Effect of clival bone growth on the localization of the abducens nerve at the petroclival region: a postmortem anatomical study.

PURPOSE: To investigate the effect of the clival bone pattern on the abducens nerve (AN) localization in the petroclival region between the Pediatric and Adult Groups. METHODS: This study used 12 pediatric and 17 adult heads obtained from the autopsy. The length and width of the clivus and the length of the petrosphenoidal ligaments (PSLs) were measured. The ratio of the length and width of the clivus was accepted as the clival index (CI). The localization of the AN at the petroclival region below the PSL, classified as lateral and medial, were recorded. RESULTS: The average length of the clivus was 26.92 ± 2.88 mm in the Pediatric Group, and 40.66 ± 4.17 mm in the Adult Group (p < 0.001). The average width of the clivus was 22.35 ± 2.88 mm in the Pediatric Group, and 29.96 ± 3.86 mm in the Adult Group (p < 0.001). The average value of the CI was 1.20 in the Pediatric Group and 1.36 in the Adult Group (p = 0.003). The length of the PSL was 7.0 ± 1.47 mm in the Pediatric Group and 11.05 ± 2.95 mm in the Adult Group (p < 0.001). The nerve was located below the medial side of the PSL in the Pediatric Group and below the lateral side in the Adult Group (p = 0.002). CONCLUSIONS: The petrous apex localization of the AN in adults compared with pediatric subjects could be related to the increased growth in the length of the clivus than its width.

Reappraisal of the types of trigeminal porus and importance in surgical applications.

OBJECTIVE: The detailed information regarding the types of trigeminal porus (TP) and related surgical approach is lacking in the literature. Therefore, we performed this study to elucidate further the types of TP and the relationships with critical surgical landmarks in the skull base. METHODS: The study was performed on 19 formalin-fixed cadavers of the cranial base (52.6% male, n = 10; 47.4% female, n = 9) on both sides. Calculations were made of the vertical dimension (VD), horizontal dimension (HD), and types of TP, the thickness of the TP, the HD and VD of the internal acoustic meatus, the distance between the TP-IAM, the thickness of the ossifying tissue that forms the TP, the trigeminal nerve (CN V) in both types and the distance between the CN V-VI. RESULTS: The elliptical (42.1% left, 36.8% right), oval (52.6% left, 36.8% right) and slit-like (5.3% right) types of TP were detected (X2 = 11.722). The HD of the TP was, on average, 8.02 mm (female) and 9.2 mm (male) on the right side, and 8.26 mm (female) and 8.81 mm (male) on the left side. The VD of the TP was, on average, 1.99 mm (female) and 2.65 mm (male) on the right side, and 2.42 mm (female) and 2.94 mm (male) on the left side. CONCLUSIONS: In our study, ellipse and slit-like types of TP are taken into account in order to plan the surgical approaches to remove or prevent the extension of tumors. A combined surgical technique is recommended to reach the TP easily without damaging the nearby surgical structures during surgery. The oval type of TP allows a wide range of movements, so it is more advantageous in skull base surgery.

Anatomical location of the abducens nerves (VI) in the ventral approach of clival tumors.

The aim of this work was to determine reliable anatomical landmarks for locating and preserving the abducens nerves (6th cranial nerves) during trans-facial or trans-nasal endoscopic approaches of skull base tumors involving the clivus and the petrous apex. In order to describe this specific anatomy, we carefully dissected 10 cadaveric heads under optic magnification. Several measurements were taken between the two petro-sphénoidal foramina, from the bottom of the sella and the dorsum sellae. The close relationship between the nerves and the internal carotid artery were taken into account. We defined a trapezoid area that allowed drilling the clivus safely, preserving the 6th cranial nerve while being attentive to the internal carotid artery. The caudal part of this trapezium is, on average, 20 mm long at mi-distance between the two petro-sphenoidal foramina. The cranial part is at the sella level, a line between both paraclival internal carotid arteries. Oblique lateral edges between the cranial and caudal parts completed the trapezium.

Unusual array of neural communications in the infratemporal fossa: Useful for skull base surgery.

Variations in the branching pattern of the mandibular nerve frequently accounts for failure to obtain adequate local anesthesia in routine oral and dental procedures, and also for unexpected injury to the nerves during surgery. The knowledge of the neurovascular relationships of the infratemporal region is relevant in odontostomatology practice. In this article we present a rare case of atypical communication between the inferior alveolar nerve and lingual nerve and the mylohyoid and lingual nerves. Further, the clinical implications of these communications on the development of the supplementary innervation and their possible role in anesthesia is discussed in detail. The communication between mylohyoid and lingual nerve was found in this case near the submandibular ganglion after the lingual nerve passes in close relation to third molar tooth, which makes it more susceptible to injury during third molar extractions. The communicating branch between the mylohyoid nerve and lingual nerve may also innervate the tongue, and surgeons should be aware of this variation to avoid post- operative complcations after oral surgeries. Thus the precise anatomy of structures of infratemporal region and its variations may prove beneficial to clinicians, especially to oral and maxillofacial surgeons.

Morphometric characteristics of caudal cranial nerves at petroclival region in fetuses.

Morphometric measurements of cranial nerves in posterior cranial fossa of fetus cadavers were carried out in an attempt to identify any asymmetry in their openings into the cranium. Twenty-two fetus cadavers (8 females, 14 males) with gestational age ranging between 22 and 38 weeks (mean 30 weeks) were included in this study. The calvaria were removed, the brains were lifted, and the cranial nerves were identified. The distance of each cranial nerve opening to midline and the distances between different cranial nerve openings were measured on the left and right side and compared. The mean clivus length and width were 21.2 ± 4.4 and 13.2 ± 1.5 mm, respectively. The distance of the twelfth cranial nerve opening from midline was shorter on the right side when compared with the left side (6.6 ± 1.1 versus 7.1 ± 0.8 mm, p = 0.038). Openings of other cranial nerves did not show such asymmetry with regard to their distance from midline, and the distances between different cranial nerves were similar on the left and right side. Cranial nerves at petroclival region seem to show minimal asymmetry in fetuses.

[VEGETATIVE REACTIONS AS PROGNOSTIC FACTOR IN POSTERIOR FOSSA SURGERY].

Mortality rate related to posterior fossa tumors resection varies from 1 to 8 percent, according to various authors. It depends on tumor size and its growth characteristics. To determine the physiological acceptability of surgery, physiological significance of vegetative reactions associated with tumors resection has to be assessed. We divide these reactions (centrogenic reactions - CR) into 2 main groups. The first group has a relatively precise morphofunctional structure, similar to the classic reflex arc. They appear due to irritation of local centers or cranial nerves nuclei with mixed motor-vegetative structure. In most cases they are not connected with anatomic damage of CNS structures. The second group of CR is correlated with dysfunction of brain and represents brain s attempt to turn into a new functional state. Their presence should be considered as a functional degradation symptom, which might be even irreversible. Emergence from anesthesia in the operative room is not recommended in this clinical situation. Neurovegetative stabilization should be provided for a period of 6 to 24 hours after tumor resection.

High-resolution MRI of cranial nerves in posterior fossa at 3.0 T.

OBJECTIVE: To evaluate the influence of high-resolution imaging obtainable with the higher field strength of 3.0 T on the visualization of the brain nerves in the posterior fossa. METHODS: In total, 20 nerves were investigated on MRI of 12 volunteers each and selected for comparison, respectively, with the FSE sequences with 5 mm and 2 mm section thicknesses and gradient recalled echo (GRE) sequences acquired with a 3.0-T scanner. The MR images were evaluated by three independent readers who rated image quality according to depiction of anatomic detail and contrast with use of a rating scale. RESULTS: In general, decrease of the slice thickness showed a significant increase in the detection of nerves as well as in the image quality characteristics. Comparing FSE and GRE imaging, the course of brain nerves and brainstem vessels was visualized best with use of the three-dimensional (3D) pulse sequence. CONCLUSIONS: The comparison revealed the clear advantage of a thin section. The increased resolution enabled immediate identification of all brainstem nerves. GRE sequence most distinctly and confidently depicted pertinent structures and enables 3D reconstruction to illustrate complex relations of the brainstem.

Assessment of cognitive function before and after surgery for posterior cranial fossa lesions using computerized and conventional tests.

Cognitive function has not been well studied after neurosurgery for posterior fossa lesions despite its potential importance in determining surgical indications and approaches. The present study evaluated changes in cognitive functions after posterior fossa surgery to detect any differences between the middle cranial fossa and lateral suboccipital approaches in 50 patients with posterior fossa lesions such as tumors and vascular diseases. Twenty-five patients underwent surgery via the middle fossa and 25 via the lateral suboccipital approaches. Computerized test battery (CogState) and conventional neuropsychological tests (serial seven-word learning test and mini-mental state examination) were examined before, 1 month after, and 3 months after surgery. All scores of the neuropsychological tests remained within normal limits after surgery. However, the scores of one computerized test battery and serial seven-word learning tests decreased significantly 1 month after surgery and recovered within 3 months, indicating temporary deterioration of short-term memory in the middle fossa group. The computerized tests detected significantly larger numbers of patients with worsened results than the conventional tests. The middle fossa approach and operation time showed correlations with the postoperative neuropsychological declines. The computerized tests could be performed easily and were beneficial for detecting subtle changes of the cognitive function after surgery. Cognitive function, especially short-term memory, may decline temporarily with the middle fossa approach and long operation time.

Virtual neuroendoscopy: MRI-based three-dimensional visualization of the cranial nerves in the posterior cranial fossa.

This article presents the advances of three-dimensional (3D) virtual neuroendoscopy of the cranial nerves (CN) in the posterior fossa. Interactive 3D visualizations were generated and the anatomical landmarks, such as the root entry/exit zones (REZ) and cisternal segments of the CN were evaluated. Twenty patients (M:F, 6:14) with trigeminal neuralgia (TN) underwent MRI constructive interference in steady state (MRI(CISS)) imaging and subsequent 3D visualization based on explicit segmentation of the MRI(CISS) data and interactive evaluation with direct volume rendering including implicit segmentation. The 3D topography of the interesting CN V-X were evaluated with interactive and virtual neuroendoscopy. The anatomical landmarks of the CN V-X could be visualized in all 20 cases (100%). The systematic application of virtual neuroendoscopy could be realized in all patients for the non-invasive observation of the CN without any technical difficulties. Interactive 3D visualization using explicit and implicit techniques for segmentation, and 3D direct volume rendering is demonstrated to successfully identify 3D neurovascular relations in patients with trigeminal neuralgia. It has the ability to provide a useful tool for surgeons in the pre- and intraoperative evaluation of such cases.

[MRI performance and diagnosis of schwannomas from cranial nerves in posterior cranial fossae].

BACKGROUND & OBJECTIVE: Cranial nerve schwannomas originate frequently in posterior cranial fossae and have various and complex MRI performances, some of which are still not well known. This study was to explore MRI performances and features of schwannomas from cranial nerves in posterior cranial fossae. METHODS: The MRI performances of 75 cases of schwannoma from cranial nerves in posterior cranial fossae, including trigeminal (n=9), facial (n=1), acoustic (n=53), 9th-11th (n=9) and hypoglossal (n=3) schwannomas, confirmed by surgical and pathologic findings, were analyzed retrospectively. RESULTS: Most of schwannomas in posterior cranial fossae were solid-cystic lesions when their sizes were larger than 1.5 cm in diameter. Small lesions (less than 1.5 cm in diameter) may be completely solid, which were closely related to cranial nerves. On T1WI, the solid part of tumor appeared iso- or slightly hypointense, while cystic part was hypointense. On T2WI, solid part appeared high or slightly high signal intensity, but cystic part appeared very high signal intensity. On contrast-enhanced T1WI, there was obvious enhancement in the solid part, but not in the cystic part. Some typical signs were very useful to infer tumor origin, such as, dumbbell-shaped trigeminal schwannoma extended across the middle and posterior cranial fossa, enlargement of internal auditory canal, widened jugular foramen and hypoglossal foramen caused by acoustic schwannoma, the 9th-11th shcwannoma, and hypoglossal schwannoma, respectively. The correct ratio for qualitative diagnosis of schwannoma was 92% using MRI, but the incorrect ratio for identifying the nerve of tumor origin was 8.7%. CONCLUSION: MRI is a good method in qualitative diagnosis of schwannoma and identifying cranial nerves of tumor origin in posterior cranial fossae.

[Anatomy of the hypoglossal nerve and the hypoglossal ansa cervicalis]. / Anatomie du couple nerf hypoglosse, anse cervicale.

The hypoglossal nerve is the motor nerve of the tongue and the ansa cervicalis is a motor nerve for the sub-hyoid muscles. The hypoglossal nerve seems to give the innervation of the thyrohyoid although it is a sub-hyoid muscle. Most of axons in the ansa cervicalis arise from the three first cervical nerves. These nerves are in close contact because of the cervical ontogeny of the tongue and the hypoglossal nerve. Nerve impulse in the superior root of the ansa cervicalis runs caudally to rostrally. This is why neurotization techniques using the superior root of the ansa cervicalis produce poor results in the treatment of facial palsy sequelae.

Duplication of the abducens nerve at the petroclival region: an anatomic study.

OBJECTIVE: During its course between the brainstem and the lateral rectus muscle, the abducens nerve usually travels forward as a single trunk, but it is not uncommon for the nerve to split into two branches. The objective of this study was to establish the incidence and the clinical importance of the duplication of the nerve. METHODS: The study was performed on 100 sides of 50 autopsy materials. In 10 of 11 cases of duplicated abducens nerve, colored latex was injected into the common carotid arteries and the internal jugular veins. The remaining case was used for histological examination. RESULTS: Four of 50 cases had duplicated abducens nerve bilaterally. In seven cases, the duplicated abducens nerve was unilateral. In 9 of these 15 specimens, the abducens nerve emerged from the brainstem as a single trunk, entered the subarachnoid space, split into two branches, merged again in the cavernous sinus, and innervated the lateral rectus muscle as a single trunk. In six specimens, conversely, the abducens nerve exited the pontomedullary sulcus as two separate radices but joined in the cavernous sinus to innervate the lateral rectus muscle. In 13 specimens, both branches of the nerve passed beneath the petrosphenoidal ligament. In two specimens, one of the branches passed under the ligament and the other passed over it. In one of these last two specimens, one branch passed over the petrosphenoidal ligament and the other through a bony canal formed by the petrous apex and the superolateral border of the clivus. In all of the specimens, both branches were wrapped by two layers: an inner layer made up of the arachnoid membrane and an outer layer composed of the dura during its course between their dural openings and the lateral wall of the cavernous segment of the internal carotid artery. This finding was also confirmed by histological examination in one specimen. CONCLUSION: Double abducens nerve is not a rare variation. Keeping such variations in mind could spare us from injuring the VIth cranial nerve during cranial base operations and transvenous endovascular interventions.

Anatomical evidence for the absence of a morphologically distinct cranial root of the accessory nerve in man.

The accessory nerve is conventionally described as having a cranial and spinal root. According to standard descriptions the cranial root (or part) is formed by rootlets that emerge from the medulla between the olive and the inferior cerebellar peduncle. These rootlets are considered to join the spinal root, travel with it briefly, then separate within the jugular foramen to become part of the vagus nerve. In 15 fresh specimens we exposed the posterior cranial fossa with a coronal cut through the foramen magnum and explored the course of each posterior medullary rootlet (PMR) arising from within the retro-olivary groove. We chose the caudal end of the olive as the landmark for the caudal end of the medulla. In all specimens every PMR that did not contribute to the glossopharyngeal nerve joined the vagus nerve at the jugular foramen. The distance between the caudal limit of the olive and the origin of the most caudal PMR that contributed to the vagus nerve ranged from 1-21 mm (mean = 8.8 mm). All rootlets that joined the accessory nerve arose caudal to the olive. The distance from the caudal limit of the olive and the most rostral accessory rootlet ranged from 1-15 mm (mean = 5.4 mm). We were unable to demonstrate any connection between the accessory and vagus nerves within the jugular foramen. Our findings indicate that the accessory nerve has no cranial root; it consists only of the structure hitherto referred to as its spinal root.

Arterial and neural relations at the posterior and lateral aspects of the medullo-spinal junction.

The authors report the results of a series of 59 microdissections of the region of the foramen magnum. These dissections were made under the strict conditions of a surgical approach using an operating microscope. The major anatomic structures of the medullo-spinal junction are arranged mainly at its lateral aspect. The customary surgical approaches to the posterior cranial fossa give ready access to the cerebello- and latero-medullary cisterns. The description of the neurovascular structures contained therein assumes a particular importance because of the relative frequency of lesions developing at this level. This study deals particularly with the vertebral a. (VA), the inferior posterior cerebellar a. (IPCA), the cranial nn. IX (glossopharyngeal n.), X (vagus n.), XIc and XIs (cranial and spinal accessory n.) and XII (hypoglossal n.). The anatomy of this posterior and lateral region is characterised by the contrast between the relatively uniform course of the VA and the variable course of the IPCA, a true guideline whose very irregular arrangement accounts for the diversity of its relations with the last four cranial nn.

A new concept in Dorello's canal microanatomy: the petroclival venous confluence.

The so-called Dorello's canal was studied in 32 specimens (16 human cadaver heads) injected with colored latex and fixed in formalin (28 specimens) or studied with microscopic and ultrastructural methods (four specimens). To avoid the differences usually encountered in the description of this area, the authors preferred to consider a larger space that they have named the petroclival venous confluence (PVC). It was located between two dural layers: inner (or cerebral) and outer (or osteoperiosteal). The PVC was quadrangular on transverse section. The posterior petroclinoid fold and the axial plane below the dural foramen of the abducent nerve (sixth cranial nerve) limited the PVC at the top and bottom, respectively. Its anteroinferior limit was the posterosuperior aspect of the upper clivus and outer layer of the dura mater. Its anterior limit was the vertical plane containing the posterior petroclinoid fold, and its posterior limit was the inner layer of the dura. The PVC was limited laterally by the medial aspect of the petrous bone apex and medially by the virtual sagittal plane extending the medial limit of the inferior petrosal sinus upward. The PVC was a venous space bordered by endothelium and continuous with the cavernous sinus, the basal sinus of the clivus, and the inferior petrosal sinus. There were trabeculations between the two dural layers. The petrosphenoidal ligament of Gruber may be regarded as a larger trabeculation, and it divided the PVC into a superior and an inferior compartment. The abducent nerve generally ran through the inferior compartment, where it was fixed to the surrounding dura mater. This nerve was only separated from venous blood by a meningeal sheath of varying thinness lined with endothelium. The clinical implications of these findings are discussed.

Neurovascular relationships in the posterior cranial fossa, with special reference to trigeminal neuralgia. 1. Review of the literature and development of a new method of vascular injection-filling in cadaveric controls.

Vascular compression of cranial nerves adjacent to the brain stem has been implicated in a wide variety of disorders affecting their function. The considerable conflicts in published results relate primarily to flaws in study design. The design required of an adequate study is defined and a technique is presented, in 16 fresh human cadavers, of reliable and physiological injection-filling of both the cerebral arterial and venous systems. It allowed for the accurate observation of the normal neurovascular relationships in the posterior cranial fossa during operative simulation. Part 2 of this article concerns the use of this design in the study of trigeminal neuralgia, a disorder thought to relate to vascular compression of the fifth cranial nerve.

Neurovascular relationships in the posterior cranial fossa, with special reference to trigeminal neuralgia. 2. Neurovascular compression of the trigeminal nerve in cadaveric controls and patients with trigeminal neuralgia: quantification and influence of method.

The theory of neurovascular compression has been tested by comparing the neurovascular relationships of the trigeminal nerve in a series of operative observations in patients affected by trigeminal neuralgia with those of a control series of cadavers matched for age, sex and side, in which operative conditions were simulated during simultaneous arterial and venous injection--filling to physiological pressures, as described in Part 1 of this article. A rigorous system of classification of neurovascular relations is defined. In 46 patients with trigeminal neuralgia, 91% had a vessel in contact with the trigeminal nerve adjacent to the brain stem and in all but one a groove was created. Multiple vessels were found in 17% and in two both the root entry zone and lateral portions of the nerve were compressed. However, in 35 randomly selected fresh cadavers, not known to have suffered neurological disease, 14% had neurovascular contact and a further 26% had vessels "near" to the nerve. No vessel was associated with a groove and no multiple vessels, or sites of contact, were encountered. The difference between the control cadavers and the operative findings in patients related to an increase in the number of arteries. Injection-filling of the cadaveric vessels doubled the numbers of vessels in contact with, and near to the nerve. The technique used and system of classification applied showed an association between arterial contact and trigeminal neuralgia. The technique may provide a suitable method for the testing of the neurovascular compression theory in other conditions.

Glossopharyngeal neuralgia with cardiac syncope.

Glossopharyngeal Neuralgia is an uncommon craniofacial pain syndrome that is occasionally associated with cardiac syncope. Involvement of the glossopharyngeal nerve may be painless or may be marked by true episodic neuralgia, and this justifies the term neuralgia reported here. We present 5 cases of this uncommon syndrome, of a total of 15 observed cases of glossopharyngeal neuralgia, successfully treated by section of the rootlets of Cranial Nerves IX and X or by microvascular decompression in the posterior cranial fossa. We also analyze the relevant literature and discuss the pathogenesis and treatment of the syndrome.

Middle fossa vestibular neurectomy in retrolabyrinthine neurectomy failures.

Retrolabyrinthine vestibular nerve section is an important treatment option in patients with refractory, incapacitating vertigo. However, an indistinct cleavage plane between the cochlear and vestibular portions of the eighth cranial nerve may result in incomplete sectioning of the superior and inferior vestibular nerve fibers. We describe 11 patients in whom middle fossa vestibular neurectomy was performed following failure of a retrolabyrinthine vestibular neurectomy. A successful postoperative outcome from this revision surgery was obtained in six of 11 patients on follow-up evaluation. Patients in whom infrared video electronystagmography showed persistent function of the inferior vestibular nerve following retrolabyrinthine vestibular nerve section had a better response to middle fossa vestibular neurectomy than those with no measurable residual vestibular function. Because it provides access to the vestibular nerves where there is separation from the cochlear nerves distal to the previous section, we feel that the middle fossa vestibular neurectomy is the procedure of choice in selected patients who fail retrolabyrinthine neurectomy.