Histological analysis of extracranial carotid artery aneurysms

Abstract

Introduction: Extracranial carotid artery aneurysms (ECAA) are rare but may be accompanied with significant morbidity. Previous studies mostly focused on diagnostic imaging and treatment. In contrast, the pathophysiological mechanisms and natural course of ECAA are largely unknown. Understanding the pathophysiological background may add to prediction of risk for adverse outcome and need for surgical exclusion. The aim of this study was to investigate the histopathological characteristics of ECAA in patients who underwent complete surgical ECAA resection.

Material and methods: From March 2004 till June 2013, 13 patients were treated with open ECAA repair. During surgery the aneurysm sac was resected and processed for standardized histological analysis. Sections were stained with routine hematoxylin and eosin and special stains to detect elastin, collagen, different types of inflammatory cells, vascular smooth muscle cells and endothelial cells.

Results: Histopathological characterization revealed two distinct categories: dissection (abrupt interruption of the media; n = 3) and degeneration (general loss of elastin fibers in the media; n = 10). In the degenerative samples the elastin fibers in the media were fragmented and were partly absent. Inflammatory cells were observed in the vessel wall of the aneurysms.

Conclusion: Histological analysis in this small sample size revealed dissection and degeneration as the two distinct underlying mechanisms in ECAA formation.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1. In vivo aneurysm.

Aneurysm of a left saccular carotid artery visible between the internal carotid artery (ICA) and the external carotid artery (ECA) and originating from a dorsal loop in the ICA. The common carotid artery is ligatured in red, the ECA is identified with transparent ligatures. A, aneurysm of the ICA; BIF, carotid bifurcation; H, nervus hypoglossus; S, suture; VL, vessel loop.

Fig 2. Histology of control sample: fibrous cap atheroma.

Histology of control sample. Sample taken just distal from the bifurcation. Elastin-van Giesson (EvG) stain. In black the elastic fibers are clearly present and well organized. Atherosclerotic changes, atheroma with a lipid core. E, Elastin; Lip, Lipid core; Lum ext., lumen of the external carotid artery; Lum int., lumen of the internal carotid artery.

Fig 3. Histology of carotid aneurysms.

A-D, dissection; E and F, degeneration. A, overview of aneurysm due to dissection. Elastin-van Giesson (EvG) stain. Bar = 1.5 mm. B, higher magnification of the same staining as A. Arrow indicates the disrupted internal elastic lamina. Bar = 500 μm. C, Hematoxylin and eosin staining of the same panel as B. m, media; t, organized thrombus that replaces the absent media. Bar = 500 μm. D, CD34 immunostain showing endothelial coverage of the thrombus (in brown). Bar = 250 μm. E, overview of an aneurysm due to degeneration. Elastin-van Giesson (EvG) stain. Bar = 4 mm. F, higher magnification of the same staining as E. In black remnants of the elastic fibers of the media. Bar = 1 mm.