1. SKULL BASE

2. • The skull base forms the floor of the cranial
cavity that separates brain from facial
structures and suprahyoid neck.
• The skull base is composed of five bones: (1)
ethmoid, (2) sphenoid, (3) occipital, (4) paired
temporal, and (5) paired frontal bones.

5. Anterior skull base
• It is formed by:
• The orbital plates of the frontal bone laterally
• The cribriform plate of the ethmoid bone and
the crista galli in midline
• Posteriorly by the lesser sphenoid wing and
the anterior part of the greater wing of
sphenoid

6. • The frontal and ethmoid sinuses , nasal cavity
and the orbits are just inferior to the ACF.
• The frontal lobes and meninges are just
superior to the ACF.

7. Cribriform plate
• It forms the roof of the nasal cavity and
contains numerous small foramina that
transmits the olfactory folia from the nasal
mucosa of the olfactory bulb

9. Fovea ethmoidalis
• Part of frontal bone that separates the
ethmoidal cells from anterior cranial fossa
• It also medially connects with the lateral
lamella of cribriform plate.

11. Lateral lamella
• It connects the CP with the fovea ethmoidalis.
• Height difference between the CP and FE was
classified by KEROS classification.
• The site where the anterior ethmoid artery
enters the anterior cranial fossa (lateral lamella
of the cribriform plate) is the site of common
bony injuries and cerebrospinal fluid(CSF) leaks.

16. Middle skull base
• Formed mainly by:
• 1)The sphenoid bone
• 2)The temporal bone anterior to the petrous
ridge.

17. Sphenoid bone
• 3 compartments:
– Basisphenoid:
• Dorsum sella, posterior clinoids, sella turcica, tuberculum sella, sphenoid
sinus
• Fused to clivus in adult
– Greater wing of sphenoid
• Medial two-thirds and anterior wall of the middle cranial fossa floor
– Lesser wing of sphenoid
• Medial and superior aspects of the anterior wall of the middle cranial fossa
and the anterior clinoids
• Superior and medial edges of the superior orbital fissure

18. • The sphenoid bone articulates with cribriform
plate throug the planum sphenoidale.
• Posterior to planum sphenoidale is the sella
tursica.
• Anterior clinoid process is an anatomical land
mark that separates the SOF from the optic
canal.

19. Superior orbital fissure
Boundaries:
Medial : body of sphenoid
Superior: lesser wing of sphenoid
Inferior: greater wing of sphenoid

20. Structures passing
• Lacrimal nerve
• Frontal nerve
• Trochlear nerve
• Superior and inferior division of Occulomotor
nerve
• Nasociliary nerve
• Abducens nerve
• Superiotr and inferior ophthalmic vein

22. Pterygopalatine fossa
• Small pyramidal space situated deeply below
the the apex of the orbit.

23. Boundaries
• Anteriorly: Superomedial part of posterior
surface of maxilla

24. • Posteriorly: Root of pterygoid process,
adjoining part of anterior surface of greater
wing of sphenoid

25. • Medially: Upper part of perpendicular plate of
palatine bone

26. • Laterally: fossa opens into the infratemporal
fossa through the pterygomaxillary fissure.

27. Communications
• Anteriorly: With the orbit, via the medial end
of inferior orbital fissure

28. • Posteriorly: To the middle cranial fossa
through the F. Rotundum, F. Lacerum

30. • Medialy: with the nose through the
sphenopalatine foramen
• Lateraly: with the infratemporal fossa through
the pterygomaxillary fissure

34. PPF b/w apex of orbit and
pterygoid process

35. • Inferiorly with the oral cavity through palatine
canal

36. Pterygoid canal
• Runs through the base of
the pterygoid process to
the back wall of
pterygopalatine fossa.
• Contain: Nerve, Artery,
Vein of the pterygoid
canal.
• Nerve= Vidian
Nerve(Greater P N+
Deep P N)

39. Foramen Lacerum
• A triangular opening located in the middle
cranial fossa anterior to the petrous apex.
• It measures about 9mm in length & 7mm in
breadth

40. • F lacerum is filled with connective tissue and
transmits the small meningeal branches of
ascending pharyngeal artery and the emissary
vein from the cavernous sinus.
• The internal carotid artery passes along its
superior surface but doesn't traverse it.

42. Foramen ovale
• Oval shaped opening in the middle cranial
fossa located at hte posterior base of the
greater wing of the sphenoid bone.

44. Contents
• Mandibular div of trigeminal nerve
• Accessory meningeal artery
• Lesser petrosal nerve
• Emissery veins

45. Foramen rotundum
• Located in the middle cranial fossa
inferomedial to the superior orbital fissure at
the base of greater wing of sphenoid
• It transmits maxillary maxillary nerve branch
V2 of trigeminal nerve.

47. Foramen spinosum
• Located in the posteromedial part of the
greater wing of sphenoid bone posterolateral
to the foramen ovale.

48. • Connects middle cranial fossa with the
infratemporal fossa.
• Transmits : 1) Middle meningeal artery
• 2)Middle meningeal vein
• 3)Nervous spinosus

49. Sella tursica
• . The sella turcica is a depression in the
superior surface of the body of sphenoid bone
for pituitary gland. It is bordered anteriorly by
tuberculum sellae and posteriorly by dorsum
sellae. Floor of the sella is formed by the
sphenoid sinus. The roof of the sella turcica is
formed by a fold of dura called diaphragma
sellae, which is pierced by the pituitary stalk.

51. Cavernous sinus (CS)
• The CS extends from the orbital apex and
superior orbital fissure anteriorly to the
Meckel’s cave.
• The CS connects the superior and inferior
ophthalmic veins, pterygoid plexus, and
Sylvian vein to superior and inferior petrosal
sinuses.

52. • The internal carotid artery (ICA) is the medial
most structure inside the CS.
• Cranial nerves III and IV and the first and
second divisions of the cranial nerve V (from
superior to inferior) are located in the lateral
dural wall of the CS.
• Cranial nerve VI courses in the central part of
the CS inferolateral to the ICA.

54. Posterior skull base
• Formed mainly by:
• 1)The occipital bone
• 2)Parts of the temporal and sphenoid bone

56. Carotid canal
• Passage in the petrous temporal bone and
transmits Internal carotid artery and the
sympathetic plexus.
• Its inferior opening is called carotid foramen
and its situated anterior to the jugular fossa
and medial to the tympanic plate.
• Canal is initially directed superiorly ,then turns
anteromedially to reach upto petrous apex.

59. Jugular formen
• The jugular foramen is seen at the posterior
end of petro-occipital suture. Anteriorly the
caroticojugular spine separates the jugular
foramen from the inferior carotid opening..

60. • Fibrous or bony septum divides jugular foramen into
anteromedial pars nervosa and posterolateral pars
vascularis.
• Pars nervosa is smaller and more consistent in size, and
transmits cranial nerve IX (glossopharyngeal nerve)
with its tympanic branch (Jacobson nerve) and the
inferior petrosal sinus.
• The pars vascularis is larger and more variable in size,
transmitting the internal jugular vein, cranial nerve X
(vagus nerve) with its auricular branch (Arnold nerve),
cranial nerve XI (accessory nerve), and the posterior
meningeal artery.

61. • The right jugular foramen is larger than the left
in 75% of the population.
• When the roof of the jugular bulb is seen above
the level of floor of internal auditory canal, it is
called a high-riding jugular bulb, which is more
common on the right side.
• This is a dangerous variant and compromises
the exposure during translabyrinthine surgery

63. Hypoglossal canal
• Located anteromedial to the jugular foramen
• Content; Hypoglossal nerve
• Hypoglossal canal lies in close proximity to the
jugular foramen
• Along the medial aspect, an osseous bony bar
called the jugular tubercle separates the jugular
foramen from the hypoglossal canal.

65. Communication pathways
Internal auditory canal: Cranial nerve 7, 8 and labrynthine artery.
Jugular foramen: Cranial nerve 9, 10, Spinal accessory nerve.
Stylomastoid foramen: Facial nerve and stylomastoid artery.
Hypoglossal canal: Cranial nerve 12.
Foramen magnum: Medulla oblongata, Anterior and posterior spinal artery,
Vertebral arteries.

66. Relation of skull base to the deep
facial spaces
• The deep facial spaces are in close contact
with the base skull.
• Infections and tumours of these spaces often
extend up to the skull base.
• Para pharyngeal, masticator, carotid, and
retropharyngeal spaces are seen in close
contact with the skull base along their
cephalad aspect.

67. Parapharyngeal space
• 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. Tumors can easily
traverse across the fat within the
parapharyngeal space.

68. Masticator space
• 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.

69. Carotid space
• Vascular lesions such as jugular vein
thrombosis and neural tumors such as
schwanoma, neurofibroma, and
paraganglioma are seen in the carotid space.
These lesions usually spread longitudinally
along the length of the neck with subsequent
extension into the jugular foramina in the skull
base.