Subfalcine Herniation

Subfalcine (cingulate) herniation is displacement of the cingulate gyrus beneath the free edge of the falx cerebri, from a unilateral hemispheric mass. It is the commonest cerebral herniation and an early marker of mass effect that precedes transtentorial herniation.

Epidemiology. It occurs with frontal and parietal haematomas, tumours, abscesses, infarcts and subdural collections. It is often found as midline shift on imaging before clinical signs appear.

Causes. Subdural and intracerebral haematoma, malignant middle cerebral artery infarction, tumour with vasogenic oedema, abscess, contusion and diffuse hemispheric swelling.

Pathophysiology. The mass pushes the cingulate gyrus and anterior cerebral artery under the falx. The pericallosal artery is compressed against the falx, causing infarction in the anterior cerebral artery territory. The contralateral ventricle may be obstructed at the foramen of Monro, producing hydrocephalus.

Presentation is headache, drowsiness, abulia, contralateral leg weakness (anterior cerebral artery ischaemia), and later features of transtentorial herniation. It may be clinically silent, so the severity of midline shift on imaging matters.

Red flags.

• Midline shift of 5 mm or more, or increasing shift on repeat scans.
• Falling consciousness or new leg weakness.
• Dilated ventricle on the opposite side.

CT head or MRI: midline shift (septum pellucidum displacement), effaced lateral ventricle, enlarged contralateral ventricle, displaced anterior cerebral artery, and the cause. CT angiography if a vascular lesion is suspected. Check glucose, sodium, coagulation and gas.

Differential diagnosis. Hydrocephalus, bilateral frontal injury, anterior cerebral artery stroke without mass effect, abulia of other cause and normal asymmetry.

Assessment. Neurological examination every hour, and repeat imaging when clinical state changes or within 6 to 24 hours for rapidly evolving lesions.

General measures. Head up 30 degrees with neck neutral, systolic pressure at least 110 mmHg, normoxia, normocapnia, normoglycaemia, sodium 135 to 145 mmol/L, and treatment of fever and pain.

Hyperosmolar therapy for clinical deterioration or midline shift with symptoms.

• 3% sodium chloride 250 mL IV over 15 to 20 minutes (or 2 to 5 mL/kg), targeting sodium 145 to 155 mmol/L.
• Mannitol 20% 0.5 to 1 g/kg IV over 15 to 20 minutes, with osmolality kept under 320 mOsm/kg.

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

Seizure treatment. Levetiracetam 60 mg/kg IV (maximum 4500 mg) for seizures, with maintenance 500 to 1000 mg every 12 hours (adjusted to eGFR).

Surgery. Evacuate haematomas, drain abscess, resect tumour, and consider decompressive craniectomy for malignant infarction (best results within 48 hours in patients under 60 years) and refractory pressure. External ventricular drain for obstructive hydrocephalus.

Reverse anticoagulation with prothrombin complex concentrate 25 to 50 units/kg and vitamin K 10 mg IV (warfarin), idarucizumab 5 g IV (dabigatran), or prothrombin complex concentrate 50 units/kg (maximum 5000 units) for factor Xa inhibitors.

Monitoring. Glasgow Coma Scale and pupils hourly, repeat CT, intracranial pressure in comatose patients, and sodium every 4 to 6 hours.

Referral and escalation. Neurosurgery and neurocritical care. Transfer if neurosurgical capacity is lacking.

Special groups. In children, weight based osmotherapy. In pregnancy, left lateral tilt and obstetric input.