CT Cervical Spine

Computed tomography of the cervical spine acquires a volume from the skull base to the first thoracic vertebra with thin slices (0.5 to 1.25 mm), reconstructed in axial, sagittal and coronal planes with bone and soft tissue algorithms.

It is the first line test for suspected bony and ligamentous injury after trauma, replacing plain radiographs in most centres because it is faster and more sensitive.

The scan takes under a minute. Effective dose is about 2 to 4 mSv, and the thyroid is in the field, so dose is kept to the lowest that gives diagnostic images, with iterative reconstruction.

Cervical spine injury occurs in 2 to 4% of blunt trauma patients seen in emergency departments, and is missed on radiographs in up to 50 to 60% of fractures.

CT has a sensitivity of over 98% for clinically important fractures and a negative predictive value of over 99% for significant bony injury; it is less sensitive for purely ligamentous injury, spinal cord injury and disc herniation, for which MR is used.

Degenerative disease is nearly universal after the age of 50.

Indications. Blunt trauma with neck pain or tenderness, neurological deficit, reduced consciousness, intoxication, distracting injury, dangerous mechanism, or age over 65. Unconscious or intubated trauma patients. Part of whole body trauma CT.

Abnormal or inadequate plain radiographs. Suspected fracture dislocation, atlanto axial instability, odontoid fracture. Pre-operative planning and assessment of fusion.

Congenital anomalies, tumour and infection (bone destruction, with contrast). Degenerative disease with bony canal or foraminal stenosis, ossification of the posterior longitudinal ligament. Not for low risk patients who are alert, sober, with no midline tenderness, no deficit, no distracting injury and full painless rotation, who need no imaging.

Contraindications and precautions. No absolute contraindications. In trauma the collar and in line immobilisation are kept until the study is reported. Pregnancy: use only when the clinical need is clear; shielding of the abdomen is not needed.

Children: justify carefully, use age specific low dose settings, and prefer observation or MR for low risk children, because the thyroid and breast dose is significant. Contrast is given only for infection, tumour or vascular injury, with the usual precautions for renal function and allergy.

Preparation and technique. No preparation. The patient lies supine, shoulders pulled down (if injury allows) to show the cervicothoracic junction, head in neutral position. A scout view sets the range from the skull base to T1 or T4.

Volume data are reconstructed at 1 to 2 mm in all three planes. A bone algorithm shows the cortex, facets and canal; a soft tissue algorithm shows the cord, discs and prevertebral tissues.

Contrast CT angiography of the neck is added when blunt cerebrovascular injury is suspected (fracture through a transverse foramen, facet dislocation, subluxation, or a skull base fracture involving the carotid canal).

Normal appearances. Seven vertebrae with a gentle lordosis, aligned along four smooth curves: the anterior and posterior vertebral body lines, the spinolaminar line and the tips of the spinous processes. Vertebral body heights are even, endplates smooth, and facet joints congruent with a joint space of 2 mm or less.

The atlantodental interval is under 3 mm in adults (under 5 mm in children). The prevertebral soft tissue is under 7 mm at C2 and under 20 mm at C6 in adults. The canal is at least 13 mm wide in the sagittal diameter at mid-cervical levels, and the cord fills part of it with CSF around it.

The dens is intact, with no step between C1 lateral masses and C2 body (total overhang under 7 mm).

Interpretation.

• Atlas fracture: ring fracture of C1 with two or more breaks (burst fracture), lateral mass overhang and a widened atlantodental interval suggesting disruption of the transverse ligament.
• Odontoid fracture: type I tip avulsion, type II fracture through the base (commonest, high non-union rate), type III extending into the C2 body.
• Traumatic spondylolisthesis of C2: bilateral pars interarticularis fractures of C2 with anterolisthesis of C2 over C3.
• Subaxial fractures: compression and burst fractures (retropulsed fragments narrowing the canal), teardrop fractures (anteroinferior fragment with posterior displacement and flexion injury, unstable), facet fractures, lamina and spinous process fractures (clay shoveler fracture of C7 or T1), and transverse process fractures (check the vertebral artery).
• Facet dislocation: unilateral (anterolisthesis under 50% of the vertebral width with "naked facet" and rotation) and bilateral (anterolisthesis over 50%, flexion injury with high cord injury risk).
• Craniocervical dissociation: widened basion dens interval, widened occipital condyle to C1 interval, and prevertebral haematoma; often fatal and easily missed.
• Soft tissue signs: prevertebral swelling or haematoma, widened interspinous distance, widened disc space, and kyphotic angulation of over 11 degrees between adjacent vertebrae, all suggesting ligamentous injury needing MR.
• Degenerative: disc space narrowing, osteophytes, uncovertebral and facet hypertrophy, canal stenosis, foraminal narrowing, ossification of the posterior longitudinal ligament, and diffuse idiopathic skeletal hyperostosis (flowing anterior ossification over four or more levels).
• Inflammatory and infective: erosion of the dens (rheumatoid arthritis, with atlanto axial subluxation and pannus), ankylosis with fracture risk (ankylosing spondylitis, where even minor trauma gives unstable transverse fractures), vertebral osteomyelitis (endplate destruction, paravertebral abscess), and tuberculous spondylitis (anterior vertebral body destruction, gibbus, calcified abscess).
• Tumour: lytic or sclerotic metastases, myeloma, pathological fracture, and primary bone tumours.
• Congenital: os odontoideum, congenital fusion (Klippel-Feil), basilar invagination, and atlas assimilation.
• Vascular: transverse foramen fracture or subluxation (CT angiography to look for vertebral artery dissection or occlusion).

Critical values and findings needing immediate action.

• Unstable fracture or dislocation, canal compromise or retropulsed fragment: maintain immobilisation, urgent spinal surgical review, and MR to assess the cord.
• Neurological deficit with a normal CT: MR immediately (cord contusion, haematoma, disc herniation, epidural haematoma).
• Craniocervical dissociation: strict immobilisation without traction, immediate specialist care.
• Vertebral or carotid artery injury: antithrombotic treatment after specialist review, neurovascular imaging.
• Dens fracture with displacement: halo or surgical fixation after review.
• Epidural abscess or vertebral osteomyelitis with deficit: urgent MR, antibiotics and surgery.
• Pathological fracture with cord compression: steroid and urgent oncological and surgical review.

Limitations and artefacts.

• CT is poor at showing ligament injury, disc disruption, cord injury and early marrow oedema; a patient with deficit or persistent pain and normal CT needs MR.
• The cervicothoracic junction is hard to visualise in broad shoulders because of beam hardening; extend the scan to T4 and use thin slices.
• Motion, dental metal and shoulders cause streak artefact; repeat the scan with sedation if needed.
• Degenerative change mimics fracture and vice versa: sclerotic edges favour old change, sharp lucent lines with soft tissue swelling favour acute injury.
• Normal variants mimic injury: synchondrosis of the dens in children under 7 years, pseudosubluxation of C2 on C3 in children (up to 3 mm), absent lordosis from muscle spasm, and unfused ossification centres.
• Radiation to the thyroid is higher than with plain radiographs; avoid repeated studies without clear indication.
• The decision to clear the collar in obtunded patients differs between centres, and CT alone is accepted in many.

Special groups.

• Children: low dose settings, careful interpretation of variants, cord injury without bony abnormality is possible, so MR is used for deficit.
• Older adults: fractures after low energy falls, odontoid fractures, central cord syndrome in a stenotic canal with a normal CT.
• Ankylosing spondylitis and diffuse idiopathic skeletal hyperostosis: lower threshold for CT, because fractures are unstable and subtle.
• Pregnancy: acceptable when needed, with minimal foetal dose.
• Patients with rheumatoid arthritis: assess the atlantodental interval before surgery or intubation.
• Regions: road traffic and fall injuries are frequent, with limited access to CT and MR; clinical clearance and collar immobilisation are often the only options, and diving and sports injuries, tuberculosis of the spine and cervical myelopathy from degeneration are common.

Follow up tests. MR cervical spine (cord, ligaments, discs), CT or MR angiography of the neck for vascular injury, flexion and extension radiographs once pain allows (selected), repeat CT after reduction or surgery, bone density and metabolic screen for fragility fractures, inflammatory markers, blood cultures and biopsy for suspected infection,

serum protein electrophoresis for lytic lesions, electromyography for radiculopathy, and referral to spinal surgery, neurosurgery or rehabilitation medicine.