Neuroimaging and Outcome Assessment in Vegetative and Minimally Conscious State

Consciousness is a multifaceted concept that has two dimensions: arousal, or wakefulness (i.e., level of consciousness), and awareness (i.e., content of consciousness) (Laureys et al., 2004). An accurate and reliable assessment of the arousal and awareness of consciousness in patients with severe brain damage is of greatest importance for the differential diagnosis of low levels consciousness patients and for outcome evaluation. Following coma, some patients permanently lose all brainstem function (brain death), some progress to “wakeful unawareness” (vegetative state VS), whereas others recover typically and progress through different stages before fully or partly recovering consciousness (minimally conscious state MCS). Patients in VS can open their eyes and exhibit basic orienting responses, but show no conscious, purposeful activity. Reflex and other movements are seen, mediated by brainstem, spinal cord, and brainstem-diencephalic arousal systems (Laureys et al., 2004). VS can occur after patients emerge from an acute catastrophic brain insult causing coma, or can also be seen in degenerative or congenital nervous system disorders. The two common findings are necrosis of the cerebral cortex, thalamus and brainstem (usually after anoxic injury) and diffuse axonal injury (usually after trauma), although other pathological findings can be seen in degenerative and other disorders (Laureys, 2008). The MCS patients do not meet diagnostic criteria for coma or VS because they demonstrate some inconsistent but clear evidence of consciousness (Laureys et al., 2008; Giacino et al., 2002). In the MCS, there is variable impaired function of the cerebral cortex, diencephalons and upper brainstem. This allows occasional conscious behaviours to occur, unlike in VS or coma. Patients may enter the MCS as they emerge from coma or VS, or they can become minimally conscious as a result of acute injury or chronic degenerative diseases. Recent studies suggest a number of potential clinical and rehabilitative applications of magnetic resonance (MR) techniques. Although bedside clinical examination remains the criterion standard for establishing diagnosis, MR may provide an adjunctive diagnostic role when behavioural findings are very limited or ambiguous. The future of diagnostic and prognostic assessment of patients with disorders of consciousness (DOC) envisions a battery of neurobehavioral and neuroimaging techniques (such as structural and functional MR imaging (MRI and