Background & Purpose
Several longitudinal studies have demonstrated a significant association between increased oxygen extraction fraction (OEF) and a risk of subsequent stroke in symptomatic patients with occlusive cerebral artery disease1, 2. Elevated OEF and normal OEF were both observed in these patients. It is unclear which factors induce OEF change. We investigated an association between the collateral vasculature and elevation of OEF in patients with chronic middle cerebral artery (MCA) occlusion.
Methods
We studied 13 patients with chronic ipsilateral MCA occlusion (9 symptomatic and 4 asymptomatic; 7 men and 6 women; mean age 57. 6±11.3 years) who underwent a positron emission tomography (PET) study with O-15 steady-state inhalation method from April 2000 to December 2004. Collateral vasculature was evaluated by DSA (n=8) or MRA (n=5). The DSA or MRA was performed within 4 months before or after the PET study. We recorded (1) the side and the part of the MCA occlusion, (2) the occlusion or stenosis of the ipsilateral anterior cerebral artery (ACA) and the posterior cerebral artery (PCA), (3) the presence of the anterior and posterior communicating arteries (AcomA and PcomA, respectively), (4) the occlusion or stenosis of the contralateral major cerebral arteries, and (5) the occlusion or stenosis of the bilateral internal carotid arteries, the basilar artery, and the intracranial vertebral arteries, assessed by DSA or MRA. (6) The ipsilateral leptomeningeal collaterals were also evaluated in 8 patients by DSA. Since our normal population had OEF of 0.42±0.03, pathologically elevated OEF was defined as OEF 0.50 or more 3 .
Results
The OEF of the ipsilateral MCA area was pathologically elevated in 4 patients and normal in 9 patients. All the patients with elevated OEF had a stenosis or occlusion in the collateral vasculature (ipsilateral ACA and PcomA). The MCA horizontal segment was not seen in the DSA. The patients with pathologically elevated OEF were all symptomatic. The patients with normal OEF (n=5) had well-developed leptomeningeal collaterals through ACA or PCA. The horizontal segment of occluded MCA was visualized retrogradely.
Conclusion
The elevated OEF was specifically found in patients with MCA occlusion and co-existing multiple steno-occlusive lesions in the collateral vasculature. The vascular lesion other than occluded MCA may reduce cerebral perfusion pressure for collateral circulation. In patients with chronic MCA occlusion, the steno-occlusive lesion of collateral vasculature is one of the major factors to induce misery perfusion.