If you experience a “blackout” or “loss of consciousness” (LOC) following a blow to the head, it is often a sign of a severe brain injury. While an isolated, minor Traumatic Subarachnoid Hemorrhage (tSAH) rarely causes a total loss of consciousness on its own, its presence suggests that the head sustained an impact powerful enough to cause dangerous complications like cerebral contusions or acute subdural hematomas.
This article explains the exact mechanisms behind losing consciousness in the context of tSAH. Behind such an event, there is usually a rapid spike in intracranial pressure or a concurrent severe brain injury. If you lose consciousness—even briefly—it is critical to seek immediate neurosurgical evaluation to prevent life-threatening events like brain herniation.
1. Can an Isolated tSAH Cause a Blackout?
While it is uncommon for a small, isolated tSAH to cause a blackout, the sudden irritation of the membranes covering the entire brain by the hemorrhage can cause widespread, temporary disruption of brain function.
- Transient Loss of Consciousness (TLOC): The sheer force of the impact that caused the tSAH, combined with the irritation as blood spreads through the subarachnoid space, can trigger a temporary shutdown of brain functions similar to a concussion, resulting in a brief loss of consciousness.
2. Primary Mechanisms of Severe Loss of Consciousness (Coma/Fainting)
When tSAH leads to a serious or prolonged loss of consciousness, it is typically due to one of the following high-risk factors:
A. Rapid Spike in Intracranial Pressure (ICP)
If the volume of bleeding in a tSAH is significant, it causes a sudden increase in pressure inside the skull. This pressure compresses the brainstem—the critical region responsible for maintaining consciousness—leading to a drop in awareness or a deep coma.
B. Concurrent Cerebral Contusions
tSAH is frequently accompanied by cerebral contusions (bruising of the brain). In many clinical cases, what appears to be a “tSAH-induced blackout” is actually a loss of consciousness caused by the severe underlying brain tissue damage. The more extensive the contusion, the longer the state of unconsciousness persists.
C. Occurrence of Brain Herniation
When a massive tSAH or an associated hematoma causes extreme brain swelling, it can lead to brain herniation (a condition where part of the brain is pushed downward due to pressure). This puts direct, intense pressure on the brainstem, causing immediate, life-threatening loss of consciousness or deep coma.
Summary
It is more accurate to understand “fainting due to tSAH” as a phenomenon where the tSAH occurs alongside rising intracranial pressure or severe concurrent brain damage, which then results in the loss of consciousness.
If you lose consciousness after a head injury—no matter how briefly—it is imperative to seek emergency medical care at a neurosurgical department. A CT scan is essential to rule out intracranial hemorrhage and ensure your safety.
