Comprehensive microsurgical anatomy of the jugular foramen and review of terminology

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.

Retrosigmoid Infralabyrinthine (Suprajugular) Approach to the Jugular Foramen: Indications, Limitations, and Surgical Nuances

BACKGROUND

Among the several approaches described to the jugular foramen (JF), the retrosigmoid infralabyrinthine (suprajugular) approach was one of the most recently described.

OBJECTIVE

To describe the indications, limitations, and operative nuances of the suprajugular approach.

METHODS

We provided a pertinent review of the anatomy, indications, preoperative evaluation, surgical steps and nuances, and postoperative management.

RESULTS

The suprajugular approach is suitable for tumors occupying the intracranial compartment with limited extension into the JF. Volume, width, and configuration of the foramen dictate the feasibility of the approach. Tumors invading the venous system are not suitable for this approach. Preoperative 3-dimensional MRI and computed tomography are used to evaluate intrajugular extension, relationship between the tumor and the jugular bulb (JB), venous system invasion, and shape of the JF. During surgery, exposition of the entire posterior border of the sigmoid sinus is needed and removing the bone over the JB. After identification of the JF, the jugular notch and intrajugular process of the roof of the foramen are removed and intrajugular resection is completed. In cases of high-riding JB, it may be gently pushed down to allow visualization of the anterior foramen. In cases of JB laceration, it may be repaired using a muscle patch and usually does preclude further resection.

CONCLUSION

The suprajugular approach is variation of the retrosigmoid approach that, when properly indicated, provides excellent exposure of the medial JF, with most anatomical variations and intraoperative complications predicted by a comprehensive preoperative evaluation.

Intraforaminal Dural Septations of the Jugular Foramen: A Cadaveric Study

OBJECTIVE

The aim of this study was to define the types, prevalences, and diameters of dural septations (DSs) on the inner surface of the jugular foramen (JF) and to describe the distances between the JF, the glossopharyngeal nerve (cranial nerve [CN] IX), vagus nerve (CN X), and accessory nerve (CN XI), the internal acoustic meatus, and nearby surgical landmarks on cadaveric heads.

METHODS

Seventeen adult (9 men and 8 women) formalin-fixed cadaveric heads were used to analyze the types and prevalence of DS bilaterally. Diameters and distances between the DS and the adjacent CNs (CN IX-XI) were measured by digital microcaliper. The multiple t test (SPSS version 25) was used to analyze the comparison between both sides via diameters, numbers, distance, length, and thickness of DS.

RESULTS

The most frequent type of DS was type I (62.5%, right; 56.3%, left), followed by type II (18.8%, right; 25%, left), type III (12.5%, right; 6.3%, left), and type IV (6.3%, right; 12.5%, left). The mean diameter of the septum was 0.6-1 mm, and the mean length of the dural septa was 4.01 mm (right) and (3.83 mm) left. The difference in the length and thickness of the DS between the genders was statistically significant on both sides (P < 0.05). The DS-CN X and DS-JF distances of women were greater than those of men on the right side (P < 0.05).

CONCLUSIONS

The significant differences between dural septum types on the 2 sides of the body may indicate asymmetric location or a variant emerging site of CNs in the same individual.

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.

Cranial Nerve Foramina: Part II - A Review of the Anatomy and Pathology of Cranial Nerve Foramina of the Posterior Cranial Fossa

Cranial nerve foramina are integral exits from the confines of the skull. Despite their significance in cranial nerve pathologies, there has been no comprehensive anatomical review of these structures. Owing to the extensive nature of this topic we have divided our review into two parts; Part II, presented here, focuses on the foramina of the posterior cranial fossa and discusses each foramen's shape, orientation, size, surrounding structures, and structures that pass through it. Furthermore, by comparing foramen sizes against the cross-sectional areas of their contents, we determine the amount of free space available within each. We also review lesions that can obstruct each foramen and discuss the clinical consequences.

Complete morphometric analysis of jugular foramen and its clinical implications

INTRODUCTION

Tumors affecting structures in the vicinity of jugular foramen such as glomus jugulare require microsurgical approach to access this region. These tumors tend to alter the normal architecture of the jugular foramen by invading it. Therefore, it is not feasible to have correct anatomic visualization of the foramen in the presence of such pathologies. Hence, a comprehensive knowledge of the jugular foramen is needed by all the neurosurgeons while doing surgery in this region.

AIM

Due to the inadequate knowledge of the accurate morphology of the jugular foramen in different sexes, the aim of this osteological study was to provide a complete morphometry including gender differences and describe some morphological characteristics of the jugular foramen in an adult Indian population.

MATERIALS AND METHODS

The study was done on 114 adult human dry skulls (63 males and 51 females) collected from the osteology museum in the department. Various dimensions of both endo- and exocranial aspect of jugular foramen were measured. Presence and absence of domed bony roof of jugular fossa and compartmentalization of jugular foramen were also noticed. Statistical analysis was done using Chi-square test and Student's t-test in SPSS version 23.

RESULTS

All the parameters of right jugular foramen were greater than the left side, except the distance of stylomastoid foramen from lateral margin of jugular foramen (SMJF) which was greater on the left side. Gender differences between various measurements of jugular foramen, presence of dome of jugular fossa, and compartmentalization patterns were reported.

CONCLUSION

This study gives knowledge about the various parameters, anatomical variations of jugular foramen in both sexes of an adult Indian population, and its clinical impact on the surgeries of this region.

Fast imaging employing steady-state acquisition (FIESTA) MRI to investigate cerebrospinal fluid (CSF) within dural reflections of posterior fossa cranial nerves

OBJECTIVE

There is no consensus approach to covering skull base meningeal reflections-and cerebrospinal fluid (CSF) therein-of the posterior fossa cranial nerves (CNs VII-XII) when planning radiotherapy (RT) for medulloblastoma and ependymoma. We sought to determine whether MRI and specifically fast imaging employing steady-state acquisition (FIESTA) sequences can answer this anatomical question and guide RT planning.

METHODS

96 posterior fossa FIESTA sequences were reviewed. Following exclusions, measurements were made on the following scans for each foramen respectively (left, right); internal acoustic meatus (IAM) (86, 84), jugular foramen (JF) (83, 85) and hypoglossal canal (HC) (42, 45). A protocol describes measurement procedure. Two observers measured distances for five cases and agreement was assessed. One observer measured all the remaining cases.

RESULTS

IAM and JF measurement interobserver variability was compared. Mean measurement difference between observers was -0.275 mm (standard deviation 0.557). IAM and JF measurements were normally distributed. Mean IAM distance was 12.2 mm [95% confidence interval (CI) 8.8-15.6]; JF was 7.3 mm (95% CI 4.0-10.6). The HC was difficult to visualize on many images and data followed a bimodal distribution.

CONCLUSION

Dural reflections of posterior fossa CNs are well demonstrated by FIESTA MRI. Measuring CSF extension into these structures is feasible and robust; mean CSF extension into IAM and JF was measured. We plan further work to assess coverage of these structures with photon and proton RT plans. Advances in knowledge: We have described CSF extension beyond the internal table of the skull into the IAM, JF and HC. Oncologists planning RT for patients with medulloblastoma and ependymoma may use these data to guide contouring.

Endoscope-assisted retrosigmoid infralabyrinthine approach to jugular foramen tumors

OBJECT

Removal of jugular foramen (JF) tumors usually requires extensive skull base approaches and is frequently associated with postoperative morbidities such as lower cranial nerve injury. The endoscope-assisted retrosigmoid infralabyrinthine approach is a relatively new approach to tumors extending into the bony canal of the JF. The authors present their experience with this approach.

METHODS

The endoscope-assisted retrosigmoid infralabyrinthine approach was used in 7 patients, including 5 with schwannomas and 2 with paragangliomas. The access to the tumor, extent of its removal, postoperative neurological outcome, and approach-related morbidities were evaluated.

RESULTS

Two patients had a history of previous partial tumor removal, and 1 was treated by embolization followed by two courses of Gamma Knife radiosurgery. In this latter patient near-total resection was achieved. Gross-total resection was possible in the remaining 6 patients. Five patients benefited from endoscopic assistance: in 2 patients it showed a tumor remnant after microscopic tumor removal, while in 3 patients it allowed safe removal of the intraforaminal tumor by visualizing the surrounding structures. No permanent neurological deficit was observed after the operation. Two patients presenting with swallowing disturbance had temporary postoperative worsening that improved later. One patient developed CSF leakage that was managed with a lumbar drain.

CONCLUSIONS

This study shows that the judicious application of the endoscope-assisted retrosigmoid infralabyrinthine approach is safe and effective for removal of the schwannomas extending into the JF and selected paragangliomas without significant luminal invasion of the sigmoid-jugular system.

Anatomic relationship between the spinal accessory nerve and the jugular vein: a cadaveric study

BACKGROUND/PURPOSE

Previous studies of the course of the Spinal Accessory Nerve (SAN) and its relationship to the Internal Jugular Vein (IJV) have yielded conflicting results because of the small number of anatomic specimens and anatomic variability. Classic teaching in Head and Neck Surgery is that the SAN almost always crosses the IJV anteriorly in the upper neck. However, because of the morbidity associated with the injury to the IJV during nerve dissection, it is imperative that the surgeon is wary of the posteriorly crossing nerve. In order to further elucidate the anatomy of the SAN in relation to its surrounding structures, we have studied its anatomy at various points. Specifically, we have aimed to: (1) characterize the anatomic relationship of the SAN to the IJV at three major points: (a) within jugular foramen (JF), (b) at base of skull (BoS), and (c) at the posterior belly of the digastric muscle, (2) record the distance travelled by the SAN from the BoS to its medial to lateral crossing of the IJV, and (3) characterize the anatomy of the JF by with respect to greatest length, width, and partitioning.

METHODS

Sixty-one cadavers, 27 male, and 34 female (84 necks) were dissected and the course of the SAN was followed from the BoS to the crossing the IJV. Data recorded included the relationship of the SAN to the IJV (a) within the JF from an intracranial view, (b) exiting the JF at BoS, and (c) in the neck at the level of the posterior belly of the digastric muscle where anterior versus posterior positioning of the crossing nerve with respect to the IJV was noted. The distance travelled by the SAN from BoS until crossing the IJV, the length and width of the JF within the cranial fossa, and JF partitioning were also recorded.

RESULTS

Within the JF, the SAN travelled anteromedial to the IJV in 73/84 (87%) necks. While exiting the JF, the SAN was found lateral to the IJV in 56/84 (67%) of necks. In the anterior triangle of the neck the SAN crossed the IJV anteriorly in 67/84 (80%) necks, posteriorly in 16/84 (19%) and in the one case of IJV bifurcation, the nerve pierced the vein. The average distance travelled by SAN from BoS to crossing the IJV was 2.38 cm. The average length and width of the JF were, respectively, 1.42 and 0.78 cm, and the IJV was partitioned in 36/84 necks, with 3 of the partitions being bony and the remainder fibrinous. No relationship was found between JF dimensions/partitioning and the anatomic relationship of the structures exiting it.

DISCUSSION/CONCLUSION

In this study, the dimensions and relationship of the IJV and SAN are described in detail. This relationship is specifically noted at three major points, namely within the cranium, at the BoS, and in the anterior neck triangle. In its medial to lateral path in the anterior neck triangle, the SAN crossed the IJV anteriorly in a majority of the cases. However, a posteriorly crossing nerve was not uncommon. These findings support results in previous literature in that the SAN is located anterior to the IJV in the majority of the cases, however, it is imperative for the surgeon to be mindful to the anatomic variability and possible posterior crossing of the IJV by the SAN in the neck to avoid injury to the IJV during the dissection of the nerve. The distance travelled by the nerve prior to crossing the IJV was measured and can be used as a helpful tool for the surgeon in finding the nerve during dissections. We were not able to demonstrate a correlation between the relationship of the SAN and IJV at other recorded points and their crossing relationship. Similarly, no correlation was found between the anatomy of JF and the relationship of the SAN and IJV at any point.

Morphology and compartmentation of the jugular foramen in adult Indian skulls

PURPOSE

Knowledge of the complex anatomy of the jugular foramen is vital for a favorable surgical outcome in technically challenging operations of this region. Various reports about the compartmentation of this foramen and the contents passing through them have come up with conflicting observations.

METHOD

As many as 116 dry, adult skulls were utilized to study the morphology and the compartmentation of the jugular foramen.

RESULTS

The study demonstrates and describes the precise location and frequency of occurrence of processes bridging the foramen and clarifies the existing ambiguity and confusion regarding the compartmentation and the contents passing through. A comprehensive classification for the bridging pattern and compartmentation of the jugular foramen is suggested.

CONCLUSION

This information will be of help to the clinicians for understanding clinical presentations and progression of the lesions of the jugular foramen region and planning for the operations.

[Anatomy of the skull base and the cranial nerves in slice imaging]

Computed tomography (CT) and magnetic resonance imaging (MRI) are suitable methods for examination of the skull base. Whereas CT is used to evaluate mainly bone destruction e.g. for planning surgical therapy, MRI is used to show pathologies in the soft tissue and bone invasion. High resolution and thin slice thickness are indispensible for both modalities of skull base imaging. Detailed anatomical knowledge is necessary even for correct planning of the examination procedures. This knowledge is a requirement to be able to recognize and interpret pathologies. MRI is the method of choice for examining the cranial nerves. The total path of a cranial nerve can be visualized by choosing different sequences taking into account the tissue surrounding this cranial nerve. This article summarizes examination methods of the skull base in CT and MRI, gives a detailed description of the anatomy and illustrates it with image examples.

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.

The jugular foramen: imaging strategy and detailed anatomy at 3T

BACKGROUND AND PURPOSE

The purpose of this study was to assess how well the anatomy of the jugular foramen (JF) could be displayed by 3T MR imaging by using a 3D contrast-enhanced fast imaging employing steady-state acquisition sequence (CE-FIESTA) and a 3D contrast-enhanced MR angiographic sequence (CE-MRA).

MATERIALS AND METHODS

Twenty-five patients free of skull base lesions were imaged on a 3T MR imaging scanner using CE-FIESTA and CE-MRA. Two readers analyzed the images in collaboration, with the following objectives: 1) to score the success with which these sequences depicted the glossopharyngeal (CNIX) and vagus (CNX) nerves, their ganglia, and the spinal root of the accessory nerve (spCNXI) within the JF, and 2) to determine the value of anatomic landmarks for the in vivo identification of these structures.

RESULTS

CE-FIESTA and CE-MRA displayed CNIX in 90% and 100% of cases, respectively, CNX in 94% and 100%, and spCNXI in 51% and 0% of cases. The superior ganglion of CNIX was discernible in 89.8% and 87.8%; the inferior ganglion of CNIX, in 73% and 100%; and the superior ganglion of CNX, in 98% and 100% of cases. Landmarks useful for identifying these structures were the inferior petrosal sinus and the external opening of the cochlear aqueduct.

CONCLUSIONS

This study protocol is excellent for displaying the complex anatomy of the JF and related structures. It is expected to aid in detecting small pathologies affecting the JF and in planning the best surgical approach to lesions affecting the JF.

Reversible cochleo-vestibular deficits in two cases of jugular foramen tumor after surgery

Primary jugular foramen (JF) tumor, such as glomus jugular tumor or JF schwannoma, may manifest as a lower cranial nerve deficit; in addition, it can be accompanied by deafness or vertigo if it affects the cranial nerve (CN) VIII. Recently, we encountered JF schwannoma 1 and glomus jugulare tumor 1. Both cases invaded the adjacent cerebellopontine angle, leading to cochleo-vestibular deficits prior to the operation. After surgery, recovery of the audiovestibular function, including hearing, auditory brainstem response and caloric response, was anticipated in both patients. Therefore, cochleo-vestibular deficits in JF tumors can be attributed to compression neuropathy, rather than tumor infiltration.