Brainstem Stroke Syndromes: Trace the Pathway, Test the Pattern
Localize brainstem injury by tracing tract crossings, cranial findings, eye movements, and spared functions, then test the pattern in 25 applied cases.
A weak right arm is a clinical finding, not the name of the damaged side of the brainstem. Localize by tracing each pathway through its crossing, then ask whether the cranial-nerve and body findings can meet in one region. A syndrome is an anatomical hypothesis, not proof of a particular blocked artery.
Crossings: separate the patient's side from the lesion's side
Ipsilateral means on the same side as the lesion; contralateral means on its opposite side. Always name the reference: right facial numbness is a right-sided symptom, but left body numbness can arise from the same right brainstem lesion. Rostral means toward the midbrain; caudal means toward the spinal cord. Medial means near the midline, lateral farther away; ventral and dorsal mean front and back here.
A tract is a bundle of axons; a nucleus is a cluster of neuronal cell bodies. A cranial-nerve fascicle is the intrabrainstem segment between its nucleus and its exit. A decussation is a crossing. The corticospinal tract descends through the cerebral peduncle, ventral pons, and medullary pyramid. Most fibers cross in the caudal medullary pyramidal decussation. A lesion above that crossing interrupts commands destined for the opposite limbs; it does not damage an already-crossed corticospinal tract. Lesions at the crossing need more careful mapping. [1]
Body vibration and conscious joint-position information ascends ipsilaterally in the spinal dorsal columns, synapses in the caudal medulla, then crosses as internal arcuate fibers. The resulting medial lemniscus has already crossed. Body pain-temperature information crosses in the spinal cord and ascends in the spinothalamic tract, also already crossed in the brainstem. Thus a right pontine lesion can cause left weakness, left vibration loss, and left pain-temperature loss, but by three different routes. [1]
Facial pain-temperature fibers descend on the same side in the spinal trigeminal tract before synapsing; injury to that tract or nucleus gives ipsilateral facial loss. This explains right face plus left body pain-temperature loss without requiring bilateral lesions. Cerebellar connections need their own crossing map, not the slogan that every long tract gives contralateral signs. [3]
Predict: a right medullary lesion above the pyramidal crossing adds pyramid damage. Which limbs weaken?
The left limbs. The interrupted right corticospinal fibers have not yet crossed and would have supplied the left side below the medulla.
Levels: use a tested function, not a vague cranial symptom
Begin with alertness, language, visual fields, pupils, lids, and each eye's movements. Compare forehead movement, eye closure, and smile; test facial sensation separately from facial strength. Compare limb power, pinprick, vibration, joint position, and coordination. Dysmetria means overshooting or undershooting a target; judge it in a limb strong enough to perform the movement. Record what was actually tested. An omitted examination is not a normal examination.
Oculomotor fascicles in the midbrain, abducens and facial structures in the pons, and hypoglossal or nucleus ambiguus structures in the medulla provide useful level anchors. But trigeminal sensory nuclei extend across levels, vestibular nuclei span the pontomedullary region, and spinal accessory motor neurons lie in the cervical cord. Facial numbness, dizziness, or dysarthria alone cannot choose one floor. Nuclear patterns also have exceptions: trochlear nuclear output crosses, and oculomotor nuclear lesions can produce complex bilateral findings. [2][5]
Medullary tongue weakness is a lower motor neuron pattern. On protrusion the tongue points toward a damaged hypoglossal nucleus or fascicle because the intact genioglossus pushes it toward the weak side. Ipsilateral atrophy or fasciculations may develop; they need not be present at abrupt onset. A supranuclear cortical or corticobulbar lesion may instead weaken the opposite tongue, usually without focal denervation atrophy. Tongue deviation alone is not proof of a medullary infarct: an extracranial hypoglossal lesion can also cause it. Opposite limb tract findings supply the central localization. [4]
A facial nucleus or fascicle lesion can weaken the entire ipsilateral face, including brow and eye closure. A supranuclear lesion commonly affects the opposite lower face more than the forehead because upper-face input is bilateral. These are patterns, not infallible screening rules. An isolated whole-face palsy can be peripheral; an accompanying crossed body deficit or pontine gaze sign changes that interpretation. [2][3]
Predict: does left facial pain-temperature loss alone establish a left pontine lesion?
No. The spinal trigeminal system extends into the medulla. Add independently localizing motor, bulbar, or gaze findings before choosing the level.
Medial and lateral: build a pattern from structures
In a typical rostral medial medullary lesion, the pyramid gives contralateral limb weakness, the medial lemniscus gives contralateral vibration-position loss, and hypoglossal fascicles give ipsilateral tongue weakness. Facial strength and pain-temperature sensation may remain intact in a limited lesion. The hypoglossal nucleus is dorsal; its fibers traverse the medulla, so the clinical triad does not require all three structures to sit in one tiny superficial cluster. [3]
A classic limited lateral medullary lesion combines ipsilateral facial and contralateral body pain-temperature loss with ipsilateral ataxia through inferior cerebellar connections. Descending sympathetic damage can cause ipsilateral Horner syndrome: a smaller pupil and mild ptosis, sometimes reduced sweating. Nucleus ambiguus involvement produces dysphagia, palatal weakness, and hoarseness. The medial pyramid and lemniscus are spared in the classic limited pattern; new weakness or vibration loss should trigger a search for extension, not rejection of the original lateral localization. Not every component occurs in every patient. [3]
In the lateral caudal pons, facial nucleus or fascicle involvement can add whole-face weakness. Nearby facial taste and parasympathetic pathways can affect anterior tongue taste and lacrimation, but an isolated motor-nucleus lesion need not abolish either. Middle cerebellar connections can produce ipsilateral ataxia; vestibular and auditory involvement varies. Hearing loss raises concern for an AICA-associated process but is neither required nor exclusive to it. Labyrinthine ischemia can contribute, and the labyrinthine artery does not always arise from AICA. [3][6][7]
Medial pontine patterns may involve descending motor fibers, the medial lemniscus, or abducens fascicles. More dorsal lesions can involve gaze circuits and looping facial fibers. In the midbrain, a CN III fascicular palsy plus opposite limb weakness suggests involvement of the cerebral peduncle. CN III palsy plus opposite tremor or ataxia instead suggests tegmental cerebellar outflow connections near the red nucleus; extension can mix these patterns. The descriptive anatomy is more useful than memorizing Weber or Benedikt as rigid packages. [2][3]
Predict: right lateral medullary signs are followed by new left vibration loss. Which additional tract is implicated?
The right medial lemniscus. Its already-crossed fibers carry vibration-position information from the left body.
Eye movements: one eye's muscle versus a two-eye command
Adduction moves an eye toward the nose; abduction moves it toward the temple. CN III drives the medial rectus for adduction and several vertical movers, elevates the lid, and carries pupillary constrictor output. CN VI drives the lateral rectus for abduction. Specify the tested direction and both eyes' responses rather than writing only “gaze abnormal.” [2]
For a leftward horizontal saccade, the left paramedian pontine reticular formation (PPRF) activates the left abducens nucleus. One output drives the left lateral rectus. Interneurons cross and ascend in the right medial longitudinal fasciculus (MLF) to the right oculomotor medial-rectus neurons. Thus leftward gaze needs left-eye abduction and right-eye adduction. Reverse every side for rightward gaze. [2][5]
A left VI fascicle or nerve lesion impairs left abduction while the right eye can still adduct on attempted left gaze. A left VI nucleus lesion interrupts the coordinated leftward command for both eyes. Left PPRF damage can also impair leftward saccades. Without additional testing, a conjugate horizontal gaze deficit does not uniquely separate nucleus from PPRF. Neither is simply an isolated lateral-rectus palsy.
A left MLF lesion produces left adduction weakness on right gaze, often with nystagmus of the abducting right eye: internuclear ophthalmoplegia (INO). Preserved convergence, when tested, supports retained left medial-rectus motor output; convergence is not universally preserved in every INO. Ptosis, pupillary dilation, or additional CN III movement deficits instead raise a different or broader localization. A normal pupil alone cannot exclude a partial CN III palsy. [5]
Combine a left horizontal gaze-center or VI nucleus lesion with left MLF damage: neither eye moves left on attempted horizontal gaze, and on right gaze only the right eye abducts. This is the one-and-a-half pattern, not two eyes permanently fixed to one side. Vertical gaze has rostral midbrain circuitry. Upgaze limitation with light-near dissociation, meaning better pupil constriction to a near target than to light, can indicate dorsal midbrain dysfunction. A pineal-region mass can also obstruct the nearby cerebral aqueduct, which carries cerebrospinal fluid from the third to fourth ventricle. An aqueduct block can enlarge the lateral and third ventricles upstream while leaving the fourth unenlarged. A gradual compressive course is not an acute vascular event merely because it localizes to brainstem. [2][5][16]
Predict: on left gaze the left eye abducts normally but the right eye cannot adduct; right-eye convergence is intact. Which MLF is implicated?
The right MLF. It carries the internuclear command from the left abducens nucleus to right medial-rectus neurons.
Posterior circulation: territory is not angiography
The vertebral arteries join to form the basilar artery. Vertebral and PICA branches are associated with lateral medullary supply; anterior spinal and vertebral branches contribute medially. Basilar branches supply pontine regions, AICA commonly supplies lateral caudal pontine and anterior-inferior cerebellar territory, and SCA supplies superior cerebellar and adjacent connections. Midbrain supply includes proximal PCA and basilar branches. Collaterals and branch anatomy vary. A precise occlusion needs vascular evidence, not an eponym alone. Isolated ataxia cannot uniquely name SCA. [3][6]
Bilateral ventral pontine injury can interrupt corticospinal and corticobulbar output, producing quadriplegia and inability to articulate despite preserved awareness. In classic locked-in syndrome, vertical eye movements or blinking provide communication because relevant rostral eye circuits and arousal systems remain functional. Establish repeatable command following. Do not equate silence with unconsciousness, or promise that every cranial function remains intact. Broader lesions can abolish these spared functions. Rostral basilar territory injury can instead affect midbrain, thalamic, and posterior cerebral structures, combining eye, awareness, memory, or visual-field abnormalities. [14]
Acute vestibular syndrome means ongoing acute vertigo or dizziness with features such as spontaneous nystagmus, nausea, motion intolerance, and unsteadiness, rather than isolated brief position-triggered spells. HINTS evaluates head impulse, nystagmus, and skew in the appropriate continuous syndrome with nystagmus, by a trained examiner. Gaze-evoked nystagmus that changes direction and skew, a vertical misalignment of the eyes, are central-concerning findings. HINTS is not a home rule-out test or a checklist for any dizziness. Central or equivocal findings require further evaluation. An early normal posterior diffusion MRI cannot independently exclude stroke when the clinical pattern remains concerning. [8][9][10]
Sudden focal deficits warrant urgent stroke evaluation, even if they improve. Localization alone establishes neither ischemia nor reperfusion eligibility. Dysphagia or a wet voice requires swallow safety assessment; do not offer food, drink, or oral medication until swallowing safety is established through the clinical pathway. [11][12] Acute treatment decisions belong to the current stroke service and guideline, not this localization exercise. [13]
Predict: does normal hearing exclude lateral pontine ischemia?
No. The auditory structures and labyrinthine supply may be spared. Use the entire examination and vascular evaluation rather than making hearing an absolute gate.
Synthesis: explain the positive findings and the spared functions
Use four questions: what function failed, on which clinical side, where does its pathway cross, and what neighboring structure explains the second independent observation? Then test the proposed boundary against preserved functions. Right tongue denervation plus left limb weakness fits a right medullary nucleus/fascicle-pyramid combination; adding left vibration loss implicates the medial lemniscus. Right tongue deviation without denervation and with right lower-face and limb weakness instead raises a left supranuclear pattern. Compare the cortical stroke companion for language, neglect, and cortical sensory evidence.
Separate cause from location. Delayed pontine dysfunction after a major osmotic change can reflect osmotic demyelination, not an arterial occlusion. Slowly progressive hearing and facial sensory changes with a described cerebellopontine-angle mass suggest compression rather than an abrupt infarct. Conversely, a tiny stroke need not produce every classic syndrome sign. Do not create a negative finding by reading silence in a vignette as sparing. [15]
The spinal cord is another useful contrast. A described anterior cord lesion can interrupt bilateral motor and pain-temperature pathways below a sensory level while sparing dorsal-column modalities. That is not the same structure set as medial medulla, despite an anterior spinal artery association. A vessel name never replaces a level. Throughout the cases, any imaging findings are supplied in words; no unlabeled scan interpretation is required. [1]
Predict: an initial report says only “left adduction impaired.” Can that establish INO?
No. Test the other eye during horizontal gaze, convergence, pupils, lids, and other eye movements. A partial CN III palsy remains a competitor until the examination distinguishes it.
Practice: trace the finding, then test the prediction
For each scenario, State the anatomical answer before reading the choices; after committing, compare the strongest alternative with the finding that changes it.
Case 1
Show answer and explanations for case 1
A. Left corticospinal tract and left spinothalamic tract (Best answer)
Left corticospinal fibers above the pyramidal decussation carry commands for the right limbs. Left spinothalamic injury removes already-crossed right body pain input; preserved vibration argues against a new medial lemniscus deficit.
B. Left corticospinal tract and left medial lemniscus (Why this does not fit)
It would reduce right vibration or position sense, not selectively right pinprick; the motor component of this choice is appropriate.
C. Right corticospinal tract and left spinothalamic tract (Why this does not fit)
The left limbs, because its fibers have not crossed; the proposed spinothalamic extension matches the right pain loss.
D. Right corticospinal tract and right spinothalamic tract (Why this does not fit)
No. Above the motor crossing, right corticospinal and right spinothalamic injury would both produce left body deficits, by different crossing histories.
Takeaway: At one brainstem level, motor fibers are still uncrossed while ascending body pain fibers are already crossed.
A. Right lateral pons initially; right corticospinal tract additionally (Why this does not fit)
The bulbar motor pattern with crossed pain points more strongly to lateral medulla. The added loss is vibration-position sensation with power still preserved, favoring the medial lemniscus rather than corticospinal tract.
B. Right lateral medulla initially; right medial lemniscus additionally (Best answer)
The right lateral medulla links right spinal trigeminal, left body spinothalamic, and nucleus ambiguus-related bulbar findings. The right medial lemniscus carries already-crossed left body vibration-position signals; preserved power does not require pyramid involvement.
C. Right lateral medulla initially; right corticospinal tract additionally (Why this does not fit)
Left limb weakness rather than isolated left vibration-position loss; the initial medullary localization is appropriate.
D. Right lateral pons initially; right medial lemniscus additionally (Why this does not fit)
Hoarseness with ipsilateral palatal weakness points to nucleus ambiguus-related medullary structures, while the additional lemniscal prediction is appropriate.
Takeaway: A new modality can map lesion growth more precisely than a syndrome name.
A. Reduced left limb vibration and position sense (Why this does not fit)
A medial lemniscus lesion, not the stated facial taste and parasympathetic extension; in the left pons it would affect the right limbs.
B. Reduced right limb vibration and position sense (Why this does not fit)
No. Right limb position loss would fit left medial lemniscus injury, but the described extension is into facial nonmotor pathways instead.
C. Reduced left anterior-tongue taste and left tearing (Best answer)
Right body pain-temperature loss joins left facial weakness in a central pontine pattern. Damage to nearby left facial taste and parasympathetic pathways can reduce left anterior-tongue taste and left tearing.
D. Reduced right anterior-tongue taste and right tearing (Why this does not fit)
No. The expected added peripheral functions are left-sided; right body pain loss follows a different, already-crossed ascending pathway.
Takeaway: Whole-face weakness identifies facial motor dysfunction, not automatic loss of every CN VII function.
A. Right corticospinal tract initially; right medial lemniscus additionally (Why this does not fit)
Left vibration-position loss; the described new dysmetria and tremor at stable power instead favor cerebellar outflow involvement.
B. Right medial lemniscus initially; right cerebellothalamic pathways additionally (Why this does not fit)
Measured left limb weakness implicates right corticospinal injury; the medial lemniscus carries sensation rather than voluntary motor commands.
C. Right medial lemniscus initially; right corticospinal tract additionally (Why this does not fit)
Initial weakness is motor rather than lemniscal, and new dysmetria with unchanged power does not primarily indicate additional corticospinal injury.
D. Right corticospinal tract initially; right cerebellothalamic pathways additionally (Best answer)
Right peduncular corticospinal fibers carry commands toward the later crossing and the left limbs. Right tegmental cerebellothalamic injury can cause left ataxia or tremor without additional corticospinal weakness.
Takeaway: Stable power can make new dysmetria evidence of a second functional system rather than worsening weakness.
A. A: left hypoglossal pathway; B: right supranuclear pathway (Best answer)
Left tongue atrophy supports left hypoglossal denervation, while right limb weakness places the combined lesion centrally in the medulla. Left lower-face and limb weakness with forehead sparing supports a right supranuclear motor pattern, which can also deviate the tongue left.
B. A: left hypoglossal pathway; B: left supranuclear pathway (Why this does not fit)
A is correctly lateralized, but a left supranuclear lesion would usually affect the right lower face and limbs, unlike B.
C. A: right hypoglossal pathway; B: right supranuclear pathway (Why this does not fit)
The left-sided denervation atrophy and leftward deviation point to the left hypoglossal pathway; B is appropriately right supranuclear.
D. A: right hypoglossal pathway; B: left supranuclear pathway (Why this does not fit)
A has left lower motor tongue signs, whereas B has left-sided supranuclear deficits requiring a right-sided motor lesion.
Takeaway: The direction of tongue deviation needs its motor-neuron context.
A. Leftward movement of both eyes (Why this does not fit)
The left abducens nucleus supplies the coordinated leftward command to both eyes, so neither can move left normally.
B. Right-eye abduction only (Best answer)
The left MLF cannot convey the right abducens internuclear command to left medial-rectus neurons. Leftward gaze is lost in both eyes; on right gaze only the right eye can abduct.
C. Left-eye abduction only (Why this does not fit)
Left abduction is removed by left VI nuclear injury, so it cannot be the residual movement.
D. Rightward movement of both eyes (Why this does not fit)
The pre-existing left MLF lesion still prevents left adduction even though right abduction remains possible.
Takeaway: One-and-a-half is the sum of a gaze-center deficit and ipsilateral internuclear disconnection.
A. Right MLF and left corticospinal tract (Why this does not fit)
Right adduction on left gaze, precisely the movement that remains normal here.
B. Left MLF and right corticospinal tract (Why this does not fit)
Left MLF injury impairs left adduction, not abduction, and right pontine corticospinal injury would weaken the left limbs.
C. Left VI fascicle and left corticospinal tract (Best answer)
The right eye still adducts on left gaze, so the left abducens internuclear output is not abolished. Left pontine corticospinal damage above the decussation causes right limb weakness.
D. Left abducens nucleus and left corticospinal tract (Why this does not fit)
Right adduction on left gaze would also be impaired; it is explicitly preserved.
Takeaway: An abduction deficit becomes a conjugate gaze palsy only when the other eye also loses its paired movement.
A. Neither eye moves left; both eyes move right (Why this does not fit)
Left adduction on right gaze depends on the left MLF and cannot remain normal after its damage.
B. Both eyes move left; only the right eye abducts on right gaze (Why this does not fit)
The original conjugate leftward deficit explicitly persists; the new MLF lesion is added rather than substituted.
C. Only the left eye abducts on left gaze; neither eye moves right (Why this does not fit)
The original conjugate deficit is leftward and the added MLF deficit is left adduction, so right abduction remains rather than left abduction.
D. Neither eye moves left; only the right eye abducts on right gaze (Best answer)
The leftward conjugate gaze deficit means neither eye moves left normally. It removes left adduction on right gaze, leaving right-eye abduction as the only preserved horizontal component.
Takeaway: Test both gaze directions before declaring a one-and-a-half pattern.
A. Initial right MLF dysfunction with additional right oculomotor pathway involvement (Best answer)
The right MLF, because right adduction fails during left gaze despite preserved right convergence. New right ptosis and pupillary constrictor dysfunction require additional oculomotor pathway involvement.
B. Initial right MLF dysfunction with progression confined to that same tract (Why this does not fit)
The MLF horizontal link does not by itself account for ipsilateral lid elevation failure and a poorly reactive enlarged pupil.
C. Initial left MLF dysfunction with additional right oculomotor pathway involvement (Why this does not fit)
The eye failing to adduct, which is right; left-eye abducting nystagmus does not make this a left MLF lesion.
D. Initial right VI dysfunction with additional right oculomotor pathway involvement (Why this does not fit)
Right abduction is full; the impaired right movement is adduction on left gaze.
Takeaway: Convergence can support INO, but new pupil and lid findings demand a broader map.
A. Left CN III fascicle and left facial fibers, with intact pontine gaze circuitry (Why this does not fit)
It cannot account for loss of right-eye adduction on left gaze or left-eye abduction, and it would localize to a different brainstem level.
B. Left pontine gaze circuitry, left MLF, and left facial fibers (Best answer)
Left gaze circuitry damage removes leftward gaze, and left MLF damage removes left adduction on right gaze. Left facial fibers near dorsal caudal pontine structures account for the ipsilateral whole-face weakness.
C. Left pontine gaze circuitry and left MLF, with right facial fibers (Why this does not fit)
Right facial fiber damage would weaken the right face; the eye components are appropriately left-sided.
D. Left VI fascicle and left facial fibers, with intact MLF (Why this does not fit)
Right adduction on left gaze and left adduction on right gaze are both lost, requiring gaze-center and MLF involvement.
Takeaway: A one-and-a-half pattern with ipsilateral facial weakness can map neighboring dorsal pontine structures.
A. Right sympathetic pathway; worsening right facial pinprick loss (Why this does not fit)
No. It remains compatible with additional spinal trigeminal damage in the existing lateral medullary region.
B. Right CN III pathway; worsening right facial pinprick loss (Why this does not fit)
Initial miosis suggests sympathetic injury, while facial pinprick loss concerns trigeminal sensation rather than oculomotor output.
C. Right sympathetic pathway; new right adduction and vertical movement weakness (Best answer)
Miosis with mild ptosis and full eye movements fits right Horner syndrome in the lateral medullary context. New right adduction and vertical movement weakness would implicate additional oculomotor function, not isolated sympathetic loss.
D. Right CN III pathway; new right adduction and vertical movement weakness (Why this does not fit)
The small pupil and normal eye movements favor sympathetic loss, not the described oculomotor motor and pupillary pattern.
Takeaway: A drooping lid does not identify CN III until pupil and movement findings are considered.
A. Preserved awareness initially; extension threatens only limb strength (Why this does not fit)
It reaches dorsal arousal structures rather than simply adding more ventral corticospinal damage.
B. Absent awareness initially; extension threatens only limb strength (Why this does not fit)
Reliable meaningful eye-coded answers cannot be dismissed as the inability to articulate; dorsal extension also threatens more than limb power.
C. Absent awareness initially; consciousness may deteriorate with extension (Why this does not fit)
The person demonstrates awareness through eye communication, so the later risk is loss of a preserved function rather than persistence of initial coma.
D. Preserved awareness initially; consciousness may deteriorate with extension (Best answer)
Reproducible answers to meaningful questions through vertical eyes show awareness despite loss of limb and speech output. Arousal-system damage can impair consciousness; that is not an inevitable consequence of the original ventral motor lesion.
Takeaway: Locked-in motor failure and impaired consciousness are different dimensions of a lesion.
A. Rostral eye and arousal injury; ventral pontine motor pathways remain functional (Best answer)
Rostral midbrain eye circuitry and medial thalamic-arousal involvement fit those findings. The ventral pontine motor region is explicitly spared and useful limb power is observed; basilar occlusion is not synonymous with locked-in syndrome.
B. Rostral eye and arousal injury; obligatory bilateral pontine motor interruption (Why this does not fit)
The scan spares the ventral pons and the person retains limb power, even though the rostral deficits fit.
C. Caudal pontine horizontal gaze injury; ventral pontine motor pathways remain functional (Why this does not fit)
Vertical gaze points rostrally, consistent with the described midbrain injury, rather than an isolated caudal pontine horizontal command lesion.
D. Caudal pontine horizontal gaze injury; obligatory bilateral pontine motor interruption (Why this does not fit)
It locates the injury rostrally and spares ventral pons, matching vertical gaze dysfunction with retained limb power rather than the proposed pontine pattern.
Takeaway: The distribution of basilar-territory injury determines which functions fail.
A. Hearing must be lost; a distal AICA clot is established (Why this does not fit)
Auditory loss is not obligatory, and the available angiogram does not establish the proposed distal AICA clot.
B. Hearing can be spared; proximal basilar disease is demonstrated (Best answer)
No. Auditory involvement is variable in AICA-associated and lateral pontine ischemia. Basilar narrowing at the AICA origin is demonstrated; a separate distal AICA occlusion is not.
C. Hearing can be spared; a distal AICA clot is established (Why this does not fit)
The angiogram specifically does not show a separate distal AICA occlusion; proximal disease may affect the same supply.
D. Hearing must be lost; proximal basilar disease is demonstrated (Why this does not fit)
The claim that hearing must be lost; the demonstrated proximal vascular finding does not impose a complete textbook syndrome.
Takeaway: A territory pattern and its culprit vessel are related but not interchangeable evidence.
A. Peripheral left facial and vestibular nerve injury; precise auditory site remains unestablished (Why this does not fit)
Right body pinprick loss requires a central sensory pathway; peripheral left facial and vestibular injury cannot explain the entire examination.
B. Right pontine injury; precise auditory site remains unestablished (Why this does not fit)
The left pons, where left facial motor structures lie beside pathways carrying already-crossed right body sensory information.
C. Central pontine injury; hearing loss may be labyrinthine or central (Best answer)
Left facial motor weakness with right body pain loss cannot be explained by an isolated left inner-ear disorder. No. Vascular audiovestibular loss may involve the labyrinth or central auditory structures, so cochlear nuclear destruction is not established.
D. Central pontine injury; hearing loss proves cochlear nuclear destruction (Why this does not fit)
Labyrinthine ischemia can accompany the vascular process, even when a pontine lesion is also present.
Takeaway: Crossed signs identify a central component; hearing loss alone does not identify the cochlear nucleus.
A. HINTS is applicable and concerning; early MRI excludes stroke (Why this does not fit)
Early posterior diffusion imaging can be falsely negative, so a concerning clinical examination is not overruled by this result.
B. HINTS is inapplicable here; early MRI does not exclude stroke (Why this does not fit)
Continuous symptoms with nystagmus and a trained examiner meet the described setting for HINTS, though the scan limitation is correctly stated.
C. HINTS is inapplicable here; early MRI excludes stroke (Why this does not fit)
The clinical setting supports trained HINTS use, and early posterior MRI is not a definitive exclusion test.
D. HINTS is applicable and concerning; early MRI does not exclude stroke (Best answer)
The examiner is trained and the person has a continuous acute vestibular syndrome with nystagmus; skew and direction-changing nystagmus are central-concerning. It does not independently exclude posterior stroke; the concerning examination warrants further stroke evaluation.
Takeaway: An appropriate central vestibular examination is not nullified by early negative diffusion imaging.
A. The checklist is not a valid rule-out here; focal ischemia remains a concern (Best answer)
It was obtained after episodic symptoms resolved, without the ongoing nystagmus-associated syndrome for which the test is intended. The sudden diplopia and dysarthria are focal warning symptoms even though they resolved.
B. The checklist is not a valid rule-out here; resolution removes vascular concern (Why this does not fit)
No. Sudden transient diplopia and dysarthria can still signal a vascular event requiring urgent assessment.
C. The checklist reliably favors a peripheral cause; prior focal symptoms need separate evaluation (Why this does not fit)
The symptom-free episodic examination without current nystagmus cannot provide the claimed reliable peripheral interpretation, although the prior focal symptoms still warrant evaluation.
D. The checklist is a valid rule-out here; resolution removes vascular concern (Why this does not fit)
HINTS was used outside its intended syndrome, and transient focal neurologic symptoms can remain urgent after recovery.
Takeaway: A normal checklist outside its intended clinical setting cannot cancel a history of sudden focal deficits.
A. Sensory ataxia; SCA is identifiable from dysmetria alone (Why this does not fit)
Intact position testing with cerebellar injury favors cerebellar ataxia, and only the angiogram establishes the specific vessel.
B. Cerebellar ataxia; the SCA attribution is supported by angiography (Best answer)
Full strength and intact position sense accompany a described ipsilateral cerebellar lesion, supporting cerebellar dysmetria. The angiogram demonstrates the SCA branch occlusion; dysmetria alone would not uniquely identify that artery.
C. Cerebellar ataxia; SCA is identifiable from dysmetria alone (Why this does not fit)
Angiography, rather than the nonspecific finding of ipsilateral dysmetria.
D. Sensory ataxia; the SCA attribution is supported by angiography (Why this does not fit)
Position sense is intact and MRI describes a cerebellar infarct, while the angiographic vessel attribution is supported.
Takeaway: Name a vessel from vascular evidence, not merely from cerebellar signs.
A. Pain-temperature is preserved; the sensory level favors cord (Why this does not fit)
Vibration-position, not pain-temperature; the cord level is otherwise appropriate.
B. Pain-temperature is preserved; the sensory level favors medulla (Why this does not fit)
The stem documents pain-temperature loss below a thoracic level and spared dorsal columns, supporting preserved vibration-position in a cord lesion.
C. Vibration-position is preserved; the sensory level favors cord (Best answer)
The spinal dorsal columns, which still ascend before their medullary sensory crossing. A thoracic below-level pattern and matching spinal imaging do not require the cranial-long-tract combination of a medial medullary lesion.
D. Vibration-position is preserved; the sensory level favors medulla (Why this does not fit)
No. It supports spinal localization; shared anterior spinal supply terminology does not erase the level difference.
Takeaway: Anterior spinal supply at cord and medulla does not imply identical affected structures.
A. Basilar-territory ischemic infarction (Why this does not fit)
The delayed deterioration after osmotic correction and nonterritorial symmetric distribution favor demyelination; absence of basilar occlusion alone would not exclude all infarction.
B. Pineal-region compression (Why this does not fit)
Dorsal midbrain and aqueduct-related functions, generally with a compressive course, rather than this delayed osmotic central pontine pattern.
C. Cerebellopontine-angle mass (Why this does not fit)
A focal extra-axial mass usually produces a progressive regional pattern, not symmetric central pontine dysfunction after osmotic correction.
D. Osmotic demyelination (Best answer)
A large rapid osmotic change followed by a delayed second neurological phase and symmetric central pontine injury fits osmotic demyelination.
Takeaway: Pontine dysfunction can be osmotic rather than arterial; tempo is part of localization reasoning.
A. Dorsal midbrain dysfunction with obstruction between third and fourth ventricles (Best answer)
Upgaze impairment with light-near dissociation fits dorsal midbrain dysfunction in the described compression. Aqueduct obstruction lies between third and fourth ventricles, leaving the fourth downstream of the block.
B. Dorsal midbrain dysfunction with obstruction beyond the fourth ventricle (Why this does not fit)
The fourth ventricle is not enlarged and the scan directly describes aqueduct compression, placing the block above it.
C. Caudal pontine gaze dysfunction with obstruction between third and fourth ventricles (Why this does not fit)
The vertical gaze and light-near pattern is dorsal midbrain, not the caudal pontine horizontal gaze system; the aqueduct site is otherwise appropriate.
D. Caudal pontine gaze dysfunction with obstruction beyond the fourth ventricle (Why this does not fit)
The eye pattern points to dorsal midbrain and the ventricular distribution to an aqueduct block above the fourth ventricle.
Takeaway: One compressive lesion may disrupt nearby gaze circuitry and CSF flow through different mechanisms.
A. Left lower-face weakness with spared brow and new right body pain-temperature loss (Why this does not fit)
Peripheral left facial motor injury should include the upper face, while the explicitly spared central long tracts do not predict new right body pain loss.
B. Left whole-face weakness with unchanged body pain-temperature sensation (Best answer)
A left facial motor nerve lesion weakens the left brow, eye closure, and smile. The central spinothalamic pathways are explicitly unaffected, so peripheral facial motor compression does not add a crossed body sensory deficit.
C. Left whole-face weakness with new right body pain-temperature loss (Why this does not fit)
New right body pain loss would require additional left central spinothalamic involvement, contrary to the stated sparing of brainstem long tracts.
D. Left lower-face weakness with spared brow and unchanged body pain-temperature sensation (Why this does not fit)
A facial motor nerve lesion affects upper and lower face, so brow sparing is not the expected pattern; the body prediction respects the boundary.
Takeaway: Neighboring nerves can be compressed gradually without creating a crossed long-tract syndrome.
A. Both eyes fail to move right while left gaze is full (Why this does not fit)
A right horizontal gaze-center or abducens nuclear lesion, since right abduction and left adduction fail together.
B. Left abduction fails while right adduction on left gaze is full (Why this does not fit)
An isolated left abduction deficit suggests left VI motor dysfunction, not the left adduction failure that needs explanation.
C. Right abducting nystagmus on right gaze, intact left convergence, normal lids and pupils (Best answer)
Preserved left convergence despite failed left adduction on right gaze supports an intact motor output with impaired internuclear input, especially with right abducting nystagmus.
D. Left adduction failure during gaze and convergence with left ptosis (Why this does not fit)
Failure during convergence and ptosis add medial-rectus output and lid dysfunction beyond an isolated horizontal internuclear deficit.
Takeaway: An incomplete eye description supports a differential, not a confident eponym.
A. Left lateral medullary pattern; normal power establishes safe water intake (Why this does not fit)
Limb motor pathways can be spared while bulbar swallowing pathways are impaired, as the dysphagia and hoarseness indicate.
B. Left medial medullary pattern; swallowing safety remains unestablished (Why this does not fit)
A limited medial medullary lesion emphasizes pyramid, lemniscus, and hypoglossal pathways, not this crossed pain-temperature and hoarseness combination.
C. Left medial medullary pattern; normal power establishes safe water intake (Why this does not fit)
The examination favors lateral rather than medial medulla, and preserved limb power does not establish safe swallowing.
D. Left lateral medullary pattern; swallowing safety remains unestablished (Best answer)
Left lateral medulla connects left facial pain loss, right body pain loss, ataxia, and nucleus ambiguus-related bulbar dysfunction. No. Reported dysphagia requires swallowing safety assessment before water or other oral intake, independent of preserved limb strength.
Takeaway: A limited lateral medullary lesion can threaten swallowing while sparing limb strength.
The right body sends vibration-position input up the right dorsal columns to the caudal medullary relay. The left body, because its internal arcuate fibers have crossed into the right medial lemniscus.
B. A: right body; B: right body (Why this does not fit)
The right medial lemniscus lies after the sensory crossing and represents the left, not right, body.
C. A: left body; B: left body (Why this does not fit)
Its right dorsal-column relay is explicitly before the internal arcuate crossing and still carries right body input.
D. A: left body; B: right body (Why this does not fit)
Right body input reaches the right relay before crossing, while left body input occupies the right medial lemniscus after crossing.
Takeaway: An anatomical side is not enough: locate the lesion relative to the relevant crossing.
