Skull Cavities and Cranial Fossae

Skull Cavities and Fossae

• Consist of boundaries, contents, and connections
• Includes the orbital, nasal, paranasal sinuses, oral, temporal, infratemporal, pterygopalatine, and retromandibular cavities/fossae
• Contain openings and canals through which cranial nerves pass
• The skull consists of major cavities, each serving a specific function.

Cranial Cavity (Endocranium)

• Location: Houses the brain
• Boundaries include:
  • Roof (Calvaria): Made of frontal, parietal, and occipital bones
  • Floor (Cranial base): Made of ethmoid, sphenoid, temporal, and occipital bones
• Divisions:
  • Anterior, middle, and posterior cranial fossae
• Contents:
  • Brain (cerebrum, cerebellum, brainstem)
  • Meninges (dura, arachnoid, pia mater)
  • Cranial nerves (CN I–XII)
  • Major blood vessels (Circle of Willis)

Orbital Cavities (Orbits)

• Location: Bilateral cavities housing the eyes
• Boundaries include:
  • Roof: Frontal bone, lesser wing of sphenoid
  • Floor: Maxilla, palatine, zygomatic bones
  • Medial Wall: Ethmoid, lacrimal, sphenoid, frontal bones
  • Lateral Wall: Zygomatic and sphenoid bones
• Contents:
  • Eyeball
  • Optic nerve (CN II)
  • Six extraocular muscles
  • Lacrimal gland (tears)
• Connections:
  • Optic canal connects to the cranial cavity, transmitting the optic nerve and ophthalmic artery
  • Superior orbital fissure connects to the middle cranial fossa, transmitting CN III, IV, V1, and VI
  • Inferior orbital fissure connects to the pterygopalatine fossa
• The orbital cavity is a pyramidal bony structure that houses the eye and associated structures
• Boundaries:
  • Apex: Optic canal in the sphenoid bone
  • Lateral wall: Zygomatic and greater wing of sphenoid
  • Medial wall: Ethmoid, lacrimal, sphenoid, frontal bones
  • Floor: Maxilla, palatine bone, zygomatic bone
  • Roof: Frontal bone, lesser wing of sphenoid
• Muscles found: Six extraocular muscles (Superior, Inferior, Medial, and Lateral Rectus; Superior and Inferior Oblique)
• Nerves: Optic nerve (CN II), Oculomotor nerve (CN III), Trochlear nerve (CN IV), Abducent nerve (CN VI), and Ophthalmic nerve (CN V1)
• Blood supply comes from the ophthalmic artery, a branch of the ICA
• Lacrimal gland also exists within the contents
• Connections:
  • Superior orbital fissure connects to the middle cranial fossa, transmitting CN III, IV, V1, VI, and the superior ophthalmic vein
  • Inferior orbital fissure connects to Infratemporal and pterygopalatine fossae and transmits CN V2 branches
  • Nasolacrimal duct connects to inferior meatus of nasal cavity
• Orbital fractures may affect the openings causing diplopia, ptosis, and facial anesthesia

Nasal Cavity

• Location: Midline cavity for respiration and olfaction
• Boundaries include:
  • Roof: Cribriform plate of the ethmoid; frontal bone; sphenoid bones
  • Floor: Maxilla, palatine bones
  • Medial Wall (Septum): Vomer, perpendicular plate of ethmoid
  • Lateral Wall: Maxilla, ethmoid, inferior nasal concha, palatine
• Contents:
  • Nasal mucosa
  • Olfactory nerve endings (CN I)
  • Paranasal sinuses (frontal, ethmoid, sphenoid, maxillary)
  • Olfactory epithelium (CN I fibers)
  • Mucosa for air filtration
  • Paranasal sinus openings
  • Nasal turbinates (conchae) to warm and humidify air
• Connections:
  • Cribriform plate (ethmoid) connects to the cranial cavity, transmitting CN I
  • Nasolacrimal duct connects to the orbit, draining tears into the nasal cavity
  • Choanae connects to the nasopharynx
  • Sinus openings into meatuses
• The nasal cavity connects to the anterior cranial fossa via Cribriform plate (ethmoid) (CN I)
• Nasolacrimal duct connects to the orbit and drains tears into nasal cavity
• Nasolacrimal duct to inferior meatus
• Choanae to the nasopharynx

Paranasal Sinuses

• Air-filled spaces that lighten the head and enhance voice resonance
  • Frontal sinus connects to the middle meatus via the frontonasal duct
  • Anterior ethmoidal sinus connects to the middle meatus
  • Posterior ethmoidal sinus connects to the superior meatus
  • Sphenoidal sinus connects to the sphenoethmoidal recess
  • Maxillary sinus connects to the middle meatus via the semilunar hiatus
• Maxillary sinus and Frontal sinus infections:
  • Maxillary sinus infections are common due to drainage against gravity
  • Frontal sinus infections can lead to meningitis via the cribriform plate

Oral Cavity

• Responsible for ingestion, mastication, and articulation
• Boundaries include:
  • Roof: Hard and soft palate
  • Floor: Mylohyoid and geniohyoid muscles
  • Lateral walls: Cheeks (buccinator muscle)
• Contents:
  • Tongue, teeth, salivary glands (parotid, submandibular, sublingual)
  • Cranial nerves (V3, VII, IX, XII)
• Connections:
  • Oropharyngeal isthmus connects to the oropharynx
  • Pterygomandibular raphe communicates with lateral pharyngeal spaces
  • Oropharynx connects to the digestive tract
  • Pterygomandibular raphe connects to the lateral pharyngeal space

Middle Ear (Tympanic Cavity)

• Location: Petrous part of the temporal bone
• Contents:
  • Ossicles (malleus, incus, stapes)
  • Tympanic membrane
  • Eustachian tube (pharyngotympanic tube)
• Connections:
  • Mastoid air cells connect to the mastoid antrum
  • Eustachian tube connects to the nasopharynx

Paranasal Sinuses

• Frontal, ethmoidal, sphenoidal, and maxillary sinuses communicate with the nasal cavity

Anterior Cranial Fossa

• Boundaries include:
  • Anterior: Frontal bone
  • Middle: Lesser wing of the sphenoid
  • Posterior: Sphenoid ridge
• Contents:
  • Frontal lobes of the brain
  • Olfactory bulb (CN I)
• Connections:
  • Cribriform plate connects to the nasal cavity, transmitting the olfactory nerve

Middle Cranial Fossa

• Boundaries include:
  • Anterior: Lesser wing of the sphenoid
  • Posterior: Petrous part of the temporal bone
• Contents:
  • Temporal lobes of the brain
  • Pituitary gland (sits in the sella turcica)
  • Cranial nerves (CN II, III, IV, V, VI)
• Connections:
  • Optic canal connects to the orbit, transmitting the optic nerve and ophthalmic artery
  • Superior orbital fissure connects to the orbit, transmitting CN III, IV, V1, and VI
  • Foramen rotundum connects to the pterygopalatine fossa, transmitting CN V2
  • Foramen ovale connects to the infratemporal fossa, transmitting CN V3
  • Foramen spinosum transmits the middle meningeal artery

Posterior Cranial Fossa

• Boundaries include:
  • Anterior: Petrous temporal bone
  • Posterior: Occipital bone
• Contents:
  • Cerebellum, brainstem
  • Cranial nerves (CN VII–XII)
• Connections:
  • Internal acoustic meatus connects to the inner ear, transmitting CN VII and VIII
  • Jugular foramen connects to the neck, transmitting CN IX, X, XI, and the internal jugular vein
  • Hypoglossal canal connects to the neck, transmitting CN XII
  • Foramen magnum connects to the spinal cord

Pterygopalatine Fossa

• Boundaries include:
  • Anterior: Maxilla
  • Posterior: Pterygoid process of sphenoid
  • Medial: Palatine bone
• Contents:
  • Pterygopalatine ganglion (parasympathetic fibers for lacrimation)
  • Maxillary artery and nerve (CN V2)
• Connections:
  • Foramen rotundum connects to the middle cranial fossa, transmitting CN V2
  • Inferior orbital fissure connects to the orbit
  • Sphenopalatine foramen connects to the nasal cavity
• Contents
  • Pterygopalatine ganglion (parasympathetic)
  • Maxillary artery
• Foramen rotundum connects to the middle cranial fossa, transmitting CN V2

Infratemporal Fossa

• Location: Below and medial to the zygomatic arch
• Boundaries include:
  • Superior: Infratemporal surface of sphenoid
  • Inferior: Medial pterygoid muscle
  • Lateral: Ramus of mandible
  • Medial: Lateral pterygoid plate
• Contents:
  • Muscles of mastication (medial/lateral pterygoid, part of temporalis)
  • Mandibular nerve (CN V3)
  • Maxillary artery
  • Otic ganglion (parasympathetic to parotid gland)
• Connections:
  • Foramen ovale connects to the middle cranial fossa, transmitting CN V3
  • Pterygomaxillary fissure connects to the pterygopalatine fossa
• Contents
  • Muscules of mastication
  • Mandibular nerve (CN V3)
  • Maxillary artery
• Foramen ovale connects to the middle cranial fossa, transmitting CN V3

Temporal Fossa

• A shallow depression on the lateral skull
• Boundaries include:
  • Superior: Temporal lines
  • Inferior: Zygomatic arch
  • Medial: Skull bones (frontal, parietal, sphenoid, temporal)
  • Lateral: Temporalis fascia
• Contents:
  • Temporalis muscle (for mastication)
  • Superficial temporal artery
  • Deep temporal nerves (CN V3 branches)

Retromandibular space (Retromandibular Fossa)

• Location: Behind the ramus of the mandible
• Boundaries Include:
  • Anterior: Ramus of mandible
  • Posterior: Mastoid process
  • Superior: External acoustic meatus
  • Inferior: Angle of mandible
• Contents:
  • Parotid gland (largest salivary gland)
  • Retromandibular vein
  • Facial nerve (CN VII) branches
• Connections: Communicates with the parapharyngeal space, allowing infections to spread to deeper neck regions

Openings and Canals of the Skull

• Each opening has specific boundaries, locations, and transmitted structures.
• Fracture of the cribriform plate can lead to CSF rhinorrhea (leakage of cerebrospinal fluid through the nose)
• Superior orbital fissure syndrome results from compression of CN III, IV, V1, and VI, leading to ophthalmoplegia and loss of corneal reflex
• Foramen spinosum injury can lead to epidural hematoma due to rupture of the middle meningeal artery
• Jugular foramen syndrome leads to dysfunction of CN IX, X, and XI, causing hoarseness, difficulty swallowing, and weakness of the trapezius and sternocleidomastoid muscles
• Foramen magnum herniation can compress the brainstem, leading to respiratory arrest.

Cranial Nerve Passage Through Skull Foramina

• CN I (Olfactory) passes through the Cribriform plate
• CN II (Optic) passes through the Optic canal
• CN III (Oculomotor) passes through the Superior orbital fissure
• CN IV (Trochlear) passes through the Superior orbital fissure
• CN V1 (Ophthalmic division of Trigeminal) passes through the Superior orbital fissure
• CN V2 (Maxillary division of Trigeminal) passes through the Foramen rotundum
• CN V3 (Mandibular division of Trigeminal) passes through the Foramen ovale
• CN VI (Abducens) passes through the Superior orbital fissure
• CN VII (Facial) passes through the Internal acoustic meatus → Stylomastoid foramen
• CN VIII (Vestibulocochlear) passes through the Internal acoustic meatus
• CN IX (Glossopharyngeal) passes through the Jugular foramen
• CN X (Vagus) passes through the Jugular foramen
• CN XI (Accessory) passes through the Jugular foramen
• CN XII (Hypoglossal) passes through the Hypoglossal canal </existing_notes>