How do I perform a systematic brain‑stem examination?

How to Perform a Systematic Brainstem Examination

A systematic brainstem examination requires sequential testing of cranial nerves V through XII, assessment of consciousness level, evaluation of motor/sensory pathways, and specific brainstem reflex testing to localize lesions along the midbrain, pons, and medulla.

Algorithmic Approach to Brainstem Examination

Step 1: Level of Consciousness Assessment

• Glasgow Coma Scale scoring - Lower scores significantly associate with brainstem pathology 1
• Document responsiveness, orientation, and arousal state
• Note any fluctuations suggesting delirium versus fixed deficits

Step 2: Cranial Nerve Examination by Anatomic Level

Midbrain (CN III, IV):

• CN III (Oculomotor): Pupil size, light reflex, eye movements (medial, superior, inferior)
• CN IV (Trochlear): Downward and inward eye movement
• Look for ptosis, pupillary asymmetry, or gaze palsies

Pons (CN V, VI, VII, VIII):

• CN V (Trigeminal): Facial sensation in all three divisions, corneal reflex, jaw jerk, masseter strength 2, 3
• CN VI (Abducens): Lateral eye movement - courses through cavernous sinus 2
• CN VII (Facial): Facial muscle strength (upper and lower face), taste anterior 2/3 tongue
• CN VIII (Vestibulocochlear): Hearing, vestibular function
• Critical pitfall: Combined CN V and VII palsy raises concern for perineural tumor spread 2

Medulla (CN IX, X, XI, XII):

• CN IX/X: Palate elevation, gag reflex, voice quality, swallowing
• CN XI (Accessory): Shoulder shrug, head turning
• CN XII (Hypoglossal): Tongue protrusion, strength, fasciculations

Step 3: Specific Brainstem Reflex Testing

Essential reflexes to document 3:

• Blink reflex: Trigeminal afferent, facial efferent - tests pontine tegmentum
• Corneal reflex: Direct visualization of CN V/VII arc
• Jaw jerk: Trigeminal stretch reflex - tests pontine level
• Masseter inhibitory reflex: Assesses trigeminal motor nucleus
• Oculocephalic reflex (doll's eyes): Tests pontine-midbrain connections
• Oculovestibular reflex (cold calorics): Tests vestibular nuclei in pons

Step 4: Motor and Sensory Pathway Assessment

Look for crossed findings 4:

• Ipsilateral cranial nerve deficit + contralateral motor/sensory deficit = classic brainstem syndrome
• Test all four limbs for strength, tone, reflexes
• Sensory testing: pain, temperature, proprioception, vibration
• Document any dissociated sensory loss (suggests specific tract involvement)

Step 5: Localizing Signs by Syndrome

Midbrain syndromes:

• Weber syndrome: CN III palsy + contralateral hemiparesis
• Benedikt syndrome: CN III palsy + contralateral tremor/ataxia

Pontine syndromes 2:

• Millard-Gubler: CN VI/VII palsy + contralateral hemiparesis
• Foville syndrome: Conjugate gaze palsy + ipsilateral facial palsy
• Locked-in syndrome: Quadriplegia with preserved consciousness and vertical eye movements

Medullary syndromes:

• Lateral medullary (Wallenberg): Ipsilateral facial numbness, Horner's, ataxia + contralateral body numbness
• Medial medullary: Ipsilateral tongue weakness + contralateral hemiparesis

Critical Clinical Pitfalls

When to suspect brainstem pathology 1, 2:

• Lateralizing signs - strongly associated with structural lesions requiring imaging
• Multiple cranial nerve involvement - especially non-adjacent nerves
• Crossed motor/sensory findings - pathognomonic for brainstem
• Altered consciousness with focal findings - demands urgent imaging
• Respiratory pattern abnormalities - Cheyne-Stokes, apneustic, ataxic breathing

Risk factors demanding immediate neuroimaging 1:

• History of trauma or falls
• Anticoagulation therapy
• Focal neurologic deficit
• Headache with nausea/vomiting
• Signs of elevated intracranial pressure
• Significant deterioration of consciousness

Documentation Requirements

Record systematically:

• Each cranial nerve tested with specific findings
• Presence/absence of each brainstem reflex
• Motor examination with lateralization
• Sensory examination with dermatomal/tract patterns
• Level of consciousness with GCS
• Any crossed findings suggesting brainstem localization

Ischemic and hemorrhagic infarcts are the most frequent cause of acute brainstem syndromes, with the pons most frequently affected 2. Non-ischemic causes include demyelination, encephalitis, neoplasms, central pontine myelinolysis, and trauma 2.

The examination must be thorough enough to distinguish between supratentorial, brainstem, and peripheral lesions, as management differs dramatically 5. When acute brainstem syndrome is suspected clinically, particularly in emergency settings, proceed immediately to neuroimaging per stroke protocols 2.