11.3 Skull, Facial Bones, Sinuses & Mandible

11.3 Skull, Facial Bones, Sinuses & Mandible

Quick Answer: Control baselines (OML, IOML, MSP) so skull and facial projections are true. Know PA/Caldwell, Towne, lateral skull, Waters, upright sinuses with horizontal beam, and mandible axiolateral/PA/SMV. In major trauma, CT is often preferred, but you must still produce diagnostic radiographs when ordered and critique rotation, tilt, and air–fluid geometry under RTR.4/RTR.6.

Craniofacial radiography is less common than spine or chest in some departments because CT dominates trauma and complex sinus disease, yet it remains blueprint-relevant for general radiography competence. Examination stems love baseline errors: a Waters projection with the mouth closed when open-mouth was ordered, a sinus series done supine with no horizontal beam, or a Towne with the wrong angle that dumps the dorsum sellae into the foramen magnum incorrectly.

Baselines and Planes — The Language of the Head

Rotation vs tilt: Rotation shows unequal distances from lateral orbital margins to the skull margins or unequal mandibular rami on lateral. Tilt shows superior orbital margins at different heights or ear canals not superimposed on lateral. Fix the plane that failed—do not just increase kVp.

Skull — PA / PA Axial (Caldwell-type)

Evaluation (Caldwell 15° caudad): Petrous ridges in the lower third of the orbits; equal distance from lateral orbit to lateral skull margin bilaterally (no rotation); superior orbital margins on the same transverse level (no tilt); frontal bone and frontal sinuses demonstrated.

AP skull alternatives exist for trauma patients who cannot lie prone—expect magnification of the frontal bone and carefully match angles to the baseline in use (OML vs IOML).

Skull — AP Axial (Towne)

Evaluation: Dorsum sellae and posterior clinoids visible within the foramen magnum; symmetric petrous ridges; no rotation (equal distance from foramen magnum to lateral skull). Too little angle fails to project the dorsum into the foramen magnum; too much angle foreshortens the dorsum excessively or projects anterior anatomy incorrectly.

Skull — Lateral

Evaluation: Superimposed orbital roofs, greater wings of sphenoid, EAMs, and mandibular rami; sella turcica in profile; no superior-inferior tilt. Lateral skull is also the starting geometry for many facial lateral adaptations with tighter collimation.

Facial Bones — Waters, Caldwell, Lateral

Parietoacanthial (Waters)

Open-mouth Waters adds visualization of sphenoid sinuses through the open mouth—used in sinus series variants.

Evaluation: Petrous ridges inferior to the maxillary floors; equal orbit-to-skull margins; acanthion centered.

PA Axial Caldwell for facial / orbits

Same 15° caudad geometry as skull Caldwell but collimated and critiqued for orbital rims, frontal/ethmoid regions, and petrous placement in the lower orbits. Precise baseline control is non-negotiable for blowout-fracture screening on plain film pathways.

Lateral facial bones

True lateral of the face centered to the zygoma / midway between outer canthus and EAM depending on protocol; demonstrates superimposed facial bones, sella, and soft-tissue profiles. Used with Waters/Caldwell as a standard facial set in many departments.

Orbits

Orbital series may include Waters, Caldwell, lateral, and sometimes rhese (parieto-orbital oblique) for the optic foramen—know that Rhese places the optic foramen in the lower outer quadrant of the orbit of interest with three-point landing (chin, cheek, nose) and MSP angled ~53° in classic teaching. For suspected metallic foreign body before MRI, follow facility orbital screening protocols (often CT or dedicated radiographs per policy).

Paranasal Sinuses — Upright Technique

Air–fluid levels are a primary reason sinus radiography still appears on exams and in limited clinical pathways.

Lateral sinus upright demonstrates sphenoid, frontal, and maxillary relationships with air–fluid potential. SMV may show ethmoid and sphenoid but is uncomfortable and less used when CT is available.

Exam trap: Performing a “sinus series” fully recumbent with only vertical CR geometry defeats air–fluid demonstration. If the patient cannot sit/stand, horizontal-beam adaptations (e.g., cross-table lateral with head supported) are required—not a routine supine AP with vertical beam alone.

Mandible — PA, Axiolateral Oblique, SMV

PA mandible

Forehead and nose against IR (OML ⊥ IR); CR perpendicular to exit junction of lips or acanthion region per protocol to demonstrate rami and body. PA axial variants exist for specific body regions.

Axiolateral / axiolateral oblique mandible

This is the workhorse for demonstrating the ramus, body, or mentum of the side down/of interest without superimposition of the opposite mandible.

CR: Typically angled 25° cephalad (or head tilted 25° with perpendicular CR) to project the downside mandible free of the upside. Center to the region of interest (body vs ramus).

Evaluation: Desired mandibular segment elongated and free of opposite half; temporomandibular region included when indicated; teeth and alveolar bone sharp enough for trauma survey.

SMV (submentovertical)

Neck extended until IOML is parallel to IR; CR perpendicular to IOML through midline between mandibular angles / 2 cm anterior to EAM level depending on whether mandible, zygomatic arches, or cranial base is prioritized. Demonstrates cranial base, dens in some contexts, and zygomatic arches (bilateral) when exposure and extension allow. Contraindicated or modified in cervical trauma—never force hyperextension on an uncleared neck.

Trauma Awareness: CT Preference vs Radiographic Skill

In Canadian emergency practice, non-contrast CT is often first-line for significant head injury, complex facial fractures, and sinus disease with complications. Your professional role includes:

1. Knowing when radiographs are still ordered (limited access, specific follow-up, foreign body, mandible outpatient series, resource-limited settings).
2. Performing projections correctly the first time to avoid repeats in injured patients.
3. Recognizing limits: plain films can miss nondisplaced fractures and intracranial injury—do not reassure beyond your scope; complete the order and escalate urgent findings per policy.
4. Adapting: cross-table laterals, AP reverse Caldwell/Towne, horizontal-beam Waters-type geometry when the patient cannot be prone or sit.
5. Collar and c-spine precautions remain in force during skull/facial imaging until cleared—SMV and forced extension are inappropriate in uncleared trauma.

CAMRT stems may describe a polytrauma patient and ask which projection is obtainable without removing immobilization, or which geometry demonstrates air–fluid levels—answer with safe, baseline-correct technique while acknowledging modality pathways.

Technique and Image Quality Notes

Positioning Summary Table — Skull, Face, Sinuses, Mandible

Bottom Line for Craniofacial RTR Competence

Master baselines first—every named projection is a baseline problem in disguise. Produce Caldwell, Towne, lateral, Waters, upright horizontal-beam sinuses, and mandible axiolateral/PA/SMV that meet evaluation criteria for rotation, tilt, and petrous placement. Prefer CT awareness for heavy trauma without abandoning projection skill. That balance of classic radiography and modern clinical judgment is what the CAMRT expects from an entry-to-practice radiological technologist in RTR.4 procedure performance and RTR.6 image critique.