What is the main cause of significant narrowing in the operated carotid artery after a Carotid Endarterectomy?

Neointimal hyperplasia is the primary cause of significant narrowing in the operated carotid artery following a Carotid Endarterectomy. This phenomenon occurs as a response to vascular injury inflicted during the surgical procedure. The endarterectomy process involves the removal of atherosclerotic plaque from the carotid artery, which results in disruption of the arterial wall.

In the healing phase, smooth muscle cells migrate to the area of injury, proliferating and contributing to the formation of new tissue, specifically in the intimal layer of the artery. This results in thickening and narrowing of the lumen, ultimately leading to the re-narrowing of the artery, often referred to as restenosis. Neointimal hyperplasia is a common reaction following any vascular intervention associated with a significant injury to the vascular structure, highlighting the body's attempt to 'repair' the damaged site, albeit sometimes leading to adverse effects like significant narrowing.

Other potential options might involve complex processes such as atherosclerosis, which is a chronic condition, or thrombus formation, which can occur as a complication but is less likely to be the primary cause of significant narrowing post-surgery. External compression generally does not play a significant role in the narrowing of the artery after a carotid procedure.