Curious About Intracrani...
Highlights
- Curious about Intracranial Dissecting aneurysms? It starts with a difference in structure between Extra & Intracranial arteries. The Intracranial arteries lose their External elastic lamina & Vasa vasorum as they pierce the dura & enter the subarachnoid space.
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- Thus intracranial arteries are more fragile in the SAS. The Primary event in intracranial dissection is longitudinal disruption (along the direction of the artery) of the IEL. A new communication forms between the true & the pseudolumen. (Mizutani)
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- The media adjacent to the disrupted IEL is also disrupted. Dissection extends throughout the media or towards the adventitia (⬆️⬆️ rupture). Those that lie only within the media -more likely to cause infarction via arterial stenosis. The majority of IC-DA are entry-only (Type 1).
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- A minority of DA have an entrance & an exit (Type 2) The rupture site is usually just above the orifice of the entrance. Here, the pseudolumen is within the media. Either, both the true & the pseudolumen are patent or the pseudolumen may be more dominant OR even thrombosed
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- The IEL is the most important layer of the cerebral arterial wall for the protection of the artery against hemodynamic stress & can withstand a blood pressure of > 600 mm Hg. IEL disruption is the primary event in dissection.
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- Type 1 DA are more prone to rupture because they have NO exit point-➡️ Unlikely to withstand hemodynamic stresses with the fragile outer layer. Type 2 aneurysms (entry-exit) are more stable & asymptomatic due to flow through the pseudolumen.
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- Due to the relatively rapid formations, thinner outer layer and inability to withstand hemodynamic stress (esp Type 1), IC-DA can evolve rapidly and rupture.
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- In contrast, true Intracranial aneurysms are formed by multifactorial issues acting on the endothelium leading to remodeling, gradual IEL disruption and media thinning. They may contain all 3 layers till rupture. [10.1161/STROKEAHA.113.002390]
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- The Japanese are masters of the Cerebrovascular realm 🙏🙏. Reading their work changes your perspective! (View Tweet)