1. The offset of the C1 lateral masses relative to C2, marked by the lines on this AP open-mouth radiograph, is most consistent with which pathology?
Cervical Spine
The cervical spine has 7 vertebrae; C1 (atlas) and C2 (axis, with the dens) are atypical. A routine C-spine is an AP axial, an open-mouth (C1–C2), a lateral and often obliques.
Overview
Bones
Atypical
- C1 (atlas): no body, lateral masses
- C2 (axis): dens (odontoid process)
- C7: vertebra prominens
Typical (C3–C6)
- Body
- Bifid spinous process
- Transverse foramina
- Zygapophyseal joints (best on the lateral)
- Intervertebral foramina (best on obliques, 45°)
C-spine foramina open at 45° and are seen on the obliques; zygapophyseal joints are seen on the lateral (90°).
Registry must-knows
- Trauma: the cross-table lateral comes first and must be cleared before moving the patient. All 7 vertebrae and the top of T1 must be seen.
- Lateral C-spine: 72-inch SID reduces magnification from the large OID; depress the shoulders (weights or traction) to see C7.
- If C7–T1 still isn't shown, use the swimmer's (Twining) lateral.
- Open-mouth: line the occlusal plane and the mastoid tips up so the upper teeth and skull base don't hide the dens.
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- Posterior obliques (RPO/LPO) with a 15–20° cephalad CR show the foramina farthest from the IR; anterior obliques with a caudal CR show those closest.
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Radiographs 5
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Projections 5
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AP axial C-spine
CR: 15–20° cephalad
- Position
- Erect or supine, MSP centered, chin raised so a line from the lower edge of the upper incisors to the mastoid tip is perpendicular to the IR.
- Central ray
- 15–20° cephalad
- Centering
- C4 (at the thyroid cartilage)
- Typical technique
- 75–80 kVp · 8–12 mAs · 40" SID
Image criteria
- C3 through T2 seen; disk spaces open.
- Spinous processes equidistant from the pedicles; no rotation.
- Mandible superimposed over the occipital base and C1–C2.
AP open mouth (C1–C2)
CR: Perpendicular
- Position
- Mouth open as wide as possible; lower edge of the upper incisors and the mastoid tips aligned perpendicular to the IR.
- Central ray
- Perpendicular
- Centering
- Center of the open mouth
- Typical technique
- 75–80 kVp · 10–16 mAs · 40" SID
- Best shows
- The dens and the lateral masses of C1 on C2
Image criteria
- Dens and C1–C2 articulations seen through the open mouth.
- Upper incisors and skull base clear of the dens.
- Equal spaces between the dens and the lateral masses (no rotation).
Lateral C-spine
CR: Perpendicular
- Position
- Erect, left side against the IR, shoulders depressed, chin slightly raised.
- Central ray
- Perpendicular
- Centering
- C4 (thyroid cartilage)
- Typical technique
- 75–80 kVp · 10–16 mAs · 60–72" SID
Image criteria
- C1 through the top of T1 included.
- Zygapophyseal joints open; no rotation (posterior bodies superimposed).
- Mandible clear of C1–C2.
AP axial oblique (posterior oblique)
RPO / LPOCR: 15–20° cephalad
- Position
- Body rotated 45° (posterior oblique), head turned to the side.
- Central ray
- 15–20° cephalad
- Centering
- C4
- Typical technique
- 75–80 kVp · 10–16 mAs · 60–72" SID
- Best shows
- Intervertebral foramina and pedicles farthest from the IR
Image criteria
- Intervertebral foramina open (C2–C3 to C7–T1).
- Pedicles in profile.
- Mandible clear of the upper vertebrae.
Cervicothoracic lateral (swimmer's)
TwiningCR: Perpendicular, or 3–5° caudad if the far shoulder can't be depressed
- Position
- Left lateral (erect or recumbent). Arm next to the IR raised overhead; the other shoulder depressed and moved slightly posterior to separate the humeral heads.
- Central ray
- Perpendicular, or 3–5° caudad if the far shoulder can't be depressed
- Centering
- T1 (C7–T1): about 1 inch above the jugular notch anteriorly, at the vertebra prominens posteriorly
- Typical technique
- 75–85 kVp · 20–40 mAs · 60–72" SID
- Best shows
- C7–T1 when the shoulders hide it on the routine lateral
Image criteria
- C7–T1 interspace seen between the humeral heads.
- Vertebral bodies and disk spaces of C5–T3 in lateral view.
- Humeral heads separated vertically, not superimposed on C7–T1.
Technique values are typical starting points; follow your department's technique chart.
Labeled diagrams
Quick check
2. Which patient positioning produces this cervicothoracic (swimmer's) lateral projection?
3. For AP axial oblique (posterior oblique) projections of the cervical spine, the patient is rotated 45 degrees. How is the CR directed?
4. A patient with long-standing rheumatoid arthritis is scheduled for lateral cervical spine projections in flexion and extension. Which risk should the radiographer keep in mind when guiding the movement?
5. This cervicothoracic (swimmer's) lateral was taken to see C7 and T1. Where is the CR centered?
