Skull Base Anatomy

DEVELOPMENT
Skull base: endochondral ossification (cartilage --> bone)
Skull face: intramembranous ossification (bypasses cartilage stage)
Growth: brain doubles in size by 6 months, again at 2 yrs
Skull 35% of size at birth, 90% of size by 7 yo
SURFACE
  • Nasion: midline fronto-nasal suture
  • Glabella: most forward point on the midline supraorbial ridge
  • Pterion: junction of frontal, parietal, temporal, and greater wing of sphenoid
    • Located 2 fingerbreadths above zygomatic arch and a thumb’s breadth behind the frontal process of the zygomatic bone
  • Asterion: junction of lambdoid, occipitomastoid, and parietomastoid sutures
    • Lies on top of the lower half of the transverse/sigmoid junction
  • Lambda: junction of the lambdoid and sagittal sutures
  • Inion: marks the torcula
  • Opisthion:  posterior margin of the foramen magnum
  • Styloid process: 2nd brachial arch
    Muscles: stylohyoid (CN VII), stylopharyngeus (CN IX), styloglossus (CN XII)
    Ligaments: stylohyoid, stylomastoid
  • Slyvian Fissure: 
    75% from Nasion → Inion
    Frontozygomatic point = 2.5 cm up from orbital rim past zygomatic portion
    Sylvian fissure lies on lie connecting these two points, the pterion is 3 cm behind the frontozygomatic point along this line
  • Central Sulcus
    Upper rolandic point: 2 cm posterior to the 50% point of the midline nasion-inion line
    Lower rolandic point: junction of the line from the upper rolandic point to the mid zygomatic arch where it intersects with the sylvian fissure line OR 2.5 cm behind the pterion on this line
  • Motor Cortex: 4-5.4 cm behind the coronal suture
  • Angular Gyrus: above pinna (variable)
HOLES
Cribiform plate
Olfactory nerves
Anterior & Posterior Ethmoid arteries & nerves
Foster Kennedy
Optic Canal
CN II
Ophthalmic artery
SOF: Superior Orbital Fissure
Above:
CN 4, V1Frontal, V1Lacrimal
Sympathetic fibers from ICA
MMA (orbital branch)
SOV (superior ophthalmic vein)
Annulus of Zinn
SOF: CN 3s, CN 3i, V1NC (nasociliary), 6
Optic canal: CN 2, ophthalmic artery
Foix Syndrome
IOF: Inferior Orbital Fissure
V2 - zygomatic nerve, pterygopalatine branch
Infraorbital artery & vein
IOV: Inferior ophthalmic vein
Peterygopalatine Fossa
Maxillary artery
V2
Pterygopalatine gangliona
Vidian Nerve
Foramen Rotundum
V2
Infratemporal Fossa
Temporalis muscle
Pterygoid muscles (medial & lateral)
Maxillary artery
Pterygoid venous plexus
V3
Chorda Tympani
Otic ganglion
Inferior alveolar nerve
Lingual nerve
Buccal nerves
Foramen Ovale
V3
Lesser Petrosal Nerve
Otic ganglion
Accessory meningeal nerve
Emmissary vein
Foramen Spinosum
MMA & vein
Foramen Lacerum
Nothing - ICA traverses upper portion
Carotid Canal
ICA
Sympathetic plexus
IAC: Internal Acoustic Canal / IAM: Internal Acoustic Meatus
VII, VIII, labyrinthine vessels, +/- AICA
Stylomastoid foramen
CN VII
Stylomastoid artery
Jugular foramen
Pars nervosa: IX, Jacobsen's nerve (CN IX)
Pars venosum: X, Arnold's (X), XI, IJ vein, inferior petrosal sinus, posterior meningeal artery
Hypoglossal canal
XII, anterior meningeal artery
Foramen Magnum
XI (spinal), spinal cord
Vertebral artery, Anterior & Posterior spinal arteries
Dorello's Canal
VI
Mandibular foramen
V3 (inferior alveolar)
Mental Foramen
V3 (mental nerve)
Incisive Foramen
V2 (nasopalatine)
Vessels to hard palate
Greater Palatine Foramen
Greater palatine nerve
Vessels to hard palate
Lesser Palatine Foramen
Lesser Palatine Nerve
Vessels to soft palate
Foramen cecum
Emissary veins from SSS to frontal sinus, nose
Vidian Canal
Vidian nerve (Greater Superior Petrosal Nerve VII + Deep Petrosal Nerve X)
Greater Petrosal Foramen
Greater Petrosal Vein
Lesser Petrosal Foramen
Lesser Petrosal Vein

BONE PARTS
Stylomastoid
Muscle attachments: styloHYOID (CN VII), styloPHARYNGEAL (CN IX), styloGLOSSUS (CN XII)
Ligament attachments: styloHYOID, styloMANDIBULAR
Origin: second branchial arch