the lateral skull base is complex anatomy that is usually students finds difficult to understand. here concise literature is made to understand the skull base more easily.

1. Dr. Bomkar bam
(M.S. ENT)

2. • Scott Brown’s Otorhinolaryngology head
& neck surgery – 8th edition Vol -3
• Cummings Otolaryngology head and neck
surgery - 6th edition
• Glasscock Shambaugh surgery of the ear –
6th edition
• Grey’sAnatomy

3.  The lateral skull base represents a lateral and complex
bone structure of the skull that contribute to the floor
of the cranial cavity on which the brain lies.
 The lateral skull base covers the remaining base of the
skull between the anterior and posterior Skull base.
knowledge of this particular region is
 Anatomical
important for understanding several pathologic
conditions as well as for planning surgical procedures
and approches.

4. Skull baseboundaries:-
Anterior►Upper incisorteeth
Posterior ►Sup. nuchal lineof
occipital bone
Lateral►Remaining upperteeth
the zygomatic arch&
its posteriorroot,
the mastoid process

5. Three major areas
of the skull base
are described:
1. anterior
2. middle
3. posterior

6. Composed of fivebones:
1)Ethmoid
2)Sphenoid
3)Occipital
4) Paired temporal
5) Paired frontal bones

7. It forms the floor of the
anterior cranial fossa , and a
roof over the orbits and
ethmoid air cell
system(sinuses)
• It is formed by the
1. Frontal bone
2. Cribriform plate of ethmoid
3. The lesser wings and body
of sphenoid
7

8. 8

10. • The CSB makes up the floor of
the middle cranialfossa.
• The sphenoid bone contributes to
the most of the CSB.
• Anterior border :-
•tuberculum sellae, anterior clinoid
process, posterior margin of lesser
wing of sphenoid & anterior
superior rim of greater wing of
sphenoid.
• Posterior border :-
•superior border of petrous part of
temporal bone and the dorsum
sellae of sphenoid.
Anatomy skull
1
0

12. For diagnostic imaging
purposes, it is useful to
subdivide the CSB further into
 midline sagittal,
 off-midline parasagittal, and
 lateral compartments
by drawing vertical lines
passing medially to the
petroclival fissure and just
lateral to the foramen ovale,
respectively
Anatomy skull
1
2

13. Includes the body of the
sphenoid and the portion of
the clivus anterior to the
spheno- occipital
synchondrosis
(basisphenoid),
contains the sphenoid
sinus, and
bordered superiorly by the
sella turcica and inferiorly by
the roof and posterior wall of
the nasopharynx
Anatomy skull
1
3

14. The PBS forms the base of the
posterior cranial fossa and is
formed by the occipital bone.
It houses the cerebellar
hemispheres together with
pons and medulla oblongata

15. •Anterior margin :- The posterior surface ofthe
clivus.
•Laterally:- superiorlythe posterior surfaceof
the petrous part oftemporal bone
•Posteriorly :- mastoid
portion of temporal
bone & the squamous
partof occipitalbone.

17. The Sphenoid Bone
• It separates the anterior and middle cranial
fossa.
• looks like a bat with outstretched wings.

18. • It consist of → a central body; two sets of wings– the
greater andlesser,which course laterally ; & two
pterygoid processes, directedinferiorly.

19. Posteriorly, the
chiasmatic sulcus
forms a slight
depression & leads
laterally to the optic
canal.
The tuberculum
sellae, abony
elevation, just
posterior to thissulcus

20. Followed by,
posteriorly bysella
turcica & dorsum
sellae.
The dorsumsellae
terminates
laterally into the
posterior clinoid
processes

22. The anterior surface ofthe body of sphenoid forms the roof
& posteriorwall of nasopharynx
Thebody housesthe sphenoid sinus.
Lesserwings→Forms
medial portionof
orbital apex.
Greaterwings → Course
upward & laterally from
both sidesof the sphenoid
body-forms floor of
MiddleCranial Fossa.

23. 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
lacerum.
The lateral pterygoid plate
extends back and laterally
into the infratemporal fossa.
The plate gives attachment
to the pterygoid muscles.

25. The temporal bone is a composite structure consisting of
1. The Tympanic Bone
2. The Mastoid Process
3. The Squama(Squamous portion of the temporal bone)
4. The Petrosa(Petrous portion of the temporal bone.

26. 1)squamous bone : origin for the
temporalis muscle. zygomatic
process
2)tympanic bone - bony portion of
the external auditory canal
3)styloid bone - in an
anterior- inferior direction.
4)mastoid bone
Glenoid fossa
Macevens
triangle

27.  It interfaces with
 1) the squama at the tympanosquamous suture,
2) the mastoid at the tympanomastoid suture
3) the petrosa at the petrotympanic fissure

28. Posterior wall of the glenoid
fossa for the
temporomandibular joint (TMJ).
 The chorda tympani nerve, anterior
process of the malleus, and anterior
tympanic artery traverse the
petrotympanic fissure.
 Laterally, the tympanic bone
borders the cartilaginous
EAC,
 the annular sulcus.
 the notch of Rivinus,.
 in referred otalgia, owing both to the
proximity of the EAC and the shared
innervation by the mandibular division
of the trigeminal (fifth cranial) nerve.

29. SQUAMOUS PORTION O
F
TEMPORALBONE:
 Latera wall of Middle cranial fossa
 Parietal bone superiorly
 Zygoma,TMJ anteriorly
 Medially –middle meningeal artery
 Laterally-temporal artery

30. . It is composed of a squamous portion
(laterally) and a petrous portion
(medially) separated by Körner’s
(petrosquamous) septum
The fossa mastoidea
(Macewen’s triangle)
The fossa mastoidea, a cribrose
(cribriform) area, is identified by its
numerous, perforating small blood
vessels.
The mastoid foramen
Inferiorly, the sternocleidomastoid
muscle attaches to the mastoid tip.

31. Normal length-2.5cm
Its proximal part (tympanohyal) is ensheathed
by the vaginal process of the tympanic portion.
Its distal part (stylohyal) gives attachment to
the following:
stylohyoid ligament
stylomandibular ligament
styloglossus muscle (innervated
by the hypoglossal nerve)
stylohyoid muscle (innervated
by the facial nerve)
stylopharyngeus muscle
(innervated by the
glossopharyngeal nerve)

32.  The tympanosquamous and tympanomastoid sutures are
landmarks for the “vascular strip” incisions used in
tympanomastoid surgery. The elevation of EAC skin
and periosteum at these two sutures often requires sharp
dissection to divide the contained periosteum,
particularly at the tympanosquamous suture.
 The tip of the mastoid process is easily palpated and is a
landmark for the positioning of postauricular incisions.
 On occasion, posterior bulging of the anterior canal wall
may obscure full visualization of the tympanic
membrane. Anterior canalplasty can improve surgical
visualization but if overzealous may result in prolapse
of the TMJ into the EAC with, for example, opening the
mouth.

33.  The tympanomastoid fissure is anterior to the tip
of the mastoid and can be traced medially to the
stylomastoid foramen, which is the exit point of
the facial nerve
 Vestibular schwannoma, Middle cranial fossa
approach- A small window of squamous part of
temporal bone is removed to allow exposure of the
tumor from the upper surface of the internal
auditory canal, preserving the inner ear structures.
 Styloid Process
The Eagle syndrome

34.  LINEATEMPORALIS
The linea temporalis is an avascular
plane, a feature that makes it an ideal
location for the superior limb of the
“T” musculoperiosteal incision used in
the postauricular approach to the
tympanomastoid compartment.
 The squamous portion of the temporal
bone (the squama) extends above the
temporal line, whereas inferiorly and
anteriorly is the tympanic ring and
posteriorly the mastoid.
 The temporal line also approximates
the position of the floor of the middle
cranial fossa.

35. TYMPANOMASTOID SUTURE
• The posterior meatal skin is firmly adherent to the
tympanmastoid suture, as such sharp and careful
dissection should be carried out in this region to
prevent tear of the tympanomeatal flap.
• The facial nerve lies 8mm medial to the
tympanomastoid line.
• The tympanomastoid suture is traversed by
Arnold’s nerve (auricular branch of vagus nerve).

36.  It features the porus of the
internal auditory canal
(IAC).
 internal carotid foramen
 The sigmoid portion of the
lateral venous
 superior petrosal
 The petrous portion of the
temporal bone houses part
of the middle ear (e.g.,
ossicles) and inner ear (i.e.,
cochlear and vestibular end
organs).

37. Cochear aqueduct- connect scala tymani i
n
basal turn to CSF space around the brain
Vestibular aqueduct- bony passage runs f
r
o
m
vestibule to subarachnoid space,
IAM
Mastoid process
Sigmoid sinus sulcus
Styloid process
Jugular fossa

38.  The vertically oriented posterior face of the petrosa
dominates the posterior view of the temporal bone as it
delimits the anterolateral aspect of the posterior cranial
fossa and lies between the superior and inferior
petrosal sinuses.
 The porus of the IAC, operculum, endolymphatic
fossette cradling the endolymphatic sac, and
subarcuate fossa are the key anatomic features on this
surface.

39.  The posterior surface of the temporal bone
forms the anterior border of the posterior
cranial fossa.
 The sigmoid sulcus is an indentation at the
lateral aspect of the posterior surface .
 Anterior to the sigmoid sulcus is the foveate
fossa for the intradural portion of the
endolymphatic sac.
 the operculum, covers the intraosseous
portion of the endolymphatic sac. The
vestibular aqueduct runs anteriorly, superiorly,
and medially from the operculum to end at the
medial wall of the vestibule.
 The superior petrosal sulcus, located at the
interface of the posterior and middle cranial
fossa plates of the temporal bone, carries the
superior petrosal sinus from the sigmoidsinus
to the cavernous sinus anteriorly.

40.  In children the pinna needs to be pulled backwards, downwards and
laterally to make the external auditory canal in line for examination as
the developing temporal bone is horizontally placed which becomes
vertically placed in adult.
 The mastoid process in children is not fully developed, thus cannot
be palpated easily. Hence the postauricular incision in children
should be given more horizontally to prevent injury to the facial
nerve.
POST AURICULAR INCISION IN ADULT VSINFANT

41. • Transmit VII &VIII from pontomedullary
junction to inner ear
Divided by a bonylamina (falciform crest) into
:- 1)Smaller superior part:Superior vestibular
Nerve &Facial Nerve
2) Larger Inferior part:- Inferior vestibular
Nerve & Cochlear nerve

43. A The internal auditory canal
penetratesthe posterior
surface of the petrous ridge,
branch of the inferior vestibular nerve,
the posterior ampullary nerve or singular
nerve , which innervates the ampulla of
the posterior semicircular canal, exits the
internal auditory canal through the singular
canal.
In rare cases of chronic persistent
positional vertigo which do not
respond to physiotherapy singular nerve
neurectomy is a new surgical procedure
for treatment.

44. IMPORTANTS AREAS OF LATERAL SKULL BASE
1. Pharyngeal;
2. Tubal;
3. Neurovascular
4. Auditory;
5. Articular;
6. Infratempor

45. • Situated
centrally in the
skull base, this
area forms the
roof of the
nasopharynx.

46. Boundaries→ Formedby the line of
attachment of the pharyngealwall.
The pharyngobasilar fascia is attached to the
skull base andmedial pterygoid plates →
thickened posteriorly into a pharyngealligament
that continues inferiorly as the pharyngealraphe.
The pharyngobasilar fascia is separated from
the prevertebral muscles by the prevertebral
fascia.

48. 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

49. Thepharyngobasilarfasciaisattachedto undersurfaceof the tube, &
two 'paratubal'musclesariseoneon eachsideof it.
Thelevatorpalati arisesmedially (within the pharynx)& the tensor
palati arises laterally (outside thepharynx).
Both musclesarepartly attachedto the tube, and open it during swallowing

50. NEUROVASCULARAREA
• Posterior to the tubal area lies the neurovascular area:-
• 1). Carotid sheath;
• 2). Styloid apparatus;
• 3). Facial nerve

51. • It is attached to the skull base around the
carotid foramen and continues downwards as
far as the aortic arch.
• Content :
Internal carotid artery
Vagus nerve.
Internal jugular vein

52. • 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.

53. 3muscles : Stylopharyngeus,Stylohyoid,
Styloglossus.
Stylopharyngeus:- Passlateral toICA.
 Origin- Deepaspectof baseof
styloid process.
 Insertion-Thyroid cartilage &side wall
ofpharynx.
 Nerve supply-Ninthnerve.
Function:- Elevates
larynx &pharynx.

54. Stylohyoid:-
 Passlateral toECA.
 Origin- Backof the baseof styloid process
 Insertion- Base of greater cornu of hyoid
 Nervesupply- Facial nerve.
 Function:-Elevate & retracts the
hyoid

55. Origin- front of the styloid process&upper part of
stylohyoid ligament
Insertion-
Side of thetongue
Nerve supply-
Hypoglossalnerve
Function:-
Retract thetongue .

56. 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
of occipitofrontalis)
and a muscular branch
(supplying the posterior belly
of digastric and stylohyoid).
It then swings forward
into the parotid gland,
dividing zygomaticofacial
& cerviciofacial division

57. AUDITORY
AREA
 This small area
anterolateral to the
neurovascular area
 forming the floor and
anterior wall of the
external auditory canal
and middle ear.

58. 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.

60. Dural invagination at posterioraspect of cavernous sinus.
Containsgasserian ganglion (trigeminal).
.
Dural layers showsthinperipheral enhancement
In MRI,3sensorydivisions of
trigeminal nerve canbe
visualized leaving the
Gasserian ganglion

61. The infratemporal fossa is the
space between the skull base,
lateral pharyngeal wall and
the ramus of mandible.
Anatomy skull 6

62. Boundaries :-
Lateral- Ramus and condylar process of the mandible.
M
„ edial- Lateral pterygoid plate.
Anterior – Posterolateral wall of maxilla.
Posterior – Carotid sheath.
S
uperior - CRANIAL BASE (greater wing of the sphenoid bone).
Inferior– Medial pterygoid muscles.

63. Pterygoid muscles, medial and
Lateral
„Maxillary artery and vein
„Pterygoid plexus of veins
„Mandibular division of trigeminal
nerve
„Otic ganglion
Anatomy skull 6

64. A space between the pterygoid plates and the
posterior wall of maxillary sinus. Shaped likean
inverted pyramid.

65. 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 ofsphenoid.

66. .
ThePPFis animportant pathway for the spreadof
neoplastic andinfectious
processes:
 Med - with nasalcavity via
sphenopalatine F
.
 Lat - infratemporal fossa
via the pterygomaxillary
fissure.
 sup - with orbit via the
inferior orbitalfissure

67. Post & sup- with Meckel
cave& cavernous sinus(of
MCF) via the F.rotundum.
Post & inf- with MCF
via the vidian canal,
which transmits the
Vidian nerve.
Inferiorly - with
palate via thegreater
and lesserpalatine
canals

68. Contains:-
1)Pterygopalatine ganglion
2)Terminal third of the maxillary artery
3)MaxillaryNerve–CNV
4)Greater& deeppetrosal nerve.

69. Anatomy skull 6

70. 4

71. Anatomy skull 7

72. Anatomy skull 7
Parapharyngeal space extends caudally to the
submandibular space and cranially abuts the base skull. It
contains fat within, which acts as a medium for infection.

73. Masticator space connects the mandible to the skull base.
Odontogenic infections and oropharyngeal squamous cell
carcinoma can tract along masticator space to the base
skull. Intracranial extension of the tumor can occur via
third division of trigeminal nerve, mandibular nerve
(perineural spread) through the foramen ovale.
Vascular lesions such as jugular vein thrombosis and neural
tumors such as Schwannoma, Neurofibromas, and
Paraganglioma are seen in the carotid space.
Anatomy kull 7

75. Is actually a canal in the base of the
greater sphenoid wing, is situated just
inf & lateral to superior orbitalfissure.
It extends obliquely forward & slightly
inferiorly, connecting the MCF to
pterygopalatine fossa.
Transmits the maxillary nerve(V2),
artery of the foramen Rotundum &
emissaryveins.
Best visualized by coronalCT

76. Endocranially, its situatedpost-lat to F.rotundum;
exocranially, it is found at the base of lateral
pterygoid plate.
Contents :-
1)Mandibular Nerve
2)Accessorymeningeal
nerve
3)Lesser petrosalnerve
4)Emissary vein
5)Occasionally ant. trunk of middle meningealartery

77. Its an aperture in the greater wing of the sphenoid
posterolateral to foramen ovale.
Contents :-
1) Middlemeningeal artery
& vein.
2)Emissary vein.
3)Nervous spinosus
(Meningeal branch of
mandibularnerve)

78. Its located at the base of medial pterygoid
plate, ant tothe petrous apex.
Structures passing whole length:
1)Meningeal branch of Ascending pharyngeal
artery 2) Emissaryvein
Other structures partiallytraversing:
3)Internal carotidartery
4)Greater petrosalnerve.

79. Also c/apterygoidcanal.
Located in the floor of sphenoid sinusat the junctionof the pterygoid
process& the sphenoid body connecting the pterygopalatine fossa
anteriorly & the foramen lacerumposteriorly.
Contents:-1) VidianArtery ( Br.Of MaxillaryArtery). 2)Vidian
Nerve (greater superficialpetrosal nerve& deeppetrosal nerve)

80. JUGULAR FORAMEN
• The jugular foramen is divided by
two transverse septa(Jugular
spine) of fibrous dura (which may
ossify) into three compartments.
•The anterior compartment is
occupied by the
Glossopharyngeal nerve and the
inferior petrosal sinus.

81. The middle compartment is shared by the
vagus (X) and accessory (XI) nerves
The posterior
compartment is
filled by the
emerging
internal jugular
vein.

82. IX& XITH CNlie more laterally thanXTHCNin the foramen
The right jugular foramen is larger than the left in 75%of
thepopulation.
Whenthe roof of the jugular bulb isseenabovethe level of
floor of IAC, it is called a high riding jugular bulb, which is
more common on therigh tside.
This isadangerousvariant & exposingduring
translabyrinthine surgery.

83.  There are 4 musclesasfollow
Masseter muscle
Fr
 Origin:- From zygomaticarch
 Insertion:-Lateral aspectof
mandible from the angle forwards
along the lower border, & upwards
over the lower part ofthe ascending
ramus.
 Nerve supply:-massetericbranch
of ant. division of the mandibularN.
Action:-Elevation &
protrusion of mandible

84. Largestmuscleof mastication& fan shape.
Origin: Frominf. temporalline , floor of temporal fossa& from overlying
temporalfasciaof the sideof the skull.
Insertion:Tothecoronoid process
Action: Elevation(anteriorfibers)
& Retraction (posteriorfibers)
Nerve supply:Ant div.of
mandibularN.
BloodSupply:- middle temporal
artery, branch ofsup. temporalartery
deep temporal arteries,branches of
the maxillaryartery

85. Origin:- from 2heads:manubrium& clavicle.
Inserted:-Curvedline extendingfrom 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 horizontalgaze).

86. Twobellies united bytendon
Origin –Anterior belly from diagastricfossaof mandible. Posterior
belly from mastoid notch of temporalbone.
Insertion –into the digastric fossa on the lower edge of the mandible.
Nerve supply:- Post.belly
is supplied by Facial
nerve (nervetodigastric)
& the ant. belly by the
mylohyoid nerve( CN
V3).
Action:-Todepress& retract
the chin

87. Anatomy skull 8

88. Anatomy skull 8

89. Anatomy skull 8

90. Anatomy skull 9

91. Anatomy skull 9

92. Anatomy skull 9

93. Anatomy skull 9

94. It isthe point at which sigmoid
sinus feeds the upper end ofIJV
.
Liesbelow posterior part of the
floor of the middleear.
Inferior petrosal sinusjoints
jugular bulb atthe skull base
 GSPN+deep petrosalnerve=
vidianN.
Pterygoidcanal→PterygopalatineG.
CN IX,X,IX, Jacobsons & Arnold
nerve lies in & aroundthe
jugularforamen.

95. Lessthan 2 mm inwidth
Samewidth throughout the
length
Lighter onX-raycompared
with
fracturelines
At specific anatomicsites
Doesnot runin straight line
Curvaceous
FRACTURES
 Greater than 3mm inwidth
 Widestat the centre& narrowat the
ends
 Runsthrough both the outer & the inner
laminaof bone,henceappears darker
 Usuallyover temporoparietalarea
 Usuallyrunsin astraightline

Angularturns