Question 12

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: Indications, advantages, and disadvantages.

(100% marks)

[Click here to toggle visibility of the answers]

College answer

Aim: To explore the clinical issues of ventilated trauma management.
Key sources include: Paper 2020.2 Q14, same topic with a different approach. CanMEDS Medical Expert.
Discussion: Many candidates did well in the advantages and disadvantages section with a reasonable understanding of the disadvantages (of MRI particularly) and the relative sensitivities of the two modalities for different injuries. More emphasis on safety concerns would have improved some candidates’ answers.
Candidates could improve their answers in the indications section by reading the details given in the stem. The NEXUS criteria are not relevant in an intubated patient.
Incorrect indications included “as part of a routine pan scan” and “neurosurgery or trauma request it”.
To improve this answer the senior ICU practitioner should detail WHY the referring specialities are interested in ordering these scans for the treatment of the ventilated trauma patient. Adding these relevant facts would have allowed candidates to demonstrate depth of knowledge and score more marks.

Discussion

Question 14 from the second paper of 2020 asked for the same CT-vs-MRI comparison but only allocated 40% of the marks to the answer.

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	Widely available Already being performed routinely for the vast majority of trauma patients It picks up 97% of bony injuries and 86% of subluxation injuries; overall only 0.25% of clinically significant spinal injuries are missed by CT Incorporated into numerous protocols for C-spine clearance in unconscious patients	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.

[Submit a comment or correction]