Anatomy of the Temporal Bone
Introduction
The temporal bone contributes to the lower lateral wall of the skull. It contains the middle and inner portions of the ear and is crossed by the majority of the cranial nerves. The lower portion of the bone articulates with the mandible forming the temporomandibular joint of the jaw.
Parts Of The Temporal Bone
It has 5 parts:
- Squamous part
- Zygomatic process
- Tympanic part
- Petromastoid part
- Styloid process
Squamous Part (Squama Temporalis)
It is the largest part of the temporal bone. It is flat and plate-like, located superiorly. Its outer facing surface is convex in shape, forming part of the temporal fossa. Its lower part is the site of origin of the temporalis muscle. It articulates with:
- The sphenoid bone anteriorly; and
- The parietal bone laterally
Zygomatic Process
It arises from the lower part of the squama temporalis. It projects anteriorly, articulating with the temporal process of the zygomatic bone, forming the zygomatic arch. One of the zygomatic processes’ attachments to the temporal bone forms the articular tubercle, which is:
- The anterior boundary of the mandibular fossa
- Part of the temporomandibular joint
The masseter muscles attach some fibres to the lateral surface of the zygomatic process.
Tympanic Part
It lies inferiorly to the squamous and anteriorly to the petromastoid parts. It surrounds the external auditory opening, which leads into the external auditory meatus of the external ear.
Petromastoid Part
It is located posteriorly. It can be split into:
- Mastoid part, and
- Petrous part
Mastoid Part of Temporal Bone
There are two items of note on the mastoid. The mastoid process and the mastoid air cells:
- The mastoid process is an inferior projection of bone, palpable just behind the ear. It is a site of attachment for many muscles such as the sternocleidomastoid.
- The mastoid air cells are hallowed out areas within the temporal bone. They act as a reservoir of air cells, equalizing the pressure within the middle ear in the case of auditory tube dysfunction. They can also become infected (mastoditis).
Petrous Part of Temporal Bone
It is pyramidal shaped and lies at the base of the temporal bone. It contains the inner ear.
Styloid Process
It is located immediately underneath the opening to the auditory meatus. It acts as an attachment point for muscles and ligaments, such as the stylomandibular ligament of the temporomandibular joint.
Clinical Correlates
Fractures of the pterion
The pterion is the point is the point where the temporal, parietal, frontal and sphenoid bones meet. The skull is at its weakest and susceptible to fracture. The middle meningeal artery, which travels underneath the pterion can be injured or completely lacerated resulting in extradural haematoma.
Mastoditis
Middle ear infections (otitis media) can spread to the mastoid air cells. Due to their porous nature, they are a suitable site for pathogenic replication. The mastoid itself can get infected, and this can spread to the middle cranial fossa and into the brain, causing meningitis. If mastoiditis is suspected, the pus must be drained from the air cells.
- When doing so, be careful not to damage the nearby facial nerve.
Temporal bone fractures
The temporal bone is relatively strong, and thus it it usually only fractured as a result of blunt trauma to the skull. Ear-related disorders are commonly seen, such as vertigo or hearing loss. The facial nerve, which travels through the temporal bone can also be damaged with paralysis resulting. Other symptoms include:
- Bleeding from the ear; and
- Bruising around the mastoid process
