Alejandro Rodríguez-Vázquez, MD
As we know, the lenticuloestriate territory is irrigated by terminal, noncollateralized vascularization and thus is often damaged in acute ischemic strokes secondary to proximal middle cerebral artery (MCA) occlusions, even when a complete recanalization via mechanical thrombectomy is achieved. This territory, however, includes both grey and white matter with different susceptibility to ischemia. In this study, the authors tried to determine if early thrombectomy allows to spare the more resistant white-matter fibers in the internal capsule despite the harm on neighboring grey matter deep tissue.
This was a prospective, observational, single-center study which included 92 consecutive patients with isolated MCA occlusion, less than 6 hours from symptoms onset, mechanical thrombectomy, and follow-up diffusion-weighted image magnetic resonance (median time three days). Eighty patients (87%) achieved successful recanalization, and 89 patients (97.7%) had reperfusion of the proximal M1 segment with restoration of complete MCA lenticuloestriate artery flow. All patients showed estriatal ischemia, but only 45 of 92 patients (48.9%) had ischemic damage on the internal capsule, including three patients without M1 reperfusion. Patients with partial perfusion of the MCA perforators before thrombectomy (defined as the visibility of any of the medial or lenticuloestriate artery groups in the pre-thrombectomy arteriography) were less likely to have internal capsule ischemia (56.4% vs. 37.8%). In addition, time from symptom onset to groin puncture and to reperfusion was lower in the patients without internal capsule ischemia (medians 210 vs. 221 min, P=0.033; and 209 vs. 247 min, P<0.001, respectively). Collateral grade did not differ between groups.
Clinically, patients with internal capsule involvement had more putaminal hemorrhages (55.6% vs. 17%, P<0.001), higher NIHSS scores at day 7 or discharge (median 7 vs. 3, P<0.001), lower rates of significant neurological improvement (45.5% vs. 67.4%, P=0.055) and less functional independence at day 90 (55.6% vs. 91.2%, P<0.001). These associations remained statistically significant even when adjusting for potential confounders like age, NIHSS at admission, reperfusion grade and final infarct volume.
The results of this study showed the different resistance to ischemia between white and grey deep matter, especially when a shorter time to reperfusion is achieved. In addition to its histopathological interest, this difference also has a clinical impact, as patients with internal capsule ischemia have a worse outcome and higher risk of hemorrhagic transformation. The study, however, has some limitations. One of them is the absence of advanced neuroimaging techniques such as CT-perfusion or MRI-DWI performed on the acute setting of stroke. Due to this lack, the a priori involvement of the internal capsule is determined indirectly through the findings of the arteriography. CTP or MRI-DWI could help to elucidate more precisely the presence or absence of internal capsule ischemia before mechanical thrombectomy, therefore obtaining a better pathophysiological correlation.
