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Understanding Uncal Herniation: Causes, Symptoms, and Emergency Management
Understanding Uncal Herniation: Causes, Symptoms, and Emergency Management
Uncal herniation is a rare but life-threatening neurological emergency that demands immediate medical attention. Often associated with severe brain injuries, this condition involves the displacement of brain tissue through thebrainstem, typically due to increased intracranial pressure (ICP). Understanding uncal herniation—its causes, warning signs, and treatment—is critical for timely intervention and improved patient outcomes.
What Is Uncal Herniation?
Understanding the Context
Uncal herniation occurs when a portion of the brain, specifically the cerebral hemisphere, shifts downward through the tentorial notch—a narrow channel in the tentulum of the tentorium cerebelli—causing compression of vital structures. This displacement compresses the brainstem, impairs cerebrospinal fluid flow, and disrupts autonomic functions, potentially leading to brainstem death or cardiac arrest.
Although uncal herniation is less common compared to other forms of brain herniation (such as supratentorial or subdural), it is a critical complication most often seen in patients with traumatic brain injury (TBI), severe skull fractures, or intracranial bleeding (e.g., epidural hemorrhage).
Causes and Risk Factors
Key Insights
Uncal herniation arises primarily from elevated intracranial pressure due to:
- Severe traumatic brain injury (TBI), including epidural or subdural hematomas
- Brain tumors causing localized swelling
- Sylingooscephaly (abnormally flat skull) or other cranial malformations
- Infections or space-occupying lesions expanding within the skull
The herniation process begins when pressure overcomes the brain’s resistance, particularly affecting the convexity and cerebral convexities, triggering downward displacement across the tentorial edge.
Recognizing Symptoms Early
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Due to its rapid and severe consequences, recognizing early symptoms of uncal herniation is vital. Common warning signs include:
- Unilateral pupillary dilation (uncal sign)—one pupil appears larger and does not react to light
- Ipsilateral facial droop on the side of the herniation
- Hoarseness or voice changes due to brainstem compression
- Altered consciousness ranging from confusion to unconsciousness
- Cardiac dysrhythmias or breathing irregularities
These neurological deficits often progress quickly, necessitating immediate imaging (such as non-contrast CT scans) and urgent intervention.
Diagnostic Evaluation
Prompt diagnosis involves advanced neuroimaging:
- Non-contrast head CT scan is the first-line diagnostic tool, revealing signs like loss of normal sulcal patterns, effacement of sulci, or upward displacement of the uncus (uncal sign).
- MRI with DTI or perfusion imaging provides detailed visualization of shifting brain tissue and downstream ischemia.
- Monitoring intracranial pressure (ICP) and brain brainstem evoked potentials may assist in assessing neurological function.
Emergency Management and Treatment
Uncal herniation is a neurological emergency requiring intensive care:
