surgical anatomy related to skull base surgery

7/30/2019 Surgical Anatomy Related to Skull Base Surgery

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Surgical Anatomy related to Skull Base Surgery

Osteology of Skull Base

Skull base is formed by 5 bones (Ethmoid, Frontal, Sphenoid, Temporal, and Occipital)


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Ethmoid Bone

It is situated at the anterior, central part of the cranial base, at the roof of the nose, between the two

orbits, and contributes to each of these cavities.

It consists of four parts:

1. Cribriform plate, forming part of the base of the cranium.

2. Perpendicular plate, constituting part of the nasal septum.

3. Two lateral labyrinths, constituting the ethmoidal paranasal sinuses.

Cribiform Plate (Lamina Cribrosa):

Occupying ethmoidal notch of frontal bone and roofs in the nasal cavities.

Projecting upward from the midline of this plate is a thick, triangular process, crista galli.

The long thin posterior border of crista galli serves for the attachment offalx cerebri.

Its anterior borderarticulates with frontal bone, and presents two small projecting alae, which are

received into corresponding depressions in the frontal bone and complete the foramen cecum.

On either side of crista galli, the cribriform plate is is perforated by foramina for the passage of theolfactory nerves.

On either side of the crista galli, is an anterior foramen for nasociliary nerve & anterior

ethmoidal vessels, and a posterior foramen forposterior ethmodal vessels and nerve.
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Frontal Bone

Frontal bone consists of two portions:

o Squamal (Vertical) part: corresponding with the region of the forehead. The squama is ve

thick, consisting ofdiploic tissue contained between two compact laminae; the diploic tissu

is absent in the regions occupied by the frontal air sinuses.

o Orbital (Horizontal) part: This shares in formation of orbital and nasal cavity roofs. The orbit

portion is thin, translucent, and composed entirely ofcompact bone.

Squamal Part:

External surface:

On either side of midline, is a rounded elevation, the frontal eminence.

Below the frontal eminences, and separated from them by a shallow groove, are two arche

elevations, superciliary arches; these are prominent medially, and are joined to one another by

smooth elevation named the glabella. They are larger in the male than in the female.

Beneath each superciliary arch is a curved and prominent margin, the supraorbital margin, whic

separates the squama from the orbital portion of the bone. At the junction of its medial and midd

thirds is supraorbital notch (or foramen), which transmits supraorbital vessels and nerve.

Supraorbital margin ends laterally in the zygomatic process, which is strong and prominent, an

articulates with the zygomatic bone. Running upward and backward from this process is upp

and lower temporal lines, which are continuous with corresponding lines on parietal bone.

Between the supraorbital margins the squama projects downward forming nasal process whi

articulates on either side of the middle line with the nasal bone, and laterally with the front

process of the maxilla and with the lacrimal bone. (Nasion is the middle of frontonasal suture).

Nasal process ends below in a sharp spine (nasal spine), which enters into the formation of the ro

of nasal cavity on both sides, and in forming nasal septum.


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Internal surface:

Concave surface, and presents in the upper part of the midline a vertical groove, sagittal sulcus,

which houses the superior sagittal sinus. Edges of sagittal sulcus unite below to form the frontal

crest; which afford attachment to the falx cerebri. Crest ends below in a small foramen, foramen

cecum, by articulation with the ethmoid.

Foramen cecum varies in size in different subjects, and is frequently imperforate; when open, ittransmits a vein from the nose to the superior sagittal sinus.

On either side of the midline the bone presents depressions for convolutions of brain, and

numerous small furrows for the anterior branches of the middle meningeal vessels.

Orbital Part:

Inferior surface:

Smooth and concave.

Presents laterallya shallow depression, lacrimal fossa, for the lacrimal gland.

Near the nasal part is a depression, fovea trochlearis, for the attachment of the cartilaginous

pulley of the superior oblique muscle.

Superior surface:

Is convex, and marked by depressions for the convolutions of the frontal lobes of the brain, and

faint grooves for the meningeal branches of the ethmoidal vessels.

Ethmoidal notch, filledby cribriform plate of ethmoid, separates the two orbital plates.

Two grooves cross the medial edges transversely; they are converted into the anterior and

posterior ethmoidal canals by the ethmoid. The anterior canal transmits the nasociliary nerve and

anterior ethmoidal vessels, the posterior, the posterior ethmoidal nerve and vessels.


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Temporal Bone (TB)

Four major components of TB:

1. Squamous portion

2. Tympanic portion.

3. Mastoid portion.

4. Petrous portion.

1. Squamous portion of TB:

Articulates with the parietal bone, frontal bone, and greater wing of the sphenoid bone.

External surface:

Forms the postero-superior portion of EAC.

Just posterior to the glenoid fossa, the squama joints the tympanic portion of the temporal bone

the tympano-squamous suture.

The posterior part of the zygomatic process originates from the squama as a crest of bon

overlying the external auditory meatus, extends anteriorly to join zygomatic bone.

Zygomatic process, together with squama, form the antero-superior border of the mandibul

(glenoid) fossa, which receives the condyle of the mandible.

Provides attachment for the temporalis muscle, which is bounded inferiorly by the temporal lin

which provides an external landmark for the floor of the middle cranial fossa.


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Internal surface:

Lateral surface defines the boundary of the middle cranial fossa.

Its medial surface is grooved by a sulcus for the middle meningeal artery, whereas the middle

temporal artery runs in a groove on its lateral aspect.

2. Tympanic portion of TB:

Together with the squamal portion, forms the bony part of EAC.

Constitutes the posterior wall of the glenoid fossa for the TMJ.

Laterally, the tympanic bone borders the cartilaginous EAC, whereas medially

it bears a circular groove, the annular sulcus, which houses the annulus of TM

except superiorly, where it is deficient; notch of Rivinus (incisura typanica),

where TM attaches directly to squama.

Persistent foramen tympanicum (foramen of Huschke), is an anatomic variation of the tympanic

portion of the temporal bone due to a defect in normal ossification in the first 5 years of life .

Foramen is located at the antero-inferior aspect of EAC,postero-medial to TMJ.

It interfaces with the squama at the tympano-squamous suture, the mastoid

at the tympano-mastoid suture, and the petrosa at the petro-tympanic

fissure.

Tympano-mastoid suture is traversed by Arnolds nerve of CN X.


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Petro-tympanic fissure is traversed by chorda tympani nerve, anterio

ligament of the malleus, and anterior tympanic artery (branch of 1

part of internal maxillary A.).

Henles spine is a projection of variable prominence at the posterosuperio

aspect of the EAC.

Vaginal process, an inferior projection of tympanic bone, forms the sheath o

the styloid bone.

3. Mastoid portion of TB:

Composed of 2 Parts ; a squamous portion (laterally) and a petrous portio

(medially) separated by Krners (petros-quamous) septum, a thin plate o

bone, represents remnant of the petro-squamous suture.

Fossa mastoidea = suprameatal triangle (Macewens triangle)

defined by the temporal line, postero-superior margin of the EAC, and

tangent to the posterior margin of the EAC. It is an important surgical landmar

as it laterally overlies the mastoid antrum. Cribriform area within Macewen

triangle, is identified by its numerous, perforating small blood vessels.

Mastoid foramen, located posteriorly on the mastoid process, is traversed b

the mastoid emissary vein and one or two mastoid arteries.

Sternocleidomastoid muscle attaches to the mastoid tip.

Mastoid antrum, develops in the earliest stages of mastoid pneumatizatio

and is ordinarily present in even the least pneumatized temporal bones.

4. Petrous portion of TB:

Petrous (Greek for rocklike) due to its extreme density, which guards th

inner ear.

Can be divided into 4 parts:

1. Superior surface.

2. Posterior surface.

3. Petrous apex.

4. Basal surface.


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a) Superior surface (Middle cranial fossa): Landmarks:

1. Arcuate eminence (superior semicircular canal)

2. Meatal plane (indicative of the underlying IAC)

3. Facial hiatus (hiatus for GSPN) lies most anterior, GSPN joins with

Geniculate ganglion of the facial nerve. In some temporal bones, this

hiatus is enlarged, and the geniculate ganglion may be exposed in the

middle cranial fossa.

4. Superior tympanic canaliculus, containing lesser petrosal nerve and

superior tympanic artery (of middle meningeal A), lying lateral to and

paralleling facial hiatus.

5. Groove for superior petrosal sinus, most posteriorly, separating it

from the posterior surface.

b) Posterior (cerebellar) surface

Internal auditory meatus (canal):

- Transmits CN VII (including nervus intermedius = nerve of Wrisberg),

CN VIII, labyrinthine artery, or loop of AICA.


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- Fundus (lateral end) is divided horizontally by the falciform crest. Th

superior compartment contains the facial nerve anteriorly separated from

the superior division of the vestibular nerve posteriorly by a thin plate o

bone (Bill`s bar). The inferior compartment transmits the cochlear nerv

anteriorly and the inferior division of the vestibular nerve posteriorly.

- On average, IAC measures 3.4 mm in diameter and 8 mm in length;

Vestibular aqueduct, which transmits the endolymphatic duct and sac, ope

in a depression covered by a bony shelf (operculum) postero-lateral to IAC

and anterior to the sigmoid groove.

Foveate impression for endolymphatic sac lies below the vestibula

aqueduct aperture.

Cochlear aqueduct aperture,- Carrying the periotic (or perilymphatic) duct.

- Runs from the medial aspect of the scala tympani of the basal cochlear turn to terminate

the subarachnoid space of the posterior fossa, antero-medial to the jugular bulb. (From th

transmastoid perspective, the aqueduct is encountered when drilling medial to the jugular bul

opening the aqueduct results in the flow of cerebrospinal fluid into the mastoid, a usef

maneuver in trans-labyrinthine cerebello-pontine angle tumor surgery as it decompress

cerebrospinal fluid pressure).

- It parallels, and lies inferior to, the IAC.

- Cochlear aqueduct can be used as a guide to the lower limits of IAC dissection, becau

cranial nerve IX, the inferior petrosal sinus, and, in some cases, cranial nerves X and XI can b

found immediately inferior to its aperture.

c) Petrous apex:


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Points anteromedially and is marked by;

1. Carotid canal (& Cavernous sins), anteriorly.

2. Meckels cave for Semilunar (Gasserian) ganglion of the trigeminal

nerve.

3. Antero-laterally,Petro-clinoid ligament (thickening of dura) extends from the tip of the

petrous apex to the clinoid, Abducens nerve travels below the petroclinoid ligament in a small

canal (Dorellos canal).

d) Basal surface of petrous bone:

21 (Hypoglossal canal)

22 (Jugular foramen)

23 (Carotid canal)

24 (Foramen spinosum)

25 (Foramen ovale)

26 (Foramen lacerum)

It is wedged between greater wing of sphenoid bone anteriorly and the occipital bone posteriorly.

Separated from greater wing of sphenoid anteriorly by groove for Eustachian tube.

It provides attachment for the deep muscles of the neck.

Jugular foramen (fossa):- Lies between petrous temporal bone, anteriorly, and occipital bone posteriorly.

- Traditionally, it composed of two compartments, separated by fibrous (or bony) septum at the

intracranial portal of the foramen only:

Antero-medial compartment (Pars nervosa): containing CN IX and the inferior petrosal

sinus (IPS)

Postero-lateral compartment (Pars venosa): containing jugular bulb, CNs X and XI,

and posterior meningeal artery.

- Recent studies showed that there is no discrete compartmentalization. It was found that CNs IX,

X, and XI all lie anteromedial to the JB within the jugular foramen, enclosed by same fibrous

capsule

Foramen lacerum:

- Lies between petrous temporal bone, laterally, and clivus, medially.


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- In living, obliterated by disc of cartilage.

Carotid canal:

- Lies within the petrous bone, anterior to jugular foramen, separated from it by the jugul

carotid crest.

- Aperture of inferior tympanic canaliculus, traversed by Jacobsons nerve (CN IX), aninferior tympanic artery (of ascending pharyngeal A.) are sited in the jugulo-carotid crest.

Sphenoid Bone

Largest single bone in the skull base.

Contributes to the floor of middle cranial fossa, together with petrous and squamous parts of TB.

Composed of:1. Body (containing sphenoid sinus)

2. Lesser wings.

3. Greater wings.

4. Pterygoid plates.

1. Body:

Sella turcica is a saddle-shaped depression occupying the roof of body ofsphenoid bone.

Seat of the saddle is known as thehypophyseal fossa which holds thepituitary gland.

Located anteriorly to the hypophyseal fossa is the tuberculum sellae.

Anterior to tuberculum sellae, lies a transverse groove for optic chiasma ( chiasmatic groove

which end laterally on both sides by an optic canal.

Completing the formation of the saddle posteriorly is the dorsum sellae. The dorsum sellae

terminated laterally by theposterior clinoid processes.

o Dorsum sell together with adjucent port of occipital bone forms the clivus.

2. Lesser wing:

o Forms the posterior lip of the anterior cranial fossa, part of the orbital wall that includes the opt

canal and the anterior clinoid processes.

o Connected to the frontal bone along the posterior border of the anterior cranial fossa

3. Greater wing:
http://en.wikipedia.org/wiki/Sphenoid_bonehttp://en.wikipedia.org/wiki/Hypophyseal_fossahttp://en.wikipedia.org/wiki/Hypophyseal_fossahttp://en.wikipedia.org/wiki/Pituitary_glandhttp://en.wikipedia.org/wiki/Tuberculum_sellaehttp://en.wikipedia.org/wiki/Tuberculum_sellaehttp://en.wikipedia.org/wiki/Dorsum_sellaehttp://en.wikipedia.org/wiki/Dorsum_sellaehttp://en.wikipedia.org/wiki/Posterior_clinoid_processeshttp://en.wikipedia.org/wiki/Posterior_clinoid_processeshttp://en.wikipedia.org/wiki/Sphenoid_bonehttp://en.wikipedia.org/wiki/Hypophyseal_fossahttp://en.wikipedia.org/wiki/Pituitary_glandhttp://en.wikipedia.org/wiki/Tuberculum_sellaehttp://en.wikipedia.org/wiki/Dorsum_sellaehttp://en.wikipedia.org/wiki/Posterior_clinoid_processes


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o Form part of the floor of the middle cranial fossa.

o Extending anteriorly into the orbit, forming its posterior (lateral) wall, including the inferior lip of

superior orbital fissure. Fissure can be divided into three anatomical regions by annulus of Zinn

(cartilaginous ring that surrounds optic N, and gives origin to 5 extraoccular muscles); into lateral,

central, and inferior regions.

o At its junction with the body medially, lie foramen ovale posteriorly, and foramen rotundum

anteriorly.

o Spina angularis (sphenoidal spine), projecting off its inferior (basal) and most posterior portion,

an important landmark for identification offoramen spinosum.

4. Medial and lateral pterygoid plates:

o Extend inferiorly from the body of the sphenoid and are attached to the posterior wall of the

maxillary sinus.

o Medial pterygoid plate forms the lateral wall of the nasopharynx.

o Between the base of medial pterygoid plate and vertical segment of the palatine bone lies spheno-

palatine foramen, located 10mm above the posterior end of the middle turbinate and in front of the

choanae ((sphenopalatine artery and the posterosuperior nasal branches of the maxillary nerve)).

Bony Orbit

Skull Foramina

Foramen Location Structures TransmittedCribriform plate Ethmoid bone o Olfactory nerve (CN I)


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Foramen cecum Occipital bone o Occasional small vein

o Origin of sagittal sinus

Optic canal Body of sphenoid o Optic nerve (CN II)

o Ophthalmic artery

Superior orbital fissure Between greater and lesser wings

of sphenoid

Lateral part:

1. CNIV

2. supratrochlear, supraorbital, lacrimal nerves of

V1

3. Superior ophthalmic vein.

Central part: (pass via annular ring of Zinn).

1. CN III

2. CN VI

3. Nasociliary nerve of V1

4. Sympathetic roots of ciliary ganglion

Inferior part:

1. Inferior ophthalmic vein.

2. Orbital fat

Inferior orbital fissure Between maxilla and greater wing

of sphenoid

o Zygomatic branch of CN V2 (maxillary)

o Infraorbital vessels

Foramen rotundum Greater wing of sphenoid o CN V2(maxillary)

Foramen ovale Greater wing of sphenoid o CN V3 (mandibular)

o Accessory meningeal artery (internal maillary A)

o Lesser superficial petrosal nerve of (CN IX).

o Emissary veins (cavernous sinus to pterygoid

plexus)

+ Otic ganglion is situated directly under the foramen.Foramen spinosum Greater wing of sphenoid o Middle meningeal artery (internal maillary A)

Foramen lacerum Between petrous temporal bone

and clivus

o Closed by a fibrocartilaginous plate that contains ET

o Upper part traversed by ICA

o Vidian nerve

o Artery of the ptyregoid canal

Carotid canal Within petrous temporal bone o Internal carotid artery

Stylomastoid foramen Between styloid and mastoid

processes

o Facial nerve (CN VII)

o Stylomastoid artery

Jugular foramen Between petrous temporal bone

and occipital bone

o Beginning of the internal jugular vein; cranial nerves

IX, X, XIInternal acoustic

meatus

Petrous temporal bone o Facial nerve (CN VII);

o Vestibuloacoustic nerve (CN VIII)

o Labyrinthine A (or loop of AICA)

Hypoglossal canal Lateral edge of foramen magnum o Hypoglossal nerve (CN XII)

Foramen magnum o Spinal cord (medulla oblongata);

o Spinal accessory nerves (CN XI);

o Vertebral arteries

o Anterior and posterior spinal arteries
http://en.wikipedia.org/wiki/Accessory_meningeal_arteryhttp://en.wikipedia.org/wiki/Lesser_superficial_petrosal_nervehttp://en.wikipedia.org/wiki/Emissary_veinshttp://en.wikipedia.org/wiki/Cavernous_sinushttp://en.wikipedia.org/wiki/Pterygoid_plexushttp://en.wikipedia.org/wiki/Pterygoid_plexushttp://en.wikipedia.org/wiki/Otic_ganglionhttp://en.wikipedia.org/wiki/Accessory_meningeal_arteryhttp://en.wikipedia.org/wiki/Lesser_superficial_petrosal_nervehttp://en.wikipedia.org/wiki/Emissary_veinshttp://en.wikipedia.org/wiki/Cavernous_sinushttp://en.wikipedia.org/wiki/Pterygoid_plexushttp://en.wikipedia.org/wiki/Pterygoid_plexushttp://en.wikipedia.org/wiki/Otic_ganglion


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Intracranial Vascular Anatomy

Arterial Supply:

Arterial supply of CNS depends on internal carotid arteries and vertebral arteries.

After the internal carotid arteries pass through the petrous portion of the temporal bone and

cavernous sinus, they ramify into the anterior and middle cerebral arteries, which supply most of

the cerebrum.

Vertebral arteries run superiorly in transverse foramen of each cervical vertebra from 6th cervical

vertebrae (C6) until C1. At C1 level the vertebral arteries travel across the posterior arch of the

atlas before entering the foramen magnum.

Vertebral arteries join in the midline to form the unpaired basilar artery, which is runs just ventral

to the pons in the region of the clivus. Basilar artery forms the paired posterior cerebral, anterior

inferior cerebellar, and posterior cerebellar arteries. The cerebellar arteries also supply portions

of the brainstem.

Anterior (carotid) circulation is joined to the posterior (vertebral) circulation by the posterior

communicating arteries. These arteries and the anterior communicating arteries form the circle

of Willis.
http://en.wikipedia.org/wiki/Transverse_foramenhttp://en.wikipedia.org/wiki/Cervical_vertebrahttp://en.wikipedia.org/wiki/Cervical_vertebraehttp://en.wikipedia.org/wiki/Cervical_vertebraehttp://en.wikipedia.org/wiki/Atlashttp://en.wikipedia.org/wiki/Foramen_magnumhttp://en.wikipedia.org/wiki/Transverse_foramenhttp://en.wikipedia.org/wiki/Cervical_vertebrahttp://en.wikipedia.org/wiki/Cervical_vertebraehttp://en.wikipedia.org/wiki/Cervical_vertebraehttp://en.wikipedia.org/wiki/Atlashttp://en.wikipedia.org/wiki/Foramen_magnum


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Dural sinuses:

Superior sagittal sinus, is the largest sinus, runs in the midline, communicates with both of th

paired transverse sinuses, at a point called Torchular helophili, which receive another two sma

unpaired midline sinuses, inferior sagittal sinus, and occipital sinus.

Transverse sinuses drain on both sides into sigmoid (lateral) sinuses.

Sigmoid sinuses becomejugular bulbs, then continue as internal jugular veins.

Cavernos sinus, drain through Superior petrosal sinus (which joins the sigmoid sinus at i

junction with the transverse sinus); and smallerinferior petrosal sinus (which empties directly in

the jugular bulb).

Vein of Labbe, which drains the temporal lobe, enters the transverse sinus at a point medial to th

superior petrosal sinus. If the vein of Labbe is occluded, substantial temporal lobe edema can occu

Ventricular CSF Drainage System


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There are 4 cerebral ventricles: paired lateral ventricles, and midline third and fourth ventricles.

1. Lateral ventricles, located within the cerebrum, extending into the frontal, temporal and

occipital lobes. CSF is produced at the choroid plexus within lateral ventricles. Both

communicate via the interventricular foramina (foramina of Monro) with the third

ventricle.

2. Third ventricle , found centrally within the diencephalon (area of thalamus and hypothalamus).

It communicates via the cerebral aqueduct (aqueduct of Sylvius), located within the

midbrain, with the fourth ventricle.

3. Fourth ventricle, found between pons and cerebellum, is communicating with subarachnoid

space via 3 foramina (central foramen of Magendie and the two lateral foramina of Luschka)

permitting CSF produced in the ventricles to surround thebrainstem, cerebellum, and cerebral

cortex. The fourth ventricle is also continuous with the central canal, allowing CSF to bathe

the inside surface of the spinal cord. CSF within the subarachnoid space is eventually resorbed by the arachnoid villi along the walls of

the superior sagittal sinus.The fourth ventricle is also continuous with the central canal, allowing

CSF to bathe the inside surface of the spinal cord.

o Normal amount of CSF in an adult is 150 to 200 mL.

o CSF is produced at a rate of20 mL/hr (500 mL/day).

o Total volume of CSF is replaced every 8 hours.

Surgical Landmarks

Anterior Cranial Base (Fossa)

Posterior wall of the frontal sins forms the anterior limit of the anterior cranial base.

Cribriform plate in the midline. Roof of the ethmoidal sinuses (Fovea ethmoidalis, formed by post. table of frontal bone): A line

joining the anterior to the posterior ethmoidal arteries usually identifies the level of the floor of the

anterior cranial base. orm the floor of the anterior cranial base between the orbits. ((fovea

ethmoidalis, not the cribriform plate, is currently the most common location of iatrogenic CSF

leaks)).
http://en.wikipedia.org/wiki/Cerebrumhttp://en.wikipedia.org/wiki/Frontal_lobeshttp://en.wikipedia.org/wiki/Temporal_lobeshttp://en.wikipedia.org/wiki/Occipitalhttp://en.wikipedia.org/wiki/Interventricular_foraminahttp://en.wikipedia.org/wiki/Interventricular_foraminahttp://en.wikipedia.org/wiki/Diencephalonhttp://en.wikipedia.org/wiki/Mesencephalic_ducthttp://en.wikipedia.org/wiki/Midbrainhttp://en.wikipedia.org/wiki/Subarachnoid_spacehttp://en.wikipedia.org/wiki/Subarachnoid_spacehttp://en.wikipedia.org/wiki/Foramen_of_Magendiehttp://en.wikipedia.org/wiki/Foramina_of_Luschkahttp://en.wikipedia.org/wiki/Brainstemhttp://en.wikipedia.org/wiki/Cerebellumhttp://en.wikipedia.org/wiki/Cerebral_cortexhttp://en.wikipedia.org/wiki/Cerebral_cortexhttp://en.wikipedia.org/wiki/Cerebrumhttp://en.wikipedia.org/wiki/Frontal_lobeshttp://en.wikipedia.org/wiki/Temporal_lobeshttp://en.wikipedia.org/wiki/Occipitalhttp://en.wikipedia.org/wiki/Interventricular_foraminahttp://en.wikipedia.org/wiki/Diencephalonhttp://en.wikipedia.org/wiki/Mesencephalic_ducthttp://en.wikipedia.org/wiki/Midbrainhttp://en.wikipedia.org/wiki/Subarachnoid_spacehttp://en.wikipedia.org/wiki/Subarachnoid_spacehttp://en.wikipedia.org/wiki/Foramen_of_Magendiehttp://en.wikipedia.org/wiki/Foramina_of_Luschkahttp://en.wikipedia.org/wiki/Brainstemhttp://en.wikipedia.org/wiki/Cerebellumhttp://en.wikipedia.org/wiki/Cerebral_cortexhttp://en.wikipedia.org/wiki/Cerebral_cortex


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Optic nerve (just before it enters the optic canal) is located about 5 mm posterior to the posteri

ethmoidal artery.

Planum sphenoidale is the roof of the sphenoidal sinus. It contributes to the most posterior limit

the anterior cranial base. Immediately lateral to the planum sphenoidale are the optic canals, th

intracranial openings of which also demarcate the posterior limit of the anterior cranial base.

Middle Cranial Base (Fossa)

A. Intracranial surface:

Composed of the greater wing and body of sphenoid bone (including sella turcica), the petrous bon

anterior to the petrous ridge, and the squamous portion of the temporal bone.

Temporal lobes of the brain occupy most of the middle cranial base.

Separate location exists for the pituitary gland, which is lodged in the sella turcica.

Sella turcica is below the optic chiasm and behind the posterior wall of the sphenoidal sinu

((Trans-sphenoidal approach provides access to the middle, not the anterior, cranial base)).

Cavernous venous sinus:

o Lies on either side of the sella turcica.

o Composed of a rich network of venous channels that drain the tissues of the midface.

o It contains ICA and CNs III, IV, V1, V2, and VI.

o Cavernous sinus itself is drained by the paired superior and inferior petrosal sinuses.

Internal carotid artery:

o ICA becomes encased in the petrous portion of the temporal bone after it enters the carot

canal.

o It first proceeds in a vertical direction until it passes medially to the osseous ET, where th

artery bends in an anteromedial direction to form the horizontal segment (over the forame

lacerum).


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o Horizontal segment ends as the carotid artery turns vertically to pass alongside the lateral

wall of the sphenoidal sinus (causing an impression on lateral wall of the sinus).

o ICA traverses the cavernous venous sinus just before entering the intracranial space.

o GSPN is the most reliable intracranial landmark for the petrous portion of the internal carotid

artery. Course of GSPN is directly above and in the same direction as the horizontal portion of

the petrous portion of ICA.

Superior orbital fissure:

B. Extracranial surface:Related to:

1. Temporal fossa:

Lies between the temporalis fascia and the periosteum of the temporal bone.

Temporalis muscle effectively divides the space into a deep and superficial compartment.

Contains the internal maxillary artery and the inferior alveolar artery and nerve in its most

lower part, medial to neck of mandible.

2. Infra-temporal fossa:

Irregularly shaped cavity, situated below and medial to the zygomatic arch.

Bounderies:

o Anteriorly ,posteriorsurface ofmaxilla, andalveolar canals (which pierce post wall of maxilla,

transmitting posterior superior alveolar vessels & nerves).

o Posteriorly, spine of sphenoid bone.

o Superiorly, greater wing of the sphenoid, and by the under surface of the temporal squama.

Foramen ovale, foramen spinosum, and inferior orbital fissure open on its roof.

o Inferiorly, by the alveolar border of the maxilla

o Medially, by the lateral pterygoid plate, and pterygo-maxillary fissure.

o Laterally, by the ramus of mandible

o It has no floor
http://en.wikipedia.org/wiki/Zygomatic_archhttp://en.wikipedia.org/wiki/Zygomatic_archhttp://en.wikipedia.org/wiki/Infratemporal_surfacehttp://en.wikipedia.org/wiki/Infratemporal_surfacehttp://en.wikipedia.org/wiki/Infratemporal_surfacehttp://en.wikipedia.org/wiki/Maxillahttp://en.wikipedia.org/wiki/Alveolar_canalshttp://en.wikipedia.org/wiki/Alveolar_canalshttp://en.wikipedia.org/wiki/Greater_wing_of_the_sphenoidhttp://en.wikipedia.org/wiki/Temporal_squamahttp://en.wikipedia.org/wiki/Foramen_ovalehttp://en.wikipedia.org/wiki/Foramen_spinosumhttp://en.wikipedia.org/wiki/Alveolar_border_of_the_maxillahttp://en.wikipedia.org/wiki/Lateral_pterygoid_platehttp://en.wikipedia.org/wiki/Ramus_of_mandiblehttp://en.wikipedia.org/wiki/Zygomatic_archhttp://en.wikipedia.org/wiki/Infratemporal_surfacehttp://en.wikipedia.org/wiki/Maxillahttp://en.wikipedia.org/wiki/Alveolar_canalshttp://en.wikipedia.org/wiki/Greater_wing_of_the_sphenoidhttp://en.wikipedia.org/wiki/Temporal_squamahttp://en.wikipedia.org/wiki/Foramen_ovalehttp://en.wikipedia.org/wiki/Foramen_spinosumhttp://en.wikipedia.org/wiki/Alveolar_border_of_the_maxillahttp://en.wikipedia.org/wiki/Lateral_pterygoid_platehttp://en.wikipedia.org/wiki/Ramus_of_mandible


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Contents:

o Muscles: Lower part of the Temporalis muscle, and Medial and lateral pterygoid muscles.

o Vessels: Internal maxillary vessles, its 1st and 2nd part branches, and pterygoid venous plexus.

o Nerves: Mandibular nerve, inferior alveolar nerve,lingual nerve, buccal nerve, chorda tympa

nerve, and otic ganglion.

3. Pterygopalatine fossa:

Entrance into the pterygopalatine fossa is gained through the pterygo-maxillary fissure, whi

transmits the maxillary vessels. This fissure is situated on the medial wall of the infra-tempor

fossa and is represented by the space between the pterygoid process of the sphenoid bone an

posterior surface of the maxilla.

Fossa is pyramidal in shape (inverted cone), it apex pointing inferiorly to the palatine canal.
http://en.wikipedia.org/wiki/Temporalishttp://en.wikipedia.org/wiki/Mandibular_nervehttp://en.wikipedia.org/wiki/Inferior_alveolar_nervehttp://en.wikipedia.org/wiki/Lingual_nervehttp://en.wikipedia.org/wiki/Buccal_nervehttp://en.wikipedia.org/wiki/Chorda_tympani_nervehttp://en.wikipedia.org/wiki/Chorda_tympani_nervehttp://en.wikipedia.org/wiki/Otic_ganglionhttp://en.wikipedia.org/wiki/Temporalishttp://en.wikipedia.org/wiki/Mandibular_nervehttp://en.wikipedia.org/wiki/Inferior_alveolar_nervehttp://en.wikipedia.org/wiki/Lingual_nervehttp://en.wikipedia.org/wiki/Buccal_nervehttp://en.wikipedia.org/wiki/Chorda_tympani_nervehttp://en.wikipedia.org/wiki/Chorda_tympani_nervehttp://en.wikipedia.org/wiki/Otic_ganglion


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It is formed by three bones: the maxilla, the palatine bone, and the pterygoid process of the

sphenoid bone.

It communicates with:

1. Middle cranial fossa through foramen rotundum, which transmits the maxillary division

of the trigeminal nerve (V2).

2. Orbit via the inferior orbital fissure containing the infraorbital artery (a continuation of

the maxillary artery).

3. Nasal cavity by the sphenopalatine foramen, which carries the sphenopalatine artery.

4. Extending posteriorly from this fossa is the pterygoid (vidian) canal, which is crossed by

the nerve of the pterygoid canal (vidian nerve) formed ofdeep petrosal nerve and the

greater petrosal nerve the former carrying sympathetic fibres and the latterparasympathetic

fibres of the autonomic nervous system to blood vessels, mucous membranes, salivary

glands, and lacrimal glands. Vidian nerve then passes through foramen lacerum, togetherwith; artery of the ptyregoid canal, terminal branch of ascending pharyngeal artery,

emmissary veins.

5. Inferiorly, the fossa ends in the pterygo-palatine canal, which conducts the descending

(greater) palatine vessels and anterior palatine nerve, which emerge from the greater

palatine foramen.

It contains:

Pterygo-palatine ganglion,

- Parasympathetic ganglion of the facial nerve .

- Located high in the fossa.

- Postsynaptic parasympathetic fibers leave this ganglion and distribute with branches of the

maxillary division of the trigeminal nerve (V2). These fibers are secretomotor in function

and provide parasympathetic innervation to the lacrimal gland and the mucosal glands of the

nose, palate, and pharynx.

- Acts as a peripheral regulatory center for the innervation of the vessels of the nasal mucosa.

Stimulation of this ganglion may produce redness, swelling, increased secretions from the

nasal mucosa.
http://en.wikipedia.org/wiki/Deep_petrosal_nervehttp://en.wikipedia.org/wiki/Greater_petrosal_nervehttp://en.wikipedia.org/wiki/Parasympathetichttp://en.wikipedia.org/wiki/Autonomic_nervous_systemhttp://en.wikipedia.org/wiki/Blood_vesselshttp://en.wikipedia.org/wiki/Mucous_membraneshttp://en.wikipedia.org/wiki/Salivary_glandshttp://en.wikipedia.org/wiki/Salivary_glandshttp://en.wikipedia.org/wiki/Lacrimal_glandshttp://en.wikipedia.org/wiki/Deep_petrosal_nervehttp://en.wikipedia.org/wiki/Greater_petrosal_nervehttp://en.wikipedia.org/wiki/Parasympathetichttp://en.wikipedia.org/wiki/Autonomic_nervous_systemhttp://en.wikipedia.org/wiki/Blood_vesselshttp://en.wikipedia.org/wiki/Mucous_membraneshttp://en.wikipedia.org/wiki/Salivary_glandshttp://en.wikipedia.org/wiki/Salivary_glandshttp://en.wikipedia.org/wiki/Lacrimal_glands


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BY:Dr. Motaz Soliman Srahan

4. Parapharyngeal space:

Inverted pyramidal area, boundaries:

- Inferior limitation (apex): lesser cornua of the hyoid bone.

- Superior margin of the space is the skull base (greater wing of sphenoid).

- Medial boundary is buccopharyngeal fascia around the superior constrictor and the fascia

the tensor and levator palatini.

- Laterally, the space is defined by the superficial layer of the deep cervical fascia th

overlies the mandible, medial pterygoids, and parotid.

- Posterior border is formed by the prevertebral division of the deep layer and by the posteri

aspect of the carotid sheath at the posterolateral corner.

- Anterior boundary is pterygo-mandibular raphe, which joins the lateral pterygoid plate

the mandible.

- Postero-medially connects with the retropharyngeal space and inferiorly with th

submandibular space.

Parapharyngeal space can be subdivided into pre-styloid and post-styloid compartments by a lin

extending from medial pterygoid plate to styloid process.

Pre-styloid (muscular) compartment: contains internal maxillary artery, and V3 (mandibul

nerve) with its branches.


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Post-styloid (neuro-vascular) compartment: contains the carotid sheath and CNs IX, XI, XII,

sympathetic chain, and lymphatics.

Roof is in close proximity to several foramina:

1. Foramen ovale.

2. Foramen spinosum.

3. Foramen lacerum.

4. Carotid canal.

5. Jugular foramen.

Posterior Cranial Base (Fossa)

The posterior cranial base extends from the petrous ridge posteriorly to the occipital bones.

This region includes the clivus, which is centrally located between the foramen magnum and the

petrous tips.

Venous sinuses (petrous, sigmoid, and transverse) run along the periphery of the posterior fossa.

Anatomy of CPA


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CPA is a potential space within posterior cranial fossa, filled with CSF, roughly triangular shape

lies in the axial plane.

Bounderies:

o Superiorly: CNs V (which arises from side of pons), and VI (which arises from anterior fac

of ponto-medullary junction), superior cerebellar A, and tentorium cerebelli (upper limit).

o Inferiorly: Lower CNs, PICA, cerebellar tonsil, and medullary olives.

o Anteriorly: CN VI, basilar A., and clivus.

o Posteriorly: ventral surface of the pons and cerebellum.

o Medially: Bonto-medullary junction, and the lateral recess of the fourth ventricle. Later

opening of the fourth ventricle (foramen of Luschka), opens into the CPA.

Cranial nerves VII & VIII:

Cranial nerves VII and VIII are covered with central myelinprovided by neuroglial cells as th

cross the CPA and carry a sleeve ofposterior fossa dura into the IAC.

Transition to peripheral myelin made by Schwann cells occurs at the medial opening of IAC.

The vestibulo-cochlear nerve divides into three nerves: the cochlear nerve and the superior an

inferior vestibular nerves in medial part of IAC.


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IAC is divided into four quadrants by a vertical crest, called Bills bar, and a transverse (falciform)

crest. The CN VII comes to lie in the anterosuperior quadrant and is anterior to the superior

vestibular nerve and superior to the cochlear nerve, whereas the inferior vestibular nerve lies in the

posteroinferior quadrant.

Vertebro-basillar system:

Vertebral As unite at the level of ponto-mudullary junction, in the anterior part of CPA, to form the

basilar A. This vertebro-basilar system gives rise to 3 pairs of cerebellar A. each has an important

relation with group of nerves within the CPA:

o Superior Cerebellar A.: arises from the basilar A., related to CNs V and VI in the superior

part of CPA (artery passes sup. to V CN).

o AICA: arises from basilar A., it is first related to VI CN at its orign anteriorly, then it passes

posteriorly to loop around the VIII CNs. It has variable relations with VII and VIII CNs, butmost frequently it passes inferiorly.

o PICA: arises from vertebral A. postero-inferiorly, related to the lower 4 CNs.

Veins:

Petrosal vein (of Dandy): brings returning venous blood from the cerebellum and lateral brain

stem to superior petrosal sinus. It is generally encountered in the area of trigeminal nerve

anterior and superior to IAC. Petrosal vein often carries enough venous blood that its obstruction

can lead to venous infarction & cerebellar edema, and it should be preserved if at all possible.

Vein of Labb: carries returning venous blood from the inferior and lateral surface of the temporal

lobe to either the superior petrosal sinus or the transverse sinus. Its configuration and anatomy is

quite variable. Sudden occlusion of the vein of Labb carries high risk of venous infarction of the

temporal lobe and rapid life-threatening cerebral edema.

surgical anatomy related to skull base surgery

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