**3. Segmental anatomy of the petrous portion**

In clinical applications, for fully understanding of the tridimensional architecture of the petrous portion, a reference lines and angles can be defined on the anterior and posterior surfaces from a superior view.

Peris-Celda et al. reported that the EAM and the IAM are located in the same coronal plane on the anterior surface forming surgical triangle [9]. Tawfik-Helika et al. separated the pyramid into four compartments and described two segmentation method to provide better understanding of the distributions of these compartments. They identified four compartments based on their connections: mucosal, cutaneous, neural, and vascular [3, 21].

The mucosal compartment consists of an air filled and mucosa lined cavities from anterior to posterior: the ET, ME, and the MA (**Figure 7**). The mucosal line in an oblique anteromedial direction extends along these structures and is used for segmental description of this pyramid, and all major anatomical landmarks can be identified relative to this axis for surgical approaches [3, 9, 21].

Extending the mucosal line posteriorly, the MA is separated into medial and lateral parts, whereas anteriorly, the bony portion of the ET is localized at the junction of the petrous and squamous parts and the cartilaginous part opens into the pharynx anteriorly. Medially the line passing through the sulcus of the GSPN and laterally a straight line lying between the foramen ovale and FS are parallel to this line (**Figure 7**) [3, 9, 21].

The cutaneous compartment is composed of the EAM, which is covered by the skin and separated from the ME by the tympanic membrane medially.

The neural compartment is composed of the otic capsule, which is located medial to ME and the mucosal line. In this bony container, the cochlea, vestibule, and SCs are located from anterior to posterior around the fundus of the IAM (**Figure 7**).

#### **Figure 7.**

*(A) The margins of the anterior surface of the left petrous portion from a superior view are shown posteriorly by a (thick black) line along the PR, petrous ridge; anteriorly by a (dashed black) line lying from the preauricular burrhole to PA, petrous apex and passing through the FS, foramen spinosum; and laterally by a (dashed white) line along the petro-squamous suture. OC, optic canal; ACP, anterior clinoid process; FL, foramen lacerum; SOF, superior orbital fissure; FR, foramen rotundum; FO, foramen ovale; MMA, middle meningeal artery; IOCC, internal opening of carotid canal; GSPN, greater petrosal nerve; AE, arcuate eminence; TT, tegmen tympani; JF, jugular foramen; IAM, internal acoustic meatus; SSS, sulcus sigmoid sinus. (B) The segmentation of the left petrous pyramid into four compartments including mucosal, cutaneous, neural, and vascular is shown on the left petrous portion.*

**21**

**Figure 9.**

**Figure 8.**

and enhance education of the compartments.

The vascular compartment is composed of the ICA. The axis passing through the horizontal part of the CC is parallel and medial to the mucosal line (**Figure 7**) [3]. Moreover, Tawfik-Helika et al. described X and V segmentation methods to advance

*Schematic representation of the external and internal landmarks on the left petrous portion. V, trigeminal nerve and branches (V1, V2, V3); TI, trigeminal impression; IOCC, internal opening of carotid canal; ET, Eustachian tube; GG, geniculate ganglion; ME, middle ear; MA; mastoid antrum; EAM, external acoustic meatus; TMJ, temporomandibular joint; SCCs, semicircular canals; IAM, internal acoustic meatus; VII, facial* 

*nerve; VIII, vestibulocochlear nerve; IX, glossopharyngeal nerve; X, vagus nerve; XI, accessory nerve.*

*Schematic representations of the segmentation of the left petrous portion by using X and V methods.*

*Surgical Anatomy of the Temporal Bone DOI: http://dx.doi.org/10.5772/intechopen.93223* *Oral and Maxillofacial Surgery*

**3. Segmental anatomy of the petrous portion**

anterior and posterior surfaces from a superior view.

identified relative to this axis for surgical approaches [3, 9, 21].

skin and separated from the ME by the tympanic membrane medially.

cutaneous, neural, and vascular [3, 21].

In clinical applications, for fully understanding of the tridimensional architecture of the petrous portion, a reference lines and angles can be defined on the

Peris-Celda et al. reported that the EAM and the IAM are located in the same coronal plane on the anterior surface forming surgical triangle [9]. Tawfik-Helika et al. separated the pyramid into four compartments and described two segmentation method to provide better understanding of the distributions of these compartments. They identified four compartments based on their connections: mucosal,

The mucosal compartment consists of an air filled and mucosa lined cavities from anterior to posterior: the ET, ME, and the MA (**Figure 7**). The mucosal line in an oblique anteromedial direction extends along these structures and is used for segmental description of this pyramid, and all major anatomical landmarks can be

Extending the mucosal line posteriorly, the MA is separated into medial and lateral parts, whereas anteriorly, the bony portion of the ET is localized at the junction of the petrous and squamous parts and the cartilaginous part opens into the pharynx anteriorly. Medially the line passing through the sulcus of the GSPN and laterally a straight line lying between the foramen ovale and FS are parallel to this line (**Figure 7**) [3, 9, 21]. The cutaneous compartment is composed of the EAM, which is covered by the

The neural compartment is composed of the otic capsule, which is located medial to ME and the mucosal line. In this bony container, the cochlea, vestibule, and SCs are located from anterior to posterior around the fundus of the IAM (**Figure 7**).

*(A) The margins of the anterior surface of the left petrous portion from a superior view are shown posteriorly by a (thick black) line along the PR, petrous ridge; anteriorly by a (dashed black) line lying from the preauricular burrhole to PA, petrous apex and passing through the FS, foramen spinosum; and laterally by a (dashed white) line along the petro-squamous suture. OC, optic canal; ACP, anterior clinoid process; FL, foramen lacerum; SOF, superior orbital fissure; FR, foramen rotundum; FO, foramen ovale; MMA, middle meningeal artery; IOCC, internal opening of carotid canal; GSPN, greater petrosal nerve; AE, arcuate eminence; TT, tegmen tympani; JF, jugular foramen; IAM, internal acoustic meatus; SSS, sulcus sigmoid sinus. (B) The segmentation of the left petrous pyramid into four compartments including mucosal, cutaneous,* 

**20**

*neural, and vascular is shown on the left petrous portion.*

**Figure 7.**

#### **Figure 9.**

*Schematic representation of the external and internal landmarks on the left petrous portion. V, trigeminal nerve and branches (V1, V2, V3); TI, trigeminal impression; IOCC, internal opening of carotid canal; ET, Eustachian tube; GG, geniculate ganglion; ME, middle ear; MA; mastoid antrum; EAM, external acoustic meatus; TMJ, temporomandibular joint; SCCs, semicircular canals; IAM, internal acoustic meatus; VII, facial nerve; VIII, vestibulocochlear nerve; IX, glossopharyngeal nerve; X, vagus nerve; XI, accessory nerve.*

The vascular compartment is composed of the ICA. The axis passing through the horizontal part of the CC is parallel and medial to the mucosal line (**Figure 7**) [3]. Moreover, Tawfik-Helika et al. described X and V segmentation methods to advance and enhance education of the compartments.

The X method divides the petrous pyramid into four spaces by using two reference lines intersecting with each other at the ME; the mucosal line and the EAM-IAM line form the X letter (**Figures 8** and **9**). These four spaces around the ME and the contents in it are as follows:

The anteromedial space—the cochlea and the petrous apex including the ICA The anterolateral space—the roof of the TMJ

The posterolateral space—the lateral part of the MA

The posteromedial space—the posterior labyrinth and the medial part of the MA The V method arranges five segments around the mucosal line (**Figures 8** and **9**)

These five segments and the contents in it are as follows:

The petrous apex segment—the ICA medial to the ET

The otic capsule segment—the IAM, cochlea, vestibule and SCs

The mastoid segment—the angle around the MA

The EAM segment—the lateral part of the ME

The TMJ segment—the roof of the TMJ lateral to the ET [3].
