Skull X-Ray Positioning

Anatomical Reference Lines (Essential)

Before any projection, you must understand the key positioning lines:

Cranial positioning lines - OML and IOML

Line	Landmarks
Midsagittal Plane (MSP)	Divides skull into equal left and right halves; must always be centered and perpendicular to IR (unless lateral)
Orbitomeatal Line (OML)	Outer canthus of eye to external auditory meatus (EAM)
Infraorbitomeatal Line (IOML)	Inferior orbital margin to EAM; ~7° lower than OML
Interpupillary Line (IPL)	Between the two pupils; perpendicular to IR in frontal views

1. PA Occipito-Frontal (Occipitofrontal / 0°)

Parameter	Detail
Position	Prone (or erect); forehead and nose rest on the IR
MSP	Centered and perpendicular to IR
OML	Perpendicular to IR
CR	Perpendicular (0°), directed to nasion
IR size	24 × 30 cm (10 × 12 in.)
Centering	Nasion

Structures demonstrated: Frontal bone, frontal and anterior ethmoid sinuses, crista galli, internal auditory canals, greater and lesser wings of sphenoid, petrous ridges projected in the lower third of the orbits.

Note: Contraindicated in unconscious patients or suspected facial fractures.

2. PA Axial - Caldwell Method (15° Caudal)

Parameter	Detail
Position	Prone or erect; forehead and nose on IR
MSP	Perpendicular to IR, centered to midline
OML	Perpendicular to IR
CR	15° caudal, directed to exit at nasion
Centering	Nasion

Structures demonstrated: Frontal and ethmoid sinuses, superior orbital margins, greater and lesser sphenoid wings, superior orbital fissures, petrous ridges projected in the lower third of orbits, crista galli. Best view for fractures with medial/lateral displacement.

3. AP Projection (Reverse Caldwell)

Parameter	Detail
Position	Supine; back of head on IR
MSP	Centered and perpendicular to IR
OML	Perpendicular to IR (may use thin sponge under head)
CR	Perpendicular to midpoint of cassette
IR size	24 × 30 cm lengthwise
Upper border	~1 inch (2.5 cm) above vertex

Structures demonstrated: AP view of all major cranial bones. Used when patient cannot be prone.

(Source: Brogdon's Forensic Radiology)

4. Lateral Projection

Parameter	Detail
Position	Lateral recumbent (or erect); affected side closest to IR
MSP	Parallel to IR
IPL	Perpendicular to IR
IOML	Parallel to the long axis of the IR
CR	Perpendicular to IR, directed 2.5 cm (1 in.) superior to EAM
IR size	24 × 30 cm, placed vertically

Structures demonstrated: Lateral view of cranial bones, sella turcica, anterior/posterior clinoid processes, dorsum sellae, sphenoid sinuses, vertex.

Cross-table lateral skull - patient position and resulting X-ray

Cross-table lateral (trauma): IR placed vertically against the side of the skull; horizontal beam directed perpendicular to IR. Upper cassette border 1.9-2.5 cm above vertex. Used when the patient cannot be moved.

5. AP Axial - Towne's Method (30° or 37° Caudal)

Towne position - patient setup and resulting AP axial skull X-ray

Parameter	Detail
Position	Supine; back of skull on IR
MSP	Perpendicular to IR, centered
OML	Perpendicular to IR
CR	30° caudal (if OML is perpendicular) OR 37° caudal (if IOML is used instead)
Entry point	CR enters 1/2 inch (1.3 cm) above eyebrows
Exit point	Exits at the mastoid process area
IR centering	Centered at CR exit point

Structures demonstrated: Occipital bone, foramen magnum, dorsum sellae, petrous pyramids, posterior clinoid processes. Excellent for occipital fractures. (Brogdon's Forensic Radiology)

6. Submentovertex (SMV) - Base View

Parameter	Detail
Position	Supine (or seated); neck hyperextended
IOML	As parallel as possible to the IR
MSP	Perpendicular to IR
CR	Perpendicular to IOML, directed through sella turcica

Structures demonstrated: Cranial base, foramen ovale/spinosum/lacerum, zygomatic arches, mandibular condyles, sphenoid sinuses, petrous pyramids, carotid canals.

Contraindicated if cervical spine injury is suspected.

7. Verticosubmental (VSM) - Schüller Method

An alternative to SMV when the patient cannot hyperextend the neck:

Position: Prone
MSP: Centered to grid
CR: Perpendicular to IOML

Key Positioning Tips

Remove all artifacts before imaging: dentures, hair grips, ear clips, hearing aids, and glasses.
Grid cassette is standard for skull work.
Check the MSP is not rotated - in PA/AP views, the orbital plates, lesser wings, and petrous ridges should be symmetric.
Rotation check on lateral: orbital roofs and mandibular rami should be perfectly superimposed.
For Towne's, the dorsum sellae should project into the foramen magnum if CR angulation is correct.

Source: Brogdon's Forensic Radiology (medical library); CE4RT Skull Positioning Reference

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