Cranial Anatomy Notes

Cranial Cavity

Cranium

• Neurocranium:
  • Composed of 8 bones (2 paired, 4 unpaired).
  • Calvaria: The skullcap.
  • Intramembranous ossification: Bones formed through this process.
  • Cranial Base: The floor of the cranial cavity.
  • Endochondral ossification: Bones formed through this process.
• Viscerocranium:
  • Composed of 15 bones (6 paired, 3 unpaired).
  • Intramembranous ossification: Bones formed through this process.
  • Formed from mesenchyme of pharyngeal arches.

External Cranial Landmarks

• Frontal bone:
  • Superciliary arch.
  • Glabella.
  • Nasion.
  • Supra-orbital notch (foramen).
  • Zygomatic process (of frontal bone)
• Nasal bone
• Frontal process (of maxilla)
• Zygomatic bone
• Maxilla
  • Zygomatic process (of maxilla).
  • Infra-orbital foramen.
  • Nasal crest
  • Anterior nasal spine.
  • Alveolar process.
  • Piriform aperture
• Inferior nasal concha
• Mandible
  • Ramus of mandible.
  • Alveolar part of mandible.
  • Body of mandible.
  • Mental foramen.
  • Mental protuberance.
  • Mental tubercle.
  • Angle of mandible.
• Parietal bone
  • Sagittal suture
• Occipital bone
  • External occipital protuberance.
  • Superior nuchal line.
  • Inferior nuchal line.
  • External occipital crest.
  • Inion
• Temporal bone
  • Mastoid process.
  • Mastoid notch.
  • Oblique line.

Lateral Cranial Landmarks

• Frontal bone
  • Coronal suture.
  • Bregma
• Parietal bone
  • Sagittal suture.
  • Squamous suture.
  • Lambdoid suture.
  • Parietal foramen
• Occipital bone
  • Lambdoid suture.
  • Lambda
• Temporal bone
  • Squamous part (of temporal bone).
  • Mastoid part of temporal bone
  • Tympanic part (of temporal bone).
  • Styloid process
  • Zygomatic process (of temporal bone).
  • Parietomastoic suture
  • Asterion
• Sphenoid bone
  • Greater wing (of sphenoid bone).
  • Sphenosquamous suture.
  • Sphenoparietal suture.
• Zygomatic bone *Zygomaticofacial foramen *Temporal process (of zygomatic bone)
  • Zygomaticotemporal foramen (on deep surface of zygomatic bone).
• Lacrimal bone
• Nasal bone
• Maxilla
  • Alveolar part
• Mandible
  • Body of mandible
  • Mental foramen.
  • Ramus of mandible.
  • Angle
  • Condylar process
  • Coronoid process
• Pterion

Inferior Cranial Landmarks

• Maxilla
  • Hard palate (maxilla).
  • Incisive fossa.
  • Alveolar arch.
• Palatine bone
  • Hard palate (palatine bone).
  • Greater palatine foramen.
  • Lesser palatine foramen.
  • Pyramidal process of palatine bone
• Sphenoid bone
  • Body of sphenoid.
  • Greater wing (of sphenoid bone).
  • Pterygoid process.
  • Medial plate of pterygoid process.
  • Lateral plate of pterygoid process.
  • Scaphoid fossa.
  • Foramen lacerum.
  • Foramen ovale.
  • Foramen spinosum.
  • Opening of pterygoid canal
• Vomer
• Temporal bone
  • Mandibular fossa.
  • Articular tubercle.
  • Groove for auditory tube.
  • Petrous part of temporal bone.
  • Carotid canal.
  • Stylomastoid foramen.
  • Squamous part of temporal bone.
  • Mastoid process.
  • Mastoid notch.
  • Styloid process.
  • Jugular foramen
• Occipital bone
  • Basilar part of occipital bone.
  • Pharyngeal tubercle.
  • Occipital condyle.
  • Hypoglossal canal.
  • Foramen magnum.
  • External occipital crest.
  • Inferior nuchal line.
  • Superior nuchal line.
  • External occipital protuberance.
• Posterior nasal aperture (choana)
• Posterior nasal spine
• Hamulus
• Pterygoid fossa

Cranial Tables

• Internal & external cortical bone tables
• Separated by diploë trabecular bone
• Buttresses: Thicker areas of cranial bone help transmit forces around weaker areas of bone
• Cranial walls are thinner where muscles cover the skull
• Thinnest walls at Pterion

Meningeal Arteries

• Middle meningeal artery:
  • Position related to pterion.
  • Branch of the maxillary artery.
• Anterior meningeal arteries: from ethmoidal arteries.
• Posterior meningeal artery: from ascending pharyngeal artery.
• Meningeal branch: from ascending pharyngeal artery.
• Meningeal branch: from occipital artery.
• Meningeal branch: from vertebral artery.

Cranial Fractures

• Le Fort fractures:
  • Le Fort I
  • Le Fort II
  • Le Fort III
• Mandible fractures
  • Condylar process
  • Coronoid process
  • Ramus
  • Angle
  • Body
  • Alveolar process
  • Mental foramen
  • Mental protuberance

Cranial Development

• Face grows extensively.
• 1/8 of cranium in children to 1/3 in adults.
• Sinuses, teeth, nose.
• Fontanelles
  • Anterior, Posterior, Sphenoidal, & Mastoidal.
  • Bregma, lambda, pterion, asterion.
• Fontanelle closure
• Suture obliteration (\sim30-40 yrs. of age)
• Metopic suture
• Persistent frontal suture

Craniosynostosis

• Premature suture closure.
• 1 in 2,000 births
• Scaphocephaly: Premature closure of sagittal suture.
  • Increased A-P dimension.
• Oxycephaly/Turricephaly: Premature coronal suture closure.
  • Increased superior to inferior dimension.
• Plagiocephaly: Premature closure of coronal or lambdoidal suture on one side only.
  • Twisted or asymmetrical skull shape.

Air Sinuses

• Pneumatic sinuses
• Frontal
• Maxillary
• Sphenoidal
• Ethmoidal

Scalp

• Layers of the scalp:
  • Skin
  • Connective tissue (dense CT), blood vessels & nerves
  • Aponeurosis of occipitofrontalis
  • Loose areolar tissue
  • Pericranium/periosteum

Cranial Meninges

• Dura mater
  • External periosteal layer.
  • Internal meningeal layer.
• Arachnoid mater
• Subarachnoid space
• Arachnoid granulations
• Pia mater

Dural Folds

• Falx cerebri:
  • Runs in longitudinal cerebral fissure.
  • Crista galli to internal occipital protuberance.
• Tentorium cerebelli:
  • Between occipital lobes & cerebellum.
• Falx cerebelli:
  • Separates cerebellar hemispheres.
• Diaphragma sellae:
  • Roof over hypophyseal fossa.

Venous Sinuses

• Sinuses between dural layers.
• Superior sagittal sinus:
  • Superior border of falx cerebri.
• Inferior sagittal sinus:
  • Inferior border of falx cerebri.
• Confluence of sinuses:
  • Union of inferior sagittal sinus & great cerebral vein.
• Paired sinuses:
  • Transverse sinus.
  • Sigmoid sinus.
  • Cavernous sinus:
    • Lateral to sella turcica.
• Transverse sinus & sigmoid sinus lead from confluence of sinuses to jugular foramen.
• Cavernous sinus contents:
  • Hypophyseal fossa
    • CN III, IV, V1, V2, VI, internal carotid artery
    • Orbit, face, meninges, and brain

Innervation

• Scalp:
  • CN V
  • Ventral & dorsal rami of C2 and C3
• Dura:
  • Meningeal branches of CN V, CN X & dorsal rami of C2 and C3
• Trigeminal Nerve (CN V)
  • Ophthalmic nerve (V1)
  • Maxillary nerve (V2)
  • Mandibular nerve (V3)
  • Trigeminal ganglion

Arteries

• Basilar artery
• Right & Left vertebral arteries
• Middle meningeal artery:
  • Branch of maxillary artery
• Internal carotid artery
• Scalp is supplied by branches of: *Internal carotid artery * Supratrochlear * Supraorbital
  • External carotid artery
    • Superficial temporal
    • Posterior auricular
    • Occipital

Internal Cranial Landmarks

• Bones: Ethmoid, Frontal, Occipital, Parietal, Sphenoid, Temporal
• Ethmoid bone
  • Crista galli of ethmoid bone
  • Cribriform plate of ethmoid bone
  • Ethmoidal spine
  • Ethmoidal foramina: Anterior, Posterior
• Frontal bone
  • Frontal crest
  • Orbital part of frontal bone
• Sphenoid bone
  • Limbus of sphenoid
  • Prechiasmatic sulcus
  • Tuberculum sellae
  • Hypophysial fossa
  • Posterior clinoid process
  • Dorsum sellae
  • Lesser wing of sphenoid bone
  • Optic canal
  • Sphenoidal crest
  • Superior orbital fissure
  • Anterior clinoid process
  • Foramen rotundum
  • Carotid groove
  • Foramen ovale
  • Foramen spinosum
  • Greater wing of sphenoid bone
• Temporal bone
  • Superior border of petrous part
  • Groove for greater petrosal nerve
  • Opening of internal acoustic meatus
  • Groove for sigmoid sinus
  • Groove for transverse sinus
• Occipital bone
  • Foramen magnum
  • Internal occipital crest
  • Internal occipital protuberance
  • Hypoglossal canal
  • Clivus
• Foramen cecum
  *Note: The internal carotid artery and its accompanying sympathetic and venous plexuses actually pass horizontally across (rather than vertically through) the area of the foramen lacerum, an artifact of dry crania, which is closed by cartilage in life.

Cranial Nerves

• Olfactory nerves (CNI)
• Olfactory Bulb
• Olfactory Tract
• Optic nerve (CN II)
• Oculomotor nerve (CN III)
• Trochlear nerve (CN IV)
• Trigeminal nerve (CN V)
  • Ophthalmic nerve (CN V₁)
  • Maxillary nerve (CN V2)
  • Mandibular nerve (CN V3)
  • Trigeminal ganglion
• Abducent nerve (CN VI)
• Facial nerve (CN VII)
• Vestibulocochlear nerve (CN VIII)
• Glossopharyngeal nerve (CN IX)
• Vagus nerve (CN X)
• Spinal accessory nerve (CN XI)
• Hypoglossal nerve (CN XII)

Arteries and Sinuses

• Internal carotid artery
• Basilar artery
• Vertebral artery
• Middle meningeal artery
• Superior petrosal sinus
• Sigmoid sinus
• Transverse sinus
• Superior sagittal sinus
• Inferior sagittal sinus

Review Questions

1. Which of the following is NOT a cranial landmark?
   • A. Asterion
   • B. Pterion
   • C. Inion
   • D. Corion
2. Which of the following is NOT associated with the sphenoid bone?
   • A. foramen spinosum
   • B. optic canal
   • C. pterygoid canal
   • D. foramen rotundum
   • E. carotid canal
3. Which of the following is NOT associated with the temporal bone?
   • A. stylomastoid foramen
   • B. internal acoustic meatus
   • C. jugular foramen
   • D. carotid canal
4. Which two sinuses are found within the longitudinal fissure?
   • A. transverse sinus and straight sinus
   • B. inferior sagittal and superior sagittal sinus
   • C. sigmoid sinus and cavernous sinus
   • D. there are no sinuses within the longitudinal fissure