Temporal Bone Anatomy

31 Temporal Bone Anatomy

Cassius Vinicius Correa dos Reis and Warley Martins

Abstract

The temporal bone is composed by five portions, and is considered the most complex osseous anatomical structure of the human body. Within this bone are structures of the vestibular and auditory systems, as well as portions of the internal carotid artery (ICA), cranial nerves, and cerebral venous system.

Due to its complexity, lesions or surgical approaches involving the temporal bone are among the most challenging neurosurgical procedures, and the surgeon must be aware of all the important anatomical structures surrounding the area of interest. In this chapter, the anatomy of the temporal bone is explained.

Keywords: temporal bone anatomy, temporal bone surgery, mastoid anatomy, petrous bone anatomy, skull base surgery

31.1 Introduction

The temporal bone is composed by five portions, and is considered the most complex osseous anatomical structure of the human body. Within this bone, are structures of the vestibular and auditory systems, as well as portions of the internal carotid artery (ICA), cranial nerves, and cerebral venous system.

Due to its complexity, lesions or surgical approaches involving the temporal bone are among the most challenging neurosurgical procedures, and the surgeon must be aware of all the important anatomical structures surrounding the area of interest. To accomplish this knowledge, study of the temporal bone anatomy at the laboratory, as well as cadaveric training of the surgical approaches to and through the temporal bone, is recommended.

31.2 Surgical Anatomy

31.2.1 The Squamous Portion

The squamous portion of the temporal bone is its largest part and covers most of the temporal lobe. It articulates with the sphenoid, frontal, and parietal bones through the squamous suture. Its external surface is covered by the temporalis muscle. The squamous portion contains the squama of the temporal bone, the zygomatic process of the temporal bone, the suprameatal line, and the mandibular fossa ( Fig. 31.1a).

Fig. 31.1External anatomy of the temporal bone: (a) The squamous portion of the temporal bone is its largest part and covers almost all the temporal lobe of the brain, except the posterior portions of the superior and middle temporal gyri. The zygomatic arch is a bridge of bone connecting the zygomatic and temporal bones and is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone. (b) The tympanic portion of the temporal bone is a flat bone which forms the anterior and inferior portions of the external auditory meatus. It forms the medial portion of the tympanic bone and points toward the jugular foramen and the carotid canal. The styloid process of the temporal bone is a bone projection which is located at the inferior surface of the tympanic bone.

The squama of the temporal bone is usually thin, which makes this region vulnerable to fractures when this region suffers blunt or penetrating traumas. It covers almost all the temporal lobe of the brain, except the posterior portions of the superior and middle temporal gyri.

The zygomatic arch is a bridge of bone connecting the zygomatic and temporal bones, and is the site of attachment of the temporalis fascial superiorly and the masseter muscle inferiorly. It is usually displaced inferiorly or partially resected when a basal exposure of the middle fossa is required in some surgical approaches. The arch is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone ( Fig. 31.1a). Both structures meet at the zygomaticotemporal suture. The posterior portion of the zygomatic process of the temporal bone is wide, forming the anterior and posterior roots of the zygoma. The posterior root fuses with the suprameatal crest close to the anterior portion of the roof of the external auditory meatus. The anterior root of the zygoma is the posterior limit of the temporalis fossa.

The suprameatal line is located at the roof of the external auditory meatus, and is blended posteriorly with the supramastoid crest. Both structures are important landmarks for surgical approaches at this area, separating the middle fossa superiorly from the mastoid cavity inferiorly ( Fig. 31.1a).

The mandibular fossa is located in front of the tympanic bone, below the roots of the zygomatic arch and is the site of the temporomandibular joint.

31.2.2 The Tympanic and Styloid Portions

The tympanic portion of the temporal bone is a flat bone which forms the anterior and inferior portions of the external auditory meatus, as well as the posterior wall of the mandibular fossa. The medial portion of the tympanic bone points toward the jugular foramen and the carotid canal ( Fig. 31.1b). It can be used as an important landmark to expose the ascending portion of the petrous ICA.

The styloid process of the temporal bone is a bone projection which is located at the inferior surface of the tympanic bone, right in front of the stylomastoid foramen ( Fig. 31.1b). It is the site of attachment of the stylopharyngeus, stylohyoid, and styloglossus muscles. The styloid process covers the ICA and the internal jugular vein (IJV), and can be resected to expose these structures before entering the skull.

31.2.3 The Mastoid Portion

At the external surface of the skull, the mastoid is a pyramidal shaped bone located behind the external auditory canal (EAC), below the parietomastoid suture and in front of the occipitomastoid suture. Its tip points caudally and this bloc of bone is filled with the mastoid air cells and the structures of the middle ear.

The mastoid cavity is a honeycomb structure formed by air cells and trabeculated bone which drains toward the mastoid antrum. It is surrounded by a roof, and medial, lateral, posterior, and anterior walls and contains the antrum and the mastoid air cells. The lateral wall is formed by the cortical bone of the external surface. The medial wall is formed by the otic capsule, which contains the semicircular canals. The anterior wall is formed by the bone of the posterior wall of the EAC; the mastoid portion of the facial nerve runs within it. The roof is formed by a thin layer of cortical bone, the tegmen tympani. The posterior wall is the site of the Trautman’s triangle, and faces the dura mater of the posterior fossa.

The suprameatal triangle is formed by the intersection of three lines: (a) a tangential line to the posterior border of the EAC; (b) a line perpendicular to the spine of Henle, and (c) a line over the suprameatal crest. The suprameatal triangle is an important surgical reference to find the mastoid antrum, a big mastoid cell where the otic capsule is placed. The otic capsule is placed 1.5 cm deep to the suprameatal triangle, as well as the mastoid portion the facial nerve ( Fig. 31.2a, b).

Fig. 31.2Anatomical landmarks used to understand the position of the deep temporal bony structures. (a) The root of the zygoma, the external auditory meatus, the superior temporal line, the asterion, and the spine of Henle are identified. The suprameatal crest is an extension of the superior temporal line and is the limit between the middle fossa and the mastoid cavity. The asterion overlies the inferior border of the transverse-sigmoid junction. The spine of Henle is located at the posterosuperior rim of the external auditory meatus. (b) The mastoid antrum is about 15 mm deep to the suprameatal triangle. This triangle is formed by three lines: (1) a line positioned at the suprameatal line; (2) a perpendicular line to the posterior border of the external auditory canal; and (3) an oblique line crossing the Henle’s spine (red triangle).

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