Tag Archives: DAI

Using MRI To Predict Outcome From Diffuse Axonal Injury (DAI)

Has this happened to you? A patient with a serious head injury is not waking up as expected. There were a few punctate hemorrhages seen on the initial CT scan. Your neurosurgery colleague orders an MRI to “provide a prognosis on the patient’s injury.”

Is this a legitimate request? Sure, MRI is very sensitive at detecting very small hemorrhages that may signal the presence of diffuse axonal injury (DAI). But do more abnormalities on MRI equal a poorer prognosis or longer recovery time?

A group from Vanderbilt presented their data from a retrospective cohort study at EAST earlier this year.  They reviewed 7 years of data from 2006 to 2012, including all patients with a head CT positive for intracranial injury and an MRI within 2 weeks. They excluded penetrating injuries and patients with psychiatric or neurologic disorders. They analyzed information on three year mortality, functional outcome, and quality of life.

Here are the factoids:

  • A total of 311 patients met all inclusion/exclusion criteria, with a median age of 40 and serious injury (average ISS 29, average ICU length of stay 6 days)
  • Functional status at discharge could be assessed in 240 patients, and only 118 could be contacted for long-term followup questions
  • Only 56% of patients with severe TBI had an MRI positive for DAI
  • Functional status was lower on discharge for patients positive for DAI on MRI
  • There was no difference in Glasgow Outcome Score, quality of life, or 3 year survival in patients with MRI evidence of DAI compared to those without

Bottom line: This is a relatively large study, but there are still several weaknesses that could skew the numbers a bit. However, it appears that MRI for prognostication of outcomes in patients with clinical DAI is not very helpful. First, only about half with a clinical picture of DAI showed it on MRI. And sure, MRI may tell us a little bit about their status when they are discharged from the hospital to rehab or transitional care. But is that information very useful? It certainly does not help predict their outcome in the longer term. So why order an expensive and difficult study (think restraints, sedation, lots of pumps and monitors) to tell us what we already know based on our experience with severe TBI?

Reference: Prognosis of diffuse axonal injury with traumatic brain injury. J Trauma 85(1):155-159, 2018

Diffuse Axonal Injury (DAI)

Trauma professionals tend to focus on the two extremes of TBI: mild concussive injury because we see so much of it, and very severe injury that we have to work so hard to keep the patient alive. Today I’ll write about the one in the middle, diffuse axonal injury (DAI). People don’t talk about it nearly as much, and it seems kind of mysterious.

DAI is also known as a shear injury, because that’s what we think happens to the brain at the time of injury. Officially, it is diagnosed when a patient remains in a coma for more than 6 hours without a demonstrable mass lesion from bleeding seen on CT. It is seen in about 15% of trauma ICU patients with head injury. Essentially the substance of the brain moves around enough to disrupt a critical mass of axonal connections that results in prolonged unconsciousness. It then takes time to try to rebuild those connections and restore consciousness and some degree of cognition. Mechanisms which result in sudden acceleration or deceleration of the brain may cause this condition, and rotational forces which spin the head suddenly seem to be even worse.

CT scan of the head frequently shows no unusual findings. On occasion, small punctate hemorrhages may be seen. These are generally bad prognostic signs, because CT is so much less sensitive in showing these compared to MRI. Here are some key points about DAI:

  • If the head CT is negative,and all recreational drugs have worn off and the patient still doesn’t wake up, DAI is likely.
  • MRI can confirm the diagnosis, but is not good for giving a prognosis
  • Slow recovery of consciousness or failure to recover correlates with death
  • Hyperglycemia and the presence of a subdural also are highly correlated with mortality

Bottom line: The diagnosis of DAI can generally be made clinically with the assistance of head CT. MRI is not very useful, unless it is needed to confirm the diagnosis. It does not predict speed or degree of recovery so is otherwise not very useful. Supportive care, avoidance of complications and early therapy and rehab are the best treatments we have to offer.

Reference: Diffuse axonal injury in patients with head injuries: an epidemiologic and prognosis study of 124 cases. J Trauma 71(4):838-846, 2011.