What Is Subarachnoid Hemorrhage? Causes, Types, and Key Insights

Subarachnoid hemorrhage (SAH) is a serious medical condition characterized by bleeding into the subarachnoid space—the area between the brain and the thin tissues that cover it. This type of bleeding typically occurs when a blood vessel on the surface of the brain ruptures, spilling blood directly into the cerebrospinal fluid-filled space. SAH accounts for approximately 10% of all acute stroke cases and makes up about 20% of hemorrhagic strokes, making it a critical yet relatively uncommon form of stroke.

Understanding the Different Types of Subarachnoid Hemorrhage

Subarachnoid hemorrhages are broadly categorized into two main types: spontaneous and traumatic. Each has distinct underlying causes and clinical implications, requiring different diagnostic and treatment approaches.

Spontaneous Subarachnoid Hemorrhage

Spontaneous SAH occurs without external injury and is further divided into primary and secondary forms. Primary spontaneous SAH is most commonly caused by the rupture of intracranial aneurysms—weak spots in the walls of brain arteries, often located at the base of the brain. Another significant cause includes arteriovenous malformations (AVMs), which are abnormal tangles of blood vessels that can bleed suddenly. In these cases, blood accumulates rapidly in the subarachnoid space, leading to increased intracranial pressure and potentially life-threatening complications.

Secondary spontaneous SAH, on the other hand, arises as a consequence of bleeding from other areas of the brain. For example, when an intracerebral hemorrhage (bleeding within the brain tissue) or intraventricular hemorrhage (bleeding into the brain's ventricles) extends into the subarachnoid space, it results in secondary involvement. This form is often associated with hypertension, cerebral amyloid angiopathy, or other vascular pathologies.

Traumatic Subarachnoid Hemorrhage

Traumatic SAH is caused by head injuries, such as those sustained in falls, car accidents, or physical assaults. In these instances, the force of impact can damage blood vessels, leading to bleeding into the subarachnoid space. It may occur alongside other types of traumatic brain injuries, including epidural or subdural hematomas. While traumatic SAH is generally less severe than its spontaneous counterpart, it still requires prompt medical evaluation to prevent neurological deterioration.

Risk Factors and Clinical Presentation

Common risk factors for SAH include uncontrolled high blood pressure, smoking, excessive alcohol consumption, drug use (especially cocaine), and a family history of aneurysms. Patients often describe the onset of symptoms as a "thunderclap headache"—a sudden, severe headache unlike any they've experienced before. Other signs include nausea, vomiting, neck stiffness, sensitivity to light, and altered mental status.

Early diagnosis through imaging techniques such as non-contrast CT scans or lumbar puncture is crucial for timely intervention. Treatment options vary depending on the cause and severity but may include surgical clipping, endovascular coiling, or supportive care in an intensive care setting.

Understanding the mechanisms and classifications of subarachnoid hemorrhage empowers both patients and healthcare providers to respond swiftly and effectively, improving outcomes and reducing long-term disability.