CEREBRAL BLOOD-FLOW AND VASORESPONSIVITY WITHIN AND AROUND CEREBRAL CONTUSIONS

There is increasing evidence that regional ischemia plays a major role in secondary brain injury. Although the cortex underlying subdural he matomas seems particularly vulnerable to ischemia, little is known abo ut the adequacy of cerebral blood flow (CBF) or the vasoresponsivity w ithin the vascular bed of contusions. The authors used the xenon-enhan ced computerized tomography (CT) CBF technique to define the CBF and v asoresponsivity of contusions, pericontusional parenchyma, and the rem ainder of the brain 24 to 48 hours after severe closed head injury in 10 patients: six patients with one contusion and four with two contusi ons, defined as mixed or high-density lesions on CT scanning. The CBF within the contusions (29.3 +/- 16.4 ml/100 g/minute, mean +/- standar d deviation) was significantly lower than both that found in the adjac ent I-cm perimeter of normal-appearing tissue (42.5 +/- 15.8 ml/100 g/ minute) and the mean global CBF (52.5 +/- 17.5 ml/100 g/minute) (p < 0 .004, repeated-measures analysis of variance). A subset of seven patie nts (10 contusions) also underwent a second Xe-CT CBF study during mil d hyperventilation (a PaCO2 of 24-32 mm Hg). In only two of these: 10 contusions was vasoresponsivity less than 1% (range 0%-7.6%); in the r im of normal-appearing pericontusional tissue, it was 0.4% to 9.1%. Th e authors conclude that CBF within intracerebral contusions is highly variable and is often above 18 ml/100 g/minute, the reported threshold for irreversible ischemia. Intracontusional CBF is significantly redu ced relative to surrounding brain parenchyma, and CO2 vasoresponsivity is usually present. In the contusion and the surrounding parenchyma, vasoresponsivity may be nearly three times normal, suggesting hypersen sitivity to hyperventilation therapy. Given this possible hypersensiti vity and relative hypoperfusion within and around cerebral contusions, these lesions are particularly vulnerable to secondary injury such as that which may be caused by hypotension or aggressive hyperventilatio n.