The discontinuation of life support measures in patients in a permanent vegetative state

Cerebellar Vermis Relative Hypermetabolism: An Almost Constant PET Finding in an Injured Brain

Cortical alterations of brain metabolism, as seen in PET, obviously depend on the nature of the damage (either mechanical, toxic, anoxic, or other). However, some subcortical abnormalities seem to occur rather frequently regardless of the extension, position and cause of the damage. In particular, relative cerebellar vermis activation seems to be frequently encountered. The aim of this work was to determine the incidence of this pattern in a heterogeneous population of brain trauma, and to compare it on a quantitative basis with a group of age-sex matched controls. The case records of this study consist of 58 consecutive patients, 44 males, 14 females, age 14-69 (median 34) 44 traumatic, 8 anoxic, 4 vascular and 2 toxic injuries. In the trauma group, the visualization of the cerebellar vermis was readily appreciable as a consistent majority of cases. In particular, the mean vermis/cerebellum ratio (calculated by appropriate ROI positioning) was 1.26 +/- 0.17 SD (range 0.92-1.82); in the control group the same parameters showed much less dispersion: average 0.92 +/- 0.06, range 0.80-1.10 (P < 0.005). If, on the basis of the normal group data, a cut-off value of 1 is accepted for the v/c ratio, it is noted that 54/57 trauma patients (95%) showed a ratio above this value. In conclusion, a hypermetabolic cerebellar vermis is a common finding in a damaged brain, regardless of the nature of the trauma (probably due to the relative preservation compared with other structures of alternative metabolic pathways), and seems to be the hallmark of the injured brain.

Chronic disorders of consciousness

The vegetative state and the minimally conscious state are disorders of consciousness that can be acute and reversible or chronic and irreversible. Diffuse lesions of the thalami, cortical neurons, or the white-matter tracts that connect them cause the vegetative state, which is wakefulness without awareness. Functional imaging with PET and functional MRI shows activation of primary cortical areas with stimulation, but not of secondary areas or distributed neural networks that would indicate awareness. Vegetative state has a poor prognosis for recovery of awareness when present for more than a year in traumatic cases and for 3 months in non-traumatic cases. Patients in minimally conscious state are poorly responsive to stimuli, but show intermittent awareness behaviours. Indeed, findings of preliminary functional imaging studies suggest that some patients could have substantially intact awareness. The outcomes of minimally conscious state are variable. Stimulation treatments have been disappointing in vegetative state but occasionally improve minimally conscious state. Treatment decisions for patients in vegetative state or minimally conscious state should follow established ethical and legal principles and accepted practice guidelines of professional medical specialty societies.