The Failure of Traditional Neuroimaging
Traditional brain imaging modalities such as magnetic resonance imaging (MRI) and computed tomography (CT) provide little evidence in cases of mild-to-moderate TBI. This is likely secondary to the fact that CT and MRI detect structural defects, which in the case of mild-to-moderate TBI are likely either not present or below the imaging resolution of MRI or CT. Both certainly have their applications in helping to diagnose traumatic brain injuries (especially severe injuries). Typically, CT remains a vital first step in the assessment of any TBI due to its superior capacity to visualize hemorrhage and skull fracture. Unfortunately, the sensitivity of CT is very low for mild-to-moderate TBI, and so the majority of CT scans in mild-to-moderate TBI are read as normal.
A significant body of literature shows that single-photon emission computerized tomography (SPECT) scans are more sensitive for mild-to-moderate TBI than CT scans. In a combined sample of more than 4000 mild TBI cases, roughly 5% to 10% had abnormal CT scans.13-15 In a prospective study of 92 adult and pediatric patients with TBI compared with a database of 40 healthy individuals,16 SPECT and CT scans were performed within 72 hours of injury. The CT scans were abnormal in only 34% of cases. In contrast, the SPECT scans were abnormal in 63%. In all cases with positive SPECT scans, the findings were co-localized with lesions revealed on CT scan.
SPECT scans have also proven to be more sensitive for detecting mild-to-moderate TBI than anatomical MRI scans. In a study of 13 patients with moderate TBI compared with 21 screened controls, MRI was positive in only 50% of cases, whereas SPECT was positive in 100% of cases.17 In a retrospective study of 228 cases, SPECT revealed evidence of functional brain deficits in 68% of the cases, whereas CT and MRI scans were completely negative.18 The SPECT scans revealed that 46% of cases had frontal lobe hypoperfusion, 55% had basal ganglia/thalamic hypoperfusion, and 18% had temporal lobe hypoperfusion.
Currently, The Society of Nuclear Medicine19 and the European Association of Nuclear Medicine20 recognize SPECT as having diagnostic and prognostic value for TBI (both in acute concussion and long-standing injury). The American College of Radiology21 cites symptomatic TBI, especially in the absence of CT and/or MRI findings, as a clinical indication for the use of SPECT. It should be noted that the outdated 1996 TTASAAN report22 by the American Academy of Neurology, which concluded that SPECT was an experimental technique, was based on only 6 early studies. Its conclusions have been superseded by the more current literature.
The International Society of Applied Neuroimaging (of which I am currently the president) recently reviewed all of the extant literature on the use of SPECT neuroimaging in TBI.23 To summarize the state of current literature, 903 patients included in 19 longitudinal studies demonstrated Level II A evidence for the utility of SPECT to identify lesions in the clinical setting of TBI. Of the 19 longitudinal studies, 14 (77%) had neurological or neuropsychology outcome measures to which SPECT abnormalities were correlated. A total of 2121 patients in 52 cross-sectional studies of TBI were also reviewed.