Signs of Herniation Syndrome
Herniation syndrome presents with a classic triad of decreased level of consciousness, pupillary abnormalities (particularly unilateral pupillary dilation), and motor dysfunction, with the specific pattern depending on the type and location of herniation. 1, 2
Cardinal Signs of Transtentorial Herniation
The most critical diagnostic features include:
- Pupillary changes: Ipsilateral pupillary dilation is the hallmark sign, occurring as the third cranial nerve is compressed against the tentorial edge 2
- Altered consciousness: Progressive decrease in level of consciousness, ranging from lethargy to coma (Glasgow Coma Scale deterioration from 15 down to 3-6) 1
- Motor abnormalities: Contralateral hemiparesis progressing to decerebrate posturing (abnormal extension) or decorticate posturing 1
Clinical Grading Based on Severity
The Hunt and Hess and World Federation of Neurological Surgeons scales provide a framework for assessing severity 1:
- Grade 4: Stupor, hemiparesis, early decerebrate posturing (GCS 7-12) 1
- Grade 5: Coma, decerebrate posturing, moribund appearance (GCS 3-6) 1
Additional Clinical Features
Respiratory pattern changes occur as brainstem compression progresses, though specific patterns depend on the level of herniation 2
Vital sign abnormalities including Cushing's triad (hypertension, bradycardia, irregular respirations) may develop with increased intracranial pressure leading to herniation 1
Focal neurological deficits including cranial nerve palsies (particularly CN III, VI), peripheral nerve dysfunction, and axial weakness may be present 1
Temporal Progression
Herniation develops through a predictable sequence 2:
- Initial signs: Subtle changes in consciousness, pupillary sluggishness
- Progressive signs: Unilateral pupillary dilation, contralateral motor weakness
- Late signs: Bilateral pupillary dilation, decerebrate posturing, respiratory arrest
Critical Pitfalls to Avoid
Do not wait for bilateral pupillary dilation - this represents late-stage herniation with significantly worse prognosis; unilateral dilation with decreased consciousness is sufficient for diagnosis 2
Recognize that herniation can be reversed with aggressive medical management (hyperventilation, mannitol, hypertonic saline) if caught early, with 39% of patients achieving functional independence despite herniation 2
Second herniation episodes occur frequently (57% of patients) after initial reversal, typically within 88 hours, requiring continued vigilant monitoring 2
Midbrain involvement during herniation significantly increases mortality risk and should prompt immediate maximal intervention 2
Structural Damage Assessment
Post-herniation imaging may reveal 2:
- Hypodense midbrain lesions (21% of cases)
- Temporal lobe contusions
- Posterior cerebral artery infarction (11% of cases)
- Middle cerebral artery territory infarction