2 First author Livingston [26] Stein [27] Jeret [28] Moran [29] Borczuk [30] Iverson [31] Thiruppathy [32] Stiell [33] Stiell [33] Ono [34] Saboori [35] Year 1991 1992 1993 1994 1995 2000 2004 2005 2005 2007 2007 Table 1: Rates of complicated mild TBI in adults. Country USA USA USA USA USA USA India Canada Canada Japan Iran Total N 111 1,538 712 200 1,448 912 381 2,707 1,822 1,064 682 Number Scanned 111 1,538 702 96 1,448 912 381 2,171 1,822 1,064 682 Rehabilitation Research and Practice GCS scores % Abnormal 14-15 13–15 15 13–15 13–15 13–15 13–15 13–15 14-15 15 15 14 17.2 9.4 8.3 8.2 15.8 38.9 12.1 8.0 4.7 6.7 However, the results from a series of studies are mixed. As a group, patients with complicated MTBIs perform more poorly on neuropsychological tests in the ﬁrst two months following injury [1–6]. These diﬀerences appear to diminish by six months following injury [7, 8]. When diﬀerences occur between groups, the eﬀect sizes of these diﬀerences are lower than expected (i.e., medium to medium-large eﬀect sizes or lower on a small number of tests [1–5, 7, 9]; see Borgaro and colleagues [5] for an exception). Some researchers have reported that patients with com- plicated MTBIs have worse 6–12-month functional outcome (i.e., Glasgow Outcome Scale) compared to patients who sustained uncomplicated MTBIs [1, 10, 11], and they have similar 3–5-year outcome (i.e., Functional Status Exami- nation) as patients with a history of moderate and severe TBI [12]. There are some exceptions, however. McCauley and colleagues reported that CT abnormalities were not associated with increased risk for postconcussion syndrome at 3 months after injury [13]. Similarly, Lee and colleagues [14] reported that CT and conventional 3T MRI imaging ﬁndings do not predict neurocognitive functioning at 1 or 12 months after injury, nor functional outcome at one year after injury. It is becoming increasingly clear that complicated MTBIs represent a fairly broad spectrum of injury, with some people having very small abnormalities and excellent functional outcome and other people requiring inpatient rehabilitation and having poor outcome. The purpose of this study is to compare the outcome of patients with complicated versus uncomplicated MTBIs. To date, few studies have compared both neurocognitive outcome and self-reported symptoms following uncompli- cated and complicated MTBI. This is a prospective study, with patients identiﬁed from the emergency department undergoing MRI and a neuropsychological evaluation at approximately 3-4 weeks after injury. It was hypothesized that patients with complicated MTBIs would report more symptoms, perform more poorly on neurocognitive testing, and take longer to return to work than patients with uncom- plicated MTBIs. We hypothesized worse outcome in this group because we assume that complicated MTBIs tend to be more serious brain injuries than uncomplicated MTBIs. 2. Methods 2.1. Participants. Participants were 47 patients with MTBIs who presented to the emergency department of Tampere University Hospital, Finland (age: M = 30.3 years, SD = 9.4, Range = 16–46; education: M = 13.0 years, SD = 2.3). The patients were selected from a larger cohort of head trauma patients enrolled in a longitudinal study, based on meeting inclusion criteria below, having complete data on all outcome measures, and having a known duration of time oﬀ work. The diagnostic criteria for MTBI used in this study were from the World Health Organization Collaborating Centre Task Force on MTBI. Inclusion criteria were as follows: (i) biomechanical force applied to the head resulting in loss or alteration of consciousness, confusion, and/or posttraumatic amnesia, (ii) loss of consciousness (LOC), if present, for less than 30 minutes, (iii) Glasgow Coma Scale (GCS) score 13– 15 after 30 minutes following injury, and (iv) posttraumatic amnesia (PTA), if present, of less than 24 hours. Patients underwent computed tomography (CT) scan- ning if deemed clinically indicated, an evaluation by an ED traumatologist, and other examinations as needed. CT scan- ning was performed within 24 hours of admission and is used liberally for head trauma patients. Magnetic resonance imaging (MRI) was conducted at approximately three weeks after injury for research purposes, although the information was available to the patient’s healthcare providers (com- plicated MTBI group M = 19.3, SD = 15.0, range = 1– 53 days and uncomplicated MTBI group M = 25.8, SD = 5.5, range = 16–36 days). The MRI protocol included sagit- tal T1-weighted 3D IR prepared gradient echo, axial T2 turbo spin echo, conventional axial, and high-resolution sagittal FLAIR (ﬂuid-attenuated inversion recovery), axial T2∗, and axial SWI (susceptibility weighted imaging) series. Only trauma-related ﬁndings on CT or MRI were counted as abnormal; minor incidental ﬁndings, such as isolated white