1-05: Herniation Syndromes

Clinical Summary

Severe head injury can result in extra-axial hematoma, cerebral contusion, or diffuse cerebral edema, which, in turn, may cause one of five brain herniation syndromes: uncal, central transtentorial, cerebellotonsillar, subfalcine, and external. Uncal herniation occurs when the uncus of the temporal lobe is displaced inferiorly through the medial edge of the tentorium. Compression of cranial nerve III can cause an ipsilateral dilated pupil. Typically, patients with uncal herniation are unconscious and require intubation. A contusion to the eye may also result in a dilated, nonresponsive pupil and arouse suspicion for uncal herniation, but typically these patients are alert.

Management and Disposition

Intubate unconscious head trauma patients with a unilateral dilated pupil and transfer them immediately to a facility capable of caring for traumatic brain injury. A head CT scan without contrast can identify a subdural or epidural hematoma, diffuse edema, or temporal lobe contusion. These conditions often cause midline shift of cerebral structures and compression of the quadrigeminal cistern. Unilateral effacement of the quadrigeminal cistern confirms uncal herniation. Initial management focuses on maintaining cerebral perfusion pressure and normal tissue oxygenation as hypotension and hypoxia significantly contribute to secondary brain injury. Mannitol, hypertonic saline, burr holes, and hyperventilation should be considered in ED patients with uncal herniation. Definitive care requires neurosurgical consultation.

Pearls

1. Uncal herniation is the most common of the five herniation syndromes.

2. If a patient has a unilateral dilated pupil after head and face trauma but is awake and talking, be suspicious for isolated traumatic anisocoria rather than herniation.

3. Extra-axial blood refers to bleeding outside the brain parenchyma and includes subdural, epidural, and subarachnoid bleeding. Extra-axial blood is most likely a neurosurgical rather than a neurological condition.

4. A temporal lobe contusion in an initially neurologically intact patient may continue to expand and cause uncal herniation.

5. Excessive hyperventilation (PaCO₂ < 25 mm Hg) in patients with severe traumatic brain injury is associated with cerebral ischemia.

6. Effacement of the quadrigeminal cistern is the hallmark CT finding of uncal herniation.