Thursday, March 11, 2010

What Rules Should Guide Imaging Decisions in Injured Children?

From Medscape Emergency Medicine > Ask the Experts
William R. Mower, MD

Posted: 02/23/2010

Clinicians often find it difficult to decide whether computed tomography (CT) is appropriate is the evaluation of a child who has a blunt head injury.
CT is an exquisite means of detecting potentially dangerous intracranial injuries, but it exposes particularly vulnerable populations to ionizing radiation and the potential for lethal malignant transformation
This dilemma has stimulated recent efforts to develop clinical rules that guide imaging decisions.
Most of these efforts are ongoing and have yet to achieve conclusive results. However, based on the methodological approaches used in their development, these rules are likely to provide qualitatively similar benefits once they complete final validation.

To use these tools properly, it is important to understand that in creating decision instruments, developers consistently place high value on correctly identifying all children who harbor significant injuries.
Rules developed through this approach are very sensitive, exhibit high negative predictive value, and ensure that injuries are very unlikely to be found among "low-risk" patients. These characteristics make the tools most useful for identifying children who do not need imaging.

The recently validated PECARN rule illustrates these principle.
Children aged 2 years and older are classified as low risk if they exhibit normal mental status, no loss of consciousness, no vomiting, non-severe injury mechanism, no signs of basilar skull fracture, and no severe headache.
Children younger than 2 years of age are considered low risk if they exhibit normal mental status, no scalp hematoma except frontal, no loss of consciousness or loss of consciousness for less than 5 seconds, non-severe injury mechanism, no palpable skull fracture, and acting normally according to parents.

In clinical application the rule was found to have a negative predictive value greater than 99.95%, and correctly identified clinically important injuries in 86 of 88 children (97.7%). The rule assigned low-risk status, and would have omitted imaging, for about 21% of the children who underwent imaging on the basis of clinical judgment.[4] On the other hand, the overall performance of the rule is inferior to clinical judgment; its strict application would have increased overall imaging rates from 35% to about 42%, without increasing sensitivity.[3,4]

The rule's relatively modest benefit derives from its ability to spare imaging for a small proportion of low-risk patients who would otherwise undergo imaging based on clinical judgment.

To date, there has been little effort to develop tools to identify children who are at high risk of intracranial injury and who should undergo routine imaging. Information from current studies indicates that injury prevalence is particularly high among children who have a severe mechanism of injury, exhibit evidence of significant trauma to the calvarium (including skull fracture and lateral hematomas), and those with persistent neurological impairment (including abnormal behavior and altered level of alertness).[2,4] CT is likely to reveal significant injuries in a sizeable proportion of these patients.

While it may be convenient to have decision tools that dictate imaging requirements for all children, it is unlikely that such tools are feasible. Many children present with findings that exclude them from low-risk classification, but do not exhibit high-risk findings.

Imaging decisions in these children should be based on clinical impressions, and it is likely that clinical judgment will continue to play an important role in the foreseeable future in the treatment of many children who have sustained blunt head injury.

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