Skull Positioning on a Patient with a Collar and Dental Hardware
A 30-year-old man is referred for a skull series after a fall from a ladder with a brief loss of consciousness. He is now alert and oriented, but he has a rigid cervical collar and a scalp laceration that has been stapled. He has extensive dental amalgam and orthodontic hardware. The order is for a basic skull series including a lateral and a PA (or AP). He is able to sit upright. The provider is concerned about a skull fracture. His neck is still in the collar pending clearance.
1. How do the collar and the patient's status affect which skull projections you choose and how you position him?
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The collar means cervical movement must be avoided, and the recent loss of consciousness means he should be monitored during the exam.
Projection choices:
- Lateral skull: can be obtained with the patient upright and the beam horizontal (cross-table) while the collar stays on, or with the patient seated and the head kept still. Do not ask him to tuck or extend his chin to 'open' the skull base if that requires neck movement.
- PA skull: a true PA requires the patient to turn and place the forehead and nose against the detector, which may conflict with the collar and the scalp staples. An AP skull with the beam angled to the orbitomeatal line may be more feasible, or a PA obtained upright with the detector vertical and the head kept neutral.
- Avoid the Towne and other angled projections if they require neck extension, until the collar is cleared.
- Do not remove the collar to get a prettier image. Coordinate with the provider if a specific projection is essential.
Keep the exam efficient and monitor him for dizziness or change in status.
2. The dental hardware is producing artifacts. What is happening and how do you reduce its effect?
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Amalgam and orthodontic metal are very dense and attenuate the beam strongly, producing beam hardening and streak artifacts and obscuring adjacent structures. They also create a large density range that can make exposure difficult.
Ways to reduce the effect:
- Position the hardware out of the region of interest where possible: for a lateral skull, a slight rotation may move the dental hardware away from the area of interest, though you must not rotate the neck.
- Use a higher kVp to improve penetration and reduce the proportion of photoelectric absorption, which can lessen the contrast between metal and bone.
- Collimate tightly to the skull to reduce scatter.
- Use a grid to control scatter from the dense material.
- Choose projections that minimize overlap of the hardware with the skull vault.
- If a specific area is obscured, note it and communicate with the provider; a CT may be needed for definitive evaluation.
Document the artifact and the limitation.