Which projection is used to visualize the odontoid process and C1–C2 alignment?

• A. Visualize the odontoid process and C1–C2 alignment.
• B. Visualize the lower cervical vertebrae.
• C. Assess thoracic inlet.
• D. Evaluate the lumbar discs.

Answer: (A)

Open-mouth odontoid projection is used to visualize the odontoid process and C1–C2 alignment. By having the mouth opened wide, the view allows the X-ray beam to pass through the oral cavity so the dens and the atlas–axis joint can be seen clearly without being obscured by the teeth or skull base. This projection directly shows the relationship between the dens of C2 and the anterior arch of C1, making it the best choice for assessing C1–C2 alignment and any dens-related injuries. Other views target different parts of the spine—lower cervical vertebrae, the thoracic inlet region, or the lumbar discs—so they wouldn’t provide an optimal image of the odontoid process or C1–C2 alignment.