Mr Sensitivity And Specificity In A New Model Of Collateral Experimental Acute Ischemia

To assess the early diagnostic sensitivity of MR and the possible recurrence of ischemic events, we rested a new ischemic model termed << collateral >> since it is secondary to occlusion of one or more of the pre-Willis vessels. We studied 12 New Zealand albino rabbits (4-5 kg) which underwent general anaesthesia. Average systemic arterial pressure, heart rare, pH and blood gases were monitored throughout the experiment. Ischaemia was induced by a microsurgical technique in 8 animals by closing both common carotid arteries at the neck (from a minimum of 2h to a maximum of 24h) and in another 4 rabbits by closure of the epiaortic vessels at the aortic arch (from a minimum of 2h to a maximum of 4h). The animals were killed without prior reperfusion and studied by MR. Ischemic injury could not be assessed in one case (no.12) due to poor quality. Blurred, variable images displaying mainly monolateral linear and/or punctiform lesions in different locations were identified in eight cases.In agreement with the findings of some << terminal >> models investigated by MR, << collateral >> ischemic injury was already evident in our animals within the first two hours after both closure of the carotid arteries and the aortic arch. MR image quality was poor and difficult to reproduce. In addition, findings were aspecific, possibly due to a selective vulnerability of mesial brain structures to hypoxia. All these factors weigh against the use of this model for a systematic experimental study of ischemia and hence the efficacy of therapeutic trials, even though negative MR findings will not rule our neuronal ischemic injury.