Rad 270
Skull 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
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Frontal
Occipital
R. parietal
L. parietal
• Floor
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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
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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
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–
–
–
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Squamous portion
Tympanic portion
Styloid process
Zygomatic process
Petromastoid portion which contain the organs
for hearing and equilibrium
Skull Topography
Be able to locate the following landmarks:
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•
•
•
•
•
Glabella
Inner canthus
Outer canthus
Nasion
Infraorbital margin
Acanthion
• Gonion
• Mental point
• External auditory meatus
(EAM)
• Auricular point
• Top of ear attachment
(TEA)
Hyposthenic/Asthenic Patients
Hypersthenic Patients
Essential Projections: Cranium
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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