What Intracranial Hemorrhage (ICH)?

Intracranial hemorrhage (ICH) refers to bleeding that occurs within the skull, specifically within the brain or the spaces surrounding the brain (subarachnoid space or ventricles). It is a serious medical emergency that can result in significant neurological impairment or death if not promptly diagnosed and treated.


There are several types of intracranial hemorrhage, each with distinct characteristics and underlying causes:


  • Intracerebral Hemorrhage (ICH): This type of hemorrhage occurs when blood vessels within the brain parenchyma (brain tissue) rupture and bleed into the surrounding tissue. Common causes of intracerebral hemorrhage include hypertension (high blood pressure), cerebral amyloid angiopathy (deposition of amyloid protein in blood vessel walls), arteriovenous malformations (abnormal connections between arteries and veins in the brain), trauma, hemorrhagic stroke, or use of anticoagulant medications.


  • Subarachnoid Hemorrhage (SAH): SAH occurs when there is bleeding into the space between the arachnoid membrane and the pia mater (the layers that surround the brain). The most common cause of subarachnoid hemorrhage is the rupture of a cerebral aneurysm, which is a weakened, bulging area in the wall of a blood vessel. Other causes include arteriovenous malformations, trauma, bleeding disorders, or drug abuse.


  • Subdural Hematoma (SDH): SDH is characterized by bleeding between the dura mater (the tough outer membrane covering the brain) and the arachnoid mater. It typically occurs as a result of trauma, such as a head injury or whiplash injury, which causes tearing of the bridging veins that connect the brain to the dura mater. Chronic subdural hematomas may develop gradually over weeks to months and are more common in older adults or individuals with coagulopathy (bleeding disorders).


  • Epidural Hematoma (EDH): EDH is characterized by bleeding between the dura mater and the skull. It typically occurs as a result of traumatic head injury, such as a skull fracture that disrupts an artery, leading to rapid accumulation of blood between the dura mater and the skull. Epidural hematomas are considered neurosurgical emergencies and require prompt surgical intervention to evacuate the hematoma and relieve pressure on the brain.


What is the relationship between ICH and oxidative stress?

The relationship between intracranial hemorrhage (ICH) and oxidative stress is complex and multifactorial. While direct evidence linking oxidative stress to ICH is limited, several mechanisms suggest a potential role for oxidative stress in the pathophysiology and progression of ICH:


  • Ischemia-Reperfusion Injury: Following an ICH, there is an initial phase of hemorrhagic stroke characterized by bleeding and subsequent compression of surrounding brain tissue. This compression leads to ischemia (lack of blood flow) in the affected brain regions. When blood flow is restored (reperfusion), particularly during surgical intervention or resolution of the bleeding, it can lead to ischemia-reperfusion injury. During reperfusion, there is an influx of oxygen and inflammatory cells into the previously ischemic tissue, which can generate reactive oxygen species (ROS) and cause oxidative stress.


  • Inflammatory Response: ICH triggers a robust inflammatory response in the brain, involving the activation of microglia, astrocytes, and infiltrating immune cells. Inflammatory processes generate ROS as byproducts of immune cell activation and respiratory burst reactions. Excessive ROS production during inflammation overwhelms antioxidant defenses and leads to oxidative stress, exacerbating tissue damage and neuroinflammation in the surrounding brain tissue.


  • Blood-Derived Iron: Hemoglobin breakdown products, including iron released from lysed red blood cells, accumulate in the brain parenchyma following ICH. Iron is a potent catalyst for ROS production through the Fenton reaction, where iron reacts with hydrogen peroxide to produce highly reactive hydroxyl radicals. This iron-mediated ROS generation contributes to oxidative stress and neuronal injury in the perihematomal region surrounding the hemorrhage.


  • Mitochondrial Dysfunction: ICH disrupts mitochondrial function in the affected brain tissue, leading to impaired oxidative metabolism and increased production of ROS within the mitochondria. Mitochondria are the primary site of ROS production in cells, and mitochondrial dysfunction can lead to oxidative stress and cellular damage. Dysfunction of the mitochondrial electron transport chain during ICH may further exacerbate oxidative stress and contribute to secondary brain injury.


  • Blood-Brain Barrier Disruption: ICH can cause disruption of the blood-brain barrier, leading to extravasation of blood components, inflammatory cells, and cytokines into the brain parenchyma. Blood-brain barrier disruption allows for increased infiltration of ROS-producing cells and molecules into the brain, further contributing to oxidative stress and neuroinflammation in the perihematomal region.


Overall, oxidative stress likely plays a significant role in the pathophysiology of ICH, contributing to secondary brain injury and neurological deficits following hemorrhagic stroke.