• Scott Brown’s Otorhinolaryngology head
& neck surgery – 7th edition Vol -3
• Cummings Otolaryngology head and neck
surgery - 6th edition
• Glasscock Shambaugh surgery of the ear –
• Grey’s Anatomy
3. The skull base represents a central and complex bone
structure of the skull that forms the floor of the cranial
cavity on which the brain lies.
It separates brain from facial structures and suprahyoid
Anatomical knowledge of this particular region is
important for understanding several pathologic
conditions as well as for planning surgical procedures.
9. The Ethmoid Bone
consists of :-
• horizontal plate(cribriform plate)
• and a vertical plate in
the midline, i.e. the
10. • On closer examination, the cribriform plate
Horizontal medial lamella Vertical lateral lamella
This lateral lamella articulates
with the frontal bone.
11. The skull base in this region—the ethmoid
fovea —is formed
• medially by the lateral lamella of the
cribriform plate, which is very thin bone
• and laterally by the frontal bone, which in
contrast is a thicker bone.
12. • The frontal bone forming the ethmoid
fovea is 0.5 mm in thickness while the
lateral lamella of the cribriform plate is
• The region where the anterior ethmoidal
artery pierces the dura medially is the
thinnest area in the skull base and is only
0.05 mm in thickness.
14. KEROS CLASSIFICATION
The length of the lateral lamella and the depth
of the olfactory fossa are classified into 3
• Type I — 1-3 mm
• Type II — 4-7 mm
• Type III — 8-17 mm
15. The Sphenoid Bone
• It separates the anterior and middle cranial
• looks like a bat with outstretched wings.
16. • It consist of → a central body; two sets of wings– the
greater and lesser, which course laterally ; & two
pterygoid processes, directed inferiorly.
21. The anterior surface ofthe body of sphenoid forms the roof
& posterior wall of nasopharynx
Thebody houses the sphenoidsinus .
Greaterwings → Course
upward & laterally from
both sides of the sphenoid
body-forms floor of
Middle Cranial Fossa.
22. The medial pterygoid plate
projects back , where it
articulates with the vertical
plate of the palatine bone.
Inferiorly, it ends in the
pterygoid hamulus and
superiorly in the pterygoid
tubercle which projects
back into the foramen
The lateral pterygoid plate
extends back and laterally
into the infratemporal fossa.
The plate gives attachment
to the pterygoid muscles.
Its made up of squamous, mastoid, petrous & tympanic
parts which ossify separately and later fuse creating
squamotympanic & petrosquamous fissure
24. The squamous temporal bone contains the
hollow of the glenoid fossa joined laterally to
the zygomatic process.
25. The petromastoid bone projects forwards and
medially at 45°, wedged between the basiocciput
and the greater wing of the sphenoid; at the
apex of the wedge the three
bones do not quite meet, leaving a gap termed the
26. • Tympanic part has
styloid process →
behind its base,
mastoid bone has
the digastric notch,
medial to which
there is agroove
for the occipital
27. ANTERIOR CRANIAL FOSSA
• The anterior cranial base can be defined as that
portion of the skull base adjacent to the
anterior cranial fossa.
28. ANTERIOR CRANIAL BASE
Boundaries :- Anterior: Posterior wall of thefrontal sinus
Posterior: Lesser wing of the sphenoid & anteior clinoid processes.
Floor : roof of the nasal cavity & ethmoidsinuses medially.
Lateral wall : Orbital plates of the frontal bone
29. • An important visible landmark is the foramen
cecum, which is the site of a communication
between veins of the nasal cavity and the origin
of the superior sagittal sinus.
• The next landmark, the crista galli, protrudes
upward from the midline to provide attachment
for the falx cerebri.
• On either side of the crista are the openings of
the cribriform plate, through which olfactory
nerves are transmitted
30. Just posterior to the last of these olfactory
foramina is a smooth-surfaced area known as the
planum sphenoidale, which forms the roof of the
sphenoid sinus when the sinus is well
1 foramen cecum 2crista
galli; 3 cribriform plate;
4 planum sphenoidale;
5 optic canal
7anterior clinoid process
9, dorsum sellae;
10, foramen ovale;
11, foramen lacerum.
31. Frontal crest :- Midline bony ridge that projects
upwards & provide attachment to the falx cerebri.
Foramen caecum:-Transmits emissary vein from nose
to superior sagittal sinus
Crista galli :- Provides site for ant. most attachment
of the falx cerebri.
Thecontents & foramina'sofACF
32. Cribriform plate :- Sheet of bone contaning
many small Olfactory foramina →Transmit
olfactory nerve fibres into the nasal cavity.
33. The orbits contain several landmarks
that can help surgical orientation
during cranial base operations.
The superior orbital fissure
transmits the oculomotor, trochlear,
ophthalmic, and abducens nerves and
the ophthalmic vein, and it
communicates with the middle
The inferior orbital fissure contains
the maxillary nerve (V2) and
communicates primarily with the
pterygopalatine fossa; the lateral end
of this fissure is an important
landmark for the placement of lateral
34. The optic canal transmits the optic nerve and the
Ant & post ethmoidal foramen:-TransmitsAnt &
post. ethmoidal artery, nerve,vein
These ethmoid foramina mark the position of the
frontoethmoid suture line, a valuable guide to the
level of the ethmoid roof and the anterior fossa
The posterior ethmoid foramen is of additional
significance because of its consistent relationship
with the optic canal, found 4 to 7 mm posteriorly.
37. MIDDLE CRANIAL BASE
• The middle cranial base
forms the floor of the
middle cranial fossa.
• Boundaries (from the
Anteriorly - the
posterior edge of the lesser
Posteriorly - ends at the
posterosuperior edge of the
petrous part of the temporal
38. Subdivisions of the lateral skull base
6. Infratemporal fossa.
40. Boundaries→ Formed by the line of
attachment of the pharyngeal wall.
The pharyngobasilar fascia is attached to the
skull base and medial pterygoid plates →
thickened posteriorly into a pharyngeal ligament
that continues inferiorly as the pharyngealraphe.
The pharyngobasilar fascia is separated from
the prevertebral muscles by the prevertebral
42. TUBAL AREA
The tubal area lies just lateral to the pharyngeal
area and occupied by the Eustachian tube.
Anteriorly, the scaphoid fossa
at the base of the medial
pterygoid plate, between the
petrous bone and the greater
wing of the sphenoid
43. The pharyngobasilar fasciais attached to undersurface of the tube, &
two 'paratubal' muscles ariseone on eachside of it.
The levator palati arisesmedially (within the pharynx) & the tensor
palati arises laterally (outside thepharynx).
Both musclesare partly attached to the tube, and open it during swallowing
45. Carotid sheath
• It is attached to the skull base around the
carotid foramen and continues downwards as
far as the aortic arch.
• Content :
Internal carotid artery
Internal jugular vein
46. • In the neck, the carotid sheath + pretracheal
fascia, is firmly attached anteriorly to the
deep surface of the sternomastoid.
Posteriorly, it is not attached to the
prevertebral fascia, but is free to slide over it.
This means that pus tracking laterally from a
parapharyngeal abscess passes behind the
sheath and behind the sternomastoid, to point
in the posterior triangle.
47. • The cervical sympathetic trunk lies behind the
carotid sheath in front of the prevertebral
fascia, just medial to the vagus nerve.
• It ends superiorly at the superior cervical
The DEEP PETROSAL NERVE arises
from this ganglion and passes superiorly to
join the greater superficial petrosal nerve
to form the VIDIAN NERVE.
48. • The jugular foramen is
divided by two transverse
septa(Jugular spine) of
fibrous dura (which may
ossify) into three
• The anterior compartment
is occupied by the
and the inferior petrosal
49. The middle compartment is shared by the
vagus (X) and accessory (XI) nerves
filled by the
50. IX & XITH CNlie more laterally thanXTH CNin the foramen
The right jugular foramen is larger than the left in 75%of
When theroof of thejugular bulb isseen abovethelevel of
floor of IAC, it is called a high riding jugular bulb, which is
more common on the righ tside.
This is adangerous variant & exposing during
51. 3muscles : Stylopharyngeus, Stylohyoid,
Stylopharyngeus:- Passlateral toICA.
Origin- Deep aspect of baseof
Insertion-Thyroid cartilage & side
wall of pharynx.
Passlateral to ECA.
Origin- Back of the base of styloid process
Insertion- Base of greater cornu of hyoid
& retracts the hyoid.
53. Styloglossus:- Lateral to ICA
Origin- front of the styloid process &upper part of
Side of thetongue
Retract thetongue .
54. STYLOMASTOID FORAMEN
It transmits the facial nerve
and the stylomastoid artery.
As soon as it emerges from
the foramen, VII gives off the
posterior auricular nerve
(supplying the occipital belly
and a muscular branch
(supplying the posterior belly
of digastric and stylohyoid).
It then swings forward
into the parotid gland,
& cerviciofacial division
56. Petrotympanic fissure of Glaser –
Transmits the chorda tympani and anterior
tympanic branch of the maxillary artery,
and the corresponding veins which drain
into the pterygoid plexus.
58. Situated on each side of the body of
sphenoid bone & extend from sup. orbital
fissure anterior to petrous apex posterior.
Receives :- Sup.& inf. ophthalmic vein ,
Drains into:- Petrosal sinus, Pterygoid
plexus, Basilar plexus.
Contents:- 1) CNIII, IV,V1,V2 &VI
Thecontents & foramina's of MCF
the body in
61. Triangular shaped fissure bounded med. →body of sphenoid,
sup. → lesser wing, inf. → greater wing and is completed lat
→ frontal bone as greater & lesser wings converge.
Optic strut separates optic canal from superior orbital fissure.
Optic canal & superior orbital fissure together form the orbital
Contents are asin dia
62. Extends from pterygopalatine fossaalong orbital floor.
Separatesgreater wings of the sphenoid from the maxilla.
Content –1)Maxillary branch of trigeminal nerve 2)Infra
orbital vessels. 3) Emissary veins connecting inf ophthalmic
vein to pterygoid venous plexus. 4) Zygomatic nerve.
Dural invagination at posterior aspect of cavernous sinus.
Contains gasserian ganglion (trigeminal).
Dural layers shows thinperipheral enhancement
In MRI, 3sensorydivisions of
trigeminal nerve can be
visualized leaving the
64. Optic canal
Formed by the lesser wing of sphenoid.
from carotid plexus
Is actually a canal in the base of the
greater sphenoid wing, is situated just
inf & lateral tosuperior orbital fissure.
It extends obliquely forward & slightly
inferiorly, connecting the MCFto
Transmits the maxillary nerve (V2),
artery of the foramen Rotundum &
Best visualized by coronalCT
66. Foramen Ovale
Endocranially, its situatedpost-lat to F.rotundum;
exocranially, it is found at the base of lateral
3) Lesser petrosal nerve
5)Occasionally ant. trunk of middle meningealartery
Its an aperture in the greater wing of the sphenoid
posterolateral to foramen ovale.
1) Middlemeningeal artery
(Meningeal branch of
Its located at the base of medial pterygoid
plate, ant to the petrous apex.
Structures passing wholelength:
1)Meningeal branch of Ascending pharyngeal
artery 2) Emissaryvein
Other structures partiallytraversing:
3)Internal carotid artery
4)Greater petrosal nerve.
Also c/a pterygoidcanal.
Located in the floor of sphenoid sinus at the junction of the pterygoid
process& the sphenoid body connecting the pterygopalatine fossa
anteriorly & the foramen lacerumposteriorly.
Contents:- 1) VidianArtery ( Br.Of MaxillaryArtery). 2)Vidian
Nerve (greater superficial petrosal nerve & deeppetrosal nerve )
71. BOUNDARIES :- 1) Lat. - Ramus
and condylar process of the mandible.
2)Med.-Medial pterygoid muscle.
3)Ant. –Posterolateral wall of
4)Post. –Carotid sheath&
5)Sup. - Greaterwing of the
down with neck
72. • The contents of the fossa are :-
1. Lateral and Medial pterygoid muscles
2. The maxillary artery and its branches
3. The pterygoid venous plexus and maxillary
4. Branches of the mandibular nerve
73. Medial Pterygoid muscles
Origin:- Superficial head→ Maxillary tuberosity &
pyramidal process of palatine bone
Deep head → Medial surface of lateral
pterygoid plate of the sphenoid bone
Insertion into the angle of the mandible
74. • Action: To close the mouth and move the
mandible towards the opposite side in
Blood Supply:- Branch of Maxillary artery
Nerve supply:- Medial pterygoid nerve
branch of mandibular nerve
75. Origin:- Upper head → infra-temporal surface & crest
of greater wing of sphenoid
Lower head → Lateral surface of the lateral
Insertion into the neck of the mandible
76. Action: Depression & Protrusion of
the mandible, Side to side movement
Blood Supply:- Pterygoid vessels from
Nerve supply:- Branches from the
masseteric or buccal nerve, branch of
the ant. trunk of the mandibular nerve
77. Its the larger of the 2 terminal branches of
ECA→Enters the infratemporal fossa→
Pass forward bwt ramus of mandible &
sphenomandibular ligament → Then runs
sup or deep to the lateral pterygoid muscle
→ Pterygomaxillary fissure →
79. The pterygoid plexus & maxillary veins
Plexus → lies within and on the lateral surface of
the lateral pterygoid muscle, and receives
branches of the maxillary artery.
Drains into two short, large
maxillary veins → superficial
temporal vein and
retromandibular vein .
80. The pterygoid plexus has three important
1. The inferior
→ the facial vein.
2. A connecting vein
3. The deep facial
vein → join the
anterior facial vein.
81. The mandibular nerve
It passes through the foramen ovale.
The main trunk :
(which reenters the
2. Nerve to the
→ the tensor palati
and tensor tympani.
82. The main trunk divides into
anterior posterior divisions
• The anterior division:-
1. Buccal nerve → buccinator to supply the
mucous membrane of the cheek.
4. Lateral pterygoid.
83. The posterior division :-
1. The Mylohyoid nerve.
2. The Auriculotemporal nerve.
3. The Inferior alveolar nerve
4. The Lingual nerve is joined by the
chorda tympani 2 cm below the base of the
84. The otic ganglion lies close
to the mandibular nerve
just below the foramen
It relays secretomotor fibres
for the parotid gland,
which it receives by way of
superficial petrosal nerve
and transmits to the
85. A space between the pterygoid plates and the
posterior wall of maxillary sinus. Shaped like an
86. Boundaries :-
Medially - Perpendicular plate palatine bone
Laterally - Narrowing to pterygomaxillary fissure
Anteriorly - Post wall of maxillary sinus
Posteriorly - Med & Lat pterygoid plates
Superiorly- Undersurface of body of sphenoid.
The PPFis an important pathway for the spread of
neoplastic and infectious
Med - with nasal cavity via
Lat - infratemporal fossa
via the pterygomaxillary
Ant - with orbit via the
inferior orbital fissure
88. Post & sup- with Meckel
cave & cavernous sinus (of
MCF) via the F.rotundum.
Post & inf- with MCF
via the vidian canal,
which transmits the
Inferiorly - with
palate via the greater
and lesser palatine
90. Posterior Cranialfossa
• Anterior margin :- The posterior surface ofthe
• Laterally:- superiorlythe posterior surface of
the petrous part oftemporal bone
• Posteriorly :- mastoid
portion of temporal
bone & the squamous
partof occipital bone.
91. Thecontents & foramina's of PCF
• The foramen magnum is entirely formed within the
1. Medullaoblongata.2.Vertebral arteries andveins.
2.Anterior & posterior spinal arteries. 3.spinal
92. Also c/aant condyloid canal. Located within occipital bone.
Its paired bone passagethat runslateral & slightly forward from PCF
to nasopharyngeal carotidspace→Transmits hypoglossal nerve.
Intracanalicular enhancement isalwayspresent (emissaryveins), with linear
filling defects ( nerverootlets).
• Transmit VII &VIII from pontomedullary
junctionto inner ear
Divided by a bony lamina (falciform crest) into
:- 1)Smaller superior part:Superior vestibular
Nerve &Facial Nerve
2) Larger Inferior part:- Inferior vestibular
Nerve & Cochlearnerve
100. Internal carotid artery: Carotid foramen →curves
upwards into F.lacerum in MCF→apex of petrous
bone →enters the cavernous sinus
It lies in front of cochlea & middle ear cavity,
separated by thin plate of bone (may be dehiscent)
→gives off small intrapetrous branches, including
carotico- tympanic artery →feeding vessels for a
Structureswithin the skullbase
It is the point at which sigmoid
sinus feeds the upper end of IJV.
Lies below posterior part of the
floor of the middleear.
Inferior petrosal sinus joints
jugular bulb atthe skull base
GSPN+deep petrosal nerve=
nerve lies in & around the
102. FRACTURES SUTURES
Less than 2 mm inwidth
Samewidth throughout the
Lighter onX-ray compared
At specific anatomicsites
Doesnot run in straight line
Greater than 3mm inwidth
Widest at the centre & narrow at
Runsthrough both the outer & the
inner lamina of bone, hence appears
Usually over temporoparietalarea
Usually runs in astraightline
103. There are 4 muscles asfollow
Origin:- From zygomaticarch
Insertion:-Lateral aspect of
mandible from the angle forwards
along the lower border, & upwards
over the lower part ofthe ascending
Nerve supply:- massetericbranch
Fr of ant. division of the mandibular N.
protrusion of mandible
104. Largest muscleof mastication & fan shape.
Origin: From inf. temporal line , floor of temporal fossa & from overlying
temporal fascia of the side of the skull.
Action: Elevation (anteriorfibers)
& Retraction (posteriorfibers)
Nerve supply:Ant div. of
BloodSupply:- middle temporal
artery, branch ofsup. temporal artery
deep temporal arteries,branches of
105. Origin:- from 2heads: manubrium & clavicle.
Inserted:-Curved line extending from tip of the mastoid processto
superior nuchal line of theocciput.
Nerve supply:- Accessory nerve
Action:-Toprotract the head (moving it forwards while keeping it
vertical with a horizontal gaze).
106. Two bellies united bytendon
Origin –Anterior belly from diagastric fossa of mandible. Posterior
belly from mastoid notch of temporal bone.
Insertion –into the digastric fossa on the lower edge of the mandible.
Nerve supply:- Post. belly
is supplied by Facial
nerve (nerve todigastric)
& the ant. belly by the
mylohyoid nerve( CN
Action:-Todepress & retract