AP AXIAL PROJECTION: SELLA TURCICA

TOWNE METHOD SELLA TURCICA *

Pathology Demonstrated:

• Pituitary adenoma may be demonstrated if involvement of the sella turcica is evident.

Technical Factors:

• IR size - 18 x 24 cm (8 x 10 inches), lengthwise

• Moving or stationary grid

• 80 +- 5 kV range

• Small focal spot

• mAs 22

Shielding:

• Shield patient's upper thoracic region.

Patient Position:

• Remove all metal, plastic, or other removable objects from the patient's head.

• Take radiograph with patient in erect or supine position.

Part Position:

• Rest patient's posterior skull against table/Bucky surface.

• Flex neck to bring IOML perpendicular to midline of the grid or table/Bucky surface.

Central Ray:

• Angle CR 37° caudad if dorsum sallae and posterior clinoid processes are of primary interest.

• Angle CR 30° caudad if anterior clinoids are of primary interest.

• Center at midsagittal plane 1 1/2 inches (4 cm) above supercillary arch. (CR will exit the foramen magnum.)

• Minimum SID is 40 inches (100 cm)

Collimation:

• Callimate to a field size of approximately 4 inches (10 cm) square.

Respiration:

• Suspend respiration during exposure.

Note: To obtain sharply detailed image of the dorsum sallae, use of a small focal spot and chose collimation is essential.

Radiographic Criteria:

Structure Shown:

30° 

• Dorsum sallae, anterior and posterior clinoid processes (depending on CR angulation), foramen magnum, petrous ridges, and occipital bone are shown.

Position:

• No rotation is evident, as indicated by symmetric petrous ridges and by equal distances from the midsagittal plane (which can be identified by the perpendicular plate) to each anterior clinoid process.
• A correct position image will have the following features (CR angulation required depends on the structure of interest):

37° caudad angle: Dorsum sallae and posterior clinoid processes are projected within the foramen magnum.
30° caudad angle: Anterior clinoids are clearly visualized, adjacent to each petrous ridge, directly above the foramen magnum; dorsum sallae is projected above the foramen magnum, superimposing the occipital bone.

Collimation and CR:

• A closely collimated image, with the dorsum sallae located in the center.

Exposure Criteria:

• Density and contrast are sufficient to visualized the dorsum sallae to the adjacent skull structures.
• Sharp bony margins indicate no motion.