Object: Encephalomyosynangiosis (EMS) is a surgical treatment for moyamoya disease that is widely used to provide increased intracranial blood flow via revascularization by arterial anastomosis from the external carotid artery. However, the angiogenic mechanism responsible for the revascularization induced by EMS has not been systematically evaluated. In this study the authors investigated the chronological angiogenic changes associated with EMS to clarify the favorable factors and identify revascularization mechanisms by using an experimental internal carotid artery occlusion (ICAO) model in the miniature pig.
Methods: Fourteen miniature pigs were used, 11 of which underwent ICAO before transcranial surgery for EMS was performed. Animals were allowed to recover for 1 week (4 pigs) or 4 weeks (7 pigs) after EMS. Control group animals were treated in the same way, but without occlusion (3 pigs). Magnetic resonance imaging, angiography, and histological investigation were performed.
Results: One week after EMS, on histological examination of both the ICAO and control groups it was found that the transplanted temporal muscle had adhered to the arachnoid via a granulation zone, which was enriched with immune cells such as macrophages associated with the angiogenic process. Four weeks after EMS, angiography and histological examination of the ICAO group showed patent anastomoses between the external carotid artery and the cortical arteries without any detectable boundary between the temporal muscle and the cerebral cortex. In contrast, histological examination of the control group found scar tissue between the cerebral cortex and temporal muscle.
Conclusions: The initial step for formation of anastomoses resembles the process of wound healing associated with repair processes such as active proliferation of macrophages and angiogenesis within the new connective tissue. Functional revascularization requires a suitable environment (such as tissue containing vascular beds) and stimulus (such as ischemia) to induce vascular expansion.