The web is a rarely encountered, and probably underdiagnosed entity. It is a shelf-like protrusion of what is likely connective / fibrous tissue into the vessel lumen — typically the very proximal internal carotid artery, at the bulb. Some feel this to be a variant of Fibromuscular Dysplasia. Most seem to be asymptomatic. A spectrum exists, of course, from small to prominent webs. The latter cause progressively greater stasis of blood flow beyond the web, like a dam. Cases of embolic stroke with no other identifiable risk factor are felt to be due to clot formation at the site of stasis, with secondary embolization. The author believes in this theory. The reason for so many adjectives of uncertainty here is that worldwide experience is quite limited. There is an opinion that antiplatelets do not offer much protection, as the underlying cause is stasis — a la. atrial fibrillation. Some practitioners will stent cases presenting with recurrent stroke despite medical management. Randomized, controlled, etc. data is nonexistent, but this treatment seems to make sense.
This young patient presented with Expressive (Broca’s) aphasia
MRA of the neck shows a shelf-like protrusion into the left proximal ICA — the Web
Left CCA injection demonstrating oligemia in the region of the posterior inferior frontal convexity / operculum
Injection of the right ICA shows presence and overall partial efficacy of leptomeningeal collaterals to the region of occlusion (yellow)
Angiography beautifully shows slipstreaming of dye (white arrow) in early arterial phase, with subsequent visualization of the web (yellow) and marked contrast stasis (purple) in late venous phase just distal to the web. No other cause for embolic stroke was found
Another example, asymptomatic, below