Chapter 3: Identifying Key Anatomical Structures of the Temporal Bone for Surgical Exercises

Proper identification of temporal bone structures is critical before beginning surgical exercises. The following guidelines provide an overview of anatomical landmarks based on surface topography and dissection orientation:

Lateral Surface

Key landmarks visible on the lateral surface include:

• External Structures: Zygomatic process, mandibular fossa, temporal line, external auditory canal, tympanomastoid fissure, and Henle’s spine.
• Mastoid Region: Mastoid tip, mastoid emissary vein, and insertion points for the sternocleidomastoid and digastric muscles.
• Sutures: Tympanosquamous and squamotympanic sutures.
• Specific Areas: Suprameatal spine (Henle), McEwen’s triangle (cribriform area), and the mastoid plane (2, 7, 11).

Medial Surface

The medial surface features include:

• Bony Landmarks: Sigmoid sulcus, subarcuate fossa, and the external aperture of the vestibular aqueduct.
• Internal Structures: Internal auditory canal, superior petrosal sulcus, inferior petrosal sulcus, and canaliculus cochlearis.
• Neurological Relevance: Pathways for cranial nerves (VII, VIII) and associated vessels within the internal auditory canal (2, 7).

Superior Surface

The superior surface provides access to:

• Prominent Features: Arcuate eminence, superior semicircular canal, and the sulci for the greater petrosal nerve and middle meningeal artery.
• Cranial Sinuses: Impressions of the superior petrosal sinus and temporal lobe brain convolutions (2, 7).

Inferior Surface

Key structures visible on the inferior surface include:

• Bony Features: Mandibular fossa, zygomatic process, styloid process, and digastric groove.
• Openings: Petrotympanic fissure, jugular fossa, and the stylomastoid foramen (facial nerve exit).
• Vascular Access: Internal carotid artery and associated venous drainage points (2, 12).

Surface Topography and Setup

1. Lateral Surface Preparation: Remove periosteum and trim residual cartilaginous external auditory canal. Secure the temporal bone in a surgical holder. Identify and visualize:
   • External auditory canal, mastoid process, and Henle’s spine.
   • Suprameatal ridge, cribriform region (overlying mastoid air cells), and sigmoid sinus pathway.
2. Orientation: Determine the bone’s side by identifying external (mastoid process, glenoid fossa) and internal (middle and posterior fossa) features.
   • Middle and posterior cranial fossae landmarks include the petrous ridge, arcuate eminence, internal auditory meatus, sigmoid sinus, and niche for the endolymphatic sac.
   • Inferior surface structures like the mastoid and styloid processes, digastric groove, and stylomastoid foramen should also be clearly visualized (7, 12).

Significance for Surgical Exercises

Thorough identification of landmarks ensures safe and efficient navigation during dissection and surgery. Anticipating structures, visualizing anatomical variations, and maintaining spatial awareness are crucial for avoiding injury to neurovascular and delicate anatomical components (1, 2, 12).

This consolidated guide equips learners with the necessary framework for mastering the anatomy of the temporal bone and preparing for complex surgical exercises.

Surface Anatomy of the Temporal Bone

The temporal bone is a unique structure that interfaces with various intra- and extra-cranial regions, reflecting its integral role in the embryological development of the head and neck. It articulates with the sphenoid, parietal, occipital, and zygomatic bones, contributing significantly to the cranial structure, skull base, and facial architecture. Structurally, the temporal bone is pyramidal, with its faces forming the middle fossa floor (superior face), the anterior boundary of the posterior fossa (posterior face), muscle attachments for the neck and infratemporal fossa (anterior-inferior face), and the lateral surface of the head, covered by muscle and skin, forming the base of the pyramid. It comprises four embryologically distinct regions: the squamous, mastoid, petrous, and tympanic parts (1).

Squamous Part

The squamous portion forms the lateral wall of the middle cranial fossa. This part consists of inner and outer cortical layers separated by diploic bone. The zygomatic process extends anteriorly, creating the bony roof of the glenoid fossa. Along the most inferior insertion of the temporalis muscle, the temporal line—a horizontal ridge—aligns with the zygomatic process. This line serves as an approximation for the middle fossa floor, which is typically situated approximately 4.7 mm inferior to it (2).

Mastoid Part

The mastoid region is characterized by its bulbous shape, resulting from the expansion of air cells. The sternocleidomastoid (SCM) muscle and the posterior belly of the digastric muscle exert a downward pull, forming the mastoid tip. This tip is roughened at its surface to indicate SCM attachment. Small emissary vessels perforate the mastoid cortex, draining into the sigmoid sinus via a triangular region known as Macewan’s triangle. The stylomastoid foramen is located anteriorly to the mastoid tip, marking the sulcus of the digastric muscle. Medially, the sulcus for the occipital artery runs almost parallel to the digastric groove.

Tympanic Part

The tympanic section contributes to the anterior, posterior, and inferior walls of the bony external auditory canal (EAC), as well as the anterior floor of the middle ear. Key suture lines in this region include the tympanosquamous and petrotympanic sutures, the latter serving as the exit for the chorda tympani. The tympanomastoid suture near the posterior EAC is a vital landmark for identifying the facial nerve’s main trunk as it exits the temporal bone.

Petrous Part

The petrous portion has a pyramidal configuration, with its base adjoining the mastoid laterally and the apex oriented anteromedially, bordered by the occipital and sphenoid bones. The jugular foramen, formed at the petrous-occipital junction, is divided into the pars nervosa (posterior) and pars venosa (anterior) by the jugular spine (3).

The posterior petrous surface aligns vertically, forming the anterior boundary of the posterior cranial fossa. It features sulci for the sigmoid, superior petrosal, and inferior petrosal sinuses, with the internal auditory meatus centrally located. The meatus houses foramina for the cochlear, vestibular, and facial nerves, as well as the subarcuate artery and endolymphatic sac openings.

The inferior petrous surface is irregular, hosting the styloid process, jugular bulb, and the carotid canal. The tympanic canaliculus, which transmits Jacobson’s nerve, traverses the keel—a wedge-shaped bone separating the carotid canal from the jugular bulb (4-6).

Anterior Surface

The anterior petrous surface contributes to the posterior medial boundary of the middle cranial fossa. Distinctive features include the arcuate eminence, indicative of the superior semicircular canal, the musculotubal canal housing the tensor tympani and Eustachian tube, and a depression at the apex for the trigeminal ganglion. The greater and lesser superficial petrosal nerves run parallel to the sphenoid suture at this region (7).