In this presentation, I’ll be showing you the basic positioning guidelines and routine
views for radiographic examination of the skull.
Essential projections include the lateral, PA, PA axial (Caldwell method), AP, AP axial
(or reverse Caldwell), AP axial (Towne method), PA axial (Haas method) and the SMV (or Submentovertical
view)
For the lateral projection, the patient can be positioned upright or recumbent. If recumbent,
use of a radiopaque wedge sponge is recommended to help eliminate rotation or tilt. Place
the MSP parallel to the table and the IR. The inter-pupillary line should be perpendicular
to the IR with the infraorbital meatal line parallel to the transverse axis of the IR.
Direct the central ray to enter 2 inches superior to the EAM, and collimate to at least a 10
x 12 inch field crosswise.
Take the time to view your patient’s position in multiple planes. Rotation for the skull
occurs when the head is turned left or right as in the image at the top right of this slide.
Tilt is when the top of the cranium is angled away from the MSP like in the image below
it. One thing that helps me distinguish the two is during tilt, you make this motion when
eating a taco – I like to call it “taco-neck” where you tilt your head to one side in order
to take a bite. Rotation is what you do before you cross the street by looking both ways.
The PA and PA axial Caldwell method are very similar, except for the PA axial Caldwell
has a tube angulation while the straight PA has a perpendicular beam. The part positions
are identical though, and the images on the right on this slide include the PA view only.
The patient can be upright or prone with MSP centered to midline of the IR. Placing the
forehead and nose against the table or upright bucky generally places the OML perpendicular
to the IR – small adjustments may be needed depending on the patient. The Central Ray
should be perpendicular to the IR and exit the nasion for the PA view.
For the PA axial Caldwell position, the patient can again be either upright or supine with
OML perpendicular to the table or upright bucky. The tube should be angled 15 degrees
caudal for this view, and the CR will still exit the nasion. Both PA and PA Axial Caldwell
views should be performed with a 10 x 12 inch field or smaller. Note the images on the right.
The top image is the PA Axial Caldwell. This can be distinguished from the straight PA
view shown on the bottom because the petrous ridges fill the lower 1/3 of the orbits. In
the PA view, the petrous ridges completely fill the orbits.
Both of these views can be performed AP as well with the patient supine and the CR entering
the nasion. For the reverse Caldwell (or AP axial), the tube would need to be angled 15
degrees cephalic in the AP projection. One noticeable difference in the radiographic
presentation is the orbits will be significantly more magnified when performing these AP.
Next we have the AP Axial Townes View. For this one, you may place the OML or the IOML
perpendicular to the IR with the patient supine or seated upright. Depending on which of these
positioning lines you utilize, the degree of angulation for the tube will vary.
If using the OML, angle the tube 30 degrees caudal. If using the IOML, use 37 degrees
caudal. The central ray should exit through the foramen magnum. Collimate to a 10 x 12
inch field size. The skull will be elongated in this view, and if performed correctly,
the dorsum sellae should be visible within the foramen magnum.
A similar view can be performed with the PA Axial Haas Method. The patient is placed prone
or sitting upright facing the wall bucky. Place the OML perpendicular to the IR and
angle the tube 25 degrees cephalic. Center at a point 1 and ½ inches below the external
occipital protuberance. This should cause the CR to exit about 1 and ½ inches superior
to the nasion. Collimate to a 10 x 12 inch field size or smaller.
The Submentovertex position, or SMV Shuller method, is probably the most difficult position
for the patient to hold while sitting upright, although there are methods to perform this
supine with the torso elevated. The neck is extended so that the IOML is parallel with
the IR with the MSP centered. The CR should be perpendicular to the IR and pass through
the MSP between the angles of the mandible, which projects it through the sella turcica.
Another centering reference could be stated as ¾ inch anterior to the level of the EAM
at midline. Collimate to a 10 x 12 inch field or less. Be cautious not to clip the anatomy
of the occipital bone in this projection since you will not be able to see the light field
on the posterior aspect.