Stenvers X-Ray View: PA Oblique Petrous Bone Positioning Notes

The Stenvers X-Ray View Method (PA Oblique 45° Projection) is a specialized temporal bone projection designed to profile the petrous pyramid in its true anatomical length parallel to the image receptor.

By rotating the head 45⁰ toward the affected side and applying a 12⁰ cephalad central ray angulation, the dense occipital and facial structures are projected away, providing an unobstructed, elongated view of the petrous apex, internal acoustic canal (IAC / IAM), labyrinth (semicircular canals and cochlea), and mastoid antrum.

1. Clinical Indications & Contraindications

Detailed Indications:

• Internal Acoustic Canal (IAC) Pathologies:
  • Evaluation of asymmetric widening, cortical erosion, or funneling of the internal auditory canal caused by Vestibular Schwannoma (Acoustic Neuroma).
• Petrous Apex Lesions & Infections:
  • Assessment of Petrous Apicitis (Gradenigo’s Syndrome) presenting with deep facial pain, otorrhea, and abducens nerve (CN VI) palsy.
  • Detection of Cholesteatomas expanding into the labyrinth or petrous apex.
• Temporal Bone Fractures:
  • Evaluation of longitudinal or transverse petrous bone fractures involving the osseous labyrinth, otic capsule, or facial nerve (CN VII) canal.
• Cochlear Implant Verification:
  • Post-operative assessment of the positioning and depth of electrode array insertion within the cochlea.
• Bony Labyrinth Assessment:
  • Evaluation of otosclerosis, labyrinthitis ossificans, or congenital inner ear malformations (Mondini dysplasia).

Contraindications & Limitations:

• Unstable Cervical Spine Trauma: Head rotation and neck manipulation are contraindicated. If a petrous fracture is suspected in severe trauma, a Cross-Table Lateral and an AP Axial (Towne Method) or high-resolution Temporal Bone CT must be performed instead.
• Overlying Calvarial Pathology (Limitation): 2D plain film views cannot differentiate soft-tissue acoustic tumors <1.5 cm; MRI remains the gold standard for soft-tissue inner ear staging.

2. Technical Factors & Exposure Physics

3. Step-by-Step Patient & Part Positioning

                 [ Vertical Bucky Surface ]
                             ║
    (Affected Side Down) ◄── ║ ◄── Forehead, Nose & Malar Touching Bucky
                             ║
                      /──────║──────\
                     │  IOML ║       │ ◄── IOML ⟂ Transverse Axis of IR
                     │ ──────║────── │
                     │       ║       │ ◄── MSP forms 45° Angle to IR Plane
                      \      ║      /
                             ║
                            /
                           /  12° Cephalad Tube Tilt
                          ▲
                 [ Central Ray: 12° Cephalad ]
               (Enters 2.75" below and behind upside EAM,
                 Exits through Downside Petrous Apex)

• Patient Preparation: Remove all radiopaque materials (earrings, hearing aids, hairpins, clips, spectacles, dentures, and necklaces).
• Base Posture: Patient sits or stands erect facing the vertical Bucky (or lies semi-prone on the radiographic table). The affected side rests closest to the receptor.
• Alignment of Reference Lines & Planes:
  1. Reference Point Contact: Rest the patient’s forehead, nose, and cheek (malar bone) of the affected side firmly against the Bucky.
  2. Head Rotation (MSP): Rotate the patient’s head 45⁰ toward the affected side (the side of interest). This places the long axis of the petrous pyramid strictly parallel to the plane of the image receptor.
  3. Infraorbitomeatal Line (IOML): Adjust neck flexion/extension until the IOML is strictly perpendicular (90⁰) to the transverse axis of the IR (parallel to the horizontal floor).

4. Central Ray (CR), Tube Angle & Collimation

• Central Ray (CR) Tube Angle:12⁰ Cephalad (angled upwards toward the head).
  • Rationale: The 12⁰ cephalad angulation opens the internal auditory canal and projects the dense occipital squama away from the petrous apex.
• CR Entry Point: Enters the posterior neck approximately 7 cm (2.75 inches) inferior and 7 cm posterior to the upside (elevated) External Auditory Meatus (EAM).
• CR Exit Point: Passes obliquely through the skull base to exit directly through the downside petrous pyramid (midway between the EAM and outer canthus of the side of interest).
• Collimation: Four-sided tight collimation restricted to a 7.5 × 7.5 cm (3 × 3 inches) field over the downside temporal bone.

5. Positioning Errors & Corrective Actions

6. Radiographic Anatomy & Quality Evaluation Criteria

+───────────────────────────────────────────────────────────────────────────+
|                                                                           |
|                               [ Calvarium ]                               |
|                                                                           |
|                  /─────────────────────────────────────\                  |
|                 │                                       │                 |
|   Superior ───► │       [ Semicircular Canals ]         │                 |
|   Border        │          (Labyrinth Profile)          │                 |
|                 │              (·) (·)                  │                 |
|                 │            [ Cochlea ]                │                 |
|                 │                                       │                 |
|  Petrous Apex ─►\    (====)  ◄── Internal Acoustic      │ ◄── Mastoid     |
|   (Clear)        \   Canal      Canal (Open Profile)    │      Antrum     |
|                   \____________________________________/                  |
|                             [ Mandibular Angle ]                          |
|                                                                           |
+───────────────────────────────────────────────────────────────────────────+

• Petrous Ridge Elongation (Primary Quality Hallmark):
  • The entire petrous pyramid of the side of interest is projected in profile across its true anatomical length, parallel to the image plane.
• Internal Acoustic Canal (IAC / IAM):
  • The internal auditory canal is visualized end-on or in open horizontal profile, demonstrating distinct superior and inferior cortical margins without superimposition.
• Bony Labyrinth Visualization:
  • Clear, sharp delineation of the semicircular canals (superior, posterior, lateral), vestibule, and cochlea projected within the petrous bone density.
• Petrous Apex Clearance:
  • The petrous apex is demonstrated free of overlying superimposition from the occipital bone or contralateral temporal bone.
• Mastoid Process & Antrum:
  • Mastoid air cells and tegmen tympani demonstrated lateral to the labyrinth with sharp trabecular detail.