical area.

[Cerebral nerves - perineural tumor spread]

Perineural tumor spread in the course of head and neck tumors is a form of metastatic disease in which the tumor disseminates centrifugally or centripetally along the nerve to (non)contiguous regions. Perineural tumor spread is a potentially devastating complication and has a high impact on the therapeutic management and overall prognosis. In a large proportion of patients the disease remains asymptomatic and imaging (especially MRI) plays a crucial role in the detection of lesions. Familiarity with the pertinent anatomy, knowledge of the common spread pathways and an appropriate imaging strategy allow detection of the perineural spread of the disease in the majority of the cases.

Involvement of the cranial nerves and their nuclei in spinocerebellar ataxia type 2 (SCA2)

Although the cranial nerves, their nuclei and related fiber tracts are crucial for a variety of oculomotor, somatomotor, somatosensory, auditory, vestibular-related, autonomic and ingestion-related functions, knowledge regarding the extent of their involvement in spinocerebellar ataxia type 2 (SCA2) patients is incomplete. Accordingly, we performed a pathoanatomical analysis of these structures in six clinically diagnosed SCA2 patients. Unconventionally thick serial sections through the brainstem stained for lipofuscin pigment (aldehyde-fuchsin) and Nissl material (Darrow red) showed that all oculomotor, somatomotor, somatosensory, auditory, vestibular and autonomic cranial nerve nuclei may undergo neurodegeneration during SCA2. Similarly, examination of myelin-stained thick serial sections revealed that nearly all cranial nerves and associated fiber tracts may sustain atrophy and myelin loss in SCA2 patients. In view of the known functional role of the affected cranial nerves, their nuclei and associated fiber tracts, the present findings provide appropriate pathoanatomical explanations for some of the disease-related and unexplained symptoms seen in SCA2 patients: double vision, gaze palsy, slowing of saccades, ptosis, ingestion-related malfunctions, impairments of the optokinetic nystagmus and the vestibulo-ocular reaction, facial and tongue fasciculation-like movements, impaired centripetal transmission of temperature-related information from the face, dystonic posture of the neck, as well as abnormalities of the brainstem auditory evoked potentials.

Vertebral Artery-Posteroinferior Cerebellar Artery Aneurysms: Clinical and Lower Cranial Nerve Outcomes in 52 Patients

OBJECTIVE:

To identify factors predictive of postoperative lower cranial nerve palsy (LCNP) among patients undergoing surgery for vertebral artery (VA)- posteroinferior cerebellar artery (PICA) aneurysms. The natural history of this LCNP is defined, and its effect on postoperative patient course is analyzed. No similar study has been described in the literature.

METHODS:

Fifty-two patients with VA-PICA aneurysms, who were treated surgically between 1996 and 2002, were retrospectively studied to identify factors contributing to postoperative LCNP. The effect of LCNP on intensive care unit stay and development of nosocomial pneumonia also was analyzed. All analyses were performed with Fisher's exact test.

RESULTS:

Postoperative LCNP occurred in 25 patients (48.1%) with VA-PICA aneurysms. Of the factors investigated, the use of temporary or total occlusion was associated with increased incidence of postoperative LCNP (P < 0.001). The average length of stay in the intensive care unit was 13.8 days for patients with LCNP defined as moderate to severe, compared with 7.92 days for patients with LCNP defined as none or mild (P = 0.0014). Nosocomial pneumonia occurred only in patients with moderate to severe LCNP (P = 0.022). Postoperative LCNP resolved completely within 3 months in 12 patients (48%) and within 6 months in 19 patients (76%).

CONCLUSION:

The results of this study can help to identify the effect and natural history of LCNP after surgical clipping of VA-PICA aneurysms. This information may assist neurosurgeons in expediting treatment, decrease the cost and length of hospital stays, and result in improved outcomes.

Detailed anatomy of the motor and sensory roots of the trigeminal nerve and their neurovascular relationships: a magnetic resonance imaging study

Object. The trigeminal nerve conducts both sensory and motor impulses. Separate superior and inferior motor roots typically emerge from the pons just anterosuperomedial to the entry point of the sensory root, but to date these two motor roots have not been adequately displayed on magnetic resonance (MR) images. The specific aims of this study, therefore, were to identify the superior and inferior motor roots, to describe their exact relationship to the sensory root, and to assess the neurovascular relationships among all three roots of the trigeminal nerve.

Methods. Thirty-three patients and seven cadaveric specimens (80 sides) were studied using three-dimensional (3D) Fourier transform constructive interference in steady-state (CISS) imaging. The 33 patients were also studied by obtaining complementary time-of-flight (TOF) MR angiography sequences with and without contrast enhancement.

At least one motor root was identified in all sides examined: in 51.2% of the sides a single motor root, in 37.5% two motor roots, and in 11.2% three motor roots. The superior cerebellar artery (SCA) and the anterior inferior cerebellar artery (AICA) contacted the sensory root in 45.5% of patients and 42.9% of specimens. The SCA often contacted the superior motor root (48.5% of patients and 50% of specimens) and less frequently the inferior motor root (26.5% of patients and 20% of specimens).

Conclusions. Three-dimensional CISS and complementary 3D TOF MR angiography sequences reliably display sensory, superior motor, and inferior motor roots of the trigeminal nerve and their relationships to the SCA and AICA.

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

OBJECT

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.

METHODS

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.

CONCLUSIONS

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.

Neuro-arterial relations in the region of the optic canal

In this paper, we present the results of our investigations on the neuro-arterial relations in the region of the optic canal. A thorough knowledge of the microanatomic features of the ophthalmic artery, optic canal and optic nerve is very important for surgeons approaching lesions of this area. We aimed to extend our present knowledge of the origin of the ophthalmic artery and microsurgical anatomy of the optic canal with exposure of the optic nerve. The optic canal walls and width and height of the orbital and cranial apertures, and thickness of the bony roof of the optic canal were measured on the right and left sides of 57 sphenoid bones, 102 skull bases and 58 fixed adult cadaver heads. The ophthalmic artery originated from the rostromedial circumference of the internal carotid artery in 51.8%, from the medial circumference in 26.2% and the laterobasal circumference in 22% of the specimens. The outer diameter of the ophthalmic artery at its origin was 1.81 +/- 0.36 mm on the right and 1.75 +/- 0.37 mm on the left side.

On the mechanism of transient postoperative deficit of cranial nerves

BACKGROUND

Transient cranial nerve deficit is a common postoperative complication after surgery at the cranial base. In this type of surgery, the cranial nerves are often not macroscopically damaged or transected, but more or less manipulated during surgery. In this article, the cellular mechanisms of postoperative cranial nerve deficit are reviewed.

METHODS

Experimental and clinical papers concerning cranial and peripheral nerve damage during surgery were critically reviewed.

RESULTS

There are definite differences in the anatomical and histological structure between peripheral and intracranial nerves, which make the latter much more prone to intraoperative damage. Several pathological mechanisms are responsible for postoperative deficit, such as segmental demyelination of the nerve, comprised microcirculation within the nerve, postoperative edema, and "synaptic stripping" around the cell bodies of the affected neurons, which can be regarded as a regenerative response of the nervous system.

CONCLUSIONS

Several cellular mechanisms are responsible for postoperative cranial nerve deficit after skull base surgery. Understanding these mechanisms is important for all surgeons involved in the treatment of skull base lesions.

Postnatal development of the internal auditory canal studied by computer-aided three-dimensional reconstruction and measurement

Postnatal development of the internal auditory canal (IAC) was investigated in 20 normal human temporal bones obtained from individuals 1 month to 72 years old. Computer-aided three-dimensional reconstruction and measurement of bones showed that the superior, inferior, anterior, and posterior walls of the IAC lengthen significantly from birth until about 10 years of age, with development mainly attributable to lengthening of the part of the IAC medial to the foramen singulare. The lengths of the part of the IAC lateral to the foramen singulare and of the transverse crest and Bill's bar did not appear to develop postnatally. The IAC diameter increased slightly at the porus for about the first year after birth, but not at the fundus or the middle portion of the canal. This finding was confirmed by studying the shape of the IAC. Postnatal increases in the volume of the IAC followed patterns similar to that of increases in length of studying the shape of the IAC. Postnatal increases in the volume of the IAC followed patterns similar to that of increases in length of the IAC walls. These results show that postnatally the IAC increases significantly in length until about 10 years of age and slightly in diameter until about 1 year of age, especially medial to the foramen singulare. This concentration of growth of the IAC medially implies that its postnatal development is mainly due to growth of the bone around the otic capsule, which has implications for IAC surgery.

Postnatal development of the vestibular aqueduct in relation to the internal auditory canal. Computer-aided three-dimensional reconstruction and measurement study

To investigate a possible developmental relationship between the internal auditory canal (IAC) and the vestibular aqueduct (VA), we made the following measurements in 10 normal temporal bones from individuals 4 months to 70 years of age at death, using a computer-aided three-dimensional reconstruction and measurement method: the volume of the VA, the length of the IAC, and the distance between the IAC and the external aperture of the VA. The degree of periaqueductal pneumatization was also assessed qualitatively by means of a light microscope. The three parameters increased postnatally in parallel with the development of the periaqueductal air cells, and all pairwise comparisons of these parameters showed a statistically significant correlation. Our results indicate that the IAC and VA develop synchronously and in parallel with the development of the periaqueductal air cells. We believe that an understanding of this relationship will be of help during surgery involving the IAC and VA, and may shed some light on the morphological features of Meniere's disease.

Communicatory routes connecting the middle ear, the inner ear and the subarachnoid space via perineural space

Twenty-one rabbits received injection of Indian ink into the stylomastoid foramen. Observation of the serial sections of their temporal bones revealed Indian ink infiltration into the subarachnoid space, along the facial nerve, the auricular branch of the vagus nerve and the tympanic nerve. Along the acoustic nerve, the infiltration was found as far as the fundus of the internal auditory meatus. In some cases, however, Indian ink reached the subarachnoid space and infiltrated into the scala tympani, scala vestibuli and around the saccule by way of the cochlear aqueduct. These routes are suspected to be a course of spreading infection or tumor cells.