*2.4.4 Surgical landmarks on the inferior surface of the petrous portion*

The inferior surface articulates with the basilar part of occipital bone medially, and the greater wing of the sphenoid bone anteriorly and forms an irregular external surface of the base of the skull. Below the apex, there is a quadrilateral area that serves as an attachment for the levator veli palatini muscle. The lateral part of this area merges with the posterior margin of the greater wing of sphenoid to form the sulcus tuba in front of the cartilaginous portion of the auditory tube [4, 5, 21]. It presents some anatomical landmarks as follows:


**15**

**Figure 4.**

cochlear vein [1, 5, 14].

parotid fascia [1, 3, 5, 6].

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

> horizontal course of the SS. Abnormalities of it (80% below the FN in the mastoid cavity) result in dehiscence of the adjacent structures such as: the mediolateral enlargement of the JB results in the vestibular aqueduct, PSC, and IAC dehiscence, whereas the anteroposterior enlargement of the JB may cause the FN dehiscence. Abnormal high riding JB shows both mediolateral and antero-

*The surface landmarks on the inferior surface of the petrous portion: FM, fossa mandibularis; FS, foramen stylomastoideum; FJ, fossa jugularis; ET, eustachian tube; eocc, external opening of carotid canal; ıocc, internal* 

posterior enlargement and results in dehiscence of the FN [26].

*opening of carotid canal; star: inferior tympanic canaliculus; arrowhead: cochlear aqueduct.*

3.Between the jugular fossa and the CC, the inferior ganglion of the GPN is localized in a triangular depression, whereas the inferior tympanic canaliculus penetrates into wedge-shaped bony ridge and transmits the tympanic branch of the GPN and inferior tympanic artery. At the apex of this triangular depression, there is an external opening of the cochlear aqueduct (**Figure 4**), which connects the perilymphatic space to the subarachnoid space and transmits the

4.Behind the CC the vaginal process which is the extension of the sharp lower border of the tympanic plate wraps the root of the styloid process (**Figure 4**). The lower border of that extension serves an attachment for the deep layer of

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

*Oral and Maxillofacial Surgery*

lar artery [4, 5, 9, 14].

*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 cerebel-

*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* 

The inferior surface articulates with the basilar part of occipital bone medially, and the greater wing of the sphenoid bone anteriorly and forms an irregular external surface of the base of the skull. Below the apex, there is a quadrilateral area that serves as an attachment for the levator veli palatini muscle. The lateral part of this area merges with the posterior margin of the greater wing of sphenoid to form the sulcus tuba in front of the cartilaginous portion of the auditory tube [4, 5, 21]. It presents some anatomical landmarks as

1.The external opening of the CC, which shows an inverted L-shape course, forms the entrance for the ICA, which is surrounded by a plexus of sympathetic nerves (**Figure 4**). The anterior margin of the horizontal segment of the CC is separated from the musculotubal canal by a thin layer of bone laterally

2.The jugular fossa is a deep dome-shaped depression at the lateral wall of the JF and located behind the CC and below the floor of the tympanic cavity. It houses the superior bulb of the IJV and the mastoid canaliculus (**Figure 4**) for the entry of the Arnold's nerve, which provides sensory innervation of the EAC and auricle [9, 15]. The jugular spine in the jugular notch of the occipital bone divides the JF into the pars nervosa (anterior) and pars venosa (posterior) [4, 5, 9]. Normally, the jugular bulb is located between the IJV and the

*2.4.4 Surgical landmarks on the inferior surface of the petrous portion*

**14**

follows:

**Figure 3.**

[1, 5, 18].

#### **Figure 4.**

*The surface landmarks on the inferior surface of the petrous portion: FM, fossa mandibularis; FS, foramen stylomastoideum; FJ, fossa jugularis; ET, eustachian tube; eocc, external opening of carotid canal; ıocc, internal opening of carotid canal; star: inferior tympanic canaliculus; arrowhead: cochlear aqueduct.*

horizontal course of the SS. Abnormalities of it (80% below the FN in the mastoid cavity) result in dehiscence of the adjacent structures such as: the mediolateral enlargement of the JB results in the vestibular aqueduct, PSC, and IAC dehiscence, whereas the anteroposterior enlargement of the JB may cause the FN dehiscence. Abnormal high riding JB shows both mediolateral and anteroposterior enlargement and results in dehiscence of the FN [26].


#### *2.4.5 Internal anatomy and ossification of the petrous portion*

Internal structures in the petrous portion contain the ME and inner ear. The ME contains an air-filled tympanic cavity and the ossicular chain which is composed of the malleus, incus, and stapes [14]. The walls of the ME:


The tympanic cavity is lined with the mucous membrane that extending into the MA posteriorly and the ET anteriorly. This cavity consists of three parts changing according to the level of the tympanic membrane; the epitympanum (superior to the level of the tympanic membrane), mesotympanum (at the level of the tympanic membrane), and hypotympanum (inferior to the level of the tympanic membrane). The hypotympanum has the orifice of the ET. At the lateral part of the epitympanum below the lateral malleal ligament there is the Prussak space which is bounded by the neck of the malleus medially and the pars flaccida and scutum laterally [2, 3, 5, 14].

Inner ear is comprised of the otic capsule (osseous labyrinth), which surrounds the membranous labyrinth and is divided into three parts from anterior to posterior including the cochlea, vestibule, and three SCs [14]. Cochlea is the spiral shaped bony labyrinth of the inner ear that looks like a snail shell making 2¾ turns about the modiolus and consists of the vestibular and the tympanic and the cochlear ducts, which are formed by an inner membranous partition. The vestibular duct (scala vestibuli) locates at the superior part of the cochlear canal and contains perilymph (rich in sodium ions) and is limited by the oval window, and is separated from the cochlear duct by Reissner's membrane. The cochlear

**17**

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

30°from the transverse plane [3, 15].

six segments as follows:

portant landmark.

and vascular compression.

duct (scala media) locates at the middle part of the cochlear canal and contains endolymph (rich in potassium ions) and is separated from the tympanic duct by the basilar membrane, which has the Organ of Corti including the sensory hair cells. The stereocilia of these cells perceives the potential difference between the perilymph and the endolymph and converts that motion to electrical signals and finally hearing occurs. The tympanic duct (scala tympani) locates at the inferior part of the cochlear canal and contains perilymph as the vestibular duct and is limited by the round window [3, 5, 14, 15]. Vestibule contains the utricle and saccule. SSCs containing three semicircular ducts organized like three flower leafs that join the vestibule. They are located perpendicular to each other; the superior corresponds to the AE, the posterior is parallel to the posterior surface of the pyramid, and the lateral is perpendicular the mucosal plane and angled at

The FN passes through the anterosuperior part of the IAM and enters the fallopian canal (FC). It contains motor, sensory, and parasympathetic fibers and has

1.Cisternal segment lies from the brain stem to the IAM. This part runs together with the cisternal part of vestibulocochlear nerve in same pia mater coverage.

2.Meatal segment is the smallest part of the FC and contains Bill's bar as an im-

3.Petrous (labyrinthine) segment forms first genu (geniculate ganglion) above the cochlea at the lateral wall of the ME and gives a branch named as GSPN. Then, it enters the tympanic cavity and forms an angle ranging from 19 to 107° with tympanic segment of the FC [7, 20]. Because of this segment is the narrowest part and lack of arterial anastomoses, it is susceptible to embolic attacks

4.Tympanic segment (first part) starts from first genu and turns backwards to lie in a thin-walled bony canal that runs evenly between the lateral SSC superiorly and the oval window inferiorly and medial to the incus. A dehiscence of

5.Pyramidal segment (second part of the tympanic segment) forms second genu at the posterior wall of the ME above the pyramidal process. It forms an angle

6.In the mastoid or vertical segment, the FN gives the acoustic branch for the stapedius muscle, the chorda tympani, and sensitive branch for the auricular region. This segment is located 5.50 mm anteromedially to the SS and extends from the level of the LSC to the digastric ridge (~3.8 mm). Then it exits the

According to the classical description, the FC has four segments: labyrinthine, tympanic, pyramidal, and mastoid, but the meatal segment is important from an anatomical and surgical perspective. The stylomastoid artery, a branch of the posterior auricular or the occipital arteries, supplies the inferior parts of the FC up to the second genu and anastomoses directly with the petrosal branch of the MMA, which supplies the geniculate ganglion. The FC pathologies are composed of agenesis, aplasia, narrowing, and osteopetrosis of the canal, which result in complete or incomplete facial paralysis. Bell's palsy depending on the activation of a dormant

the bony canal is more common at this segment in average 41–75%.

ranging from 95 to 125° with mastoid segment of the FC [7, 20].

temporal bone at the SMF and enters the parotid gland [14, 27].

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

*Oral and Maxillofacial Surgery*

brium of the malleus.

*2.4.5 Internal anatomy and ossification of the petrous portion*

the malleus, incus, and stapes [14]. The walls of the ME:

Internal structures in the petrous portion contain the ME and inner ear. The ME contains an air-filled tympanic cavity and the ossicular chain which is composed of

1.Lateral wall contains the tympanic membrane and the scutum pointed inferomedially from the squamous portion. The tympanic membrane has two parts; pars flaccida is located in a fibrocartilaginous ring called the tympanic sulcus and susceptible to perforations and pars tensa is situated in the notch of Rivinus above the lateral process of the malleus. At the medial surface of the membrane a depression called umbo is formed by attachment of the manu-

2.Medial wall consists of the cochlear promontory, the FC, the oval and round windows. It is divided into three part by the bony ridges: the ponticulus superiorly and the subiculum inferiorly. The oval window (vestibular window) is located above the ponticulus whereas the round window (cochlear window) is below the subiculum, and the tympanic sinus between them is located medial to the FC. The vestibular window is closed by the base of the stapes. The facial

recess lies below the lateral SSC and superolateral to the oval window.

5.Anterior wall includes the anterior epitympanic recess superiorly, below it the tensor tympani muscle lies posteriorly and attaches to the neck of the malleus after turning laterally. The orifice of the ET and below it the CC is located

6.Posterior wall consists of the pyramidal eminence, epitympanum, and facial recess. The stapedius muscle passes through the pyramidal eminence and in-

The tympanic cavity is lined with the mucous membrane that extending into

the MA posteriorly and the ET anteriorly. This cavity consists of three parts changing according to the level of the tympanic membrane; the epitympanum (superior to the level of the tympanic membrane), mesotympanum (at the level of the tympanic membrane), and hypotympanum (inferior to the level of the tympanic membrane). The hypotympanum has the orifice of the ET. At the lateral part of the epitympanum below the lateral malleal ligament there is the Prussak space which is bounded by the neck of the malleus medially and the pars flaccida

Inner ear is comprised of the otic capsule (osseous labyrinth), which surrounds the membranous labyrinth and is divided into three parts from anterior to posterior including the cochlea, vestibule, and three SCs [14]. Cochlea is the spiral shaped bony labyrinth of the inner ear that looks like a snail shell making 2¾ turns about the modiolus and consists of the vestibular and the tympanic and the cochlear ducts, which are formed by an inner membranous partition. The vestibular duct (scala vestibuli) locates at the superior part of the cochlear canal and contains perilymph (rich in sodium ions) and is limited by the oval window, and is separated from the cochlear duct by Reissner's membrane. The cochlear

3.Superior wall, the TT, which forms the roof of the ME.

serts to the head of the stapes [2, 5, 7, 14, 18].

4.Inferior wall is a bony roof of the IJV.

inferiorly.

and scutum laterally [2, 3, 5, 14].

**16**

duct (scala media) locates at the middle part of the cochlear canal and contains endolymph (rich in potassium ions) and is separated from the tympanic duct by the basilar membrane, which has the Organ of Corti including the sensory hair cells. The stereocilia of these cells perceives the potential difference between the perilymph and the endolymph and converts that motion to electrical signals and finally hearing occurs. The tympanic duct (scala tympani) locates at the inferior part of the cochlear canal and contains perilymph as the vestibular duct and is limited by the round window [3, 5, 14, 15]. Vestibule contains the utricle and saccule. SSCs containing three semicircular ducts organized like three flower leafs that join the vestibule. They are located perpendicular to each other; the superior corresponds to the AE, the posterior is parallel to the posterior surface of the pyramid, and the lateral is perpendicular the mucosal plane and angled at 30°from the transverse plane [3, 15].

The FN passes through the anterosuperior part of the IAM and enters the fallopian canal (FC). It contains motor, sensory, and parasympathetic fibers and has six segments as follows:


According to the classical description, the FC has four segments: labyrinthine, tympanic, pyramidal, and mastoid, but the meatal segment is important from an anatomical and surgical perspective. The stylomastoid artery, a branch of the posterior auricular or the occipital arteries, supplies the inferior parts of the FC up to the second genu and anastomoses directly with the petrosal branch of the MMA, which supplies the geniculate ganglion. The FC pathologies are composed of agenesis, aplasia, narrowing, and osteopetrosis of the canal, which result in complete or incomplete facial paralysis. Bell's palsy depending on the activation of a dormant

herpes virus, is responsible for 50% of peripheral FN palsies. The FC dehiscence can be congenital or secondary to the surgical intervention or pathology of adjacent structures and results in cerebrospinal fluid (CSF) otorrhea. Several surgical approaches, including the translabyrinthine, transcochlear and retrosigmoid, are used to treat the FC pathologies [27].

Ossification of the petrous portion begins from the 14 centers that fuse to form otic capsule and is completed at birth. The petrous portion develops from the cartilaginous differentiation of the mesenchyme by endochondral ossification at the 16th week of gestation. The cementum layer in teeth roots and petrous portion of the temporal bone contain the optimal endogenous DNA substrate which can provide information to specify the geographic location for genomic analyses [28]. Damgaard et al. reported that the prevalence of the endogenous DNA contents in nonpetrous bones and teeth is ranged from 0.3 to 20.7%, while the levels for petrous bones ranges between 37.4 and 85.4% [29]. Due to the high density and resistance to harsher climatic conditions of the petrous bone, the otic capsule of the petrous bone preserves DNA substrate extremely well and has much higher endogenous DNA level than the teeth by 5.2-fold on average. So, it is currently acknowledged as the optimal substrates for ancient genomic research [28, 29].
