出血性脳卒中 I:はじめに

When a weakened blood vessel in the brain ruptures, it causes bleeding into surrounding brain tissue, forming a focal hematoma. This bleeding increases intracranial pressure, displaces neural tissue, and can obstruct cerebrospinal fluid pathways. Secondary complications like brain swelling or compression of nearby structures may develop, leading to rapid neurological deterioration.

Hemorrhagic stroke is classified into intracerebral hemorrhage and subarachnoid hemorrhage. Intracerebral hemorrhage occurs when a blood vessel ruptures and bleeds directly into the brain parenchyma. Subarachnoid hemorrhage happens when blood leaks into the space between the arachnoid mater and pia mater, typically from a ruptured berry aneurysm.

Intracerebral hemorrhage most commonly results from chronic hypertension, which induces degenerative changes in small penetrating arteries, making them prone to rupture. Age-related cerebral amyloid angiopathy is another important cause in older adults, as amyloid deposition weakens cortical vessel walls. Less frequently, arteriovenous malformations can rupture and produce intraparenchymal bleeding.

Subarachnoid hemorrhage is most commonly caused by rupture of a saccular berry aneurysm located at branch points in the circle of Willis. Head trauma can also cause this type of hemorrhage. When blood enters the subarachnoid space, it spreads through cerebrospinal fluid, irritating the meninges and increasing intracranial pressure.

A focal hematoma from hemorrhagic stroke disrupts surrounding neural tissue and impairs perfusion to affected brain regions. The expanding hematoma displaces neural structures and increases intracranial pressure, potentially obstructing cerebrospinal fluid pathways. These effects can rapidly lead to neurological deficits and secondary complications like cerebral edema.

Chronic hypertension remains the most significant risk factor for hemorrhagic stroke. Cerebral amyloid angiopathy, use of anticoagulant medications, and smoking further weaken vessel integrity or increase bleeding risk. Age-related vascular changes and structural abnormalities also contribute to hemorrhagic stroke development.

Subarachnoid hemorrhage carries a high risk of secondary complications. Vasospasm, a narrowing of blood vessels triggered by blood irritation, can reduce cerebral blood flow. Hydrocephalus, an accumulation of cerebrospinal fluid, may also develop, further increasing intracranial pressure and worsening neurological outcomes.