The Chaussé III X-Ray View Method (Transorbital Oblique / Orbitotympanic Projection) is an essential specialized projection of the temporal bone. It is specifically designed to project the middle ear cavity, epitympanic recess (attic), aditus ad antrum, ossicular area, and the bony labyrinth directly through the radiolucent window of the ipsilateral orbit, casting them free of superimposition from the dense occipital squama and petrous apex.
1. Clinical Indications & Contraindications
Detailed Indications:
- Epitympanic & Attic Cholesteatoma:
- Early detection of bone erosion along the lateral attic wall (scutum / spur of the outer attic wall) and the epitympanic recess.
- Assessment of expansion into the aditus ad antrum.
- Ossicular Chain Disruption:
- Evaluation of incudomalleolar or incudostapedial joint dislocations, fractures, or osteolytic erosion following chronic suppurative otitis media (CSOM) or blunt lateral head trauma.
- Labyrinthine & Otic Capsule Fractures:
- Detection of fine longitudinal or transverse microfractures traversing the lateral semicircular canal, vestibule, and promontory of the middle ear.
- Mastoid Antrum & Facial Nerve Canal Pathologies:
- Evaluation of bony wall integrity of the tympanic segment of the facial nerve (CN VII) canal and lateral semicircular canal fistula.
Contraindications & Limitations:
- Unstable Cervical Spine Trauma: Standard positioning involves head rotation; strictly contraindicated until C-spine clearance is complete.
- High Radiation to Ocular Lens: Direct transorbital AP beam alignment exposes the ipsilateral ocular lens to entrance radiation; PA modifications or tight coning/collimation are essential.
- Advanced Soft Tissue Staging (Limitation): High-Resolution CT (HRCT) of the temporal bone remains the diagnostic gold standard for microscopic ossicular reconstruction planning; Chaussé III serves as a high-yield specialized projection in classical radiology and board examinations.
2. Technical Factors & Exposure Physics
| Parameter | Recommended Specification | Radiographic Rationale |
| Patient Posture | Supine (Preferred) or Erect (Seated) | Supine ensures stable immobilization for precise minor head rotations |
| Image Receptor (IR) | 18 × 24 cm (Portrait) | Small format centered on the orbit/temporal bone of interest |
| SID | 100 to 115 cm (40 to 44 inches) | Standard focal distance balances spatial resolution and beam divergence |
| Grid Ratio | 8:1 to 12:1 focused grid | Absorbs high-angle scatter from dense cranial bones |
| Tube Potential (kVp) | 70 – 78 kVp | High bone-to-air contrast to delineate fine attic margins and scutum |
| mAs Range | 20 – 30 mAs | Calibrated for fine bony trabeculae (AEC center cell active) |
| Focal Spot | Small (0.6 mm) | High spatial sharpness required to resolve delicate middle ear structures |
| Collimation | Strictly Coned (5 × 5 cm) | Reduces scatter radiation and significantly protects the ocular lens |
| Breathing | Suspended respiration | Eliminates respiratory and eye/head motion blur |
3. Step-by-Step Patient & Part Positioning
[ Central Ray: 0° / 5°–10° Caudad ]
│
▼ (Enters Midpoint of Outer Canthus & EAM)
/───────────────────\
│ Vertex / Skull │
[ IOML // IR ] │ │
│ ───────┼─────────── │ ◄── Head Rotated 10°–15° AWAY from Affected Side
│ │ MSP │
\ │ /
\─────────────────/
[ Image Receptor ]
- Patient Preparation: Remove all radiopaque materials (earrings, hearing aids, hairpins, clips, spectacles, dentures, and necklaces).
- Base Posture: Patient lies supine on the radiographic table with the posterior skull (occiput) resting against the table surface.
- Alignment of Reference Lines & Planes:
- Starting Alignment: Align the head in a neutral AP position with the Mid-Sagittal Plane (MSP) perpendicular to the midline of the grid/table.
- Head Rotation (The Core Chaussé III Rule): Rotate the patient’s head 10⁰ to 15⁰ AWAY from the side of interest (e.g., to examine the Right middle ear, rotate the head 10⁰–15⁰ toward the Left).
- Purpose: This slight contralateral rotation places the long axis of the petrous pyramid and middle ear cavity directly into the open circular silhouette of the ipsilateral orbit.
- Infraorbitomeatal Line (IOML): Adjust chin flexion/extension until the IOML is strictly perpendicular (90⁰) to the plane of the image receptor.
4. Central Ray (CR), Angle & Collimation
- Central Ray (CR) Tube Angle:
- 0⁰ (Perpendicular) or 5⁰ to 10⁰ Caudad (angled downwards toward the feet).
- Rationale: A slight caudal tilt ensures the superior orbital margin does not superimpose over the upper edge of the attic and tegmen tympani.
- CR Entry Point: Centered directly through the orbit of the side of interest, entering midway between the outer canthus of the eye and the External Auditory Meatus (EAM).
- Collimation: Four-sided tight circular/square collimation restricted to a 5 × 5 cm field over the orbit to protect the ocular lens and optimize radiographic contrast.
5. Positioning Errors & Corrective Actions
| Error Type | Radiographic Sign on Film | Clinical Impact | Correction |
| Insufficient Rotation (< 10⁰) | The lateral orbital margin superimposes over the middle ear cavity and scutum. | Complete obscuration of the attic and tympanic cavity. | Increase head rotation away from the affected side to a full 10⁰ to 15⁰. |
| Excessive Rotation (> 15⁰) | The middle ear cavity is displaced medially into the nasal bones and ethmoid sinus. | Obscures the ossicular area and labyrinthine profile. | Rotate the head back slightly toward the midline. |
| Over-Flexion (Chin tucked too low) | Petrous ridge projects superiorly, superimposing over the orbital roof. | Obscures the attic and tegmen tympani. | Elevate chin slightly until IOML is perpendicular (90⁰). |
| Over-Extension (Chin tilted too high) | Middle ear structures project inferiorly into the maxillary antrum. | Distorts the anatomical baseline of the labyrinth. | Tuck chin down until IOML is perpendicular. |
6. Radiographic Anatomy & Quality Evaluation Criteria
+───────────────────────────────────────────────────────────────────────────+
| |
| /───────── SUPERIOR ORBITAL RIM ─────────\ |
| │ │ |
| │ │ |
| │ [ Lateral Semicircular Canal ] │ |
| │ (·) │ |
| │ [ Promontory / Vestibule ] │ |
| │ │ |
| Lateral ───► │ [ SCUTUM ] ◄── Outer Attic Wall │ |
| Orbital │ │ │ |
| Rim │ [ ATTIC / EPITYMPANUM ] │ ◄── Medial |
| │ (Ossicular Mass / Incus & Malleus) │ Orbital |
| │ │ │ Wall |
| │ [ TYMPANIC CAVITY / MIDDLE EAR ] │ |
| │ │ │ |
| │ [ External Auditory Meatus (EAM) ] │ |
| │ │ |
| \───────── INFERIOR ORBITAL RIM ─────────/ |
| |
+───────────────────────────────────────────────────────────────────────────+
- Transorbital Projection (Primary Quality Benchmark):
- The middle ear cavity, attic (epitympanic recess), and scutum are clearly projected inside the radiolucent shadow of the orbit, completely free of dense calvarial or petrous apex overlap.
- Scutum & Attic Integrity:
- Sharp, distinct triangular radiopaque spur representing the scutum (lateral attic wall) without blurring or osteolytic erosion.
- Clear radiolucency of the epitympanic recess and aditus ad antrum.
- Ossicular & Labyrinthine Visualization:
- Ossicular mass (shadow of the head of the malleus and body of the incus) visualized within the attic.
- The lateral (horizontal) semicircular canal and vestibule are clearly delineated medial to the attic.
- Contrast & Detail:
- High-contrast resolution that clearly separates the thin bony margins of the middle ear cleft from the surrounding aerated spaces.