This is a best estimate, folks. We've presented what we think is the closest thing to the truth about this intervention, but our data is only as good as the studies that underlie it — and often, the studies aren't as complete or as good as we'd like, and in some cases the data have not been validated. We present one number here for the NNB, but please realize this is an estimate and there is a range for actual risk in a given person. That range will depend upon the person's demographic, their subtype of possible disease, the setting of the risk assessment, their general health, and literally thousands of other variables. Using these numbers in practice means taking a number of large leaps about all of these variables, and also about the veracity of the underlying research. Therefore, as with any 'high quality' data, the application of data requires a doctor's expertise and deliberate consideration.
In Summary, if you meet the below criteria for this assessment:
- At initial examination:
- 99.6% will not require (or undergo) neurosurgery
- 0.4% will undergo neurosurgery*
- After 4-6 hours have elapsed from the injury:
- 99.92% will not require (or undergo) neurosurgery
- 0.08% will undergo neurosurgery or deteriorate
In Other Words:
- At initial examination, the risk of an injury requiring neurosurgery is 1 in 250
- After 4-6 hours have elapsed from the injury, the risk of an injury requiring neurosurgery is 1 in 1250
Criteria:
- Probable or definite loss of consciousness at initial injury, or memory lapse during examination
- Neurologically normal on physician examination (other than memory loss)
- Glasgow Coma Scale of 15 (out of 15 potential points)
Where We Get The Numbers:
Source: Stiell IG, et al. The Canadian CT Head Rule for patients with minor head injury. Lancet. 2001; 357: 1391-1396.Stiell IG, et al. Comparison of the Canadian CT Head Rule and the New Orleans Criteria in patients with minor head injury. JAMA.2005;294:1511-1518
Smits M, et al. External validation of the Canadian CT Head Rule and the New Orleans Criteria for CT scanning in patients with minor head injury. JAMA. 2005; 294: 1519-1525.
Reilly PL, et al. Patients with head injury who talk and die. Lancet, 1975; 306 (7931): 375 - 377.
Galbraith S. Misdiagnosis and delayed diagnosis in traumatic intracranial haematoma. BMJ. 1976; 1: 1438.
Jennett et al. Severe head injuries in three countries. J Neurol Neurosurg Psychiatry 1977 40: 291-298
Rose J, et al. Avoidable factors contributing to death after head injury. BMJ. 1977; 2 : 615.
Dacey RG, et al Neurosurgical complications after apparently minor head injury. J Neurosurg. 1986; 65: 203-210.
Rockswold GL, et al. Analysis of management in thirty-three closed head iniury patients who "talked and deteriorated." Neurosurgery 1987; 21: 51-55.
Rosckwold GL, et al. Patients who talk and deteriorate. Ann Emerg Med. 1993; 22(6): 1004-7.
Harm Endpoints: Neurosurgery, death, intubation
Narrative: Minor head injury is an extremely common problem experienced by people everywhere and seen by physicians everywhere.
A small proportion of patients who appear to be neurologically normal will go on to have intracranial bleeding that will typically be treated with neurosurgery, but reliably forecasting these outcomes without over-treating (or over-testing) an unacceptable proportion has been difficult. This review examines the highest quality data available from emergency department evaluation of patients with minor head injuries, and concludes that untoward outcomes appear to occur at a consistent percentage (0.4%) across multiple minor head injury study populations.1 2 3 4
Decision aids such as the Canadian CT Head decision aid are also useful.3 4 The aid suggests that neurologically normal patients who do not have signs of fracture on examination, who are under age 65, and who have not vomited 2 times or more will not require neurosurgery at any point. This is important information but should not be taken to mean that anyone with vomiting or over age 65, for instance, is likely to require neurosurgery. The data suggest, in fact, that neurologically normal patients over age 65 still have a 99% chance of requiring no further intervention, and physicians and their patients should be aware of these risks.
When minor head injury patients do have major problems such as neurologic deterioration it typically occurs in the first few hours. Rarely, it occurs beyond this time period. A substantial body of case series literature suggests that when delayed major problems occur they occur approximately in 20% of bad outcome cases and they occur after 4-6 hours.5 6 7 8 9 10 11 In many cases they occur more than 12-24 hours later, making them quite delayed and in some cases detectable neither through a full day of observation nor with an immediate CT scan.
Caveats: These data are from studies of head injured patients being evaluated in ED's. This will not apply to many minor head injuries for whom risk is lower as their condition did not prompt them to seek care. In addition, many enrolled patients are in a subset of minor head injuries that is at higher risk than average because of their loss of consciousness, and the typical selection bias that comes with study enrollment (study subjects are usually higher risk than those who do not get enrolled in such studies). Therefore these risk estimates are likely to be high when applied to a general minor head injury population.
Alternately, the reported cohorts here were evaluated thoroughly by physicians for signs of skull fractures, neurologic abnormalities, and other signs and symptoms of brain injury. Therefore in the absence of this thorough physician evaluation it is not possible to know whether or not a specific patient is appropriately classified as a minor head injury meeting the above criteria.
Finally, the above estimates of risk of delayed deterioration (the 'talk and deteriorate' or 'talk and die' syndrome) are based on extrapolation from case series' of these patients, combined with the data from major minor head injury studies. They are not an observed set of outcomes, but rather a statistical speculation about the likelihood of delayed events after an initial 4-6 hours of normal neurologic findings.
Author: David Newman, MD
Published/Updated: September 21, 2010
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