Skull base anatomy

1. Skull Base Anatomy

2. Overview
• Forms the floor of the cranial cavity
• Separates the brain from other facial
structures

3. Overview
• Formed by ethmoid, sphenoid, occipital,
paired frontal, and paired temporal bones.

4. Overview
• Subdivided into 3 regions: the anterior,
middle, and posterior cranial fossae.

5. Anterior Cranial Fossa
• Most shallow and superior of the three cranial fossae
• Lies superiorly over the nasal and orbital cavities
• Accommodates the anteroinferior portions of the frontal lobes of the
brain

6. Anterior Cranial Fossa: Borders
• Anteriorly and laterally bounded by the inner surface of the frontal bone
• Posteriorly and medially bounded by the limbus of the sphenoid bone
• Posteriorly and laterally it is bounded by the lesser wings of
the sphenoid bone
• The floor consists of the frontal bone, ethmoid bone and the anterior
aspects of the body and lesser wings of the sphenoid bone

7. Anterior Cranial Fossa : Contents
• Frontal crest: acts as a site of attachment for the falx cerebri (a sheet of
dura mater that divides the two cerebral hemispheres)
• Crista galli: midline of ethmoid bone, acts as another point of attachment
for the falx cerebri
• Cribriform plate: on either site of the crista galli, supports the olfactory
bulb and has numerous foramina that transmit vessels and nerves.
• Anterior clinoid processes: rounded ends of the lesser wings, serve as a
place of attachment for the tentorium cerebelli (a sheet of dura mater
that divides the cerebrum from the cerebellum)

8. Anterior Cranial Fossa : Foramina
• Cribriform plate: numerous small foramina, transmiting olfactory nerve
fibers. 2 larger foramen;
• Anterior ethmoidal foramen transmits the anterior ethmoidal artery,
nerve and vein
• Posterior ethmoidal foramen transmits the posterior ethmoidal artery,
nerve and vein

9. Anterior Cranial Fossa : Clinical Relevance
• Cribriform plate: thinnest part, most likely to fracture
• Anosmia
• CSF rhinorrhoea: leakage of CSF into the nasal cavity

10. Middle Cranial Fossa
• As its name suggests, centrally in the cranial floor
• Butterfly shaped
• Anteriorly and laterally: lesser wings of the sphenoid bone
• Anteriorly and medially: limbus of the sphenoid bone
• Posteriorly and laterally: superior border of the petrous part of the temporal bone
• Posteriorly and medially: dorsum sellae of the sphenoid bone
• Floor: the body and greater wing of the sphenoid, and the squamous and petrous
parts of the temporal bone.

11. Middle Cranial Fossa: Central Part
• Formed by the body of the sphenoid bone
• Contains the sella turcica(turkish saddle), acts to hold and support the
pituitary gland
• Tuberculum sellae (horn of the saddle): anterior wall of the sella turcica,
and the posterior aspect of the chiasmatic sulcus
• Hypophysial fossa or pituitary fossa (seat of the saddle): a depression in
the body of the sphenoid, which holds the pituitary gland
• Dorsum sellae (back of the saddle): posterior wall of the sella turcica,
separates the middle cranial fossa from the posterior cranial fossa.

12. Middle Cranial Fossa: Lateral Parts
• Formed by the greater wings of the sphenoid bone,
and the squamous and petrous parts of the temporal bones
• Support the temporal lobes of the brain
• The site of many foramina

13. Foramina of the Sphenoid Bone
• Optic canals: optic nerves (CN II) and ophthalmic arteries, connected by
the chiasmatic sulcus
• Superior orbital fissure: opens anteriorly into the orbit;
contains the oculomotor nerve (CN III), trochlear nerve (CN IV),
ophthalmic branch of the trigeminal nerve (CN V1), abducens nerve (CN
VI), opthalmic veins and sympathetic fibers
• Foramen rotundum: transmits the maxillary branch of
the trigeminal nerve (CN V2).
• Foramen ovale: the mandibular branch of the trigeminal nerve (CN V3)
and accessory meningeal artery
• Foramen spinosum: transmits the middle meningeal artery, middle
meningeal vein and a meningeal branch of CN V3

14. Foramina of the Temporal Bone
• Hiatus of the greater petrosal nerve: transmits the greater petrosal nerve
(a branch of the facial nerve), and the petrosal branch of the middle
meningeal artery
• Hiatus of the lesser petrosal nerve – transmits the lesser petrosal nerve (a
branch of the glossopharyngeal nerve).
• Carotid canal – located posteriorly and medially to the foramen ovale. This
is traversed by the internal carotid artery, the deep petrosal nerve also
passes through this canal
• Foramen lacerum: At the junction of the sphenoid, temporal and occipital
bones, filled with cartilage

15. Clinical Relevance: Pituitary Surgery
• The pituitary gland lies in the sella turcica of the sphenoid bone
• In cases of a pituitary tumour, it may need to be removed surgically.
• usually by a endoscopic transsphenoidal approach
• The sphenoid sinus is opened and the endoscope passes through to the
pituitary gland
• Complications of pituitary surgery include CSF rhinorrhoea, meningitis,
diabetes insipidis, haemorrhage and visual disturbances

16. Posterior Cranial Fossa
• Most posterior and deep of the three cranial fossae
• Accommodates the brainstem and cerebellum
• Three bones: the occipital bone and the two temporal bones.
• Anteriorly and medially: dorsum sellae of the sphenoid bone
• Anteriorly and laterally: superior border of the petrous part of
the temporal bone.
• Posteriorly: internal surface of the squamous part of the occipital bone
• Floor: mastoid part of the temporal bone and the occipital bone

17. Posterior Cranial Fossa - Foramina
• Internal acoustic meatus: transmits the facial nerve (CN
VII), vestibulocochlear nerve (CN VIII) and labrynthine artery
• Foramen magnum: transmits the medulla of the brain, meninges,
vertebral arteries, spinal accessory nerve (ascending), dural veins and
anterior and posterior spinal arteries
• Jugular foramina: transmits the glossopharyngeal nerve, vagus
nerve, spinal accessory nerve (descending), internal jugular vein, inferior
petrosal sinus, sigmoid sinus and meningeal branches of the ascending
pharyngeal and occipital arteries.
• Hypoglossal canal: Hypoglossal nerve

18. Clinical Relevance: Cerebellar Tonsillar Herniation
• Downward displacement of the cerebellar tonsils through the foramen
magnum
• Produced by a raised intracranial pressure; causes include hydrocephalus,
space occupying lesions, and a malformed posterior cranial fossa
• Cerebellar tonsillar herniation results in the compression of
the pons and medulla, which contain the cardiac and respiratory centers

19. References
• TeachMeAnatomy. (2017). The Anterior
Cranial Fossa. [online] Available at:
http://teachmeanatomy.info/head/areas/crani
al-fossa/anterior/ [Accessed 30 Mar. 2017].
• Skull Base Anatomy. (2016, June 28). Retrieved
March 30, 2017, from
http://emedicine.medscape.com/article/8826
27-overview