Study Notes on Skull Anatomy and Facial Bones

Chapter 11: Cranium, Facial Bones, and Paranasal Sinuses

Part A: Overview of Skull Anatomy

  • The skull consists of two main parts:

    • Cranium: Composed of 8 bones.

    • Facial bones: Composed of 14 bones.

  • Pathology related to the skull can be studied on pages 402 and 403 of the referenced material.

Skull Anatomy

  • Cranial Bones:

    • Total of 8 bones, including:

      • Frontal

      • Parietal (Right and Left)

      • Temporal (Right and Left)

      • Occipital

      • Ethmoid

      • Sphenoid

    • The cranial anatomy is viewed from both frontal and lateral perspectives.

  • Cranial Skullcap (Calvaria): 4 bones which make up the skullcap include:

    • Frontal

    • Right Parietal

    • Left Parietal

    • Occipital

Frontal Bone

  • Articulates with 4 other bones.

  • Contains the supraorbital groove, a slight depression found above each eyebrow.

Parietal and Occipital Bones

  • Parietal Bone: Articulates with 5 other bones.

  • Occipital Bone: Articulates with 6 other bones, located at the back of the skull.

  • The parietal tubercles are located at the widest portion of the cranium.

Occipital Bone

  • Notable features:

    • Foramen magnum: Opening for spinal cord.

    • Occipital condyles: Form a joint with the first cervical vertebra (atlanto-occipital joint).

    • External occipital protuberance (inion): The prominence at the back of the skull.

Temporal Bone

  • Lateral View:

    • Contains several parts:

      • Mastoid process

      • External acoustic meatus (EAM)

      • Styloid process

    • Houses organs critical for hearing and equilibrium.

  • Vulnerability to Fractures: Most fragile area of the skull.

Sphenoid Bone

  • Notable features:

    • The sella turcica, which contains the pituitary gland.

    • Articulates with multiple cranial bones, providing structural importance.

    • Contains foramen ovale, through which the mandibular nerve runs, often accessed surgically.

Ethmoid Bone

  • Located between the eye sockets, articulates with various cranial and facial bones.

  • Key features:

    • Crista galli: The vertical midline bony ridge.

    • Cribriform plate: Contains foramina for olfactory nerves.

    • Nasal conchae: Scroll-like projections mixing air in the nasal cavity.

Cranial Sutures and Junction Points

  • Cranial Sutures:

    • Coronal

    • Lambdoidal

    • Squamosal

    • Sagittal

  • Junction Points:

    • Asterion

    • Bregma

    • Lambda

    • Pterion

  • Wormian bones: Small irregular bones in sutures, mainly in the lambdoidal suture.

Infant Cranial Sutures and Fontanels

  • Six fontanels covered by membrane, including:

    • Anterior (last to close at 18 months)

    • Posterior

    • Right and left sphenoid

    • Right and left mastoid

Anatomy Review of Projections

  • Various anatomical projections, such as:

    • AP Axial Projection

    • Lateral Projection

    • PA Caldwell Projection

Anatomy of Organs of Hearing and Equilibrium

  • External Ear:

    • Auricle (Pinna), External Acoustic Meatus, and Tympanic Membrane.

  • Middle Ear:

    • Communicates with the nasopharynx through the Eustachian Tube, which equalizes pressure and provides a pathway for pathogens.

  • Auditory Ossicles:

    • Malleus (hammer)

    • Incus (anvil)

    • Stapes (stirrup)

  • Internal Ear:

    • Responsible for hearing (Cochlea) and balance (Semicircular canals).

Paranasal Sinuses Anatomy

  • Groups of sinuses include:

    • Frontal

    • Ethmoid

    • Sphenoid

    • Maxillary (antrum of Highmore)

    • Sinuses communicate with the nasal cavity.

  • Maxillary Sinuses: Positioned above upper teeth; unique because they are not housed in cranial bones.

  • Frontal Sinuses: Location varies, rarely symmetric, might be absent in some individuals.

  • Ethmoid Sinuses: Found in the lateral masses and communicate with other sinuses.

  • Sphenoid Sinus: Located near the sella turcica, can indicate fractures if air-fluid levels are present.

Current and Historical Perspectives

  • CT of Sinuses: Most efficient in coronal view for evaluation of sinus conditions.

Quiz Questions for Review

  • Identifying cranial bones, articulations, and anatomical landmarks based on provided descriptions and visual references.

Facial Bones

  • Total of 14 bones, including:

    • Maxilla

    • Zygoma

    • Nasal

    • Lacrimal

    • Palatine

    • Mandible

  • Maxilla: Articulates with 2 cranial and 7 facial bones; houses upper teeth.

  • Mandible: Largest facial bone; only movable bone in skull; includes ramus, body, and mentum.

  • Temporomandibular Joint (TMJ): Joint formed by temporal bone and mandibular condyle.

  • Sutural or wormian bones: Irregular bones found in some sutures of the skull.

Clinical Considerations

  • Blowout fractures and Tripod fractures: Injuries to the orbit that can be evaluated through imaging techniques.