Brainstem Stroke Syndromes: One Localization Table for Weber, Wallenberg, and the Rest
Eponyms are just coordinates: which level, which side of the midline. The crossed face-body rule plus one table localizes nearly every brainstem stroke — and explains why a devastating one can score 2 on the NIHSS.
Crossed signs are the brainstem's signature — cranial nerve on one side, body on the other.
- →The whole localization game reduces to two axes: which level (midbrain = CN III/IV, pons = V–VIII, medulla = IX–XII) and medial or lateral (medial = motor tract + medial lemniscus + a midline nerve; lateral = spinothalamic + sympathetics + cerebellar signs).
- →Crossed findings — an ipsilateral cranial nerve palsy with contralateral hemiparesis or sensory loss — put the lesion in the brainstem before any scan does.
- →Wallenberg (lateral medullary) is the syndrome to master cold: vertigo, ipsilateral facial and contralateral body pain-temperature loss, Horner, dysphagia, ataxia — and classically no limb weakness at all.
- →The NIHSS undercounts the brainstem: vertigo, dysphagia, gaze palsies, and ataxia score little or nothing. A low score with these findings is a trap, not reassurance.
- →Two never-miss patterns: progressive bilateral signs with declining consciousness (basilar occlusion) and the quadriplegic patient with preserved vertical gaze (locked-in — awake, and listening).
Brainstem syndromes are taught as a memory contest — a parade of nineteenth-century eponyms — and forgotten accordingly. But the eponyms are just coordinates. The brainstem is a cable conduit a few centimeters wide: long motor and sensory tracts running through, cranial nerve nuclei stationed at floors, and paired arteries feeding it in medial and lateral wedges.3 Learn the wedges and the floors, and every syndrome becomes a street address.
The two rules that do the work
Rule one — the level is named by the cranial nerve. III and IV live in the midbrain; V, VI, VII, VIII in the pons; IX through XII in the medulla. A "down-and-out" eye says midbrain; a facial palsy that takes the whole face (not sparing the forehead) says pons; hoarseness and dysphagia say medulla.
Rule two — medial versus lateral is named by the tracts. Medial wedges (paramedian perforators) carry the corticospinal tract, the medial lemniscus, and midline nerves: expect contralateral weakness and proprioceptive loss with an ipsilateral midline cranial nerve palsy. Lateral wedges (circumferential arteries — PICA, AICA, SCA) carry the spinothalamic tract, sympathetic fibers, cerebellar connections, and CN V's nucleus: expect pain-temperature crossing, Horner, ataxia, vertigo — and typically no weakness.
The famous corollary is the crossed sign: because cranial nerves exit before the tracts cross, a brainstem lesion hits the nerve ipsilaterally and the body contralaterally. Face on one side, body on the other, in any combination, is a brainstem lesion until proven otherwise.
| Syndrome | Level / vessel | Ipsilateral | Contralateral |
|---|---|---|---|
| Weber | Medial midbrain (PCA perforators) | CN III palsy | Hemiparesis (peduncle) |
| Claude | Midbrain tegmentum | CN III palsy | Ataxia (red nucleus / SCP) |
| Benedikt | Midbrain tegmentum, larger | CN III palsy | Ataxia + tremor/involuntary movements |
| Millard-Gubler | Ventral pons | CN VI ± VII palsy | Hemiparesis |
| Wallenberg | Lateral medulla (vertebral/PICA) | Facial pain-temp loss, Horner, ataxia, dysphagia/hoarseness (IX/X) | Body pain-temp loss; no weakness |
| Dejerine (medial medullary) | Medial medulla (vertebral/ant. spinal) | CN XII palsy (tongue deviates to lesion) | Hemiparesis + proprioceptive loss |
| Top of the basilar | Rostral basilar embolism | Bilateral: somnolence, vertical gaze palsy, visual field loss, memory change — behavioral more than motor1 | |
| Locked-in | Bilateral ventral pons (basilar) | Quadriplegia + anarthria with preserved consciousness and vertical gaze/blinking | |
Wallenberg, the one to know cold
Lateral medullary infarction is the highest-yield syndrome on the list because it is common, weaponless (no weakness to flag it), and dangerous through its complications. In Kim's 130-patient series the recurring elements were vertigo and gait ataxia, ipsilateral facial and contralateral body pain-temperature loss in the classic crossed pattern, Horner syndrome, dysphagia, and hoarseness — in inconstant combinations that map to exactly which slice of the lateral medulla the vertebral/PICA territory took.2 Three service-level implications: the swallow is a threat (the dysphagia here is neurogenic and aspiration-prone — screen before anything passes the lips, per the dysphagia chapter); the underlying vessel is often a vertebral dissection in younger patients (neck pain before the vertigo — see cervical artery dissection); and the late sequel worth naming at follow-up is central post-stroke pain, for which Wallenberg is notorious.
Why the NIHSS undercounts all of this
Score a full Wallenberg on the NIHSS: vertigo scores nothing, dysphagia nothing, Horner nothing, hoarseness nothing; ataxia one or two points if the limbs cooperate. A patient who cannot stand, swallow, or see straight can carry a score of 2 — below many triage thresholds. The scale was engineered around anterior-circulation deficits; the posterior circulation lives in its blind spots, a theme we walk through from the PCA side in the PCA stroke guide. The operational fix is not a better scale at the door — it is refusing to let a low number overrule a brainstem exam, and remembering that acute vestibular syndromes have their own bedside discrimination pathway (the frame of our dizziness guide).
A patient who cannot stand, swallow, or look up is not "NIHSS 2." The scale is measuring the wrong hemisphere of the problem.
The two presentations that cannot wait
Basilar occlusion in evolution announces itself as stuttering, bilateralizing brainstem signs — dysarthria then diplopia then a hemiparesis that switches sides — with consciousness sliding. It is the posterior circulation's large-vessel emergency, and modern trials have put basilar thrombectomy firmly on the table: the moment of recognition is a vessels-now, EVT-conversation-now event. And locked-in syndrome is the examination's most consequential catch: bilateral ventral pontine infarction leaves quadriplegia and anarthria with consciousness intact and vertical eye movements preserved. Ask for an upgaze before concluding coma — the difference is a human being who can hear every word said at the bedside.
The bottom line
Drop the mystique and keep the grid: level by cranial nerve, medial versus lateral by tracts, crossed signs as the brainstem's watermark. Know Wallenberg in your sleep, protect its swallow, and chase its vertebral artery. Distrust low NIHSS scores wearing brainstem clothing. And hold the two alarms — bilateralizing signs with fading consciousness, and the "comatose" patient who can look up — because those are the minutes where localization stops being academic.
Frequently asked questions.
What are crossed signs in a brainstem stroke?
An ipsilateral cranial nerve deficit combined with contralateral body findings — for example, a left facial sensory loss with right body sensory loss. Cranial nerves exit the brainstem before the long tracts cross, so one lesion catches the nerve on its own side and the body pathways destined for the other side. Crossed findings localize to the brainstem before imaging does.
What is Wallenberg syndrome?
Lateral medullary infarction, usually from vertebral artery or PICA occlusion: vertigo and gait ataxia, ipsilateral facial and contralateral body pain-temperature loss, Horner syndrome, dysphagia, and hoarseness — classically without limb weakness. Its practical dangers are aspiration from neurogenic dysphagia and, in younger patients, an underlying vertebral dissection.
Why can a serious brainstem stroke have a low NIHSS score?
The NIHSS gives little or no weight to vertigo, dysphagia, gaze palsies, Horner syndrome, hoarseness, and truncal ataxia — the core brainstem deficits. A disabling lateral medullary or cerebellar-pathway stroke can score in the low single digits, which is why clinical suspicion must outrank the number in posterior-circulation presentations.
What is locked-in syndrome?
Bilateral ventral pontine injury — most often from basilar artery occlusion — causing quadriplegia and loss of speech with fully preserved consciousness. Vertical eye movements and blinking survive because the midbrain is spared. Testing upgaze in an apparently comatose patient is how it is recognized.
How does basilar artery occlusion present?
Often stutteringly: progressive or fluctuating bilateral brainstem signs — dysarthria, diplopia, alternating or bilateral weakness — with declining level of consciousness, sometimes preceded by vertigo or posterior headache. It is a large-vessel emergency; recognition should trigger immediate vessel imaging and a thrombectomy-pathway conversation.
References.
- Caplan LR. "Top of the basilar" syndrome. Neurology. 1980;30(1):72-79. PubMed
- Kim JS. Pure lateral medullary infarction: clinical-radiological correlation of 130 acute, consecutive patients. Brain. 2003;126(Pt 8):1864-1872. PubMed
- Tatu L, Moulin T, Bogousslavsky J, Duvernoy H. Arterial territories of the human brain: cerebral hemispheres. Neurology. 1998;50(6):1699-1708. PubMed
Related guides
Keep building the picture.
- NIHSS calculator The scale whose blind spots this article maps.
- PCA stroke guide The adjacent territory — thalamus, occipital lobe, and Percheron.
- Post-stroke dysphagia Wallenberg's most dangerous complication, screened before anything passes the lips.
- Thrombectomy eligibility The conversation basilar occlusion should trigger immediately.
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