Subfalcine Herniation

A subfalcine herniation may not initially cause severe clinical symptoms. The initial presentation can be as benign as a headache. It is common to have headaches, nausea, and vomiting, or altered mental status. When a patient develops a subfalcine herniation, the cingulate gyrus is forced under the falx cerebri and can compress the ipsilateral anterior cerebral artery resulting in contralateral leg weakness.[5] If the herniation affects the dominant hemisphere and involves the contralateral arcuate fasciculus, patients present with conduction aphasia, receptive/sensory aphasia, or expressive/motor aphasia.[14]

If the primary lesion becomes large enough, uncal or central herniation may develop. As the lesion grows and herniation becomes prominent, patients may develop anisocoria, a decreased level of consciousness, changes in respiratory pattern, changes in muscle tone, and posturing. Hypertension, bradycardia, and irregular decreased respiration is the classical Cushing's triad may be present indicating imminent brain herniation.[5]  While a subfalcine herniation can occur coincident to other cerebral herniation syndromes, subfalcine herniation is not the cause of the other herniation syndromes. The primary injury should be identified and treated.

Patients presenting with signs or symptoms of neurologic compromise require a thorough history and physical. The history may raise suspicion of intracranial lesions that might lead to neurologic compromise. A head computed tomography (CT) scan is the preferred study in TBI. If there is a suspicion of a brain tumor, magnetic resonance imaging (MRI) with and without contrast enhancement is preferred as it shows the lesion with better details and can also exclude other non-tumoral etiologies.  All patients with a neurologic injury require frequent re-evaluation. If there is a significant change that raises the possibility of intracranial herniation, a non-contrast (CT) brain scan should be ordered immediately as it is the preferred modality of neuroimaging in these deteriorating patients. The CT scan accurately detects acute hemorrhagic lesions and subtle subsequent midline shifts. It is generally available and produces rapid results which can improve prognosis and outcome.[15][16] MRI is not always available and studies take significantly longer than CT scans. While CT scans are the gold standard for immediate neuroimaging and evaluation for herniation syndromes, other methods of evaluation can be used including non-invasive ICP monitoring and transcranial Doppler ultrasonography to expose patients to less radiation.[17]

Management of herniation syndromes depends on etiology, but all methods of resuscitation focus on support of the patient's respiratory and cardiovascular systems while attempting to decrease the intracranial pressure. Patients presenting with evidence of herniation are treated using a tiered emergency neurological life support (ENLS) management protocol.[5] If one tier does not arrest or reverse the herniation, progress to the next tiers is done sequentially. During the resuscitation, it is crucial to identify and treat the cause. Neurologic resuscitation often requires patience. If resuscitation is successful, clinical and radiological improvement will be noted. When resuscitation is less successful, more invasive therapies are available including ventriculostomy, removal of space-occupying lesions (hemorrhages, tumors, abscesses), and decompressive craniectomy. Guidelines for the management of severe TBI were published in 2017 by the brain trauma foundation to address treatment interventions, monitoring, and treatment thresholds.[18]

Medical management:

• Head of the bed elevated to >30°
• Isotonic fluid (or hypertonic as treatment)
• Corticosteroid therapy only for tumors
• Hyperosmolar therapy with hypertonic saline or mannitol -Hypertonic saline is available in concentrations from 2 to 23.4 % and can be administered as a bolus with set serum sodium goals; serum sodium level is checked every 4–6 h. Mannitol administered as 0.5–1 g/kg intravenous bolus and may be repeated every 4–6 h if serum osmolality is monitored.
• Sedation with propofol
• Hypothermia
• Pentobarbital for electroencephalographic burst suppression
• Hyperventilation in the early acute phase before a definite treatment is performed
• Seizure prophylaxis

 Surgical management:

• ICP monitoring
• External ventricular drain to measure ICP and to drain CSF
• Craniotomy to remove a hematoma or brain mass
• Decompressive craniectomy

Subfalcine herniation does not have a differential diagnosis, but the primary lesion causing the herniation needs to be differentiated from other primary conditions.

In the absence of trauma, the following etiologies should be excluded:

Tumor

Hematoma

Stroke

Infection

Edema

Radiation necrosis

Hydrocephalus

Prognosis depends on the cause of the herniation, the elevation in intracranial pressure, the presence and duration of resultant ischemia, and the intracranial structures affected. While some patients make a full recovery, many are left with deficits and disabilities. Reports suggest mortality rates as high as 33% in children with severe nonpenetrating traumatic brain injuries and 60% in patients who develop transtentorial herniation.[19][20] It has been reported that 17% of TBI patients had poor outcomes with moderate to severe disability, or persistent coma.[21] Overall, morbidity and mortality rates from traumatic brain injury have been decreasing in recent years, and a 2017 CDC surveillance report noted that 73% of patients discharged following traumatic brain injury had a good functional recovery.[9]

The primary complication of subfalcine herniation is the compromise of the blood flow through the anterior cerebral artery that results in ischemia in the frontal and parietal lobes. This ischemia will lead to changes in level of consciousness, hemiparesis, respiratory difficulty, coma, and death. Seizures may result from ischemic tissue.

Brain herniation can cause severe disability or death. The patient's immediate family should be oriented about the cause of patients herniation syndrome, and the treatment protocols so they can do informed consent decisions that will ultimately influence the outcome of the patient. In some cases of subfalcine herniation, the patients are alert and can make their own decisions. Brain herniation is potentially reversible with appropriate and timely therapy. A timely diagnosis and management will ultimately benefit the patient and improve their outcome.

• Subfalcine herniation is noted in many conditions that cause an increase in one of the three compartments within the skull:
  
  1. Increased brain volume due to tumor, hemorrhage, or edema
  2. Increased cerebral spinal fluid volume due to hydrocephalus
  3. Increased blood volume due to increased cerebral blood flow
• Subfalcine herniation may present with very subtle clinical symptoms
• Subtle clinical changes in patients with subfalcine herniation must be taken seriously to prevent significant morbidity and mortality
• Subfalcine herniation can progress to uncal or central herniation syndromes
• Subfalcine herniation identified by neuroimaging, requires close observation and monitoring

Patients with subfalcine herniation will frequently require neurosurgical consultation and monitoring by critical care physicians in a medical or neurological intensive care unit. The interprofessional team should be prepared to intervene aggressively to prevent progressive herniation, morbidity, and mortality. Because symptoms of subfalcine herniation may present subtly or present with rapid deterioration, it is important that the interprofessional healthcare team maintain open and clear lines of communication. It is likely that nurses will first recognize subtle neurologic changes or more problematic neurologic changes. If a family member recognizes a change, it must be reported to the patient’s nurse. The nurse should examine the patient for the changes reported and contact the physician responsible for the patient’s care. A thorough evaluation by the physician must follow, and imaging studies ordered immediately. If subfalcine herniation is detected, the team should immediately start resuscitation to stabilize the airway, maintain adequate cardiovascular perfusion, and decrease the intracranial pressure.