Rad 270Skull Lecture

Skull Anatomy

• Comprised of 22 separate bones divided into two groups:– Cranial bones – 8– Facial bones – 14

• Cranial bones further subdivided into – Calvaria – Floor

Cranial Bones• Calvaria

– Frontal

– Occipital

– R. parietal

– L. parietal

• Floor– Ethmoid

– Sphenoid

– R. temporal

– L. temporal

Skull Anatomy

• Sutures = fibrous joints that connect the bones of the skull– Coronal = between frontal and parietal bones

– Sagittal = on top of head between two parietal bones

– Squamosal = between temporal bone and the parietal bones

– Lambdoidal = between occipital and the parietal bones

Skull Morphology

• Typical skull = mesocephalic– Petrous pyramids project anteriorly and

medially at angle of 47 degrees from MSP

• Brachycephalic skull

– Petrous pyramids project anteriorly and medially at angle of 54 degrees from MSP

– Short from front to back, broad from side to side, and shallow from vertex to base

Skull Morphology

• Dolichocephalic skull– Petrous pyramids project anteriorly and

medially at angle of 40 degrees from MSP– Long from front to back, narrow from side to

side, and deep from vertex to base

• Asymmetry of outer features should be noted while positioning; for example, the nose may not always be in the midline

Slide 8

Frontal Bone

• Landmarks to note– Frontal eminences– Supraorbital margins– Supraciliary arches– Supraorbital foramina– Glabella

Ethmoid Bone

• Consists of – Horizontal plate– Vertical plate– Two light, spongy masses = labyrinths

Parietal Bones

• Somewhat square-shaped

• Have a convex external surface and concave internal surface

• Parietal eminence = prominent bulge near center of external surface of each bone– This is the point where the width of the skull

should be measured to set technique

Sphenoid Bone

• Irregular, wedge-shaped bone that resembles a bat (somewhat)

• Located in base of cranium anterior to temporal bones and basilar portion of occipital

Occipital Bone

• Situated at posteroinferior part of cranium

• Forms posterior half of cranial base and greater portion of posterior cranial fossa

• Has four parts– Squama– Two occipital condyles– Basilar portion

Temporal Bones

• Consist of – Squamous portion– Tympanic portion– Styloid process– Zygomatic process– Petromastoid portion which contain the organs

for hearing and equilibrium

Skull Topography

• Glabella

• Inner canthus

• Outer canthus

• Nasion

• Infraorbital margin

• Acanthion

• Gonion

• Mental point

• External auditory meatus (EAM)

• Auricular point

• Top of ear attachment (TEA)

Be able to locate the following landmarks:

Hyposthenic/Asthenic Patients

Hypersthenic Patients

Essential Projections: Cranium• Lateral • PA• PA axial (Caldwell method)• AP• AP axial• AP axial (Towne method)• PA axial (Haas method)• Submentovertical (SMV)

– For cranial base

Lateral Projection• Patient position

– Seated upright or semiprone

• Part position– MSP of head parallel to IR– IPL perpendicular– IOML parallel to transverse axis of cassette

• CR– Perpendicular to center of IR– Enters 2 superior to EAM

Lateral Projections

• Entire cranium without rotation or tilt• Superimposed orbital roofs and greater

wings of sphenoid• Superimposed mastoid regions and EAMs• Superimposed TMJs• Sella turcica in profile• Penetration of parietal region• No overlap of C-spine by mandible

PA/PA Axial (Caldwell)

• Patient position– Seated erect or prone– MSP centered to midline – Forehead and nose resting on table or upright

Bucky

• Part position– OML perpendicular to IR plane – MSP perpendicular to IR– IR centered to nasion

PA/PA Axial (Caldwell)

• CR for PA projection– Perpendicular– Exits nasion

• CR for PA axial (Caldwell)– Angled 15 degrees caudad– Exits nasion

PA Projection• Entire cranial perimeter showing three tables of

squamous bone

• No rotation– Equal distance from lateral borders of skull to

lateral border of orbits– Symmetric petrous ridges

• Petrous ridges fill orbits

• Penetration of frontal bone without excessive density at lateral borders of skull

PA Axial (Caldwell Method)

• Same as for PA projection, except– Petrous ridges demonstrated in lower one

third of orbit

AP/AP Axial Projection

• Same as PA and PA axial projections

• Anatomy more magnified in AP and AP axial projections

AP Axial (Towne Method)• Patient and part position

– Supine or seated erect

– MSP centered to midline

– MSP perpendicular

– OML or IOML perpendicular

• IR top border level with skull vertex

• IR center at or near foramen magnum

• CR

– Directed through foramen magnum

– OML – 30 degrees caudal

– IOML – 37 degrees caudal

AP Axial (Towne Method)

• No rotation– Equal distance from lateral border of skull to

lateral margin or foramen magnum– Symmetric petrous ridges

• Dorsum sellae and posterior clinoid processes visible within foramen magnum

• Penetration of occipital bone without excessive density at parietals

PA Axial (Haas)

• Projection of dorsum sellae and posterior clinoid processes within foramen magnum

• Equal distance from lateral border of skull to lateral margin of foramen magnum

• Symmetric petrous pyramids

• Entire cranium

SMV Projection (Schüller)

• Patient position– Seated upright or supine– Torso elevated if supine

• Part position– MSP centered to midline– IOML parallel with IR– MSP perpendicular to IR

SMV Projection (Schüller)

• CR– Through sella turcica perpendicular to IOML– Enters MSP of throat between angles of

mandible– Passes through a point ¾ (1.9 cm) anterior to

level of EAM– Center IR to CR

SMV Projection (Schüller)• No rotation or tilt

– Equal distance from lateral border of skull to mandibular condyles

– Symmetric petrous pyramids

• Penetration sufficient to demonstrate structures of cranial base

• Superimposition of mental protuberance over anterior frontal bone, indicating full neck extension

• Mandibular condyles anterior to petrous pyramids

SMV Projection (Schüller)

• Superimposition of mental protuberance over frontal bone – indicates full neck extension

• Condyles of mandible anterior to petrous pyramids