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 Floor Frontal Occipital R. parietal L. parietal 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 Brachycephalic skull 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

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 Be able to locate the following landmarks: Gonion Mental point External auditory meatus (EAM) Auricular point Top of ear attachment (TEA) Glabella Inner canthus Outer canthus Nasion Infraorbital margin Acanthion

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 Part position CR 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

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