Skull & Facial Bones Positioning Quizlet

Lateral skull

SID : 40 inches

Lateral skull

head position : MSP parallel to IR; IPL perpendicular to IR

Lateral skull

CR : Perpendicular, about 2 inches superior to the EAM

Lateral skull

breathing : Suspend respiration

Lateral skull

what should I see? : Entire cranium with sella turcica in profile

True lateral skull

positioning clue : Paired structures should be superimposed with no rotation

PA skull

head position : OML perpendicular to IR; MSP perpendicular to IR

PA skull

CR : Perpendicular and exits at the nasion

PA skull

what should I see? : Symmetric skull with petrous ridges projected high in the orbital region

AP axial Towne

CR angle : 30° caudad to the OML

AP axial Towne

CR entrance : About 2.5 inches (6 cm) superior to the glabella

Towne

if patient cannot tuck chin enough : Use IOML perpendicular to IR and increase CR angle to 37° caudad

Towne

what should I see? : Dorsum sellae and posterior clinoid processes projected within the foramen magnum

Towne

rotation check : Petrous pyramids should appear symmetric

Towne memory clue

30° DOWN → dorsum + posterior clinoids IN the foramen magnum

PA axial Caldwell

head position : OML perpendicular to IR

PA axial Caldwell

CR : 15° caudad and exits at the nasion

Caldwell

what should I see? : Petrous ridges in the lower one-third of the orbits

Caldwell memory clue

15° DOWN → petrous ridges DOWN into lower ⅓ of eyes

SMV / submentovertex

head position : Hyperextend the neck until the IOML is parallel to the IR

SMV

MSP : Perpendicular to the IR

SMV

CR : Perpendicular to the IOML and IR

SMV

what does it demonstrate? : Base of the skull and zygomatic arches

SMV memory clue

Head WAY back → looking up at the skull base

Lateral facial bones

head position : MSP parallel to IR; IPL perpendicular to IR

Lateral facial bones

CR : Perpendicular, centered near the zygoma midway between the outer canthus and EAM

Lateral facial bones

evaluation : Orbital roofs and mandibular rami should be superimposed; sella turcica in profile

Waters / parietoacanthial

tube angle : No tube angulation; CR is perpendicular

Waters

head position : Extend the chin until the MML is perpendicular to the IR

Waters

OML : About 37° to the IR

Waters

CR exit : Acanthion

Waters

nose-to-IR distance : About 0.75 inch (2 cm)

Waters

what should I see? : Maxillae, maxillary sinuses, and inferior orbital margins

Waters

petrous ridge position : Petrous ridges should be below the maxillary sinuses

Waters memory clue

Chin UP → petrous ridges DROP below maxillary sinuses

Modified Waters

OML : About 55° to the IR

Modified Waters

tube angle : No tube angulation; CR perpendicular

Modified Waters

CR exit : Acanthion

Modified Waters

best use : Orbital floors, especially suspected blowout fractures

Facial bones Caldwell

CR : 15° caudad, exiting the nasion

Facial bones Caldwell

what should I see? : Superior orbital margins and maxillae

Caldwell vs Waters

Caldwell = tube angled 15°; Waters = tube straight but head extended

Towne vs Caldwell

Towne = 30° caudad; Caldwell = 15° caudad

Waters vs SMV

Waters = chin extended; SMV = neck hyperextended much farther

Projection for zygomatic arches

SMV

Projection signature

dorsum sellae + posterior clinoids in foramen magnum : AP axial Towne

Projection signature

petrous ridges in lower ⅓ of orbits : PA axial Caldwell

Projection signature

petrous ridges below maxillary sinuses : Waters