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

• 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:
  1. Mid-Sagittal Plane (MSP): Align strictly perpendicular to the midline of the grid/table (ensures zero head rotation).
  2. Orbitomeatal Line (OML): Flex the patient’s neck until the OML is perpendicular (90∘) to the image receptor.
  3. 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.
  4. 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

• 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.