Skull Positioning

Five Common Positioning Errors

1.Rotation 2.Tilt 3.Excessive flexion (C-spine) 4.Excessive extension (C-spine) 5.Incorrect CR angle

Glabella

A single bony prominence of the frontal bone located between the superciliary arches in the inferior part of the frontal bone above the root of the nose.

Interpupilary line

An imaginary horizontal line drawn between the centers of the pupils of the eyes. The length of the line is the interpupillary distance.

AP Axial (Towne Method)

Basic Patient: Supine MSP centered to midline and perpendicular OML or IOML perpendicular

AP Axial (Towne Method) CR interseption

CR 2 ½ inches above the glabella

AP Axial (Towne Method) CR Angle:

CR Angle: 30° caudad to OML or 37° to IOML

Skull Positioning and Technical Considerations

Erect vs. recumbent kV range: Analog: 65-85 Digital: 75-90 SID minimum 40 in Small focal spot Shielding of radiosensitive organs

Acanthiomeatal line (AML)

From acanthion to EAM

Glabellomeatal line (GML)

From glabella to EAM

Infraorbitomeatal line (IOML)

From infraorbital margin to EAM

Mentomeatal line (MML)

From mental point (center of chin) to EAM

Orbitomeatal line (OML)

From outer canthus to EAM

Hyposthenic/asthenic patients usually need support at chest to elevate cervical spine (C-spine).

Helps prevent downward tilt of MSP

Hypersthenic patients require radiolucent support at head.

Helps prevent upward tilt of MSP

Skull Classifications

Mesocephalic: Average shaped Head Brachycephalic: Short (front to back) Broad (side to side) Dolichocephalic: Long (front to back) Narrow (side to side)

Acanthion

Midline point at the junction of the upper lip & nasal septum (where nose & upper lip meet)

Interpupillary line (IPL)

Perpendicular line between pupils of eyes

Dolichocephalic skull

Petrous pyramids project anteriorly and medially at 40-degree angle from MSP * Long from front to back, narrow from side to side, and deep from vertex to base

Typical skull = Mesocephalic

Petrous pyramids project anteriorly and medially at 47-degree angle from midsagittal plane (MSP)

Brachycephalic skull

Petrous pyramids project anteriorly and medially at 54-degree angle from MSP * Short from front to back, broad from side to side, and shallow from vertex to base

Mesocephalic skull

Skull of average shape Width 75% to 80% of length

Inner canthus

The corner of the eye where the upper and lower eyelids meet

Angle of mandible (gonion)

The forensic term for the midpoint of the mandibular angle is the gonion.

Infraorbital margin

The infraorbital margin is the lower margin of the eye socket. It consists of the zygomatic bone and the maxilla, on which it separates the anterior and the orbital surface of the body of the maxilla.

Nasion

The nasion (also known as bridge of the nose) is the midline bony depression between the eyes where the frontal and two nasal bones meet, just below the glabella.

Mental point

Tip of chin

Recumbent position

Trauma

Outer canthus

Where eyelids meet on the outside of the eye

Skull Routine Basic

•AP axial (Towne) •Lateral both sides •PA 15° (Caldwell), PA 25° to 30° or PA 0°

Erect position

•Air-fluid levels shown •Easier for hypertension patients

Evaluation Criteria: AP Axial (Towne)

•Dorsum sellae projected within foramen magnum •Entire skull visualized •Occipital Bone in Profile •No rotation or tilt •Petrous ridges symmetric •Optimal exposure factors

Skull Special views

•PA axial (Haas) •SMV (submentovertex)