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

Parameter	Recommended Setting	Radiographic Rationale
Patient Posture	Erect (Seated) or Prone	Erect seated gives superior control over the 45⁰ head rotation
Image Receptor (IR)	18 x 24 cm (Portrait/Landscape)	Tight format centered specifically over the affected petrous pyramid
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	Essential to absorb scatter from dense cranial base structures
Tube Potential (kVp)	70 – 80 kVp	High bone-to-air contrast resolution for inner ear labyrinths
mAs Range	25 – 35 mAs	Calibrated based on temporal bone thickness (AEC center cell active)
Focal Spot	Small (0.6 mm)	High spatial sharpness required to visualize delicate semicircular canals
Marker	“R” or “L” lead marker	Essential to distinguish right/left petrous ridges
Breathing	Suspended respiration	Eliminates breathing and head tremor motion artifacts

3. Step-by-Step Patient & Part Positioning

Stenvers Method – Positioning Card

Stenvers Method: Patient Positioning

PA Oblique (45°)

[ Vertical Bucky Surface ]
Affected Side Resting on IR

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3-Point Contact: Forehead, Nose & Cheek
(Firm contact with Bucky)

MSP Rotated 45° Toward Affected Side
(Petrous bone parallel to IR)

IOML ⟂ Transverse Axis of IR (90°)

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Central Ray: 12° Cephalad Tube Tilt
Enters 2.75″ below/behind upside EAM ➔ Exits downside apex

45° Head Turn

Rotates the petrous ridge parallel to the image receptor for true anatomical length visualization.

12° Cephalad Tilt

Directs the beam upward to project the dense occiput clear of the internal acoustic canal (IAC).

3-Point Touch Rule

Forehead, malar bone, and tip of the nose must touch the cassette simultaneously to prevent tilt.

IOML Baseline

Infraorbitomeatal line is kept perpendicular to prevent vertical pitch distortion.

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

Positioning Error	Radiographic Sign on Film	Clinical Impact	Correction
Under-Rotation (< 45⁰)	Petrous pyramid appears foreshortened; internal auditory canal is closed or obscured.	Fails to project the petrous ridge in true anatomical profile.	Increase head rotation until the MSP forms exactly 45⁰ to the IR.
Over-Rotation (> 45⁰)	Semicircular canals and cochlea superimpose heavily over the petrous apex; mastoid obscures the IAC.	Obscures petrous apex margins and the internal auditory canal.	Rotate the head slightly back toward the PA position to restore the 45⁰ angle.
Insufficient Cephalad Angle (< 12⁰)	The occipital bone superimposes over the petrous ridge and IAC.	Complete obscuration of the internal acoustic meatus.	Increase the cephalad tube angle to a full 12⁰.
Improper Neck Flexion (IOML not level)	Petrous ridge appears tilted, superimposing over the supraorbital margin or maxillary sinus.	Distorts the horizontal baseline of the labyrinth.	Realign the IOML perpendicular to the transverse axis of the IR.

6. Radiographic Anatomy & Quality Evaluation Criteria

Stenvers Method Anatomical Evaluation Diagram

Stenvers Method: Radiographic Anatomy & Quality Criteria

PA Oblique Petrous Ridge

Elongated Profile of the Petrous Pyramid

Diagnostic Quality Criteria

IAC

Internal Acoustic Canal Profile

IAC is visualized in an open horizontal profile with parallel superior and inferior cortical walls, free of foreshortening.

Apex

Petrous Apex Delineation

Medial petrous apex is clearly isolated and projected clear of superimposition from the dense occipital squama.

Labyrinth

Inner Ear Semicircular Canals

Distinct visualization of the superior and horizontal semicircular canals, vestibule, and cochlea within the dense otic capsule.

Antrum

Tegmen & Mastoid Trabeculae

Sharp superior border (tegmen tympani) with laterally positioned mastoid air cells and antrum free of motion blur.

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.