Herniation syndromes and emergency neurosurgical referral

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Compensatory displacement of venous blood and CSF delays pressure rise, but once intracranial compliance is exhausted, an expanding haematoma, oedema, infarct, tumour or blocked CSF pathway generates steep pressure gradients. Tissue then shifts beneath the falx, through the tentorial opening or through the foramen magnum. Neural compression, arterial distortion, venous obstruction and secondary infarction amplify oedema.

Localisation helps anticipate danger but should never delay action. Subfalcine shift moves the cingulate gyrus under the falx and may compromise the anterior cerebral artery. Uncal shift pushes the medial temporal lobe across the tentorial edge, compressing the third nerve, cerebral peduncle and posterior cerebral artery. Central descent moves the diencephalon and brainstem downward. Tonsillar descent compresses the medulla; posterior-fossa masses can also cause upward transtentorial displacement.

Herniation is a clinical-radiological syndrome, not a requirement to document one ICP number. Sedation, paralysis, ocular trauma and pre-existing deficits can obscure signs. Resuscitation, examination, imaging, osmotic rescue and referral therefore proceed in parallel, with the neurosurgical team deciding whether evacuation, EVD, decompression or another operation addresses the causal anatomy.

Key points

Herniation is tissue displacement driven by intracranial compartment pressure gradients; it can occur with or without a recorded global ICP above a threshold.
Uncal herniation classically causes falling consciousness, an ipsilateral dilated pupil and contralateral weakness, but false-localising ipsilateral weakness can occur from contralateral peduncle compression.
Central descent produces progressive coma, evolving pupil and motor abnormalities and respiratory failure; tonsillar descent threatens the medulla and can cause abrupt apnoea and cardiovascular collapse.
Activate a brain-code response at the first compatible deterioration: ABC stabilisation, head elevation above 30 degrees, neutral neck, correction of hypoxia or hypotension, seizure control and urgent CT when transport is safe.
Use hypertonic sodium or mannitol as a monitored temporary bridge selected from sodium, volume, blood pressure, renal function and local protocol; brief controlled hyperventilation is reserved for active herniation while definitive treatment is prepared.
Definitive treatment is cause-specific: evacuate an expanding mass, drain acute obstructive hydrocephalus or decompress selected refractory swelling; do not let transient improvement delay surgery.
For traumatic head injury, NICE requires neurosurgical discussion for surgically significant imaging, persisting coma, post-admission GCS deterioration, progressive focal signs or seizure without full recovery, regardless of imaging.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Expanding mass

Traumatic or spontaneous haemorrhage, tumour, abscess and large infarction can add focal volume, distort compartments and drive tissue across the falx or tentorium.

Diffuse swelling

Traumatic, hypoxic, inflammatory or metabolic brain oedema can exhaust global compliance and produce central descent, sometimes without one surgically removable mass.

CSF obstruction

Acute ventricular obstruction from blood, tumour or posterior-fossa swelling enlarges upstream ventricles and can cause downward or upward shifts depending on compartment anatomy.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Compliance exhaustion
Early displacement of venous blood and CSF buffers added volume, but after reserve is consumed, small increments produce steep rises in pressure and reduced perfusion.
2
Compartment gradient
Unequal pressure across rigid dural partitions pushes tissue beneath the falx, through the tentorial notch or into the foramen magnum.
3
Neural compression
Displaced tissue compresses arousal pathways, cranial nerves and corticospinal tracts, producing falling consciousness, pupil abnormalities, weakness and posturing.
4
Vascular amplification
Arterial distortion and venous obstruction cause infarction and additional oedema, creating a self-reinforcing cycle of swelling, reduced perfusion and further displacement.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Uncal transtentorialRed flag

Acute reduced consciousness with an ipsilateral enlarging pupil and usually contralateral weakness reflects third-nerve and peduncular compression. Posterior cerebral artery compromise can add occipital infarction.

Central transtentorialRed flag

Progressive drowsiness advances to coma, pupils evolve from small reactive to mid-position fixed, motor responses progress from flexion to extension, and breathing becomes abnormal as the brainstem descends.

Subfalcine shift

Cingulate displacement beneath the falx may be clinically subtle or cause contralateral leg-predominant weakness through anterior cerebral artery compression; progression can precede transtentorial herniation.

Tonsillar descentRed flag

Inferior cerebellar tonsils compress the lower brainstem, producing neck stiffness, altered consciousness, irregular respiration, apnoea, bradycardia and circulatory collapse, especially with a posterior-fossa lesion.

Upward posterior-fossa shift

A posterior-fossa mass or ill-judged CSF pressure change can displace cerebellar structures upward through the tentorial opening, worsening brainstem compression and obstructive hydrocephalus.

False localisation

Compression of the opposite cerebral peduncle against the tentorial edge can cause weakness on the same side as the mass, so laterality alone should not determine the operative target.

Red flags requiring action

A unilateral enlarging or fixed pupil with reduced consciousness, especially with opposite-sided weakness, is uncal herniation until an urgent assessment proves otherwise.
Progressive drowsiness, small then mid-position fixed pupils, abnormal flexion or extension and irregular breathing suggests descending central transtentorial herniation.
Sudden apnoea, bradycardia, neck stiffness or flaccidity in a patient with posterior-fossa disease suggests tonsillar compression of the medulla.
Leg-predominant weakness with major midline shift can reflect subfalcine displacement and anterior cerebral artery compression before obvious brainstem signs.
Do not wait for the complete Cushing response of hypertension, bradycardia and irregular respiration; ENLS describes the concurrence as uncommon and often late.
A normal earlier CT does not neutralise falling GCS, new anisocoria, a seizure without recovery or progressive focal signs; lesions and oedema evolve.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Immediate serial neurological examinationFirst step
Why
Identify the evolving syndrome and provide a response baseline without delaying resuscitation.
Interpretation and limitations
Record GCS components, pupils, gaze, motor asymmetry, posturing and breathing. One new pupil abnormality or motor decline can be decisive even without a full triad.
02
Non-contrast CT head
Why
Locate haemorrhage, mass, hydrocephalus, infarction, midline shift and cisternal effacement that require definitive treatment.
Interpretation and limitations
The causal lesion and threatened compartments guide evacuation, drainage or decompression. Transport must be safe, and treatment is not withheld from a crashing patient merely to obtain images.
03
CT angiography or venography
Why
Investigate vascular occlusion, aneurysm, venous thrombosis or another vascular cause when stable enough and clinically indicated.
Interpretation and limitations
Vascular imaging refines cause-specific treatment but should not postpone decompression of an immediately life-threatening mass already evident on initial CT.
04
Arterial blood gas
Why
Detect hypoxaemia, hypercapnia and acid–base disturbance and guide ventilation during airway management.
Interpretation and limitations
Correct hypoxaemia and ventilatory failure. Temporary PaCO2 reduction may bridge active herniation, but prolonged or excessive hypocapnia risks cerebral ischaemia.
05
Invasive ICP and CPP
Why
Quantify pressure burden and treatment response when a monitor is already present or specialist insertion is indicated.
Interpretation and limitations
A normal local reading cannot exclude compartmental herniation. Adult severe-TBI thresholds are not universal; integrate waveform, MAP, examination and CT.
06
Glucose and reversible-mimic screen
Why
Find hypoglycaemia, seizure, intoxication or metabolic contributors while structural disease is addressed.
Interpretation and limitations
Correct a reversible abnormality immediately, but do not let an alternative explanation defer CT and neurosurgical discussion when focal or pupillary signs persist.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Drug or sedation effect

Opioids, sedatives and neuromuscular blockade can reduce responsiveness or alter pupils, but do not explain every focal asymmetry and must not delay structural assessment.

Non-convulsive seizure

Ictal activity can cause coma, gaze deviation or transient weakness; treat active seizure and use EEG when needed while excluding haemorrhage, swelling and hydrocephalus.

Metabolic encephalopathy

Hypoglycaemia, severe sodium disturbance, hypercapnia and hepatic failure can depress consciousness, yet a new pupil or lateralising sign still requires urgent imaging.

Primary ocular abnormality

Trauma, surgery or topical agents can alter one pupil, but concurrent consciousness or motor change indicates a neurological emergency until proven otherwise.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Emergency pathwayClinical brain herniationFirst stepAcute consciousness decline with new pupil, motor, posturing or respiratory abnormality suggesting intracranial tissue shift.

1Activate critical care, anaesthesia and neurosurgery; assess airway, oxygenation and circulation, obtain IV access, elevate the head above 30 degrees and keep the neck midline without delaying cervical-spine protection where relevant.
2DefinitiveCorrect hypoxia, hypotension, fever, seizure and severe sodium disturbance; give protocol-led hypertonic sodium or mannitol rescue chosen from the patient's physiology while preparing definitive treatment.
3Obtain immediate CT when safe and communicate the examination trajectory, pupils, anticoagulants, lesion, shift, cisterns, hydrocephalus, treatment already given and response to the accepting neurosurgeon.
4Proceed to evacuation, CSF drainage, decompression or disease-specific treatment as advised; use brief controlled hyperventilation only for persisting active herniation during preparation, not as prolonged routine therapy.

02Trauma referralEmergency neurosurgical discussionHead injury with surgically significant imaging or clinical deterioration that meets NICE referral criteria regardless of imaging.

1Call neurosurgery for new surgically significant imaging, persisting GCS 8 or less after resuscitation, post-admission GCS deterioration, progressive focal signs or seizure without full recovery.
2Continue resuscitation and establish comprehensive monitoring before transfer; intubate and ventilate when airway protection or neurological trajectory requires it.
3Send images and a concise time course while arranging trained transfer staff and ongoing communication with the neuroscience unit.

03Monitor discordanceHerniation signs despite normal ICPThe patient has new focal, pupillary or consciousness deterioration while the displayed pressure is normal or equivocal.

1Treat the clinical deterioration immediately and verify the monitor waveform, position, reference and compartment without waiting for technical resolution.
2Repeat CT to identify evolving mass, regional pressure gradient, hydrocephalus or device complication and obtain direct neurosurgical review.
3Revise the monitoring and treatment plan according to anatomy; a local pressure sample cannot overrule a convincing herniation syndrome.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Provides rapid temporary osmotic reduction of cerebral water while imaging and definitive neurosurgical treatment are organised.

Hypertonic sodium chloride

Use the institution's adult neurocritical-care emergency bolus concentration and volume, selected for venous access and physiology; no single regimen applies across traumatic, vascular, tumour and posterior-fossa causes.

Monitor sodium, chloride, renal function, acid–base state, volume status and access; avoid uncontrolled sodium loading and do not delay evacuation or CSF diversion after transient improvement.

Temporarily lowers ICP through an osmotic gradient and can be selected when sodium loading is undesirable.

Mannitol intravenous solution

Use a local adult emergency weight-based bolus protocol; ENLS v5 describes 0.5–1 g/kg over 5–15 minutes, with repeat dosing governed by response and safety rather than a fixed schedule.

Correct hypotension and hypovolaemia, follow urine output, creatinine, volume status and osmolar gap, and avoid automatic repeat dosing when clinical or pressure response is absent.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Brainstem infarction

Sustained compression and perforator distortion injure the midbrain, pons or medulla, leading to coma, respiratory failure and irreversible neurological loss.

Territorial infarction

Anterior or posterior cerebral arteries may be compressed during subfalcine or uncal shift, adding infarction and oedema beyond the original lesion.

Secondary haemorrhage

Stretching of small brainstem vessels can produce Duret haemorrhages during severe descending transtentorial displacement and signals advanced injury.

Cardiorespiratory arrest

Tonsillar or advanced central herniation disrupts medullary respiratory and cardiovascular control, causing apnoea, bradycardia and circulatory collapse.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Repeat GCS components, pupils, gaze, motor response and respiratory pattern continuously through deterioration, treatment, scanning and transfer; record exact time of every change.
Track oxygenation, ventilation, MAP, temperature, glucose, sodium and seizure activity because secondary physiological insults amplify ischaemia during herniation.
After osmotic rescue, document pupil, motor, consciousness, MAP and ICP response within minutes while continuing the definitive surgical pathway.
During transfer, maintain comprehensive airway, ventilation, haemodynamic and neurological monitoring with a team trained for acute brain injury and direct communication to the neuroscience unit.
After evacuation, drainage or decompression, watch for recurrent anisocoria, falling GCS, new focal deficit, seizures and pressure rise that may signal rebleeding, swelling, hydrocephalus or device failure.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Herniation can precede global pressure

A local mass can create a compartmental gradient and tissue shift before a single monitor location records a sustained global ICP elevation.

Kernohan sign reverses laterality

The opposite cerebral peduncle may be compressed against the tentorium, creating weakness ipsilateral to the mass and confounding simple side-based localisation.

Cushing response is late

Hypertension, bradycardia and irregular breathing reflect advanced brainstem compromise. The triad's absence offers no reassurance in a patient with earlier pupil or consciousness change.

Posterior fossa is unforgiving

Limited reserve means a small lesion can obstruct the fourth ventricle and compress the brainstem. CSF drainage strategy needs neurosurgical control because gradients may worsen.

Referral and resuscitation coexist

The referral call should occur while airway, perfusion, seizure, osmotic and imaging tasks proceed. Waiting to complete one stream loses time without improving information.

11Common pitfallsFrequent interpretation and management errors.

01
Waiting for hypertension, bradycardia and irregular respiration before recognising or referring suspected herniation.
02
Allowing a normal earlier CT or a normal local ICP reading to override new anisocoria, motor decline, posturing or falling consciousness.
03
Using lumbar puncture to investigate a patient with acute mass effect, obstructive hydrocephalus or a posterior-fossa herniation syndrome.
04
Treating with repeated osmotic boluses while definitive evacuation, CSF diversion or decompression remains unarranged.
05
Assigning the lesion side solely from weakness and overlooking false-localising peduncular compression.
06
Transferring a critically ill patient without airway, perfusion and monitoring stabilisation or without direct communication to the neurosurgical unit.

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