Lower skull base: anatomic study with surgical implications

Lower Four Cranial Nerves in the Management of Glomus Jugulare: Anatomical Study

Introduction  The surgical management that achieves minimal morbidity and mortality for patients with glomus and non-glomus tumors involving the jugular foramen (JF) region requires a comprehensive understanding of the complex anatomy, anatomic variability, and pathological anatomy of this region. Objective  The aim of this study is to propose a rational guideline to expose and preserve the lower cranial nerves (CNs) in the lateral approach of the JF. Methods  The technique utilized is the gross and microdissection of 4 fixed cadaveric heads to revise the JF's surgical anatomy and high part of the carotid sheath compared with surgical cases to understand and preserve the integrity of lower CNs. The method involves radical mastoidectomy, microdissection of the JF, facial nerve, and high neck just below the carotid canal and the JF. The CNs IX, X, XI, and XII are microscopically dissected and kept in sight up to the JF. Results  This study realized well the surgical and applied anatomy of the lower CNs with relation to the facial nerve and JF. Conclusions  The JF anatomy is complicated, and the key to safely operate on it and preserving the lower CNs is to find the posterior belly of the digastric muscle, to skeletonize the facial nerve, to remove the mastoid tip preserving the stylomastoid foramen, to skeletonize the sigmoid sinus and posterior fossa dura not only anterior but also posteroinferior to reach and drill the jugular tubercle.

Comparison of Lower Cranial Nerve Function Between Tympanojugular Paraganglioma Class C1/C2 With and Without Intracranial Extension: A Four-Decade Experience

OBJECTIVE

To compare preoperative and postoperative lower cranial nerve (LCN) function between Class C1 and C2 tympanojugular paraganglioma (TJP) with/without intracranial intradural (Di)/extradural (De) extensions, according to the experience of a single surgeon over four decades.

STUDY DESIGN

Retrospective review.

SETTING

Quaternary referral center for otology and skull base surgery.

MATERIAL AND METHODS

A chart review was conducted of all the patients operated for C1/C2 TJPs from September 1983 to December 2018. The tumors were classified as: Limited-Group (C1/C2 without Di/De extensions) and Extended-Group (C1/C2 with Di/De extensions).

RESULTS

Of 159 patients, 107 (67.3%) were women; the mean age at surgery was 46.5 years. The Limited-Group (56.6%) comprised C1 (41.1%) and C2 (58.9%) tumors; the Extended-Group (43.4%) comprised C1+Di/De (14.5%) and C2+Di/De (85.5%) tumors. The prevalence of preoperative LCN palsy was 11.9 times higher in Extended than Limited tumors: 61.9% versus 4.9% (p < 0.05). The risk for postoperative LCN palsy was 4.7 times greater in Extended than Limited tumors: 29.2% versus 12.9%, p = 0.01.

CONCLUSION

Especially in younger patients, complete removal of Limited C1/C2 tumors, before they extend intracranially, reduces the risk of dysfunctionality of LCNs and the burden of residual tumor. The incidence of new tumors increased over four decades. However, new-postoperative LCN palsy did not occur in any Limited C1/C2 tumors operated after the year 2000, and declined to less than 10% of Extended C1/C2 tumors.

Anatomical study of jugular foramen in the neck

INTRODUCTION

The anatomical complexity of the jugular foramen makes surgical procedures in this region delicate and difficult. Due to the advances in surgical techniques, approaches to the jugular foramen became more frequent, requiring improvement of the knowledge of this region anatomy.

OBJECTIVE

To study the anatomy of the jugular foramen, internal jugular vein and glossopharyngeal, vagus and accessory nerves, and to identify the anatomical relationships among these structures in the jugular foramen region and lateral-pharyngeal space.

METHODS

A total of 60 sides of 30 non-embalmed cadavers were examined few hours after death. The diameters of the jugular foramen and its anatomical relationships were analyzed.

RESULTS

The diameters of the jugular foramen and internal jugular vein were greater on the right side in most studied specimens. The inferior petrosal sinus ended in the internal jugular vein up to 40mm below the jugular foramen; in 5% of cases. The glossopharyngeal nerve exhibited an intimate anatomical relationship with the styloglossus muscle after exiting the skull, and the vagal nerve had a similar relationship with the hypoglossal nerve. The accessory nerve passed around the internal jugular vein via its anterior wall in 71.7% of cadavers.

CONCLUSION

Anatomical variations were found in the dimensions of the jugular foramen and the internal jugular vein, which were larger in size on the right side of most studied bodies; variations also occurred in the trajectory and anatomical relationships of the nerves. The petrosal sinus can join the internal jugular vein below the foramen.

Management of the Vertebral Artery at the Craniocervical Junction

OBJECTIVES: To study the surgical anatomy of the vertebral artery at the craniocervical junction and its related structures defining reliable landmarks for its safe exposure.

DESIGN: Ten sides of 5 fresh cadavers were dissected using the lateral approach to the craniocervical junction.

RESULTS: Experience gained in studying the anatomic details of the vertebral artery at the craniocervical junction in cadavers from its exit at the transverse foramen of the second cervical vertebra to the vertebrobasilar junction provided the initial background for us to use the lateral approaches to the skull base to safely manage 4 cases with pathology reaching the close vicinity of vertebral artery at the craniocervical junction.

CONCLUSION: Thorough knowledge of the anatomy of the vertebral artery is mandatory before attempting surgery at the craniocervical junction. There are reliable landmarks that, when followed, could facilitate safe exposure and identification of the artery.

Surgical Approaches to the Jugular Foramen: A Comprehensive Review

Introduction Multiple surgical approaches and combinations thereof have been described to gain access to the jugular foramen. In an area laden with important neurovascular structures, care must be taken in choosing the best surgical approach for treatment of rare pathologies involving this region. Methods This manuscript provides a comprehensive review of the relevant anatomy along with an overview of the various approaches to the jugular foramen. In an attempt to simplify the various concepts, we propose a basic distinction into anterolateral and posterolateral approaches based on the main trajectory targeting the jugular foramen. Conclusion The anatomy surrounding the jugular foramen is exceedingly complex and requires in-depth understanding of skull base and head and neck relationships.

[Approach to the jugular foramen and related structures - an analysis of the surgical technique based on cadaver simulation]

This study presents consecutive stages of the approach to the jugular foramen and related structures. Eleven simulations of the approach were performed on non-fixed human cadavers without any known pathologies in the head and neck. The consecutive stages of the procedure were documented with photographs and schematic diagrams. The starting point for the discussed approach is removal of the mastoid and petrosal parts of the temporal bone, as well as the jugular process and the jugular tuberculum. It allows penetration of the jugular foramen from the back. Widening of the approach enables penetration of the jugular foramen from above and the front. Approach to the jugular foramen is a reproducible technique, which provides surgical penetration of this foramen and related structures. This approach is particularly useful in the surgical treatment of tumours expanding in the petrous pyramid, surroundings of the petrosal part of the internal carotid artery, cerebellopontine angle, subtemporal fossa and nervous-vascular bundle of the neck.

Nonvascular lesions of the jugular foramen: the gruppo otologico experience

Tumors other than paragangliomas in the jugular foramen are uncommon. Of these, schwannomas and meningiomas predominate. Little clinical data are available in the literature on these tumors at this site. The purpose of this article is to review our experience at the Gruppo Otologico of the management of these tumors. A retrospective series is presented of 32 consecutive patients affected by jugular foramen schwannomas and meningiomas in which their clinical and radiological signs, together with surgical techniques and outcomes, were reviewed. A single-stage resection was possible for the majority of patients when the petro-occipital trans-sigmoid (POTS) approach was used. This allowed resection of both intra- and extradural components of the tumor with hearing preservation and avoidance of facial nerve transposition. No deaths occurred. Lower cranial nerve palsies constituted the major cause of morbidity, but none of the patients required an adjunctive procedure such as vocal cord medialization, tracheostomy, or percutaneous gastrostomy.

An anatomical and radiological study of the high jugular bulb on high-resolution CT scans and alcohol-fixed skulls of adults

Although many reports mention a "high jugular bulb" (HJB), it is often not clearly defined. We examined the relationship between the jugular bulb (JB) and the internal auditory canal (IAC) in 200 temporal bones on high resolution CT scans and alcohol-fixed skull bases of adults. The average distance (+/-standard deviation) between the IAC and the JB was 7.5+/-2.3mm (range, 1-16 mm). The JB was higher on the right side than its companion in 53.3% of patients (left side only in 22%; no side dominance in 23.7% of bases). When the JB reached or exceeded the floor of the IAC (16.5%), it was defined as a HJB; 61% of HJB were found in females. Bilateral HJB was found in 0.5% of patients. The HJB was not associated with a contralateral flat JB. Preoperative multiplanar high resolution CT reconstructions make the most detailed assessment of structural topography.

The Medial wall of the Jugular Foramen

OBJECTIVE: To better understand the variable and complex anatomy of the jugular foramen (JF) and the relationship between the neurovascular structures in the medial wall of the jugular bulb (JB).

STUDY DESIGN: A temporal bone anatomic study.

SETTING: A temporal bone laboratory within a hearing research facility.

SUBJECTS AND METHODS: Twenty-two temporal bones were dissected under the operating microscope. The JF anatomy was exposed by using the modified infratemporal fossa approach (no rerouting of the facial nerve). Pictures were taken at various intervals during the dissection. Distances between important structures were measured with two-point calipers and transferred to a millimetric scale.

RESULTS: The right JF was found to be larger than the left side in 72.7 percent of the dissected temporal bones. A fibrous septum separated the glossopharyngeal (CN IX) from the vagus (CN X) and accessory (CN XI) nerves in 19 specimens (86.4%), and a complete bony septum was present in three specimens (13.6%). The CNs IX, X, and XI traveled anteromedially to the JB within the JF. The inferior petrosal sinus (IPS) drained into the medial wall of the JB at various locations by two or more channels. In most of the specimens (86.4%), the IPS separated CNs IX and X.

CONCLUSION: The lower cranial nerves have an intimate relationship to the medial wall of the JB. Within the JF, the neurovascular structures vary in size, shape, and location. To minimize surgical morbidity, the surgeon should be familiar with the complex anatomy of the JB and its variations.

Detailed MR imaging anatomy of the cisternal segments of the glossopharyngeal, vagus, and spinal accessory nerves in the posterior fossa: the use of 3D balanced fast-field echo MR imaging

BACKGROUND AND PURPOSE

The cisternal segments of the lower cranial nerves (CNs) adjacent to the jugular foramen (JF) are difficult to identify reliably by routine MR imaging. We performed a 3D balanced fast-field echo imaging technique (3D-bFFE) to obtain detailed anatomy of the cisternal segments of CNs IX, X, and XI.

MATERIALS AND METHODS

3D-bFFE was used to image the cisternal segments of the lower CNs in 20 healthy volunteers. As an anatomic landmark, CSF recesses adjacent to the JF were divided into 3 parts: the recess for the cochlear aqueduct, the recess for CN IX, and the recess for the CN X/XI complex. MR images were evaluated to identify the cisternal segment of each cranial nerve in relation to these anatomic landmarks.

RESULTS

The mean angles of the recess for the cochlear aqueduct for CN IX and CN X/XI to the posterior petrous bone were 41.6 +/- 2.5 degrees , 69.7 +/- 3.1 degrees , and 76.0 +/- 3.4 degrees , respectively (P < .01). The mean length of the recess for the cochlear aqueduct for CN IX and the CN X/XI complex was 5.91 +/- 0.19, 5.08 +/- 0.11, and 4.76 +/- 0.13 cm, respectively (P < .01). 3D-bFFE adequately depicted the cisternal segments of CN IX on 38 sides (95%) and the CN X/XI complex on 39 sides (97.5%).

CONCLUSIONS

The cisternal segments of CN IX, CN X, and CN XI are well identified by using 3D-bFFE, especially by determining the angles of the CSF recesses adjacent to the JF.

Imaging of the nasopharynx and skull base

The prerequisite for the correct diagnosis and accurate delineation of skull base lesions is familiarity with the complex anatomy of the skull base. Imaging plays a central role in the management of skull base disease because this region is often difficult to evaluate clinically. CT and MR imaging are complementary; they are often used together to demonstrate the full disease extent. This article focuses on the critical anatomy of the skull base and how this knowledge contributes to accurate disease assessment.

Infratemporal Fossa Approach to the Hypoglossal Canal: Practical Landmarks for Elusive Anatomy

OBJECTIVE

At the conclusion of the article the readers should be able to safely and reliably find the hypoglossal canal using the infratemporal fossa approach.

HYPOTHESIS

Very little has been written on the regional anatomy of the hypoglossal canal as seen through a transtemporal approach. This project attempts to further define the anatomy of the hypoglossal canal and provide the surgeon with guidelines for reaching it. Our hypothesis is that the hypoglossal canal can be safely and consistently reached by way of the temporal bone with preservation of hearing and cranial nerves (CN) IX to XI.

STUDY DESIGN

Prospective anatomic study.

METHODS

The study was performed using cadaver temporal bones. Infratemporal fossa Fisch type-A dissections were performed. The hypoglossal canal was then completely exposed. The distance from the canal to the jugular bulb, carotid artery, round window, lateral canal, and roots of CN IX to XI were recorded.

RESULTS

Fifteen temporal bones were dissected and measured. The position of the hypoglossal canal is consistently located anterior, inferior, and medial to the jugular bulb. The distance from midcanal to the jugular bulb and the roots of CN IX to XI at the posterior fossa dura was 5.3 mm +/- 0.82 and 7.1 mm +/- 2.49, respectively. The distance from the carotid artery where it meets the jugular vein to the midcanal was 15.3 mm +/- 2.09. The distance from the round window to the canal was 21.7 mm +/- 3.17.

CONCLUSIONS

The hypoglossal canal can be consistently reached using the infratemporal fossa approach. Hearing and CN IX to XI can be preserved. The distance from the jugular bulb and roots of CN IX to XI can be used as guideposts. If a tumor is involving the bulb, then the carotid artery and the round window are the next most reliable indicators of position.

Imaging of the nasopharynx and skull base

The prerequisite for the correct diagnosis and accurate delineation of skull base lesions is familiarity with the complex anatomy of the skull base. Imaging plays a central role in the management of skull base disease because this region is often difficult to evaluate clinically. CT and MR imaging are complementary; they are often used together to demonstrate the full disease extent. This article focuses on the critical anatomy of theskull base and how this knowledge contributes to accurate disease assessment.

Lateral craniofacial approaches to the skull base and infratemporal fossa

The field of skull base surgery has expanded dramatically the surgical horizons in the treatment of skull base neoplasms, which, previously, were considered inoperable because of their locations and relation to vital structures. This article aims to offer improved understanding of surgical indications and appreciation for some of the details of surgical techniques involved.

Comprehensive microsurgical anatomy of the jugular foramen and review of terminology

The microsurgical anatomy of the jugular foramen was studied in 12 formalin preserved cadavers (24 foramina) and 40 dry-skulls (80 foramina). The jugular foramen was exposed by microsurgical dissection with drilling from a superior to inferior direction. Observations regarding dural architecture of the jugular foramen and relationships between neurovascular structures passing through the foramen were noted in cadavers. Normal bony construction of the foramen and its variational anatomy were examined in dry-skull specimens. Using photographs and drawings, the anatomy of the jugular foramen is presented and related terminology is discussed in the light of a literature review.

Jugular foramen: microscopic anatomic features and implications for neural preservation with reference to glomus tumors involving the temporal bone

OBJECTIVE

Our goals were to study the normal histological features of the jugular foramen, compare them with the histopathological features of glomus tumors involving the temporal bone, and thus provide insight into the surgical management of these tumors with respect to cranial nerve function.

METHODS

Ten jugular foramen blocks were obtained from five human cadavers after removal of the brain. Microscopic studies of these blocks were performed, with particular attention to fibrous or bony compartmentalization of the jugular foramen, the relationships of the caudal cranial nerves to the jugular bulb/jugular vein and internal carotid artery, and the fascicular structures of the nerves. In addition, we studied the histopathological features of 11 glomus tumors involving the temporal bone (10 patients), with respect to nerve invasion, associated fibrosis, and carotid artery adventitial invasion.

RESULTS

A dural septum separating the IXth cranial nerve from the fascicles of Cranial Nerves X and XI, at the intracranial opening, was noted. Only two specimens, however, had a septum (one bony and one fibrous) producing internal compartmentalization of the jugular foramen. The cranial nerves remained fasciculated within the foramen, with the vagus nerve containing multiple fascicles and the glossopharyngeal and accessory nerves containing one and two fascicles, respectively. All of these nerve fascicles lay medial to the superior jugular bulb, with the IXth cranial nerve located anteriorly and the XIth cranial nerve posteriorly. All nerve fascicles had separate connective tissue sheaths. A dense connective tissue sheath was always present between the IXth cranial nerve and the internal carotid artery, at the level of the carotid canal. The inferior petrosal sinus was present between the IXth and Xth cranial nerves, as single or multiple venous channels. The glomus tumors infiltrated between the cranial nerve fascicles and inside the perineurium. They also produced reactive fibrosis. In one patient, in whom the internal carotid artery was also excised, the tumor invaded the adventitia.

CONCLUSION

Within the jugular foramen, the cranial nerves lie anteromedial to the jugular bulb and maintain a multifascicular histoarchitecture (particularly the Xth cranial nerve). Glomus tumors of the temporal bone can invade the cranial nerve fascicles, and infiltration of these nerves can occur despite normal function. In these situations, total resection may not be possible without sacrifice of these nerves.

Usefulness of the C1 transverse process as a reference guide in the dissection of the upper lateral neck

In this investigation we dissected 3 cadavers with the lateral cervical approach to assess the usefulness of the transverse process of the atlas (TPA) as a reference guide in the upper lateral neck. Our results indicate that all the important structures in this space can be identified systematically. Lateral to the TPA sits the posterior belly of the digastric muscle, the stylohyoid muscle, and the occipital artery. Anterior to the TPA, the styloid process can be exposed. The internal jugular vein and cranial nerves X, XI, and XII sit between the styloid process and the TPA. Superior to the TPA, tracing the carotid sheath upward, the carotid canal and jugular foramen can be reached. Anteroinferior to the jugular foramen, the hypoglossal nerve emerges from the cranial cavity through the hypoglossal canal. Posterior to the TPA, the suboccipital triangle can be recognized. Within the triangle, the vertebral artery and its accompanying venous complex can be identified.

The jugular foramen: a comparative radioanatomic study

BACKGROUND

Advances in microsurgical techniques made possible the removal of advanced jugular foramen (JF) lesions, which once had been accepted as unoperable. However, successful surgery requires detailed knowledge of the JF anatomy.

METHODS

Sixteen jugular foramina in eight formalin-preserved adult cadavers were scanned with axial and coronal high resolution computed tomography (HRCT) prior to dissection. After craniectomy and removal of brain tissue, the relationships of the neurovascular structures in the JF were determined by drilling the temporal bones from superior to inferior on planes parallel to the skull base.

RESULTS

No bony partition of the JF was observed. A dural band consistently divided the JF into two parts. Anterior to it was the glossopharyngeal nerve (IX) while the vagus (X) and accessory (XI) nerves were located posteriorly. There was a notch in which the IX nerve entered the JF. It was also identified on the CT scans and defined as the glossopharyngeal recess. The IX nerve made a genu within the JF in all specimens. Then, it ran inferiorly through a bony canal in three specimens (18.75%), and through an incomplete bony canal in two (12.5%), which were also defined on the CT images. The inferior petrosal sinus ran through a sulcus anteromedial to the glossopharyngeal recess. The posterior meningeal artery was found to be located between the X and XI nerves within the JF.

CONCLUSIONS

This study revealed a complex and highly variable pattern of the relationships of the neurovascular structures in the JF, and their HRCT images correlated well with the anatomic microdissections.

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.

The cochlear aqueduct: an important landmark in lateral skull base surgery

The cochlear aqueduct (CA) is used as a landmark in lateral skull base surgery. In this study anatomic relationships between the CA and adjacent neurovascular structures were examined by dissecting 32 temporal bones. Observations of the relationship of the external opening (EO) of the CA with the ninth, tenth, and eleventh cranial nerves, inferior petrosal sinus (IPS), and intrapetrous carotid artery (ICA) were noted. In addition to the distance of the EO of the CA to the vertical portion of the ICA, the entire length of the CA and the width of the EO were also measured. The ninth nerve was the only structure lodged at the EO of the CA in 34.4% of bones. However, in 40.6% of bones only the IPS crossed the EO of the CA, although the ninth nerve was situated just anteroinferiorly in the vicinity of the EO. In 15.6% of bones it was possible to observe both the ninth nerve and the IPS crossing the EO. In 9.4% of bones the EO of the CA was found to be occupied by the tenth and eleventh nerves. It was also observed that the ICA was located anteriorly on the same sagittal plane with the EO in 15.6% of bones. It was concluded that although in 90% of cases the EO of the CA was in close relation with the ninth nerve, other structures such as the IPS, the tenth and eleventh cranial nerves, and the ICA were also at risk during drilling in this area because of their intimate relationships with the EO of the CA.

Anatomical considerations of high jugular bulb in lateral skull base surgery

In order to study high jugular bulb management in lateral skull base surgery, an anatomical study was conducted on 30 temporal bones by examining the relationship between the internal auditory canal (IAC) and the jugular bulb. The following parameters were measured: 1) Height of the jugular bulb (H)... distance between the level of jugular bulb dome and the line passing through the confluence of the sigmoid sinus with the jugular bulb (SS-JB), 2) Mastoid length (ML)... distance between the mastoid process and middle cranial fossa dura, 3) Distance between the most inferior part of the porus acousticus and jugular bulb dome (A), 4) Distance between the porus acousticus and SS-JB (B). The jugular bulb was defined as high when it occupied more than two thirds of (B). The incidence of a high jugular bulb was 23 per cent in this study. When the jugular bulb was high, the mean (H) and (A) were 9.4 +/- 1.9 mm and 2.7 +/- 0.5 mm, respectively. (H) was higher on the right side than on the left side. No statistically significant difference was found between small and large mastoids (t-test: p > 0.05). It was concluded that when a high jugular bulb was encountered during lateral skull base surgery, the jugular bulb position allows a very small working area inferior to the IAC. In these cases, a 3 or 4 mm depression of the jugular bulb is necessary in order to expose the lower cranial nerves. This can be accomplished by lowering the jugular bulb with the technique already described.

Intraoperative Vagal Nerve Monitoring

A variety of benign and malignant neoplasms occur in the superior cervical neck, parapharyngeal space or the infratemporal fossa. The surgical resection of these lesions may result in postoperative iatrogenic injury to the vagus nerve with associated dysfunctional swallowing and airway protection. Anatomic and functional preservation of this critical cranial nerve will contribute to a favorable surgical outcome.

Fourteen patients with tumors of the cervical neck or adjacent skull base underwent intraoperative vagal nerve monitoring in an attempt to preserve neural integrity following tumor removal. Of the 11 patients with anatomically preserved vagal nerves in this group, seven patients had normal vocal cord mobility following surgery and all 11 patients demonstrated normal vocal cord movement by six months. In an earlier series of 23 patients with tumors in the same region who underwent tumor resection without vagal nerve monitoring, 18 patients had anatomically preserved vagal nerves. Within this group, five patients had normal vocal cord movement at one month and 13 patients demonstrated normal vocal cord movement at six months.

This paper will outline a technique for intraoperative vagal nerve monitoring utilizing transcricothyroid membrane placement of bipolar hook-wire electrodes in the vocalis muscle. Our results with the surgical treatment of cervical neck and lateral skull base tumors for patients with unmonitored and monitored vagal nerves will be outlined.