Disorder of Executive Function of the Brain after Head Injury and Mild Traumatic Brain Injury – Neuroimaging and Diagnostic Criteria for Implementation of Administrative Support in Japan

The diagnotic criteria for disorder of the executive function of the brain (DEFB) as a syndrome of sequela were administratively established (ad-DEFB) in Japan in 2006 to support disabled patients whose impairment, limited to cognition (memory, attention, execution, and behavior), emerges after organic brain injuries regardless of physical deficits. However, some patients suffering from traumatic brain injury (TBI) have been excluded from receiving medico-social services. In particular, this tendency is more prominent in patients with mild TBI because no lesions are apparent on conventional computed tomography (CT) or magnetic resonance imaging (MRI) in the chronic phase. Recent development of new MRI neuroimaging modalities and positron emission tomography (PET) imaging makes it possible to detect regions of minute organic lesions and metabolic dysfunction in the brain where organic lesions may be absent or cannot be detected on conventional CT or MRI. In this review, we discuss diagnostic criteria for mild TBI and ad-DEFB, the relationship between the two disorders, characteristic neuroimaging [(MRI and 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET)] of diffuse brain injury including cerebral concussion, which is the principal cause of mild TBI, and suggested pathological mechanisms of ad-DEFB in DBI.