**Abstract**

Numerous neurological lesions and tumors of the paranasal sinuses and oral cavity may spread into the middle and posterior cranial fossae through the anatomical apertures. For the appropriate management of these pathologies, many extensive surgical approaches with a comprehensive overview of the anatomical landmarks are required from the maxillofacial surgery's point of view. The surgical significance lies in the fact that iatrogenic injury to the petrous segment of the temporal bone including the carotid artery, sigmoid sinus, and internal jugular vein, can lead to surgical morbidity and postoperative pseudoaneurysm, vasospasm, or carotid-cavernous fistula. To simplify understanding complex anatomy of the temporal bone, we aimed to review the surgical anatomy of the temporal bone focusing on the associations between the surface landmarks and inner structures. Also, breaking down an intricate bony structure into smaller parts by compartmental approach could ease a deep concentration and navigation. To identify the anatomic architecture of the temporal bone by using reference points, lines and compartments can be used to supplement anatomy knowledge of maxillofacial surgeons and may improve confidence by surgical trainees. Especially, this systematic method may provide an easier way to teach and learn surgical spatial structure of the petrous pyramid in clinical applications.

**Keywords:** maxillofacial surgery, segmentation, surface landmarks, surgical anatomy, temporal bone

## **1. Introduction**

The temporal bone is a dense complex bone that constitutes the lower lateral aspect of the skull and has complex anatomy because of the three-dimensional relationships between neurovascular structures. The petrous portion of the temporal bone has a role as the partition between the middle and posterior cranial fossae. It articulates with the occipital bone (occipitomastoid suture) posteriorly, the parietal bone (squamous suture) superiorly, the sphenoid bone (sphenosquamosal suture) and the zygomatic bone (arcus zygomaticus) anteriorly, and the mandible (temporomandibular joint) inferiorly [1, 2]. It contains multiple intrinsic channels, along with the internal carotid artery (ICA), cranial nerves, and sigmoid sinus (SS), all within intricate spatial architecture. Owing to a complex web of foramina and neurovascular structures of the temporal bone, the lateral skull base is a technically difficult region for surgeons. Because the middle and inner ear structures of hearing and equilibrium are preserved in the temporal bone,

a surgical dissection of it requires thorough understanding of three-dimensional (3D) map of the topographic anatomy to avoid iatrogenic risks. The relationship between the surface landmarks and expected internal structures and the segmentation of the temporal structures by using key surgical lines and spaces allow a better understanding of its anatomic architecture. Each temporal bone consists of five distinct osseous segments including the squamous, tympanic, petrous, mastoid, and styloid portions [3, 4].

## **2. External anatomy of the temporal portions**

#### **2.1 The squamous portion**

The anterosuperior part of the temporal bone is a large flattened scale-like plate that forms the lateral boundary of the middle cranial fossa. It has three borders and two surfaces [1].

#### *2.1.1 Borders and surfaces of the squamous portion*

Superiorly, it overlaps the sculpted squamous margin of the middle third of the parietal bone and constructs the squamosal suture. Posteriorly, it forms the occipitomastoid suture with the squamous part of the occipital bone. Also, there is an angle, parietal notch, between the squamous and mastoid portions of the temporal bone (**Figure 1**). Antero-inferiorly, its thick serrated margin takes part in pterion formation and articulates with the greater wing of the sphenoid bone to form the spheno-squamosal suture. Inferiorly, it fuses and forms the petro-squamous suture with the superior surface of the petrous portion by extending medially as tegmen tympany [5, 6].

External surface, the greater part of the temporal fossa, provides origin to the temporalis muscle and is limited below by the curved line, the temporal line, that lies from the supra-meatal crest to the mastoid cortex posteriorly. Below this line, just above and behind the external acoustic meatus (EAM), the supra-meatal triangle (Macewen's triangle) contains the supra-meatal spine, spine of Henle and the cribriform area (**Figure 1**). Also, the squamo-mastoid suture is located approximately 1 cm below the temporal line [5–7]. On this smooth surface, there is a sulcus for the middle temporal artery, which is the medial branch of the superficial temporal artery (STA). Antero-inferiorly, the zygomatic process projects by two roots: the upper border of the posterior root forms the supra-meatal crest and the lower border forms a laterally based projection, known as post-glenoid tubercle or process (PGP). Inferiorly, the concavity along the surface of the anterior root is called the glenoid fossa (GF), which is bounded by the articular eminence (ArE) anteriorly and the PGP posteriorly [5–7].

Internal surface is rough and concave in shape, and the anterior and posterior divisions of middle meningeal artery (MMA) run in a groove on this surface that defines the boundary of middle cranial fossa with impressions for the gyri of the temporal lobe. Inferiorly, it forms the petro-squamosal suture with the anterior surface of the petrous part [5, 6].

#### *2.1.2 Surgical landmarks and ossification of the squamous portion*

The Macewen's triangle, a surgical surface marking for the mastoid antrum (MA), is formed between the temporal line superiorly, the posterosuperior wall of the EAM antero-inferiorly, and the opening of the mastoid emissary vein or

**5**

**Figure 1.**

*process.*

enlarged and placed 1 cm behind it [6, 9].

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

sinodural angle posteriorly (**Figure 1**). The temporal line corresponds to the tegmen tympani (TT), which is a bony plate below the middle cranial fossa dura and over the mastoid air cells. The mastoid cortex posterior to the spine of Henle is a guide to the lateral wall of the MA and located 15 mm deep to it in adults but in new born about 2 mm [5, 6, 8]. The cribriform area in Macewen's triangle is perforated by numerous small holes that serve as a passage for the vessels of the mucosa of the antrum. The dissection along the margins of this triangle is safer because the vital neurovascular structures are absent. Peris-Celda et al. reported that the temporal line is supratentorial and infratentorial in 93% and 7% of the cases, respectively [9]. During retro-auricular mastoidectomy, the MA may be exposured by drilling the cribriform area and provides a safer surgical approach to the tympanic cavity. The tympanic portion and the styloid process may show variations depending on the shape and the position of the spine of Henle. The MA is located in the same line of the spine of Henle at about 10 years; then the MA is

*The surface landmarks on the squamous portion: 1, temporal fossa; 2, supra-meatal crest; 3, temporal line; 4, external acoustic meatus; 5, supra-meatal triangle (Macewen's triangle); 6, middle temporal artery; 7, squamo-mastoid suture; 8, mandibular fossa (glenoid fossa); 9, articular eminence; 10, zygomatic process; 11, petrotympanic fissure (Glaserian fissure); 12, mastoid foramen; 13, parietal notch; 14, mastoid process; 15, mastoid notch (digastric fossa); 16, occipital sulcus; 17, tympano-mastoid suture; 18, vaginal process; 19, styloid* 

The MMA lies underneath the pterion which is a common junction between the temporal, parietal, frontal, and sphenoid bones. The fracture of this weakest bony part may result in an epidural bleeding. Between the temporal muscle and fascia, the STA and the superficial temporal vein (STV) courses in close proximity with the zygomaticotemporal (ZTN) and the auriculotemporal (ATN) nerves, branches *Surgical Anatomy of the Temporal Bone DOI: http://dx.doi.org/10.5772/intechopen.93223*

#### **Figure 1.**

*Oral and Maxillofacial Surgery*

toid, and styloid portions [3, 4].

**2.1 The squamous portion**

two surfaces [1].

tympany [5, 6].

and the PGP posteriorly [5–7].

surface of the petrous part [5, 6].

**2. External anatomy of the temporal portions**

*2.1.1 Borders and surfaces of the squamous portion*

a surgical dissection of it requires thorough understanding of three-dimensional (3D) map of the topographic anatomy to avoid iatrogenic risks. The relationship between the surface landmarks and expected internal structures and the segmentation of the temporal structures by using key surgical lines and spaces allow a better understanding of its anatomic architecture. Each temporal bone consists of five distinct osseous segments including the squamous, tympanic, petrous, mas-

The anterosuperior part of the temporal bone is a large flattened scale-like plate that forms the lateral boundary of the middle cranial fossa. It has three borders and

Superiorly, it overlaps the sculpted squamous margin of the middle third of the parietal bone and constructs the squamosal suture. Posteriorly, it forms the occipitomastoid suture with the squamous part of the occipital bone. Also, there is an angle, parietal notch, between the squamous and mastoid portions of the temporal bone (**Figure 1**). Antero-inferiorly, its thick serrated margin takes part in pterion formation and articulates with the greater wing of the sphenoid bone to form the spheno-squamosal suture. Inferiorly, it fuses and forms the petro-squamous suture with the superior surface of the petrous portion by extending medially as tegmen

External surface, the greater part of the temporal fossa, provides origin to the temporalis muscle and is limited below by the curved line, the temporal line, that lies from the supra-meatal crest to the mastoid cortex posteriorly. Below this line, just above and behind the external acoustic meatus (EAM), the supra-meatal triangle (Macewen's triangle) contains the supra-meatal spine, spine of Henle and the cribriform area (**Figure 1**). Also, the squamo-mastoid suture is located approximately 1 cm below the temporal line [5–7]. On this smooth surface, there is a sulcus for the middle temporal artery, which is the medial branch of the superficial temporal artery (STA). Antero-inferiorly, the zygomatic process projects by two roots: the upper border of the posterior root forms the supra-meatal crest and the lower border forms a laterally based projection, known as post-glenoid tubercle or process (PGP). Inferiorly, the concavity along the surface of the anterior root is called the glenoid fossa (GF), which is bounded by the articular eminence (ArE) anteriorly

Internal surface is rough and concave in shape, and the anterior and posterior divisions of middle meningeal artery (MMA) run in a groove on this surface that defines the boundary of middle cranial fossa with impressions for the gyri of the temporal lobe. Inferiorly, it forms the petro-squamosal suture with the anterior

The Macewen's triangle, a surgical surface marking for the mastoid antrum (MA), is formed between the temporal line superiorly, the posterosuperior wall of the EAM antero-inferiorly, and the opening of the mastoid emissary vein or

*2.1.2 Surgical landmarks and ossification of the squamous portion*

**4**

*The surface landmarks on the squamous portion: 1, temporal fossa; 2, supra-meatal crest; 3, temporal line; 4, external acoustic meatus; 5, supra-meatal triangle (Macewen's triangle); 6, middle temporal artery; 7, squamo-mastoid suture; 8, mandibular fossa (glenoid fossa); 9, articular eminence; 10, zygomatic process; 11, petrotympanic fissure (Glaserian fissure); 12, mastoid foramen; 13, parietal notch; 14, mastoid process; 15, mastoid notch (digastric fossa); 16, occipital sulcus; 17, tympano-mastoid suture; 18, vaginal process; 19, styloid process.*

sinodural angle posteriorly (**Figure 1**). The temporal line corresponds to the tegmen tympani (TT), which is a bony plate below the middle cranial fossa dura and over the mastoid air cells. The mastoid cortex posterior to the spine of Henle is a guide to the lateral wall of the MA and located 15 mm deep to it in adults but in new born about 2 mm [5, 6, 8]. The cribriform area in Macewen's triangle is perforated by numerous small holes that serve as a passage for the vessels of the mucosa of the antrum. The dissection along the margins of this triangle is safer because the vital neurovascular structures are absent. Peris-Celda et al. reported that the temporal line is supratentorial and infratentorial in 93% and 7% of the cases, respectively [9]. During retro-auricular mastoidectomy, the MA may be exposured by drilling the cribriform area and provides a safer surgical approach to the tympanic cavity. The tympanic portion and the styloid process may show variations depending on the shape and the position of the spine of Henle. The MA is located in the same line of the spine of Henle at about 10 years; then the MA is enlarged and placed 1 cm behind it [6, 9].

The MMA lies underneath the pterion which is a common junction between the temporal, parietal, frontal, and sphenoid bones. The fracture of this weakest bony part may result in an epidural bleeding. Between the temporal muscle and fascia, the STA and the superficial temporal vein (STV) courses in close proximity with the zygomaticotemporal (ZTN) and the auriculotemporal (ATN) nerves, branches

of the trigeminal nerve (TN). Because of a vessel running superficial to the nerve (80% STA), the underlying nerve may be compressed and results in temporal migraine headache. Lee et al. reported that the intersection (compression) point among the ATN, STA, and STV was at an average of 40mm superior and 10mm anterior to the tragus, which is a significant surface landmark at the most anterosuperior point of the EAM. The applications of surgical decompression of the ATN in these compression points improve migraine headache [10].

The anterior articular part of the GF is formed by a gentle sloped area of the squamous portion, which facilitates the movement of the temporomandibular joint (TMJ) during wide mouth opening. At the lateral aspect of the ArE, a small bony ridge, articular tubercle (AT), serves as an attachment for the lateral collateral ligament. The PGP inhibits backward displacement of mandibular head and participates to the superior wall of the EAM [8]. The posterior nonarticular part of the GP is formed by the tympanic portion and the squamo-tympanic suture intervenes between them. The inferior edge of the TT (petrous part) divides this suture into two: a petro-squamosal fissure in front and a petrotympanic fissure (Glaserian fissure) behind (**Figure 1**). The chorda tympani nerve, a branch of the facial nerve, exits the temporal bone through the Glaserian fissure and joins the lingual nerve as the parasympathetic input to start the submandibular and sublingual gland secretions [2, 4, 5].

The articulation between the GF and the condyle of the mandible is called TMJ, which plays an essential role in speech, respiration, swallowing, and specially mastication. Because the TMJ is in close proximity with the MMA, some surgical landmarks around the TMJ and foramen spinosum (FS) play a critical role in surgical approaches. Miller et al. reported that researchers measured the distances from the zygomatic root (first projection of the zygomatic arch = PGP) to some surgical landmarks such as the arcuate eminence (AE), the head of the malleus (HM) under the TT, and the FS to identify the location of the internal auditory meatus (IAM) or the superior semicircular canal (SSC). Also, they described the superior petrosal triangle as a consistent triangle between the zygomatic root, the FR, and the HM to localize the bony tegmen over the tympanic cavity [11]. Baur et al. offered simply identifiable reference landmarks including the AE, the most lateral aspect of the Glaserian fissure and the FS and measured the distances between them to predict the location of the MMA [12]. According to these researchers, the internal landmarks including the HM and Bill's bar (the vertical crest in the fundus of the internal auditory canal) are in a single plane with the zygomatic root [11].

After the ArE forming the anterior limit of the GF, the anterior root continues in front as a bony ridge that forms the posterior boundary of the infratemporal fossa, which is a small triangular area transmitting the neurovascular structures between the pterygopalatine fossa and temporal fossa. Then, a serrated anterior end of the zygomatic process passes straight forward and articulates with the temporal process of the zygomatic bone and completes the zygomatic arch. The temporal fascia inserts to this arch and the temporal line superiorly and also the masseter muscle origins from the arch inferiorly. The lateral temporomandibular ligament attaches to the AT, and the GF is covered with an articular disc to construct the synovial TMJ with the condyle of the mandible [5–7].

Anteriorly, the small part of squamous portion takes part in the infratemporal fossa formation with the zygomatic bone and the greater wing of the sphenoid bone. Below the zygomatic bone, the branches of the first and second mandibular parts of the MA with veins and the pterygoid plexus of veins, the mandibular and lingual nerves pass through the infratemporal fossa. During the infratemporal fossa approaching for surgical removal of tumors localized in the orbit, the maxillary and sphenoid sinuses, the detailed anatomical knowledge of these neurovascular

**7**

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

**2.2 The mastoid portion**

surfaces [5, 6].

this suture [5, 14, 15].

occipital artery [4, 6].

cranial fossae [2, 5, 9, 16].

landmarks can be used to prevent ICA injury [13].

*2.2.1 Borders and surfaces of the mastoid portion*

of three parts; the petrous, squamous, and the tympanic [1].

structures is needed. Depending on the position of the infratemporal fossa below the floor of the middle cranial fossa and posterior to the maxilla, it is in close proximity with the parapharyngeal and masticator spaces. The parapharyngeal carotid artery enters the carotid canal (CC) behind the FS and foramen ovale. During transpterygoid infratemporal fossa approach, the positions of these surgical

Ossification of the squamous portion starts intramembranously from one center

The mastoid portion forms the pneumatized thick posterior part of the temporal bone. It fuses with the squamous portion antero-superiorly and the tympanic portion anteriorly and the petrous portion anteromedially. It has three borders and two

Posteriorly, it articulates with the squamous part of the occipital bone between lateral angle and the jugular process and constructs the occipitomastoid suture. Inferiorly, the mastoid process extends as a rough and conical shaped projection and filled with mastoid cells variable in shape and size. Anteriorly, it associates with the tympanic portions of the temporal bone to form the tympano-mastoid suture, and the inferior auricular branch of the vagus nerve (Arnold's nerve) exits through

Near the squamo-mastoid suture, the occipital belly of occipito-frontalis and auricularis posterior muscles attach on the external surface that is perforated by numerous small foramina. At the posterior border of the mastoid portion or the occipitomastoid suture, the largest one, mastoid foramen is located and transmits an emissary vein connecting the SS with the posterior auricular vein and a branch of occipital artery to the dura mater (**Figure 1**). The mastoid process serves for the attachment of the sternocleidomastoid, splenius capitis, and longissimus capitis muscles and shows variations in shape and size with respect to sex. The posterior belly of the digastric muscle is originated from the mastoid notch (digastric fossa), which is a depression on the inferomedial margin of the mastoid process (**Figure 1**). More medial to the notch lies a sulcus, the occipital sulcus, forming a groove for the

The internal surface includes a well-defined and curved sigmoid sulcus lying along its junction with the posterior surface of petrous part and lodges the SS, partially the transverse sinus, which are separated from mastoid air cells by a thin plate of bone. The mastoid foramen transmitting the mastoid emissary vein may be open to this sulcus. The SS begins as the continuation of the transverse sinus and lies downward in a S-shaped groove and opens into the superior jugular bulb. There is a sinodural angle between the dura plates of the SS and middle and posterior

The mastoid process shows tree types of pneumatization patterns including pneumatic (full air cell), sclerotic (solid mass of bone), and mixed (air cells and bone marrow) types. Especially, in the anterosuperior part of the mastoid process,

*2.2.2 Surgical landmarks and ossification of the mastoid portion*

around the zygomatic process at the 2nd month. At birth it fuses with the other membranous bone, tympanic portion. Normally, at birth the temporal bone consists

#### *Surgical Anatomy of the Temporal Bone DOI: http://dx.doi.org/10.5772/intechopen.93223*

structures is needed. Depending on the position of the infratemporal fossa below the floor of the middle cranial fossa and posterior to the maxilla, it is in close proximity with the parapharyngeal and masticator spaces. The parapharyngeal carotid artery enters the carotid canal (CC) behind the FS and foramen ovale. During transpterygoid infratemporal fossa approach, the positions of these surgical landmarks can be used to prevent ICA injury [13].

Ossification of the squamous portion starts intramembranously from one center around the zygomatic process at the 2nd month. At birth it fuses with the other membranous bone, tympanic portion. Normally, at birth the temporal bone consists of three parts; the petrous, squamous, and the tympanic [1].

#### **2.2 The mastoid portion**

*Oral and Maxillofacial Surgery*

tions [2, 4, 5].

of the trigeminal nerve (TN). Because of a vessel running superficial to the nerve (80% STA), the underlying nerve may be compressed and results in temporal migraine headache. Lee et al. reported that the intersection (compression) point among the ATN, STA, and STV was at an average of 40mm superior and 10mm anterior to the tragus, which is a significant surface landmark at the most anterosuperior point of the EAM. The applications of surgical decompression of the ATN in

The anterior articular part of the GF is formed by a gentle sloped area of the squamous portion, which facilitates the movement of the temporomandibular joint (TMJ) during wide mouth opening. At the lateral aspect of the ArE, a small bony ridge, articular tubercle (AT), serves as an attachment for the lateral collateral ligament. The PGP inhibits backward displacement of mandibular head and participates to the superior wall of the EAM [8]. The posterior nonarticular part of the GP is formed by the tympanic portion and the squamo-tympanic suture intervenes between them. The inferior edge of the TT (petrous part) divides this suture into two: a petro-squamosal fissure in front and a petrotympanic fissure (Glaserian fissure) behind (**Figure 1**). The chorda tympani nerve, a branch of the facial nerve, exits the temporal bone through the Glaserian fissure and joins the lingual nerve as the parasympathetic input to start the submandibular and sublingual gland secre-

The articulation between the GF and the condyle of the mandible is called TMJ,

which plays an essential role in speech, respiration, swallowing, and specially mastication. Because the TMJ is in close proximity with the MMA, some surgical landmarks around the TMJ and foramen spinosum (FS) play a critical role in surgical approaches. Miller et al. reported that researchers measured the distances from the zygomatic root (first projection of the zygomatic arch = PGP) to some surgical landmarks such as the arcuate eminence (AE), the head of the malleus (HM) under the TT, and the FS to identify the location of the internal auditory meatus (IAM) or the superior semicircular canal (SSC). Also, they described the superior petrosal triangle as a consistent triangle between the zygomatic root, the FR, and the HM to localize the bony tegmen over the tympanic cavity [11]. Baur et al. offered simply identifiable reference landmarks including the AE, the most lateral aspect of the Glaserian fissure and the FS and measured the distances between them to predict the location of the MMA [12]. According to these researchers, the internal landmarks including the HM and Bill's bar (the vertical crest in the fundus of the

internal auditory canal) are in a single plane with the zygomatic root [11].

with the condyle of the mandible [5–7].

After the ArE forming the anterior limit of the GF, the anterior root continues in front as a bony ridge that forms the posterior boundary of the infratemporal fossa, which is a small triangular area transmitting the neurovascular structures between the pterygopalatine fossa and temporal fossa. Then, a serrated anterior end of the zygomatic process passes straight forward and articulates with the temporal process of the zygomatic bone and completes the zygomatic arch. The temporal fascia inserts to this arch and the temporal line superiorly and also the masseter muscle origins from the arch inferiorly. The lateral temporomandibular ligament attaches to the AT, and the GF is covered with an articular disc to construct the synovial TMJ

Anteriorly, the small part of squamous portion takes part in the infratemporal fossa formation with the zygomatic bone and the greater wing of the sphenoid bone. Below the zygomatic bone, the branches of the first and second mandibular parts of the MA with veins and the pterygoid plexus of veins, the mandibular and lingual nerves pass through the infratemporal fossa. During the infratemporal fossa approaching for surgical removal of tumors localized in the orbit, the maxillary and sphenoid sinuses, the detailed anatomical knowledge of these neurovascular

these compression points improve migraine headache [10].

**6**

The mastoid portion forms the pneumatized thick posterior part of the temporal bone. It fuses with the squamous portion antero-superiorly and the tympanic portion anteriorly and the petrous portion anteromedially. It has three borders and two surfaces [5, 6].

#### *2.2.1 Borders and surfaces of the mastoid portion*

Posteriorly, it articulates with the squamous part of the occipital bone between lateral angle and the jugular process and constructs the occipitomastoid suture. Inferiorly, the mastoid process extends as a rough and conical shaped projection and filled with mastoid cells variable in shape and size. Anteriorly, it associates with the tympanic portions of the temporal bone to form the tympano-mastoid suture, and the inferior auricular branch of the vagus nerve (Arnold's nerve) exits through this suture [5, 14, 15].

Near the squamo-mastoid suture, the occipital belly of occipito-frontalis and auricularis posterior muscles attach on the external surface that is perforated by numerous small foramina. At the posterior border of the mastoid portion or the occipitomastoid suture, the largest one, mastoid foramen is located and transmits an emissary vein connecting the SS with the posterior auricular vein and a branch of occipital artery to the dura mater (**Figure 1**). The mastoid process serves for the attachment of the sternocleidomastoid, splenius capitis, and longissimus capitis muscles and shows variations in shape and size with respect to sex. The posterior belly of the digastric muscle is originated from the mastoid notch (digastric fossa), which is a depression on the inferomedial margin of the mastoid process (**Figure 1**). More medial to the notch lies a sulcus, the occipital sulcus, forming a groove for the occipital artery [4, 6].

The internal surface includes a well-defined and curved sigmoid sulcus lying along its junction with the posterior surface of petrous part and lodges the SS, partially the transverse sinus, which are separated from mastoid air cells by a thin plate of bone. The mastoid foramen transmitting the mastoid emissary vein may be open to this sulcus. The SS begins as the continuation of the transverse sinus and lies downward in a S-shaped groove and opens into the superior jugular bulb. There is a sinodural angle between the dura plates of the SS and middle and posterior cranial fossae [2, 5, 9, 16].

#### *2.2.2 Surgical landmarks and ossification of the mastoid portion*

The mastoid process shows tree types of pneumatization patterns including pneumatic (full air cell), sclerotic (solid mass of bone), and mixed (air cells and bone marrow) types. Especially, in the anterosuperior part of the mastoid process, there is an irregular cavity that is larger than other mastoid cells and called MA, which corresponds to the cribriform area. It is covered with the mucous membrane of the tympanic cavity and communicates anteriorly with the epitympanic recess of the middle ear via the aditus ad antrum. The tegmen antri, a roof of the MA, separates it from the middle cranial fossa. During embryonic period, the squamous and petrous portions fused each other and forms the petro-squamous suture. In adults, it forms a thin bony septum, the Körner's septum, by extending into the mastoid process [1, 4, 6, 9, 17]. Körner's septum divides the mastoid air cells in the mastoid process into a deep petrous part medially and a superficial squamous part laterally. The petro-squamosal sinus or the mastoid emissary vein may infrequently be observed along this septum. During mastoidectomy or transmastoid approaches, awareness of this crucial landmark and its variations is essential to avoid iatrogenic complications. The squamous part starts to develop at 8th week, whereas the petrous part develops later at 6th months during embryogenesis, and each part opens into the MA separately [1]. Also, the mastoid cells are separated by bony plates from the adjacent structures such as the posterior wall of the EAM anteriorly, tegmen plate superiorly, SS posteriorly, digastric ridge inferiorly, and the lateral semicircular canal (LSC) or solid triangle medially. The solid triangle is a compact bony angle between three SCs. During the mastoidectomy, all the air cells around this septum and adjacent bony structures should be removed without damaging the bony plates. To avoid iatrogenic injury to the adjacent structures, the MA must be open superiorly toward TT. The tympano-mastoid suture at the posterior wall of the MA is surface marking of the course of the vertical portion of the facial nerve (FN) [9, 16, 18]. Peris-Celda et al. reported that the parietal notch corresponds to the posterior petrosal point and the SS (the transverse-SS junction) in 66 and 34% of the cases, respectively [9].

Ossification of the mastoid portion is endochondral which is identical to the petrous and styloid portions. At birth, the mastoid process is absent, and the MA is invisible and covered by a thin bony plate that is extension of the squamous portion. At the first year, the mastoid process becomes prominent and the petro-squamous suture arises. The antrum can be seen obviously at about the fifth year. During puberty, the thickness of the process increases, and it becomes pneumatic that is lined by mucous membrane. In adults, the mastoid process may not contain air cells in 20% cases [1, 2, 17].

#### **2.3 The tympanic portion**

An annular shaped part of the temporal bone forms the tympano-mastoid suture posteriorly and the squamo-tympanic suture superiorly (**Figure 1**). Medially, it fuses with the petrous portion, whereas a free lateral part of it constructs the major part of the EAM and also serves an attachment for the cartilaginous part of the external auditory canal (EAC). Its inferior margin is free, and it has two parts on the lateral surface; posterosuperior part forms the EAM, and anteroinferior part limits the mandibular fossa posteriorly [5, 19].

#### *2.3.1 Borders and surfaces of the tympanic portion*

Medially, just above the GF, this suture is subdivided by a thin tegmen part of the petrous portion into two: the petrotympanic fissure posteriorly and the petrosquamosal fissure anteriorly. Lateral part of this upper margin fuses with the back of the PGP to form the nonarticular part of the GF. Inferiorly, the lateral part of the margin gives an attachment for the deep part of the parotid fascia and forms the vaginal process, which wraps the root of the styloid process laterally [2, 4].

**9**

[3, 4, 21].

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

near the stylomastoid foramen (SMF) [2, 4, 19].

*2.3.2 Surgical landmarks and ossification of the tympanic portion*

portions [1, 4, 14, 20].

fissure, anteriorly [19, 20].

**2.4 The petrous portion**

Laterally, external surface is bounded by the cartilaginous part of the EAC which extends from the auricle to the tympanic membrane. The EAC is an

S-shaped tube, about 2.5 cm in long, that is composed of the lateral third cartilaginous part and the medial two-thirds osseous part [14, 15, 18]. The tympanic part constructs the anterior wall and floor and the lower part of posterior wall of the EAM, whereas the squamous part forms the superior and upper part of the posterior wall of it (**Figure 1**). The tympanic part grows from the tympanic ring, which is open U-shaped possessing two edge anterior and posterior. The anterior edge forms the tympano-squamous fissure within the anterosuperior part of the EAM and the petrotympanic fissure within the middle ear, whereas the posterior edge forms the tympano-mastoid fissure within the posteroinferior part of the EAM

The internal surface fuses with the petrous portion and forms the tympanic sulcus for the lodgement of the tympanic membrane, which forms an angle about 55° with the floor of the EAM and separates the external and middle ear (ME). At the upper part, the tympanic sulcus does not fuse each other by forming the greater and lesser tympanic spines and a notch called Rivinus between them. This notch is closed by the pars flaccida of the tympanic membrane. The notch of Rivinus corresponds to the junction between the squamous and tympanic

Ossification starts from the four centers around the tympanic ring at the end of the embryonic period (8th week) via intramembranous ossification of the EAM. The tympanic ring at first is nearly straight and then turns into horseshoe shape (annular) and then, the open arms extending upwards terminate in a notch for the location of the tympanic membrane between them. After birth, the upper segment of the tympanic bone grows rapidly but because of the gradual development of the lower segment, a deep notch (tympanic foramen) is left in the anterior part of the bony EAM. Normally, the tympanic ring fuses until the age of 5 year but a dehiscence may persist (range 4.6−22.7%) at the anteroinferior aspect of the EAM, called foramen of Huschke (foramen tympanicum). This fusion defect is not a true foramen, but it may cause a connection between the EAM and the posteromedial part of the TMJ and results in TMJ herniation and the secretion of the parotid gland and also the dissemination of tumor and infections into the EAM [1, 14, 19, 20]. Anteriorly, the EAM may communicate with the retromandibular part of the parotid gland via the fissures of Santorini within the anterior cartilage. Peris-Celda et al. reported that the SSC dehiscence can be observed approximately 1.5 cm posterior to the middle point of the EAM in 86% of the cases [9]. In newborn, the tympanic membrane is infiltrated with air and the tympanic ring forms a bony plate, which may cause the development of a cleft, the auricular fissure, posteriorly and a cleft, the tympano-squamous

The petrous portion is a dense pyramid-shaped bone and composed of the labyrinth of the internal ear, the tympanic cavity of the middle ear and a bony part of the auditory Eustachian tube (ET), and canals for the passage of the ICA and the FN. It is ossified from the otic capsule by forming a 45° angle with the horizontal axis. It has a base, an apex, and three surfaces and three borders

#### *Surgical Anatomy of the Temporal Bone DOI: http://dx.doi.org/10.5772/intechopen.93223*

*Oral and Maxillofacial Surgery*

of the cases, respectively [9].

in 20% cases [1, 2, 17].

**2.3 The tympanic portion**

the mandibular fossa posteriorly [5, 19].

*2.3.1 Borders and surfaces of the tympanic portion*

there is an irregular cavity that is larger than other mastoid cells and called MA, which corresponds to the cribriform area. It is covered with the mucous membrane of the tympanic cavity and communicates anteriorly with the epitympanic recess of the middle ear via the aditus ad antrum. The tegmen antri, a roof of the MA, separates it from the middle cranial fossa. During embryonic period, the squamous and petrous portions fused each other and forms the petro-squamous suture. In adults, it forms a thin bony septum, the Körner's septum, by extending into the mastoid process [1, 4, 6, 9, 17]. Körner's septum divides the mastoid air cells in the mastoid process into a deep petrous part medially and a superficial squamous part laterally. The petro-squamosal sinus or the mastoid emissary vein may infrequently be observed along this septum. During mastoidectomy or transmastoid approaches, awareness of this crucial landmark and its variations is essential to avoid iatrogenic complications. The squamous part starts to develop at 8th week, whereas the petrous part develops later at 6th months during embryogenesis, and each part opens into the MA separately [1]. Also, the mastoid cells are separated by bony plates from the adjacent structures such as the posterior wall of the EAM anteriorly, tegmen plate superiorly, SS posteriorly, digastric ridge inferiorly, and the lateral semicircular canal (LSC) or solid triangle medially. The solid triangle is a compact bony angle between three SCs. During the mastoidectomy, all the air cells around this septum and adjacent bony structures should be removed without damaging the bony plates. To avoid iatrogenic injury to the adjacent structures, the MA must be open superiorly toward TT. The tympano-mastoid suture at the posterior wall of the MA is surface marking of the course of the vertical portion of the facial nerve (FN) [9, 16, 18]. Peris-Celda et al. reported that the parietal notch corresponds to the posterior petrosal point and the SS (the transverse-SS junction) in 66 and 34%

Ossification of the mastoid portion is endochondral which is identical to the petrous and styloid portions. At birth, the mastoid process is absent, and the MA is invisible and covered by a thin bony plate that is extension of the squamous portion. At the first year, the mastoid process becomes prominent and the petro-squamous suture arises. The antrum can be seen obviously at about the fifth year. During puberty, the thickness of the process increases, and it becomes pneumatic that is lined by mucous membrane. In adults, the mastoid process may not contain air cells

An annular shaped part of the temporal bone forms the tympano-mastoid suture

Medially, just above the GF, this suture is subdivided by a thin tegmen part of the petrous portion into two: the petrotympanic fissure posteriorly and the petrosquamosal fissure anteriorly. Lateral part of this upper margin fuses with the back of the PGP to form the nonarticular part of the GF. Inferiorly, the lateral part of the margin gives an attachment for the deep part of the parotid fascia and forms the vaginal process, which wraps the root of the styloid process laterally [2, 4].

posteriorly and the squamo-tympanic suture superiorly (**Figure 1**). Medially, it fuses with the petrous portion, whereas a free lateral part of it constructs the major part of the EAM and also serves an attachment for the cartilaginous part of the external auditory canal (EAC). Its inferior margin is free, and it has two parts on the lateral surface; posterosuperior part forms the EAM, and anteroinferior part limits

**8**

Laterally, external surface is bounded by the cartilaginous part of the EAC which extends from the auricle to the tympanic membrane. The EAC is an S-shaped tube, about 2.5 cm in long, that is composed of the lateral third cartilaginous part and the medial two-thirds osseous part [14, 15, 18]. The tympanic part constructs the anterior wall and floor and the lower part of posterior wall of the EAM, whereas the squamous part forms the superior and upper part of the posterior wall of it (**Figure 1**). The tympanic part grows from the tympanic ring, which is open U-shaped possessing two edge anterior and posterior. The anterior edge forms the tympano-squamous fissure within the anterosuperior part of the EAM and the petrotympanic fissure within the middle ear, whereas the posterior edge forms the tympano-mastoid fissure within the posteroinferior part of the EAM near the stylomastoid foramen (SMF) [2, 4, 19].

The internal surface fuses with the petrous portion and forms the tympanic sulcus for the lodgement of the tympanic membrane, which forms an angle about 55° with the floor of the EAM and separates the external and middle ear (ME). At the upper part, the tympanic sulcus does not fuse each other by forming the greater and lesser tympanic spines and a notch called Rivinus between them. This notch is closed by the pars flaccida of the tympanic membrane. The notch of Rivinus corresponds to the junction between the squamous and tympanic portions [1, 4, 14, 20].

#### *2.3.2 Surgical landmarks and ossification of the tympanic portion*

Ossification starts from the four centers around the tympanic ring at the end of the embryonic period (8th week) via intramembranous ossification of the EAM. The tympanic ring at first is nearly straight and then turns into horseshoe shape (annular) and then, the open arms extending upwards terminate in a notch for the location of the tympanic membrane between them. After birth, the upper segment of the tympanic bone grows rapidly but because of the gradual development of the lower segment, a deep notch (tympanic foramen) is left in the anterior part of the bony EAM. Normally, the tympanic ring fuses until the age of 5 year but a dehiscence may persist (range 4.6−22.7%) at the anteroinferior aspect of the EAM, called foramen of Huschke (foramen tympanicum). This fusion defect is not a true foramen, but it may cause a connection between the EAM and the posteromedial part of the TMJ and results in TMJ herniation and the secretion of the parotid gland and also the dissemination of tumor and infections into the EAM [1, 14, 19, 20]. Anteriorly, the EAM may communicate with the retromandibular part of the parotid gland via the fissures of Santorini within the anterior cartilage. Peris-Celda et al. reported that the SSC dehiscence can be observed approximately 1.5 cm posterior to the middle point of the EAM in 86% of the cases [9]. In newborn, the tympanic membrane is infiltrated with air and the tympanic ring forms a bony plate, which may cause the development of a cleft, the auricular fissure, posteriorly and a cleft, the tympano-squamous fissure, anteriorly [19, 20].

#### **2.4 The petrous portion**

The petrous portion is a dense pyramid-shaped bone and composed of the labyrinth of the internal ear, the tympanic cavity of the middle ear and a bony part of the auditory Eustachian tube (ET), and canals for the passage of the ICA and the FN. It is ossified from the otic capsule by forming a 45° angle with the horizontal axis. It has a base, an apex, and three surfaces and three borders [3, 4, 21].

#### *2.4.1 Borders of the petrous portion*

Superiorly, the petrous ridge is the longest border and a boundary between the posterior part of the middle cranial fossa (the anterior surface of the petrous part) and the anterior part of the posterior cranial fossa (the posterior surface of the petrous part). It contains a groove that lodges the superior petrosal sinus (SPS) and the lateral margin of tentorium cerebelli attaches to this margin (**Figure 2**). Posteriorly, the medial part of the posterior margin articulates with the basilar part of occipital bone along the petro-clival fissure and forms a groove that lodges the inferior petrosal sinus (IPS) that extends from the posteroinferior part of the cavernous sinus to the internal jugular vein (IJV). The lateral part of the posterior margin is free and limits the jugular foramen (JF) supero-laterally and has a triangular notch for the lodgement of the inferior ganglion of the glossopharyngeal

#### **Figure 2.**

*The surface landmarks on the anterior surface of the petrous portion: a, petrous ridge (sulcus of the superior petrosal sinus); b, arcuate eminence; c, tegmen tympani; d, sulcus of the lesser petrosal nerve; e, sulcus of the greater petrosal nerve; f, trigeminal impression; g, petrous apex; ıocc, internal opening of carotid canal.*

**11**

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

enters the cavernous sinus adjoining the ICA [1, 7, 16].

It consists of some marking landmarks (**Figure 2**).

tissue that separates the ET from the ICA [23].

*2.4.2 Surgical landmarks on the anterior surface of the petrous portion*

nerve (Jacobson's nerve = GPN). Anterolateral border is formed by the ET extending from the anteroinferior wall of the tympanic cavity to the nasopharynx [3, 4, 9]. The base is integrated with the inner surface of the squamous and mastoid portions, whereas the apex forms the posterolateral margin of the foramen lacerum (FL) and faces the Meckel's cave medially. There is a fibrocartilage connection between the apex and the clivus. The internal opening of the carotid canal (IOCC) is observed at the apex for the intracranial entry of the ICA. At the anterolateral part of the FL, the petro-sphenoid ligament connects the tip of the apex to the dorsum sellae of the sphenoid and the abducent nerve lies below this ligament and

Anterior surface describes a triangular area, between the linear lines as follows: a horizontal line that starts from the preauricular burrhole in front of the tragus to petrous apex at the FL and passes through the FS anteriorly, the petrous ridge posteriorly and the petro-squamous suture, which lies along the junction of the petrous pyramid with the vertical part of the squamous portion laterally [3, 16, 22].

a.The anteromedial two-third of the musculotubal canal is cartilaginous, whereas the posterolateral third is bony. The bony part consists of two small canals that are separated by a thin bony septum at the lateral part the petrous portion. The tensor tympani muscle passes through the superior semicanal, whereas the inferior semicanal forms the bony portion of the ET. The tensor tympani muscle originates from the greater wing of the sphenoid and inserts into the upper part of the medial surface of the handle of malleus after making a bend around the processus cochleariformis in the tympanic cavity [4, 6]. The ET lies between the tympanic orifice and the isthmus, which has the smallest diameter at the intersection point of the petrous and squamous parts of the temporal bone just behind the sphenoid spine. Brown et al. reported that the ET is subdivided by genu within the membranocartilaginous part into two portions; posterior horizontal ET between the genu and the anterior attachment of the tympanic membrane ridge, whereas the anterior vertical ET lies from the genu to the nasopharyngeal orifice and opens into the nasopharynx. During endoscopic eustachian tube obliteration, the ET is cannulated to treat refractory CSF rhinorrhea by identifying three anatomic parameters: the ET length, isthmus diameter, and genu location. According to a new surgical classification, the cartilaginous portion of the ET is divided into the petrous, lacerum, pterygoid, and nasopharyngeal parts. The bony part attaches to the ET sulcus or sulcus tuba, which is contiguous to the FL medially. The FL is located in the incomplete confluence of the union of the body and the lingular process of the greater sphenoid wing anteriorly, the clivus of the occipital bone medially and the petrous apex posteriorly and covered with the fibrocartilaginous

b.The internal opening of the CC is located near the FL for the passage of the ICA, which is freed at the petrous apex into the cavernous sinus (**Figure 2**). It is localized medial to the ET, below the greater superficial petrosal nerve (GSPN), a branch of the FN and the trigeminal ganglion [1, 3, 4]. The petrous segment of the ICA within the CC has four anatomic parts, called vertical, posterior genu, horizontal, and anterior genu. During endoscopic endonasal surgery, the junctional part of the ET at the sphenoid spine and FS is crucial landmark to identify and protect the petrous segment of the ICA [13]. The anatomical and

#### *Surgical Anatomy of the Temporal Bone DOI: http://dx.doi.org/10.5772/intechopen.93223*

*Oral and Maxillofacial Surgery*

*2.4.1 Borders of the petrous portion*

Superiorly, the petrous ridge is the longest border and a boundary between the posterior part of the middle cranial fossa (the anterior surface of the petrous part) and the anterior part of the posterior cranial fossa (the posterior surface of the petrous part). It contains a groove that lodges the superior petrosal sinus (SPS) and the lateral margin of tentorium cerebelli attaches to this margin (**Figure 2**). Posteriorly, the medial part of the posterior margin articulates with the basilar part of occipital bone along the petro-clival fissure and forms a groove that lodges the inferior petrosal sinus (IPS) that extends from the posteroinferior part of the cavernous sinus to the internal jugular vein (IJV). The lateral part of the posterior margin is free and limits the jugular foramen (JF) supero-laterally and has a triangular notch for the lodgement of the inferior ganglion of the glossopharyngeal

*The surface landmarks on the anterior surface of the petrous portion: a, petrous ridge (sulcus of the superior petrosal sinus); b, arcuate eminence; c, tegmen tympani; d, sulcus of the lesser petrosal nerve; e, sulcus of the greater petrosal nerve; f, trigeminal impression; g, petrous apex; ıocc, internal opening of carotid canal.*

**10**

**Figure 2.**

nerve (Jacobson's nerve = GPN). Anterolateral border is formed by the ET extending from the anteroinferior wall of the tympanic cavity to the nasopharynx [3, 4, 9].

The base is integrated with the inner surface of the squamous and mastoid portions, whereas the apex forms the posterolateral margin of the foramen lacerum (FL) and faces the Meckel's cave medially. There is a fibrocartilage connection between the apex and the clivus. The internal opening of the carotid canal (IOCC) is observed at the apex for the intracranial entry of the ICA. At the anterolateral part of the FL, the petro-sphenoid ligament connects the tip of the apex to the dorsum sellae of the sphenoid and the abducent nerve lies below this ligament and enters the cavernous sinus adjoining the ICA [1, 7, 16].

#### *2.4.2 Surgical landmarks on the anterior surface of the petrous portion*

Anterior surface describes a triangular area, between the linear lines as follows: a horizontal line that starts from the preauricular burrhole in front of the tragus to petrous apex at the FL and passes through the FS anteriorly, the petrous ridge posteriorly and the petro-squamous suture, which lies along the junction of the petrous pyramid with the vertical part of the squamous portion laterally [3, 16, 22]. It consists of some marking landmarks (**Figure 2**).


surgical relationships between the ET and the petrous segment of the ICA are as follows:

The first curve, posterior genu is located at the level of the bulging basal turn of the cochlea within the bend of the CC. Laterally, the bony part of the ET and the tendon of the tensor tympani muscle; posterolaterally, the promontory and posterosuperiorly, geniculate ganglion are paramount landmarks for the posterior genu of the ICA. The V3 lying anteromedially to the FS and the parapharyngeal segment of the ICA, which passes posteroinferiorly to the sphenoid spine, are critical landmarks. Posterolaterally, the petroclival fissure cartilage is an important landmark to separate the pharyngobasilar fascia from the anterior genu of ICA.

The second turn of the ICA, anterior genu, above the fibrous tissue of the FL is in close proximity to the lacerum segment of the cartilaginous ET laterally and continues as the paraclival ICA in the carotid groove. During the endoscopic approach, the Vidian artery and nerve (VN) are critical landmarks for the second curve of the ICA.

For safe manipulation of the horizontal part of the ICA, the GSPN can be used as surgical landmark. Above the anterolateral margin of the FL the union of the GSPN and the deep petrosal branch of the carotid neural plexus forms the VN which is located anteroinferiorly and lateral to the second turn of the ICA. Malignancies that involve the petrous apex or the carotid artery require the extended endoscopic endonasl approach (EEA). During this procedure, the medial and lateral optico–carotid recesses in the cavernous sinus and the vidian canal (VC) are vital surgical landmarks, which allow to identify the position of the ICA for safe surgical resection near the ICA [13].


**13**

Mortazavi [1, 4, 6].

to the posterior SSC [2, 18].

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

transpterygoid extension of EEA [24].

the pterygoid venous plexus posteroinferiorly [25].

*2.4.3 Surgical landmarks on the posterior surface of the petrous portion*

exists from the JF together with the cranial nerves (IX-XI) [1, 6, 9].

starts from the hiatus of the facial canal and lodges the GSPN, a branch of the FN and the petrosal branch of the MMA, whereas the lateral one lodges the lesser superficial petrosal nerve, a branch of GPN (**Figure 2**) [3, 9, 16, 22].

Kaen et al. described the "VELPPHA" area indicating the posterior limit of the transpterygoid EEA. It is composed of the VC (V), the ET (E), the FL (L), the petroclival fissure (P), the pharyngobasilar fascia (PHA), and multiple cartilaginous fibers between them. The posterior opening of the VC, the posterior limit of surgical corridor in the transpterygoid approach, is located above the ET and below the petrous ICA. Behind the posterior margin of the medial pterygoid process, the superomedial border of the ET attaches to the cartilaginous fibers of the FL. The petroclival fissure is situated between the lateral border of the clivus (occipital bone) and the petrous part of the temporal bone and lodges the IPS. The horizontal segment of the petrous ICA turns upward at the medial border of the petrous apex to form the anterior genu of the ICA, and then it continues as the lacerum segment, second vertical segment of the ICA. So, the VC-ET junction is a safe and critical landmark for efficient localization of the lacerum segment of the ICA, as part of the

Tayebi Meybodi et al. described the pterygoclival ligament as a thickened extension of the pharyngobasilar fascia from the pterygoid process to the anteromedial aspect of the lacerum segment of the ICA and reported that the course of the pterygoclival ligament consistently refers to the anteromedial aspect of the lacerum ICA. So, they suggested that the pterygoclival ligament can be used as a safe landmark in case of tumor invasion of the VN, and drilling along the medial aspect of this ligament is more reliable way compared with the VN to avoid the ICA injury during extended EEA. Also, they remarked that this ligament may localize in a venous compartment, which is in contact with the cavernous sinus superiorly and

The posterior surface, anterior wall of the posterior cranial fossa, is encircled by a venous triangle that is formed by the grooves for SS posteriorly and SPS at the petrous ridge and IPS at the junction of the pars lateralis of the occipital bone and the temporal bone anteroinferiorly. The SS drains into the bulb of the IJV, which

a.The IAM is a short canal, about 1 cm long, and has a large orifice, which allows passage of the vestibulocochlear nerve below the FN, the superficial petrosal artery (a branch of the MMA) and the labyrinthine artery (branch of the basilar artery). The bottom (fundus) of the IAM is subdivided into unequal superior and inferior portions by a transverse falciform crest, and into the anterior and posterior portions by a vertical segment, Bill's bar, respectively (**Figure 3**) [2, 15]. The localization of the nerves within the IAM is determined by a triangular shaped Bill's bar as follows; posteriorly the superior and inferior vestibular nerves, anteroinferiorly the cochlear nerve, anterosuperiorly the FN and nervus intermedius pass through the foramina of the fundus (**Figure 3**)

b.The aqueductus vestibuli is a bony canal which contains the saccus and ductus endolymphaticus. Its opening is an oblique slit behind the IAM (**Figure 3**). The endolymphatic sac is located at the lateral part of the posterior surface medial

f. On the TT, a bony roof of the geniculate ganglion, there are two foramina, which continue as a small groove adjoining anteromedially; the medial one

#### *Surgical Anatomy of the Temporal Bone DOI: http://dx.doi.org/10.5772/intechopen.93223*

*Oral and Maxillofacial Surgery*

the anterior genu of ICA.

second curve of the ICA.

as follows:

surgical relationships between the ET and the petrous segment of the ICA are

The first curve, posterior genu is located at the level of the bulging basal turn of the cochlea within the bend of the CC. Laterally, the bony part of the ET and the tendon of the tensor tympani muscle; posterolaterally, the promontory and posterosuperiorly, geniculate ganglion are paramount landmarks for the posterior genu of the ICA. The V3 lying anteromedially to the FS and the parapharyngeal segment of the ICA, which passes posteroinferiorly to the sphenoid spine, are critical landmarks. Posterolaterally, the petroclival fissure cartilage is an important landmark to separate the pharyngobasilar fascia from

The second turn of the ICA, anterior genu, above the fibrous tissue of the FL is in close proximity to the lacerum segment of the cartilaginous ET laterally and continues as the paraclival ICA in the carotid groove. During the endoscopic approach, the Vidian artery and nerve (VN) are critical landmarks for the

For safe manipulation of the horizontal part of the ICA, the GSPN can be used as surgical landmark. Above the anterolateral margin of the FL the union of the GSPN and the deep petrosal branch of the carotid neural plexus forms the VN which is located anteroinferiorly and lateral to the second turn of the ICA. Malignancies that involve the petrous apex or the carotid artery require the extended endoscopic endonasl approach (EEA). During this procedure, the medial and lateral optico–carotid recesses in the cavernous sinus and the vidian canal (VC) are vital surgical landmarks, which allow to identify the

position of the ICA for safe surgical resection near the ICA [13].

the cranial nerves (III, IV, VI), and the petrous ICA [13, 23].

d.Behind the trigeminal impression, the roof of the IAM is indicated as a shallow fossa, then it continues with the AE, which is a surgical landmark for the middle fossa approach and located at the junction of the posterior third and the anterior two-thirds of the petrous portion (**Figure 2**). It is a valuable guide to signify the SSC and the roof of the vestibule up to 93% of the temporal bones

e.The TT is a thin bony layer covering all of the anterior surface (**Figure 2**). It forms the roof of the mucosal line including from behind to forward the MA, tympanic cavity and ET which are lined with mucosa. Also, its lateral edge turns downward to subdivide the squamo-tympanic fissure into two parts [1, 3].

f. On the TT, a bony roof of the geniculate ganglion, there are two foramina, which continue as a small groove adjoining anteromedially; the medial one

c.At the apex above the CC, a shallow fossa called trigeminal impression (**Figure 2**) is located for the lodgement of the sensory ganglion of the TN (semilunar ganglion or Gasser's ganglion) that is covered by a pouch-shaped dura mater called Meckel's cave [3]. Vascular compression and arachnoid adherence of the TN branches result in trigeminal neuralgia. During endoscopic vascular decompression and Meckel's cave approaches, the VC, the bone between V2 and the VC and the pneumatization of the sphenoid sinus form a safe route to access and to decompress Gasser's ganglion with branches,

**12**

[19, 22].

starts from the hiatus of the facial canal and lodges the GSPN, a branch of the FN and the petrosal branch of the MMA, whereas the lateral one lodges the lesser superficial petrosal nerve, a branch of GPN (**Figure 2**) [3, 9, 16, 22].

Kaen et al. described the "VELPPHA" area indicating the posterior limit of the transpterygoid EEA. It is composed of the VC (V), the ET (E), the FL (L), the petroclival fissure (P), the pharyngobasilar fascia (PHA), and multiple cartilaginous fibers between them. The posterior opening of the VC, the posterior limit of surgical corridor in the transpterygoid approach, is located above the ET and below the petrous ICA. Behind the posterior margin of the medial pterygoid process, the superomedial border of the ET attaches to the cartilaginous fibers of the FL. The petroclival fissure is situated between the lateral border of the clivus (occipital bone) and the petrous part of the temporal bone and lodges the IPS. The horizontal segment of the petrous ICA turns upward at the medial border of the petrous apex to form the anterior genu of the ICA, and then it continues as the lacerum segment, second vertical segment of the ICA. So, the VC-ET junction is a safe and critical landmark for efficient localization of the lacerum segment of the ICA, as part of the transpterygoid extension of EEA [24].

Tayebi Meybodi et al. described the pterygoclival ligament as a thickened extension of the pharyngobasilar fascia from the pterygoid process to the anteromedial aspect of the lacerum segment of the ICA and reported that the course of the pterygoclival ligament consistently refers to the anteromedial aspect of the lacerum ICA. So, they suggested that the pterygoclival ligament can be used as a safe landmark in case of tumor invasion of the VN, and drilling along the medial aspect of this ligament is more reliable way compared with the VN to avoid the ICA injury during extended EEA. Also, they remarked that this ligament may localize in a venous compartment, which is in contact with the cavernous sinus superiorly and the pterygoid venous plexus posteroinferiorly [25].

#### *2.4.3 Surgical landmarks on the posterior surface of the petrous portion*

The posterior surface, anterior wall of the posterior cranial fossa, is encircled by a venous triangle that is formed by the grooves for SS posteriorly and SPS at the petrous ridge and IPS at the junction of the pars lateralis of the occipital bone and the temporal bone anteroinferiorly. The SS drains into the bulb of the IJV, which exists from the JF together with the cranial nerves (IX-XI) [1, 6, 9].


**Figure 3.**

*The surface landmarks on the posterior surface of the petrous portion: a, petrous ridge; b, arcuate eminence; h, internal acoustic meatus; ı, subarcuate fossa; j, aqueductus vestibuli; k, sigmoid sinus sulcus; m, sulcus of the middle meningeal artery; 12, mastoid foramen.*

c.The subarcuate fossa is an indistinct depression (large in new born) located behind the IAM (**Figure 3**) and transmits a small vein and the subarcuate artery, which is a branch of the meatal segment of the anterior inferior cerebellar artery [4, 5, 9, 14].
