Anatomy of the Lateral Skull Fossae and Temporomandibular Joint

Anatomy of the Temporal Fossa, Infratemporal Fossa, Pterygopalatine Fossa & Temporomandibular Joint

• Lecturer: Dr. Ahmed Yaqinuddin MD PhD.
• Department: Anatomy | Faculty of Medicine.
• Duration: $50\,min$.
• Core Objective: Understanding the architecture of the lateral skull as a foundation for dental, maxillofacial, and neurosurgical practice.

Learning Objectives

• Define and describe the boundaries and contents of the temporal, infratemporal, and pterygopalatine fossae.
• Identify the four principal muscles of mastication, including their attachments, actions, and innervation.
• Describe the structure, ligaments, and movements of the temporomandibular joint (TMJ).
• Explain the distribution of the mandibular nerve ($V3$) and maxillary artery within the infratemporal fossa.
• Describe the contents and communications of the pterygopalatine fossa.
• Apply anatomical knowledge to clinical scenarios (e.g., TMJ disorders, mandibular dislocation, and nerve blocks).

Lecture Road Map

• Section 1: Temporal Fossa (~$8\,min$): Boundaries, contents, temporalis muscle, and the pterion.
• Section 2: Infratemporal Fossa (~$12\,min$): Boundaries, contents, $V3$, maxillary artery, and pterygoid muscles.
• Section 3: Pterygopalatine Fossa (~$8\,min$): Boundaries, communications, contents, and the pterygopalatine ganglion.
• Section 4: Temporomandibular Joint (~$12\,min$): Structure, disc, ligaments, movements, and the masticatory cycle.
• Section 5: Clinical Correlations (~$10\,min$): Trismus, TMJ dislocation, TMJ syndrome, and Frey's syndrome.

Section 1: The Temporal Fossa

• Definition: A shallow depression on the lateral surface of the skull, situated above the zygomatic arch. It is the most superficial of the three fossae.
• Primary Function: Serves as the origin for the temporalis muscle.
• Boundaries:
  • Superior & Posterior: Superior and inferior temporal lines on the parietal and frontal bones.
  • Anterior: Frontal process of the zygomatic bone and the zygomatic process of the frontal bone.
  • Inferior: Zygomatic arch and the infratemporal crest of the greater wing of the sphenoid.
  • Floor: Parts of the frontal, parietal, temporal, and greater wing of the sphenoid bones (the pterion region).
  • Roof: Temporal fascia (heavy deep fascia overlying the temporalis muscle).
• Content Detail:
  • Temporalis Muscle: Fan-shaped; arises from the floor and fascia; inserts onto the coronoid process of the mandible.
  • Deep Temporal Nerves: Anterior and posterior branches from the anterior trunk of $V3$.
  • Deep Temporal Arteries: Anterior and posterior branches of the maxillary artery.
  • Temporal Fascia: Attaches superiorly to the temporal line and splits inferiorly to attach to the inner and outer lips of the zygomatic arch.
• The Pterion Clinical Pearl:
  • Anatomy: The thinnest part of the lateral skull where the frontal, parietal, temporal, and sphenoid bones meet.
  • Significance: The middle meningeal artery runs in a groove deep to this point. A fracture to the pterion can rupture this artery, leading to an extradural (epidural) haematoma, which is a neurosurgical emergency.

Section 2: The Infratemporal Fossa (ITF)

• Definition: An irregularly shaped space deep to the ramus of the mandible and medial to the zygomatic arch.
• Key Concept: The Absence of a Floor: The ITF has no physical floor; it is open inferiorly and communicates freely with the neck.
• Clinical Significance of "No Floor":
  • Dental abscesses (from lower third molars) can spread into the parapharyngeal space.
  • Infection can track to the retropharyngeal space, potentially causing airway compromise (Ludwig's angina).
• Boundaries of the ITF:
  • Roof: Infratemporal surface of the greater wing of the sphenoid and the infratemporal crest.
  • Anterior: Posterior (infratemporal) surface of the maxilla.
  • Medial: Lateral pterygoid plate of the sphenoid bone.
  • Lateral: Medial surface of the ramus of the mandible.
  • Posterior: Styloid process, its associated muscles, and the parotid gland.
• Communications:
  • Superiorly: To the temporal fossa (deep to the zygomatic arch).
  • Medially: To the pterygopalatine fossa (via the pterygomaxillary fissure).
  • Superiorly/Anteriorly: To the orbit (via the inferior orbital fissure).
• Contents of the ITF:
  • Muscles: Lateral pterygoid, medial pterygoid, and the lower portion of the temporalis tendon.
  • Arteries: Maxillary artery (terminal branch of ECA), middle meningeal artery, inferior alveolar artery, deep temporal arteries.
  • Veins: Pterygoid venous plexus.
  • Nerves:
    • Mandibular nerve ($V3$): Exits via foramen ovale.
    • Inferior alveolar nerve: Supplies mandibular teeth; exits at mental foramen as the mental nerve.
    • Lingual nerve: General sensation to the anterior $2/3$ of the tongue.
    • Buccal nerve: Sensory only to the cheek mucosa.
    • Chorda tympani ($CN\,VII$): Joins the lingual nerve for taste and parasympathetics.
    • Nerve to mylohyoid: Motor to the mylohyoid and anterior belly of digastric.
    • Auriculotemporal nerve: Supplies the ear, TMJ, and carries parasympathetics to the parotid.
    • Otic Ganglion: Parasympathetic relay to the parotid gland.

Section 3: The Mandibular Nerve ($V3$)

• Nature: The largest division of the Trigeminal nerve ($CN\,V$); it is a mixed nerve (sensory and motor).
• Exit: Skull base via foramen ovale to enter the ITF.
• Anterior Trunk (Mainly Motor):
  • Motor Branches: Deep temporal nerves, masseteric nerve, and nerve to lateral pterygoid.
  • Sensory Branch: Buccal nerve (supplies cheek mucosa).
• Posterior Trunk (Mainly Sensory):
  • Auriculotemporal Nerve: Wraps around the neck of the mandible; supplies temporal skin and ear; carries postganglionic parasympathetics from the otic ganglion to the parotid gland.
  • Lingual Nerve: Supplies general sensation to the anterior $2/3$ of the tongue. Chorda tympani ($CN\,VII$) joins it to carry taste and preganglionic parasympathetics to the submandibular ganglion.
  • Inferior Alveolar Nerve: Enters the mandibular foramen and travels the mandibular canal to supply lower teeth. Exits as the mental nerve supplying the chin and lower lip skin.
• Proprioception: $V3$ carries proprioceptive info from muscles of mastication to the brainstem to determine the force of the bite.

Section 4: The Maxillary Artery

• Origin: Terminal branch of the external carotid artery (ECA).
• Division into Three Parts:
  • 1st Part (Mandibular): Medial to the neck of the mandible. Branches include the deep auricular, anterior tympanic, middle meningeal (enters foramen spinosum), accessory meningeal, and inferior alveolar.
  • 2nd Part (Pterygoid): Located among the pterygoid muscles. Branches include deep temporal (anterior/posterior), pterygoid, masseteric, and buccal arteries.
  • 3rd Part (Pterygopalatine): Located in the pterygopalatine fossa. Branches include posterior superior alveolar, infraorbital, descending palatine, sphenopalatine (primary nasal supply), pharyngeal, and the artery of the pterygoid canal.

Section 5: The Pterygopalatine Fossa (PPF)

• Description: A small pyramidal space medial to the pterygomaxillary fissure, acting as an anatomical crossroads.
• Boundaries:
  • Anterior: Posterior surface of the maxilla.
  • Posterior: Anterior surface of the pterygoid process and greater wing of the sphenoid.
  • Medial: Perpendicular plate of the palatine bone.
  • Lateral: Open to the ITF via the pterygomaxillary fissure.
  • Superior: Orbital process of the palatine bone and the body of the sphenoid.
  • Inferior: Greater palatine canal.
• The Seven Communications:
  • Lateral: To Infratemporal fossa via Pterygomaxillary fissure.
  • Superior: To Orbit via Inferior orbital fissure.
  • Medial: To Nasal cavity via Sphenopalatine foramen.
  • Inferior: To Hard palate via Greater palatine canal.
  • Posterior (Nasopharynx): Via Palatovaginal canal.
  • Posterior (Middle Cranial Fossa): Via Foramen rotundum (transmits $V2$).
  • Posterior (Vidian Canal): Via Pterygoid canal (transmits Nerve of Pterygoid canal).
• Contents:
  • Maxillary Nerve ($V2$): Purely sensory. Branches into zygomatic, posterior superior alveolar, and infraorbital nerves.
  • Pterygopalatine Ganglion: Largest parasympathetic ganglion in the head. Preganglionic fibers arrive via the greater petrosal nerve ($CN\,VII$); postganglionic fibers supply the lacrimal gland and nasal/palatal mucosa.
  • Maxillary Artery (3rd Part): Terminal portion providing blood to the nasal cavity and palate.

Section 6: The Temporomandibular Joint (TMJ)

• Joint type: Synovial condylar joint.
• Articular Surfaces:
  • Mandibular condyle (head).
  • Mandibular (glenoid) fossa of the temporal bone.
  • Articular tubercle (primary load-bearing surface).
  • Important: Surfaces are covered in fibrocartilage, not hyaline cartilage.
• Intra-articular Disc: Biconcave fibrocartilage dividing the joint into two compartments:
  • Upper Compartment: Between the disc and temporal bone; facilitates gliding (translation).
  • Lower Compartment: Between the disc and mandibular condyle; facilitates rotation (hinge).
• Ligaments:
  • Lateral (Temporomandibular): Primary reinforcement; limits posterior displacement.
  • Sphenomandibular: Remnant of Meckel's cartilage; limits distraction of the condyle.
  • Stylomandibular: Accessory; limits excessive protrusion.
• Masticatory Cycle Phases:
  • Phase 1 (Opening): Lateral pterygoids pull condyle and disc anteriorly (translation in upper; rotation in lower).
  • Phase 2 (Closing): Masseter, temporalis, and medial pterygoid elevate the mandible.
  • Phase 3 (Power Stroke): End of closure; involves forward/downward/lateral elliptical arc to create shearing forces for grinding.

Section 7: Final Summary of Muscles of Mastication

• Principal Muscles (Innervated by $V3$):
  • Temporalis: Elevation (anterior fibers) and Retraction (posterior fibers).
  • Masseter: Elevation (jaw closing). Most powerful.
  • Medial Pterygoid: Elevation and side-to-side movement. Forms a "pterygoid sling" with the masseter.
  • Lateral Pterygoid: Protrusion and Depression (opening). It is the only principal muscle that opens the jaw.
• Accessory Muscles (Suprahyoids):
  • Mylohyoid: Elevates floor of mouth; assists depression (innervated by $V3$).
  • Digastric (Anterior belly): Depresses mandible (innervated by $V3$).
  • Digastric (Posterior belly): Elevates hyoid (innervated by $CN\,VII$—2nd arch origin).
  • Geniohyoid: Depresses mandible (innervated by $C1$ fibers via $CN\,XII$—not $V3$!).

Section 8: Clinical Scenarios

• Clinical Scenario 1: Trismus:
  • Patient has difficulty opening mouth (only $5\,mm$ compared to normal $>40\,mm$) after wisdom tooth extraction.
  • Mechanism: Refractive spasm of medial/lateral pterygoids and masseter due to infection spreading from the tooth socket into the infratemporal fossa.
• Clinical Scenario 2: Anterior Dislocation:
  • Mandibular condyles move anteriorly past the articular tubercle.
  • Sign: Bilateral preauricular hollowing.
  • Reduction: Hippocratic method (downward pressure on molars to disengage condyles from tubercle).
• Clinical Scenario 3: TMJ Syndrome:
  • Facet of internal derangement where the disc is displaced (usually anteriorly).
  • Symptoms: Clicking/locking and referred ear pain.
  • Explanation: Ear pain occurs because the auriculotemporal nerve supplies both the joint and the external ear.
• Clinical Scenario 4: Frey's Syndrome:
  • Gustatory sweating (sweating while eating) following parotidectomy.
  • Mechanism: Damage to the auriculotemporal nerve leads to aberrant re-innervation. Parasympathetic fibers intended for the parotid gland instead re-innervate cutaneous sweat glands.
• The Edentulous Mandible:
  • Loss of teeth causes resorption of the alveolar process.
  • The mental foramen appears to move superiorly, potentially placing the mental nerve at risk of compression by dentures.