Neuromagnetic assessment of pathophysiologic brain activity induced by minor head trauma

Abstract

Background and purpose: Patients with mild traumatic brain injury (TBI) often show significant neuropsychological dysfunction despite the absence of abnormalities on traditional neuroradiologic examinations or EEG. Our objective was to determine if magnetic source imaging (MSI), using a combination of MR imaging and magnetoencephalography (MEG), is more sensitive than EEG and MR imaging in providing objective evidence of minor brain injury.

Methods: Four subject groups were evaluated with MR, MSI, and EEG. Group A consisted of 20 neurologically normal control subjects without histories of head trauma. Group B consisted of 10 subjects with histories of mild head trauma but complete recovery. Group C consisted of 20 subjects with histories of mild head injury and persistent postconcussive symptoms. The 15 subjects included in group D underwent repeat examinations at an interval of 2 to 4 months.

Results: No MR abnormalities were seen in the normal control group or the asymptomatic group, but five (20%) of the patients with persistent postconcussive symptoms had abnormal MR findings. EEG was abnormal for one subject (5%) from the normal control group, one (10%) from the asymptomatic group, and five (20%) from the group with persistent postconcussive symptoms. MSI was abnormal for one subject (5%) from the normal control group, one (10%) from the asymptomatic group, and 13 (65%) from the group with persistent postconcussive symptoms. There was a direct correlation between symptom resolution and MSI findings for the symptomatic head trauma group.

Conclusion: MSI indicated brain dysfunction in significantly more patients with postconcussive symptoms than either EEG or MR imaging (P < .01). The presence of excessive abnormal low-frequency magnetic activity provides objective evidence of brain injury in patients with postconcussive syndromes and correlates well with the degree of symptomatic recovery.

Figures

fig 1.

Spontaneous MEG data are waveforms showing how magnetic flux changes with time. Data regarding the trauma patients often show generalized slowing of the background activity and focal slow waves. Ten seconds of data are shown from several channels. Two examples of slow waves are marked by the green and red lines. One way to express the data is as a power spectrum, shown on the right. Most slow waves have complicated magnetic field patterns, as shown by the leftmost iso-field contour map. Some slow waves have very dipolar patterns, and the source can be localized and plotted on spatially aligned MR images. The red dot shows the location of the indicated slow wave, with black dots showing slow-wave sources from other points in time

fig 2.

Summary of initial neuroimaging data from all subjects. Group A represents the normal control subjects, group B is the asymptomatic head trauma subjects, and group C is the symptomatic head trauma patients. The set diagram shows what diagnostic tests, if any, provided abnormal findings for each subject. Of particular note are the low false-positive rates for group A and B subjects (all without symptoms), the high sensitivity of MEG to abnormalities in patients with postconcussive symptoms, and the finding that MEG identified abnormalities in all group C subjects who had MR imaging or EEG abnormalities plus seven additional group C subjects who had normal MR imaging and EEG findings

fig 3.

A–C, Magnetic source localization images of a 29-year-old man who, 2 months before the examinations, hit his head after falling from a ladder. At the time of the study, attentional problems and neck pain had precluded his return to work. The results of MR imaging and clinical EEG were normal, but MEG showed focal right parietal ALFMA.

fig 4.

A and B, Magnetic source localization images of a 17-year-old patient who suffered diffuse blows to the head during a fight at school. The patient showed a significant cognitive decline and manifestation of an attentional deficit syndrome subsequent to the trauma. An initial examination was performed 4 months after the trauma occurred (A). The results of MR imaging and EEG were normal. MEG revealed abnormal m-SI values bilaterally at temporal and parietal sites. Multiple dipole clusters of low-frequency activity were found in each hemisphere. Sources spread throughout the right and left parietal and frontal regions, with more activity on the right. At the 9-month follow-up examination (B), the patient continued to show an impaired cognitive profile, and similar MEG results were found. There was some minor lessening of the right hemisphere MEG abnormalities, but the residual ALFMA was still significant and widespread.