32 Microsurgical Anatomy of the Jugular Foramen
Guilherme Henrique Weiler Ceccato, Duarte N. C. Cândido, Jean G. de Oliveira, and Luis A. B. Borba
Abstract
The jugular foramen (JF) forms a space or gap between the temporal and occipital bones, closely related to the carotid canal and tympanic cavity and is positioned deeply and inferiorly in the posterior half of the skull base. If we plan on dealing with pathologies affecting this region we have to predict that for accessing this foramen we will have the internal carotid artery (ICA) and the mandible ramus limiting it anteriorly, the styloid process of the temporal bone and facial nerve anterolaterally, the tympanic cavity and otic capsule superiorly, mastoid tip and facial nerve (intramastoid segment) laterally, transverse process of the atlas and the vertebral artery inferiorly, and the hypoglossal nerve medially. The study of this foramen is of great importance when planning treatment for pathologies at the base of the skull. Because of its deep location and the complexity of structures that surrounds it or travels through it, mastering this regional anatomy become the key part of exposure and adequate approach, as a way to prevent injuries in the treatment of the challenging pathologies encountered here.
Keywords: skull base, glomus tumor, glomus jugulare, brain tumor, brain anatomy
32.1 Introduction
Unlike the rest of the axial and appendicular skeleton, the skull develops from the elements derived from the mesoderm and neural crest. In particular, the jugular foramen (JF), derived from mesoderm by endochondral ossification, is influenced especially by nerve and vascular structures that pass through it.1 This is probably the reason for such diversity between the JFs of different individuals, and even in the same individual, asymmetries between each side, with a prominent right side in the majority of population (demonstrated in the right transverse and sigmoid sinus).
The JF forms a space or gap between the temporal and occipital bones, closely related to the carotid canal and tympanic cavity and is positioned deeply and inferiorly in the posterior half of the skull base. If we plan on dealing with pathologies affecting this region, we have to predict that for accessing this foramen we will have the internal carotid artery (ICA) and the mandible ramus limiting it anteriorly, the styloid process of the temporal bone and facial nerve anterolaterally, the tympanic cavity and otic capsule superiorly, mastoid tip and facial nerve (intramastoid segment) laterally, transverse process of the atlas and the vertebral artery inferiorly, and the hypoglossal nerve medially.
Radiologically it can be classified into pars nervosa and pars vascularis. The pars vascularis corresponds to the posterolateral part, composed by the transition of the sigmoid sinus and jugular vein and meningeal branches of the ascending pharyngeal and occipital arteries. The pars nervosa corresponds to the anteromedial part through which the glossopharyngeal (IX), vagus (X), and accessory (XI) nerves cross the terminal part of the inferior petrosal sinus.2 , 3 , 4 , 5
Using a microsurgical classification, this foramen can be divided into three compartments, two being venous compartments and one neural (or intrajugular)5 , 6 , 7: (1) Sigmoid part, containing important venous drainage through the sigmoid sinus, located posterolaterally; (2) petrosal part, with a minor venous drainage component from the inferior opening of the inferior petrosal sinus and its tributaries, draining into the jugular bulb and internal jugular vein in single or multiple apertures; and (3) neural part (intrajugular), passage for the glossopharyngeal (IX), vagus (X), and accessory (XI) nerves, descending from the skull in the medial and anterior wall of the internal jugular vein.
32.2 Anatomy
This space when viewed from its intracranial surface has an oblique direction, and lateral to medial and upper to inferior directions, disposed between the supracondylar part of the occipital bone—the jugular process of the occipital bone—and the petrous part of the temporal bone. It contains the following structures in its respective parts: (1) Sigmoid part—sigmoid sinus, jugular bulb, and posterior meningeal artery (meningeal branch from the ascending pharyngeal artery most frequently); (2) petrosal part—inferior opening of inferior petrosal sinus with its tributaries and the cochlear aqueduct; and (3) neural part (intrajugular)—glossopharyngeal (IX), vagus (X), and accessory (XI) nerves, tympanic branch of glossopharyngeal nerve (Jacobson’s nerve), auricular branch of vagus nerve (Arnold’s nerve).3 , 6 , 12 , 13
32.3 Bone and Osseous Relations
When viewed from the intracranial surface and by its oblique direction from posterolateral to anteromedial, directed from back to forward and from top to bottom, a margin is formed composed by the temporal bone anterolaterally and another margin composed by the occipital bone posteromedially. The most anteromedial border of the foramen is intersected by the petroclival fissure, space between the lateral border of the clival part of the occipital bone and the petrosal part of the temporal bone. The most posterolateral border correlates with the occipitomastoid suture, between the occipital bone and the mastoid part of the temporal bone (Fig. 32.1).
Fig. 32.1Intracranial view of osseous relationships at jugular foramen region. (a) Bony anatomy. (b) Some surrounding neurovascular structures. Hypog. Canal, hypoglossal canal; IAC, internal auditory canal; Inf. Pet. Sin., inferior petrosal sinus; Intraj. Proc., intrajugular process; JF, jugular foramen; Jug. Tuberc., jugular tubercle; Mid. Mening. A., middle meningeal artery; Oc. Cond., occipital condyle; Occipitomast. Sut., occipitomastoid suture; Pet. Part, petrosal part; Petrocl. Fissure, petroclival fissure; Pyram. Fossa, pyramidal fossa; Sig. Part, sigmoid part; Sig. Sulc., sigmoid sulcus; Sig. Sin., sigmoid sinus; Sup. Pet. Sin., superior petrosal sinus; Vest. Aqued., vestibular aqueduct.
In dry skulls, we are able to define two parts in the JF intracranially: one more lateral, larger, and with a prominent sulcus for the sigmoid sinus (sigmoid sulcus), the sigmoid part (or pars vascularis); and a more medial and smaller part related to the inferior petrous sinus, the petrosal part (or pars nervosa) (Fig. 32.2). These parts are well distinguished as at their junction are bone prominences called the intrajugular process of the temporal bone and intrajugular process of the occipital bone. The former being most prominent in the majority of cases; they are joined by a fibrous septum and in some skulls ossification occurs with creation of two distinct foramina for the petrous and sigmoid parts (Fig. 32.3). Through the sigmoid part in direction toward the extracranial surface, the superior sigmoid sulcus creates a contour in the temporal bone where a fossa or dome is formed, the jugular fossae; this forms the ceiling where the jugular bulb is located.
Fig. 32.2Intracranial view depicting the petrosal and sigmoid parts of jugular foramen, separated by intrajugular processes of temporal and occipital bones. (a) Intracranial view of a skull demonstrating the positioning of jugular foramen. (b, c) Computed tomographic (CT) three-dimensional reconstruction. Petrosal and sigmoid parts are not clearly seen from a superior point of view; however, they are better demonstrated from a posterior to anterior angle of view. IAC, internal auditory canal; Intrajug. Proc., intrajugular process; Oc. Cond., occipital condyle; Pet. Part, petrosal part; Petrocl. Fissure, petroclival fissure; Sig. Part, sigmoid part; Sig. Sulc., sigmoid sulcus.
Fig. 32.3Jugular foramen osseous relationships. (a, b) Intracranial view of a right jugular foramen. Intrajugular processes of temporal and occipital bones divide jugular foramen into petrosal and sigmoid parts, and in some cases, both build an osseous bridge. (c) Inferior view of a left jugular foramen region. (d, e) Different angles of view of inferior aspect of a left jugular foramen region, depicting also tympanic and mastoid canaliculi. (f) Inferior view demonstrating posterior and lateral condylar canals, transmitting veins connecting extracranial venous plexus with jugular foramen region. Digast. Gr., digastric groove; Ext. Aud. Meat., external auditory meatus; Hypog. Canal, hypoglossal canal; IAC, internal auditory canal; Inf. Pet. Sin., inferior petrosal sinus; Intrajug. Crest, intrajugular crest; Intrajug. Proc., intrajugular process; JF, jugular foramen; Jug. For., jugular foramen; Jug. Tuberc., jugular tubercle; Lat. Cond. Canal, lateral condylar canal; Mast. Proc., mastoid process; Mast. Canalic., mastoid canaliculus; Oc. Cond., occipital condyle; Occipitomast. Sut., occipitomastoid suture; Petrocl. Fissure., petroclival fissure; Petros. Part, petrosal part; Sig. Part, sigmoid part; Post. Cond. Canal, posterior condylar canal; Sig. Sulc., sigmoid sulcus; Styloid Proc., styloid process; Stylomast. For., stylomastoid foramen; Tymp. Canalic., tympanic canaliculus; Vest. Aqued., vestibular aqueduct; Zygom. Arch, zygomatic arch.
Continuing from the intrajugular process of the temporal bone, in anterior and medial direction, the intrajugular crest is formed, accompanying the medial margin of the jugular fossa. In the petrosal part of the JF, accompanying superiorly, the anterior wall of the petrous portion of the temporal bone is formed, medially to the intrajugular crest, a small recess, the pyramidal fossa, which at its apex receives the external opening of the cochlear canaliculum (Fig. 32.1). The glossopharyngeal nerve penetrates the petrosal part of JF, medially to the intrajugular process of the temporal bone and intrajugular crest, sometimes creating a small sulcus in its passage near this crest. The vagus (X) and accessory (XI) nerves penetrate the dura through the medial region to the intrajugular process of the temporal bone, but they change their direction to pass laterally to the intrajugular crest in a position juxtaposed to the jugular bulb. Above the jugular fossa, within the temporal bone, we find the cochlea and tympanic cavity (Fig. 32.4). In the posteromedial portion of the JF, formed with the occipital bone and the intrajugular process of the occipital bone, there is an oval prominence, the jugular tuberculum (Fig. 32.1 and Fig. 32.3). This forms the upper part of the hipoglossus canal and has a shallow surface through which the glossopharyngeal, vagus, and accessory nerves pass to penetrate the JF (Fig. 32.5).
Extracranially we verify that the aperture of the carotid canal is located anterior to the medial half of the JF (Fig. 32.4 and Fig. 32.6). These are separated by a prominence in the anteromedial part of the foramen, the carotid crest, which continues with the intrajugular crest. At this point we find the tympanic canaliculus, through which the Jacobson’s nerve (tympanic branch of the glossopharyngeal nerve) ascends toward the tympanic cavity. In the anterolateral part of the foramen, we find a small sulcus, the sulcus for Arnold’s nerve (auricular branch of the vagus nerve), which ends in a small foramen, the mastoid canaliculus, which will give passage to this nerve until its exit at the inferolateral part of the tympanomastoid suture ( Fig. 32.3D and Fig. 32.3E). Near the extracranial opening of the foramen, in a lateral position to this, we find the styloid process (from the temporal bone), which extends from the vaginal process of the tympanic part of the temporal bone and gives fixation to the stylohyoid, styloglossus, and stylopharyngeus muscles (Fig. 32.7). Laterally at the base of the styloid process, we have the stylomastoid foramen, where the facial nerve (VII) leaves the skull toward the parotid gland—it will ramify for innervation of the facial musculature. This stylomastoid foramen will give passage to the stylomastoid artery for vascularization of the 7th nerve (Fig. 32.8).
Fig. 32.5Nerve relationships in jugular foramen. (a) Lower cranial nerves running toward jugular foramen and passing over jugular tubercle. Glossopharyngeal nerve exits the foramen more anteriorly. Accessory nerve is identified crossing over internal jugular vein moving backwards. Vagus and hypoglossal nerves course inferiorly, and hypoglossal nerve close to carotid bifurcation turns forward and gives a branch to ansa cervicalis. Hypoglossal nerve arises medial to jugular foramen and gradually runs inferolaterally. (b, c) Demonstration of the course of internal carotid artery, jugular vein, and lower cranial nerves just lateral to transverse process of C1. (d–f) Anatomical relationships of lower cranial nerves running toward jugular foramen, hypoglossal nerve to hypoglossal canal, and the positioning of jugular tubercle between hypoglossal canal and jugular foramen. Vertebral artery and posterior inferior cerebellar artery are closely related to these structures. CN, cranial nerve; gg, gasserian ganglion; ICA, internal carotid artery; IJV, internal jugular vein; Inf. Obliq., inferior oblique muscle; JB, jugular bulb; JT, jugular tubercle; PICA, posterior inferior cerebellar artery; Rec. Cap. Post. Maj., rectus capitis posterior major; Scap. Lev., scapula levator muscle; Sup. Obliq., superior oblique muscle; SCCs, semicircular canals; VA, vertebral artery.
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