Carotid Near-Occlusion: A Comprehensive Review, Part 1--Definition, Terminology, and Diagnosis

Abstract

Carotid near-occlusion is distal ICA luminal collapse beyond a tight stenosis, where the distal lumen should not be used for calculating percentage stenosis. Near-occlusion with full ICA collapse is well-known, with a threadlike lumen. However, near-occlusion without collapse is often subtle and can be overlooked as a usual severe stenosis. More than 10 different terms have been used to describe near-occlusion, sometimes causing confusion. This systematic review presents what is known about carotid near-occlusion. In this first part, the foci are definition, terminology, and diagnosis.

Fig 1.

A case with near-occlusion with full collapse, reprinted with permission from Fox et al. Lateral common carotid angiogram shows the thin, threadlike, collapsed lumen (arrows) of the ICA above a prominent ICA stenosis at the bulb (not shown).

Fig 2.

A case with near-occlusion without full collapse, reprinted with permission from Fox et al. Lateral carotid angiogram shows a reduced ICA lumen distal to the stenosis (larger arrow); the diameter is slightly less than the ECA diameter (smaller arrow). The distal ICA lumen is normal-appearing (not threadlike).

Fig 3.

A case with a conventional carotid stenosis and no distal collapse. Axial CTA at the level of the distal extracranial ICA. The distal ICA (white arrow) is similar to, though slightly smaller than, the contralateral ICA (black arrow) and is wider than the right ECA (arrowhead).

Fig 4.

A case with near-occlusion without full collapse. A, Axial CTA at the level of the distal extracranial ICA. B, Sagittal reformat of A. The distal right ICA (white arrow) is narrower than the contralateral ICA (black arrow) and similar to the right ECA (arrowhead) but otherwise is normal-appearing (not threadlike).

Fig 5.

A case with near-occlusion with full collapse. Axial CTA at the level of the distal extracranial ICA. The distal right ICA (white arrow) is clearly collapsed with a threadlike appearance, clearly narrower than the contralateral ICA (black arrow) and the right ECA (white arrowhead). The black arrowhead points to the left ascending pharyngeal artery, ensuring that this is not an ICA occlusion.

Fig 6.

Schematic drawing of the 4 criteria for near-occlusion on conventional angiography. Delayed filling (A), evidence of intracranial collaterals when the contralateral side is examined (B), ipsilateral distal ICA less than the contralateral distal ICA (C), and ipsilateral distal ICA equal to or less than the ipsilateral ECA (D). In all figures, the contrast is gray.

Fig 7.

Sonographic findings of near-occlusion with full collapse. It is difficult to discern the narrow flow channel despite the low-flow setting and very low-flow velocities with systolic spikes without diastolic flow. CTA confirmed the diagnosis with a patent fully collapsed distal ICA (not shown).