Long-Term Histopathology of Intracranial Aneurysms after Endovascular Treatment with Coils

Abstract

<jats:p> We describe the results of electron microscopic examination in two patients with ruptured intracranial aneurysms who were successfully treated by endovascular coil embolization. The aneurysms were seen completely occluded on the follow-up angiograms. Autopsies of these patients were performed five and 26 months after endovascular treatment when they died of pneumonia and thalamic hemorrhage, respectively. The aneurysms were densely filled with the coils, which were readily identified through the thin and transparent wall of the aneurysmal dome. The orifice of the aneurysm was completely occluded so that macroscopically the coils were not directly visualized through the orifice. </jats:p><jats:p> To examine any evidence of endothelialization across the orifice of the aneurysms, scanning electron microscopic examination was performed. In both cases, evidence of well regenerative endothelialization was observed across the aneurysmal orifice, being contiguous with the endothelial layer of the adjacent parent vessels. These ultrastructural findings indicate that the aneurysms are completely isolated from the lumen of the parent artery by a continuous lining of the regenerated endothelial cells following the endovascular treatment with coils, and further suggest that aneurysms have a potential of being cured permanently by this treatment modality. This is, to the best of our knowledge, the first report in humans verifying a complete endothelialization of the luminal surface at the aneurysmal neck after coil embolization, as evidenced by scanning electron microscopy. </jats:p>

Mechanisms of Healing in Coiled Intracranial Aneurysms: A Review of the Literature

“…Three to twelve months following embolization, there is increased vascularized connective tissue within the aneurysm dome and about the coils. Continued foreign body reaction with multinucleated giant cells is seen about the aneurysm coils 17, 23, 25 . One case report demonstrated that the neck is completely covered by a layer of long slender cells resembling endothelium during this time period (Figure 1e) 17 .…”

“…Swine models of aneurysm healing demonstrate robust neointima formation with a thick layer of vascular smooth muscle cells and robust deposition of endothelial cells 4, 33 . Endothelial cells are primarily seen growing along the coils at the aneurysm neck which has led some investigators to believe that the endothelial cells arise from the adjacent vessel wall 18, 25 . However, recent studies suggest that endothelial cells found at the aneurysm neck may originate from bone marrow derived endothelial progenitor cells rather than migration of adjacent endothelial cells 34, 35 .…”