Vasa Vasorum Densities in Human Carotid Atherosclerosis Is Associated with Plaque Development and Vulnerability

The extensive vasa vasorum network functions as a conduit for the entry of inflammatory cells or factors that promote the progression of angiogenesis and plaque formation. Therefore, we investigated the correlation between the carotid vasa vasorum activities and carotid plaque vulnerability using indocyanine green video angiography (ICG-VA) during carotid endarterectomy (CEA).

Sixty-nine patients who underwent CEA were enrolled prospectively from September 2015 to December 2017. During CEA, a bolus of ICG was injected intravenously before and after resecting the atheroma. Additionally, we performed immunohistochemistry using CD68 (a surface marker of macrophages), CD117 (a surface marker of mast cells), and CD4 and CD8 (surface markers of T-cells) antibodies to analyze the resected plaque specimens.

The density of active vasa vasorum was observed in all patients using ICG-VA. The vasa vasorum externa (VVE) and interna (VVI) were seen in 11 (16%) and 57 patients (82.6%), respectively. Macroscopically, the VVE-type patterns were strongly associated with preoperative angiographic instability (81.8%, p=0.005) and carotid plaque vulnerability (90.9%, p=0.017). In contrast, the VVI-type patterns were weakly associated with angiographic instability (31.6%) and plaque vulnerability (49.1%). CD68-stained macrophages and CD117-stained mast cells were observed more frequently in unstable plaques than in stable plaques (p<0.0001, p=0.002, respectively).

The early appearance of VVE, along with the presence of many microvessel channels that provided nutrients to the developing and expanding atheroma during ICG-VA, was strongly associated with unstable carotid plaques. The degree of infiltration of macrophages and mast cells is possibly related to the formation of unstable plaques.