Rehabilitation Research and Practice 4. Discussion A substantial minority of patients who sustain an MTBI and are evaluated in an emergency department will have a visible abnormality on early CT scanning (Table 1). These patients are conceptualized as having a complicated MTBI. Researchers have reported that those with complicated MTBIs, as a group, are more likely to have early cognitive deﬁcits [1–6] and worse medium [1, 10, 11] and long-term [12] functional outcome. In contrast, however, some re- searchers have not found important diﬀerences between those with complicated versus uncomplicated MTBIs. For example, in one study, patients with complicated MTBIs were not more likely to have a postconcussion syndrome at three months after injury [13], and another research group reported that neuroimaging ﬁndings did not predict cog- nitive functioning at one or 12 months after injury, or func- tional outcome at one year after injury [14]. In the present study, as hypothesized, patients with com- plicated MTBIs took longer to return to work. It has been noted that most patients return to work after injury despite having some symptoms [22]. In this study, we did not expli- citly examine if the patients had symptoms prior to returning to work. Yet, the majority of the study population had re- turned to work by the time of the neuropsychological as- sessment. Therefore, their self-reported symptoms at the time of evaluation likely reﬂect their situation after returning to work, supporting the idea that it is common to return to work while still having some symptoms. One possible reason for why intracranial lesions were correlated with longer time oﬀ work may be that doctors are likely to grant longer sick leaves when there is objective evidence of brain injury; in that case the duration of the postinjury sick leave might reﬂect, in part, the behavior of doctors in the Finnish system. We have no way of determining whether, or not, doctors in the community are likely to grant longer sick leaves to patients with complicated MTBIs, but we have anecdotal evidence from emergency department physicians that they tend to prescribe longer initial periods of leave for patients with more serious injuries such as those with intracranial ab- normalities. In the present study, the patients with complicated versus uncomplicated MTBIs were compared on neurocognitive testing and symptoms ratings at approximately 3-4 weeks after injury. It was hypothesized that those with complicated MTBIs would perform more poorly on cognitive testing and report more symptoms than those who did not have imaging abnormalities. Contrary to these hypotheses, there were no diﬀerences between the two groups on neurocognitive test- ing or symptom reporting. Surprisingly, there were trends toward those with complicated MTBIs reporting fewer sym- ptoms and performing somewhat better on cognitive testing. There are methodological diﬀerences and limitations with the present study, in comparison to previous studies, that might have inﬂuenced the results. First, there were a small number of subjects in this study that were identiﬁed as having imaging abnormalities; thus, the statistical analyses were underpowered. However, when examining the means and SDs, there was not a trend toward greater symptoms or 5 Figure 1: Hemosiderin detected with multiecho susceptibility weighted imaging using a 3 Tesla scanner. Multiecho SWI image (Philips Achieva 3T; 5 echoes; voxel size = 0.32 × 0.32 × 0.75 mm3). Courtesy of Alexander Rauscher, Ph.D., UBC MRI Research Centre, Department of Radiology, University of British Columbia, Vancouver, Canada. worse cognitive test performance in the complicated MTBI group. In fact, there were trends toward fewer symptoms and better performance in this group. This reduces the likelihood that the present ﬁndings represent a Type 2 statistical error. Second, most previous studies classiﬁed patients as having complicated MTBIs based on day-of-injury CT scanning only, and some of these studies are older and the CT technol- ogy might have been less reﬁned. The present study identiﬁed subjects based on CT and MRI, with some of our sample not showing day-of-injury CT abnormalities—only abnor- malities on MRI. Third, some previous studies have included subjects with complicated MTBIs who required inpatient rehabilitation. None of the present patients were injured that badly. Finally, some previous studies have included patients in litigation, whereas no patients in this study were involved in litigation. Therefore, it is possible that the present group of patients with complicated MTBIs were less severely injured than some of the samples from previous studies. As technology evolves, some researchers will be tempted to broaden the criteria for complicated MTBI. In the past, intracranial abnormalities were identiﬁed using CT or conventional MRI. With advancements in technology, smaller and smaller abnormalities can be detected using structural imaging. For example, the area of hemosiderin (iron-rich staining of tissue from an area with past blood) shown in Figure 1 using multiecho susceptibility weighted imaging (SWI) with 5 echoes [23, 24] on a 3 Tesla MRI scanner would be undetectable with a modern CT scan and would likely be missed using 1.5 or 3.0 Tesla MRI conventional sequences [25]. Therefore, in past studies this subject would be classiﬁed as having an uncomplicated MTBI, but in future studies this abnormality might qualify for classiﬁcation as a complicated MTBI. However, this subject was actually a healthy control subject in one of our studies. He had no known history of an injury to his brain.