Outline the limitations of CT scanning in the assessment of traumatic brain injury.
Many candidates restricted their answers to limitations of the scan itself, and did not consider other clinical issues related to putting a critically ill patient into a CT scanner. Candidates should consider asking themselves “why don’t we perform more of this investigation?”.
Physical limitations include:
• patient size,
• usually distant from resuscitation area, thus patient needs to be moved,
• some patients may require GA for the investigation when they otherwise wouldn’t have had a GA,
• difficulty monitoring and attending to patient during scanning (especially if intubated and ventilated and “sick”).
Clinical limitations include:
• may be other priorities (eg urgent laparotomy which precludes early CT)
• interpretation is difficult/impossible if other previous IV contrast Xray investigation
• normal CT head doesn’t exclude underlying injury (eg diffuse axonal injury, vascular injury, ischaemia, hypoxic injury) – so may need to repeat it within 24 hrs
• CT head findings do not correlate with ICP value (unless CT findings of herniation – and then ICP bound to be too high and too late a detection)
• CT findings are not generally good predictors of patient outcome (though may be useful in some situations eg the Marshall score [used to prognosticate outcome], and the presence of traumatic SAH on CT which portends a poor prognosis).
• poor visualisation of posterior fossa and brainstem.
The CT scan of the brain has the following limitations when it comes to traumatic brain injury:
Relevance to clinical setting
There is an excellent article which discusses the advantages and limitations of various neuroimaging techniques:
Lee, Bruce, and Andrew Newberg. "Neuroimaging in traumatic brain imaging." NeuroRx 2.2 (2005): 372-383.
Miller, M. Todd, et al. "Initial head computed tomographic scan characteristics have a linear relationship with initial intracranial pressure after trauma." Journal of Trauma-Injury, Infection, and Critical Care 56.5 (2004): 967-973.