Tonsillar Herniation

Tonsillar herniation is downward displacement of the cerebellar tonsils through the foramen magnum, compressing the medulla and upper cervical cord. It leads to respiratory arrest and cardiovascular collapse and is rapidly fatal.

Epidemiology. It complicates posterior fossa mass lesions (haemorrhage, infarction, tumour, abscess) and diffuse supratentorial pressure rise. A dangerous cause is lumbar puncture in a patient with raised intracranial pressure.

Causes. Cerebellar haemorrhage or infarction, posterior fossa tumour, hydrocephalus, severe traumatic brain injury, diffuse cerebral oedema, lumbar puncture or lumbar drain in a patient with mass effect, and Chiari malformation (chronic tonsillar descent, not acute herniation).

Pathophysiology. A pressure gradient between the cranium and the spinal canal pushes the tonsils into the foramen magnum, obstructing CSF flow, compressing the medullary respiratory and cardiovascular centres, and compromising the posterior inferior cerebellar artery.

Presentation is severe occipital headache, neck stiffness or head tilt, vomiting, vertigo, ataxia, falling consciousness, ataxic or irregular breathing and apnoea, sudden hypertension then hypotension and bradycardia, quadriparesis, and pinpoint pupils or sudden pupillary dilation. Clinical signs may progress to arrest within minutes.

Red flags.

• Sudden apnoea or irregular breathing.
• Neck stiffness and head tilt in a patient with a posterior fossa lesion.
• Deterioration after lumbar puncture.

Emergency CT head (obliterated fourth ventricle and basal cisterns, tonsils descending through the foramen magnum, hydrocephalus) and MRI when stable. Do not perform lumbar puncture. Check glucose, coagulation, sodium and gas.

Differential diagnosis. Brainstem stroke, basilar artery occlusion, central pontine injury, drug overdose, central sleep apnoea and meningitis.

Immediate.

• Secure the airway and ventilate (induction with ketamine 1 to 2 mg/kg or etomidate 0.3 mg/kg, with rocuronium 1.2 mg/kg). Hyperventilate briefly to PaCO2 of 4.0 to 4.5 kPa (30 to 35 mmHg) for active herniation only.
• Position the head neutral, raised 30 degrees.
• Hyperosmolar therapy: 3% sodium chloride 250 mL IV over 15 to 20 minutes (or 23.4% sodium chloride 30 mL IV over 10 to 20 minutes through a central line), or mannitol 20% 0.5 to 1 g/kg IV over 15 to 20 minutes (osmolality under 320 mOsm/kg).
• Maintain systolic pressure at least 110 mmHg and treat seizures with levetiracetam 60 mg/kg IV (maximum 4500 mg).

Surgery. Emergency posterior fossa decompression with evacuation of haematoma, external ventricular drain for obstructive hydrocephalus (insert with caution, because rapid drainage can cause upward herniation, so remove CSF slowly and avoid over drainage), and resection or biopsy for tumour.

Corticosteroid. Dexamethasone 10 mg IV then 4 mg every 6 hours for tumour or abscess oedema.

Antibiotics. For abscess, ceftriaxone 2 g IV every 12 hours with metronidazole 500 mg IV every 8 hours (and vancomycin if staphylococcal disease is likely).

After herniation. Brain death testing when criteria are met, and early discussions with the family.

Monitoring. Respiratory pattern, pupils, blood pressure, intracranial pressure by drain, sodium and repeat CT.

Referral and escalation. Neurosurgery and neurocritical care at once.

Special groups. In children, posterior fossa tumours are common and 3% sodium chloride is 2 to 5 mL/kg. In anticoagulated patients, reverse the anticoagulant (prothrombin complex concentrate 25 to 50 units/kg with vitamin K 10 mg IV for warfarin).