Skull Base Anatomy 1


Label 1- 6

  • 1 – optic canal 
  • 2 – superior orbital fissure
  • 3 – foramen ovale
  • 4 – foramen lacerum
  • 5 – jugular foramen 
  • 6 – internal auditory meatus

What runs through 1?

  • Optic nerve
  • Ophthalmic artery (lies inferior and lateral to optic nerve) 

Name four structures that run through 2.

  • Superior and inferior divisions of the oculomotor nerve
  • Trochlear nerve
  • Abducens nerve
  • Lacrimal, fontal and nasociliary branches of the ophthalmic nerve
  • Ophthalmic veins – superior and inferior divisions. (The inferior division also runs through the inferior orbital fissure)
  • Sympathetic nerve fibres

Name three structures that run through 3.

  • Mnemonic – ‘OVALE’

  • Otic ganglion (inferior)

  • V3 – Mandibular branch of the trigeminal nerve

  • Accessory meningeal artery

  • Lesser petrosal nerve, branch of the glossopharyngeal nerve

  • Emissary vein – connects the cavernous sinus with the pterygoid plexus of veins

Which nerves run through 4?

Greater petrosal nerve joins with deep petrosal nerve to form the Vidian nerve  (Nerve of pterygoid canal)

Name 4 structures that run through 5.

  • Glossopharyngeal nerve
  • Vagus nerve
  • Accessory nerve
  • Sigmoid sinus vein
  • Inferior petrosal sinus

What runs through 6?

Facial nerve

Supporting Information
Anatomy- Skull base  

Bony skullAttachments
Pharyngeal tubercleSuperior pharyngeal constrictor
MastoidSCM
Posterior digastric
Splenius capitus
Longissimus capitis
Styloid processStylomandibular ligament
Stylohyoid ligament
Stylohyoid muscle
Stylopharyngeus
Styloglossus


Foramen and contents

ForamenStructure passing through
Optic canal
(ethmoid bone)
Optic nerve
Ophthalmic artery
Superior orbital fissure
(sphenoid)
Oculomotor  nerve CN III
Trochlear nerve CN IV
Ophthalmic division of trigeminal nerve CN V1 and its branches
– Nasociliary
– Frontal
– Lacrimal
Abducens nerve CN VI
Ophthalmic vein
Inferior orbital fissure
(Sphenoid)
Maxillary nerve
Parasympathetic pterygopalatine ganglion
Inferior ophthalmic vein
Infraorbital vessels
Foramen Rotundum
(Sphenoid)
Maxillary division trigeminal nerve CN V2
Foramen Ovale
(sphenoid)
O- otic ganglion
V-  Mandibular division trigeminal nerve CN V3
A- accessory meningeal artery
L-  Lesser petrosal branch of glossopharyngeal nerve – CN IX
E- emissary veins
Foramen spinosum
(sphenoid)
Meningeal branch of the mandibular nerve
Middle meningeal artery
Middle meningeal vein
Foramen lacerum
(between sphenoid, temporal and occipital)
Internal carotid- across lacerum (through carotid canal)
Greater petrosal branch facial nerve CN VII
Internal auditory meatus
(Temporal bone)
Vestibulocochlear nerve CN VIII
Facial nerve CN VII and nervus intermedius
Labyrinthine artery from basilar artery
Carotid canal
(temporal bone)
Internal carotid artery
Carotid plexus of nerves
Jugular foramen
(Temporal bone)
Anterior- glossopharyngeal nerve CN IX
Posterior- Vagus nerve CN X, Accessory nerve CN XI
Hypoglossal canal
(occipital bone)
Hypoglossal nerve CN XII
Foramen magnum 
(occipital bone)
Spinal accessory nerve entering
Spinal arteries
Vertebral arteries
Meninges
Spinal cord
Stylomastoid foramen
(temporal bone)
Branches of facial nerve
TZBMC and posterior auricular nerve
Stylomastoid artery from greater auricular artery encountered before facial artery in parotidectomy. 
Inferior tympanic canal
(temporal bone)
Lesser petrosal nerve from glossopharyngeal nerve. Runs through the middle ear as jacobson’s nerve (tympanic branch of glossopharyngeal) and then to infratemporal fossa after exiting foramen ovale. 

Superior orbital fissure syndrome- trauma (blow-out fracture), cancer, infection and inflammatory.

  • Double vision and Ptosis due to 3rd nerve function
  • Numbness to upper eyelid due to superior orbital nerve dysfunction

Orbital apex syndrome– as above but with blindness due to dysfunction of orbital apex. 
External Carotid Artery
Superior thyroid artery- thyroid gland
Ascending pharyngeal artery– base of skull
Lingual artery– genioglossus
Facial artery-muscles of facial expression. Branches in the nose (superior labial to little’s area). Tonsil
Occipital artery – occiput, scalp
Maxillary artery– deep structures of the face. Meninges via middle meningeal artery. 
Posterior auricular artery– scalp and ear. 
Superficial temporal artery– temporal, scalp
Layers of the scalp- skin, connective tissues, aponeurosis of occipitofrontalis, loose areolar tissue, pericranium
Arterial supply-

  • Anterior- supraorbital, and supratrochlear arteries
  • Posterior- occipital artery 
  • Laterally superficial temporal and posterior auricular Dural venous sinuses- network of cerebral veins drain into the venous sinuses. Channels between the dura and periosteum which contain no valves. 
  • Superior sagittal sinus- superior falx cerebri and runs from the crista galli anteriorly to the internal occipital protuberance posteriorly to the confluence of the sinuses. 
  • Inferior sagittal sinus- inferior falx cerebri- joins the great cerebral vein to become the straight sinus
  • Straight sinus– formed as above- runs inferoposterior to confluence of the sinuses
  • Transverse sinuses– laterally from the confluence to form the sigmoid sinuses (left and right)
  • Sigmoid– curves medially and then exits via the jugular foramen to become the internal jugular vein
  • Occipital sinus epidural plexus of veins –> confluence of the sinuses
  • Cavernous sinus– either side of the sella turcica. They drain the opthalmic, sphenoparietal and middle cerebral veins to the superior and inferior petrosal sinus. 
  • Superior petrosal– from above to the junction between the sigmoid and transverse sinuses
  • Inferior petrosal sinus– as above and drains into internal jugular vein
  • Basilar sinuses connect the inferior petrosal sinuses to the epidural plexus of veins. 
  • Emissary veins connect the intra and extra cranial veins
  • Medial- sella turcica
  • Lateral– sphenoid bone
  • posterior– optic chiasm
  • Communicate with each other via the intercavernous sinus. 
  • Contents: internal carotid, CN III, IV, V1,2, VI and sympathetic oculomotor, trigeminal – ophthalmic/maxillary, trochlear, abducens)

Features of cavernous sinus lesions:

  1. Oculomotor and / or trochlear cranial nerve palsy
  2. Combined patterns of ophthalmoplegia
  3. Painful ophthalmoplegia
  4. Anaesthesia in the distribution of the ophthalmic division of the trigeminal nerve
  5. Decreased or absent corneal reflex
  6. Anaesthesia in the distribution of the maxillary division of the trigeminal nerve
  7. Non-reactive pupil if sympathetic and parasympathetic fibres are affected
  8. Endocrine signs (e.g., galactorrhoea, features of acromegaly)
  9. Visual defects (unitemporal, bitemporal)

Eye nerve supply-

  • Parasympathetic– 
    • Iris and ciliary muscles
    • Preganglionic in Edinger-Westphal nucleus of oculomotor nerve in the brainstem
    • They travel in the oculomotor nerve to 
    • Ciliary ganglion and then 
    • To the eye as short ciliary nerves. 
  • Sympathetic:
    • Dilator pupillae, the superior tarsal, muscle, the inferior tarsal muscle and the orbitalis
    • Preganglionic – intermediolateral column of the spinal
    • Travel to superior cervical ganglion
    • To the eye in the internal carotid plexus which divide at the cavernous sinus
    • Meet short and long ciliary muscles

Infections can spread from the nose and sinuses via the facial and ophthalmic veins as they are valveless into the cavernous sinus causing thrombosis. It manifests as a swollen painful eye, gradual loss of vision and cranial nerve 3-4-5-6 palsy. It can spread to contralateral sinus. 

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