Question 5

Compare and contrast the use of computed tomography (CT) with magnetic resonance imaging (MRI) in the assessment of suspected cervical spine injury, in ventilated patients following blunt trauma.

Please tabulate your answer under the following headings:

a) Indications.    (5 marks)
b) Advantages and disadvantages.    (5 marks)

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College Answer


Syllabus topic/section:

2.1.20 Radiology in Intensive Care.
2.1.13 Trauma Intensive Care – L1.

Aim:
To explore the clinical issues of ventilated trauma management.

Discussion:
This question is a repeat from the 2023.1 March paper and the candidate answers have improved in the quality, attention to detail and depth of knowledge of this core topic from the previous sitting.
The marking examiner noted that some candidates achieved a high score with only 1 page of writing if it was well structured and concise. This is a useful fact when considering time management strategies in the examination. This answer benefits from a tabulated structure and most candidates were able to take advantage of this.
Marks could have been gained by considering that 50% of the marks were allocated to the discussion of indications for both modalities, marks were missed because they prioritised the advantages and disadvantages to the exclusion of a section that had equal mark allocation. Candidates are advised to use the marks allocated to manage time effectively during the written examination.
The disadvantage of having to remain in a collar while waiting for an MRI under GA was omitted by many of the candidates. Most had also failed to mention the prognostic advantages of being able to image the internal structure of the spinal cord. Some candidates referred to MRI as the "gold standard", without specifying which structures it is the gold standard for. Many candidates referred to contrast as being a disadvantage of either modality, but neither modality requires contrast for the evaluation of C-spine injury.
Many candidates wrote about the rationale for CT or MRI (e.g., good at picking up ligamentous injuries) rather than the indications as the question asked (e.g., a patient with abnormal neurological examination needs an MRI even if CT doesn't detect an injury etc).
 

Discussion

This is a repeat of Question 12 from the first paper of 2023.

Modality CT MRI
Indications
  • Investigation of bony C-spine injuries 
  • Investigation of soft tissue injuries associated with neck trauma, including spinal cord and nerve root injuries
  • Indicated for the investigation of ligamentous injury where the C-spine is  mechanically unstable but there is no bony injury on CT
Advantages
  • Highly sensitive for injured soft tissue structure and spinal cord injury
  • Gold standard for the evaluation of spinal cord trauma
  • No radiation exposure is required
  • May be necessary for surgical planning
Disadvantages
  • Ligamentous injuries could have clinically significant consequences, and these may be missed
  • Only gives limited information about the disc
  • Image quality and interpretation can be degraded by previous C-spine surgery or degenerative change
  • Loses its sensitivity for ligamenous injury over the first week 9as the oedema diminishes)
  • High false positive rate (as high as 40% in some studies)
  • Availability of MRI, particularly MRI set up to accept intubated patients, is lower than CT
  • May not be possible if the patient has had interventions which have resulted in MRI-incompatible implants (eg. IVC filters)
  • Waiting for the MRI may prolong the period of C-spine immobilisation unnecessarily

References

Jo, Alexandria S., et al. "Essentials of spine trauma imaging: radiographs, CT, and MRI." Seminars in Ultrasound, CT and MRI. Vol. 39. No. 6. WB Saunders, 2018.

Malhotra, Ajay, et al. "Utility of MRI for cervical spine clearance in blunt trauma patients after a negative CT." European radiology 28.7 (2018): 2823-2829.

Patel, Mayur B., et al. "Cervical spine collar clearance in the obtunded adult blunt trauma patient: A systematic review and practice management guideline from the Eastern Association for the Surgery of Trauma." Journal of Trauma and Acute Care Surgery 78.2 (2015): 430-441.

Morris, C. G. T., and E. McCoy. "Clearing the cervical spine in unconscious polytrauma victims, balancing risks and effective screening." Anaesthesia 59.5 (2004): 464-482.