Modified Towne’s View Zygomatic Arches: Radiographic Positioning Notes
The Modified Towne’s View (AP Axial for Zygomatic Arches) is a specialized cranial projection designed to demonstrate both zygomatic arches simultaneously in symmetry.
It serves as the primary non-invasive alternative to the Submentovertex (SMV / “Jug-Handle”) view, especially in trauma patients with cervical spine precautions or severe neck stiffness who cannot hyperextend their neck.
Modified Towne AP Axial Radiograph. Source: mr.suphachai praserdumrongchai / Getty Images
1. Clinical Indications & Contraindications
Detailed Indications:
- Bilateral Zygomatic Arch Fractures: Symmetrical comparison of medial or lateral displacement, greenstick, comminuted, or V-shaped depressed fractures of the zygomatic arches.
- Component of Zygomaticomaxillary Complex (ZMC / Tripod) Fractures: Evaluating displacement of the posterior temporal process of the zygomatic bone.
- Trauma Alternative to SMV: Indicated in polytrauma patients where hyperextension of the cervical spine is strictly contraindicated.
- Coronoid Impingement Evaluation: Assessment of whether a depressed zygomatic arch impinges onto the coronoid process of the mandible, causing trismus (inability to open the mouth).
- Bone Lesions & Post-Reduction Verification: Assessment of fibrous dysplasia, osteomas, or surgical elevation and fixation using titanium plates/wires.
Contraindications & Limitations:
- Isolated Anterior Zygoma Evaluation (Limitation): Distorts and foreshortens the anterior maxillary body and infraorbital rim. A Waters (Parietoacanthial) or Caldwell view must accompany this projection for comprehensive facial bone evaluation.
2. Technical Factors & Exposure Physics
Because the zygomatic arches are thin and superficial, exposure factors are reduced compared to a standard skull base Towne view to prevent burning out the delicate cortical bone.
| Parameter | Recommended Specification | Radiographic Rationale |
|---|---|---|
| Patient Posture | Supine (Trauma standard) or Erect | Erect is comfortable; supine is ideal for trauma with immobilizers |
| Image Receptor (IR) | 24×30 cm (10×12 inches), Landscape/Crosswise | Captures full bilateral lateral spread of the arches |
| SID | 100 to 115 cm (40 to 44 inches) | Standard distance to reduce geometric unsharpness |
| Grid Ratio | 8:1 to 12:1 focused grid | Essential to absorb scatter from the calvarium |
| Tube Potential (kVp) | 70−75 kVp (Reduced from standard Skull Towne) | Prevents burnout of the delicate zygomatic arches |
| mAs Range | 15−25 mAs (Lower than standard Skull Towne) | Balances soft tissue profile and fine cortical bone margins |
| Focal Spot | Small (0.6 mm) | High spatial resolution for subtle hairline fracture lines |
| Breathing | Suspended respiration | Eliminates respiratory and motion blur |
3. Step-by-Step Patient & Part Positioning
AP Axial Cranium (Towne Method): Patient Positioning
Occipital / Petrous View
Central Ray: Caudad Tube Angle
30° Caudad (OML ⟂) OR 37° Caudad (IOML ⟂)
30° Caudad (OML ⟂) OR 37° Caudad (IOML ⟂)
▼ (Enters ~2.5″ Superior to Glabella ➔ Exits Foramen Magnum)
Orbitomeatal Line (OML) ⟂ IR (90°)
(Standard 30° caudal tube tilt protocol)
(Standard 30° caudal tube tilt protocol)
IOML ⟂ IR (Alternative for Hypersthenic/Trauma)
(Requires 37° caudal tube tilt)
(Requires 37° caudal tube tilt)
Mid-Sagittal Plane (MSP) ⟂ IR (90°)
(Centered strictly along vertical midline)
(Centered strictly along vertical midline)
▼
[ Image Receptor Surface ]
Top of cassette aligned with skull vertex
Top of cassette aligned with skull vertex
1
Dual-Angle Rule (30° vs. 37°)
Use 30° caudad when OML is perpendicular; increase to 37° caudad if patient can only tuck chin to IOML perpendicular.
2
Central Ray Trajectory
Beam passes through the glabella/hairline level to exit through the foramen magnum and inion base.
3
MSP Perpendicular (90°)
Zero head rotation ensures bilateral petrous pyramids and internal auditory canals (IAC) project symmetrically.
4
Dorsum Sellae Placement
Correct caudal angulation projects the dorsum sellae and posterior clinoids directly within the foramen magnum.
- Patient Preparation: Remove all metallic and radiopaque objects (earrings, hairpins, clips, glasses, necklaces, dentures, and hearing aids).
- Base Posture:
- Supine (Trauma Standard): Patient lies supine on the radiographic table with the posterior skull (occiput) resting against the table surface.
- Erect (Alternative): Patient seated or standing with the back of the head flat against the vertical Bucky.
- Alignment of Reference Lines & Planes:
- Mid-Sagittal Plane (MSP): Align strictly perpendicular to the midline of the grid/table (ensures zero head rotation).
- Orbitomeatal Line (OML): Flex the patient’s neck until the OML is perpendicular (90∘) to the image receptor.
- Trauma Adaptation (IOML): If the patient is immobilized in a rigid C-collar and cannot tuck the chin, ensure the Infraorbitomeatal Line (IOML) is perpendicular to the IR instead.
- Interpupillary Line (IPL): Must be strictly parallel to the IR surface (ensures zero lateral tilt).
4. Central Ray (CR), Tube Angle & Collimation
- CR Tube Angulation:
- 30∘ Caudad when the OML is perpendicular to the IR.
- 37∘ Caudad when the IOML is perpendicular to the IR (compensates for the 7∘ difference between OML and IOML).
- CR Centering / Entry Point:
- Directed through the midline, entering at the Glabella (approximately 2.5 cm or 1 inch superior to the nasion) and passing midway between the zygomatic arches at the level of the mandibular angles.
- Collimation: Four-sided collimation adjusted tightly:
- Superiorly: Just above the orbits/glabella.
- Inferiorly: Below the mandibular gonions.
- Laterally: To the outer skin borders of the zygomatic arches.
5. Positioning Errors & Radiographic Signs
| Error Type | Radiographic Sign on Film | Clinical Impact | Correction |
|---|---|---|---|
| Insufficient Caudal Angle (<30∘) | Petrous pyramids and mandibular condyles superimpose over the zygomatic arches. | Obscures the arches completely. | Increase the caudal tube angle to a full 30∘ (or 37∘ for IOML). |
| Excessive Caudal Angle (>30∘) | Mandibular body and alveolar processes superimpose over the inferior margins of the arches. | Causes severe vertical distortion and foreshortening. | Decrease the caudal angle back to 30∘. |
| Head Rotation (MSP not 90°) | One zygomatic arch is projected wider; the opposite arch superimposes over the lateral skull wall. | Mimics unilateral arch displacement or depression. | Realign the Mid-Sagittal Plane (MSP) perpendicular to the IR. |
| Head Tilt (IPL not parallel) | Bilateral zygomatic arches lie at unequal vertical levels. | Causes structural asymmetry. | Realign the IPL parallel to the plane of the IR. |
6. Radiographic Anatomy & Quality Evaluation Criteria
AP Axial (Towne Method): Anatomical Evaluation
Occipital & Petrous Profile
Towne View: Dorsum Sellae Projected into Foramen Magnum
1
Dorsum Sellae & Posterior Clinoids
Projected sharply within the shadow of the foramen magnum without superimposition.
2
Bilateral Petrous Ridge Symmetry
Petrous pyramids are visualized symmetrically across the transverse axis, verifying zero rotation.
3
Occipital Bone Visualization
Entire squamous portion of the occipital bone is spread out clearly without foreshortening.
4
Lateral Zygomatic Arches
Zygomatic arches project laterally to the cranial margins, evaluated for depression fractures.
- Bilateral Arch Projection (Primary Quality Hallmark): Both zygomatic arches are projected symmetrically and laterally beyond the outer margins of the mandibular rami and cranial vault.
- Symmetry:
- Equal distance from the lateral margins of the skull vault to the outer apex of each zygomatic arch.
- Symmetrical petrous pyramids and mandibular condyles.
- Cortical Sharpness: Clear cortical boundaries along the entire span of the temporal process of the zygoma and the zygomatic process of the temporal bone without bone burnout.
- Absence of Motion Blur: Crisp trabecular detail across adjacent facial and calvarial bones.
