Skull Anatomy Overview

Skull Anatomy

• Comprised of 22 bones separated into two groups:
  • Cranial bones: 8 bones
  • Facial bones: 14 bones

Cranial Bones

• Divided into two categories:
  • Calvaria: The roof of the skull
  • Floor: The base of the skull

Facial Bones

• Have anterior and lateral aspects

Orbits

• Each orbit is formed by seven bones:
  • Frontal bone
  • Sphenoid bone
  • Ethmoid bone
  • Maxilla bone
  • Zygoma bone
  • Lacrimal bone
  • Palatine bone

Paranasal Sinuses

• Air-filled cavities within the skull

Skull Topography (Landmarks)

• Key landmarks include:
  • Glabella
  • Inner canthus
  • Outer canthus
  • Nasion
  • Infraorbital margin
  • Acanthion
  • Gonion
  • Mental point
  • External acoustic meatus (EAM)
  • Auricular point
  • Top of ear attachment (TEA)

Radiographic Reference Lines

• Essential lines used in positioning and image interpretation:
  • Orbitomeatal line (OML)
  • Infraorbital line (IOML)
  • Glabellomeatal line (GML)
  • Interpupillary line (IPL)
  • Acanthiomeatal line (AML)
  • Mentomeatal line (MML)

Facial Lines

• Lines used for facial imaging:
  • Supraorbital margin
  • Interpupillary line
  • Infraorbital margin
  • Median sagittal plane
  • Orbitomeatal baseline (OMBL)

General Body Position for Cranial Imaging

• Both recumbent (table) and upright positions are used
• Body type may influence positioning to prevent MSP tilting:
  • Hyposthenic/asthenic patients require chest support
  • Hypersthenic patients require head support

Essential Cranial Radiographic Projections

• Multiple projections are required to visualize bone structures:
  • PA or PA axial (Caldwell method): Fractures, tumors, metastasis, Paget disease
  • PA axial (Haas method): Frontal sinus and ethmoid sinuses
  • AP axial: Base of skill, foramen magnum
  • AP axial (Towne method): Fractures of the occipital bone
  • Lateral: Right or left lateral to view skull profile, dorsal decubitus to view foramen magnum
  • Submento vertical (SMV): Cranial base
  • Anteroposterior (AP): Used for sinuses
  • Posteroanterior (PA): Used for sinuses

PA or PA Axial (Caldwell Method) Positioning

• Patient: Seated erect or prone with MSP centered on midline of grid
• Part: Head resting on table or upright Bucky, OML perpendicular to IR, MSP perpendicular to IR
• Central Ray (CR): 15-degree caudal angle, exits at Nasion
• Collimation: 10 X 12 inches (24 X 30 cm)
• Lead Shields: Use to protect sensitive areas

PA or PA Axial (Caldwell Method) Evaluation Criteria

• Image quality: ID, date, side marker visible, proper collimation, entire cranium without rotation or tilt, symmetric petrous ridges, MSP aligned with collimated field, orbits filled by petrous ridges, petrous pyramids in lower third of orbits, three distinct tables of squamous bone, penetration of frontal bone

Explore the fascinating structure of the skull, which includes 22 bones divided into cranial and facial categories. This quiz covers the details of cranial and facial bones, the orbits, paranasal sinuses, and key landmarks, along with essential radiographic reference lines used in interpretation. Test your knowledge on this critical aspect of human anatomy!