Medial vs lateral medullary syndrome: artery, structures and signs
Split the medulla at the olive level into a medial strip and a lateral part. Each has its own artery, its own structures and its own signs, and the two syndromes mirror each other.
Chapters (10)
Distinguish medial and lateral medullary syndromes by vascular territory and the structures damaged.
The short version
- Medial medullary syndrome is the anterior spinal artery: opposite weakness, opposite loss of vibration and position sense, and a tongue that deviates toward the lesion.
- Lateral medullary (Wallenberg) syndrome is the posterior inferior cerebellar or vertebral artery: same-side face and opposite-side body loss of pain and temperature, hoarseness, Horner syndrome and ataxia.
- The medial strip holds the pyramid, the medial lemniscus and the hypoglossal nucleus with its fibres; the lateral part holds the spinothalamic tract, spinal trigeminal nucleus and tract, nucleus ambiguus, vestibular nuclei, inferior cerebellar peduncle and descending sympathetic fibres.
- The syndromes are mirror images: medial spares pain and temperature, and lateral classically spares strength.
The medulla at the olive level: medial strip and lateral part
To compare medial vs lateral medullary syndrome, picture a cross section of the medulla at the level of the olives and divide it into a medial strip, beside the midline, and a lateral part. Every sign in both syndromes follows from which structures sit in which half.[2][4]
| Medial strip | Lateral part |
|---|---|
| Pyramid, carrying the corticospinal tract | Spinothalamic tract |
| Medial lemniscus | Spinal trigeminal nucleus and tract |
| Hypoglossal nucleus with its fibres | Nucleus ambiguus |
| Vestibular nuclei | |
| Inferior cerebellar peduncle | |
| Descending sympathetic fibres |
The medial strip has three key structures for the exam (the medial longitudinal fasciculus also runs here). At the olive level the hypoglossal nucleus lies dorsally, near the midline, and its fibres run ventrally through the medial medulla, so "medial strip" is a simplification.[2][7]
Two territories, two arteries
The medial strip is supplied by the anterior spinal artery. The lateral part is supplied by the posterior inferior cerebellar artery (PICA) or the vertebral artery. Lateral medullary syndrome most commonly follows PICA or vertebral artery infarction.[1][2][8]
Medial infarcts can also arise from paramedian branches of the vertebral artery; the anterior spinal artery is the exam convention used in this lesson.[7]
Three other vessels are worth ruling out by territory. The anterior inferior cerebellar artery supplies the anterior inferior cerebellum, the superior cerebellar artery supplies the superior cerebellum and the tectum, and the posterior cerebral artery supplies the occipital lobe, the medial temporal lobe and the thalamus. None of them supplies the medial strip, and the superior cerebellar and posterior cerebral arteries do not supply the medulla at all.[2][9][10]
Lateral medullary (Wallenberg) syndrome, sign by sign
Read each sign straight off the damaged structure.[1][4]
| Structure | Sign |
|---|---|
| Spinal trigeminal nucleus and tract | Pain and temperature lost on the same side of the face |
| Spinothalamic tract (already crossed) | Pain and temperature lost on the opposite side of the body |
| Nucleus ambiguus (cranial nerves IX and X) | Hoarse voice and difficulty swallowing |
| Descending sympathetic fibres | Horner syndrome on the same side: ptosis, small pupil, reduced sweating |
| Vestibular nuclei | Vertigo, nystagmus and vomiting |
| Inferior cerebellar peduncle | Ataxia on the same side |
The result is a crossed pattern: face on one side, body on the other. Classically there is no weakness, because the pyramid lies medially.[1][4]
Worked case: a left lateral medullary infarct
A 55-year-old man collapses with sudden vertigo and vomiting. His voice is hoarse, he chokes on water, and his left eyelid droops over a small pupil. Pain and temperature are lost on the left side of his face but on the right side of his body, and his limbs are strong.
- Hoarseness and chokingNucleus ambiguus.
- Left face pain lossLeft spinal trigeminal nucleus and tract.
- Right body pain lossLeft spinothalamic tract.
- Left Horner syndromeLeft descending sympathetic fibres.
- Strong limbsThe pyramid lies medially and is spared.
Everything is lateral and on the left: a left lateral medullary infarct.[1][4]
Medial medullary (Dejerine) syndrome
Three structures give three signs.[4][7]
| Structure | Sign |
|---|---|
| Pyramid (corticospinal tract) | Weakness of the opposite arm and leg; the face is spared |
| Medial lemniscus | Vibration and position sense lost in the opposite arm and leg |
| Hypoglossal nucleus and fibres | Tongue weak on the same side, deviating toward the lesion |
The face is spared because the facial nucleus lies in the pons, and its corticobulbar fibres leave the descending tract there, above the lesion.[11] The tongue deviates toward the damaged side.[3]
Pain and temperature are spared, because the spinothalamic tract is lateral. That is medial medullary syndrome, from the anterior spinal artery.[2][7]
Medial vs lateral medullary syndrome: the mirror image
| Medial (Dejerine) | Lateral (Wallenberg) | |
|---|---|---|
| Artery | Anterior spinal artery | Posterior inferior cerebellar or vertebral artery |
| Strength | Opposite weakness | Classically spared |
| Pain and temperature | Spared | Same face, opposite body |
| Vibration and position sense | Lost on the opposite side | Not part of the picture |
| Tongue | Deviates toward the lesion | Not involved |
| Voice and swallowing | Normal | Hoarse, difficulty swallowing |
Practice question
Original · USMLE styleA 63-year-old woman with hypertension and diabetes mellitus has sudden weakness of her left arm and leg. On examination, her tongue deviates to the right when she protrudes it, and vibration and position sense are reduced in the left arm and leg. Pain and temperature sensation are intact. Her face and voice are normal.
Common questions
What is the difference between medial and lateral medullary syndrome?
Medial medullary syndrome comes from the anterior spinal artery and causes opposite weakness, opposite loss of vibration sense and tongue deviation toward the lesion. Lateral medullary syndrome comes from the posterior inferior cerebellar or vertebral artery and causes crossed pain and temperature loss, hoarseness, Horner syndrome and ataxia.
Which artery causes Wallenberg syndrome?
Lateral medullary, or Wallenberg, syndrome most commonly follows infarction of the posterior inferior cerebellar artery or the vertebral artery.
Why is there no weakness in lateral medullary syndrome?
The pyramid lies in the medial strip of the medulla, away from the lateral infarct, so strength is classically spared. Opalski syndrome is a rare exception.
Why does the tongue deviate toward the lesion in medial medullary syndrome?
The hypoglossal nucleus and its fibres lie in the medial strip, so damage weakens the tongue on the same side and it deviates toward the damaged side.
Why are pain and temperature spared in medial medullary syndrome?
The spinothalamic tract lies in the lateral part of the medulla, outside the territory of the anterior spinal artery.
Transcript
Read the full narration, by chapter718 words
0:00A collapse with crossed findings
A 55-year-old man collapses with sudden vertigo and vomiting. His voice is hoarse, he chokes on water, and his left eyelid droops over a small pupil. Pain and temperature are lost on the left side of his face, but on the right side of his body. And his limbs are strong. One small stroke in the medulla, and a pattern that looks impossible. Today: tell the medial and lateral medullary syndromes apart by their artery and the structures they damage.
0:29The medulla at the olive level
Picture a cross section of the medulla at the level of the olives, and divide it into a medial strip and a lateral part. The medial strip, beside the midline, holds three key structures: the pyramid, which carries the corticospinal tract; the medial lemniscus; and the hypoglossal nucleus with its fibres. The lateral part holds the spinothalamic tract, the spinal trigeminal nucleus and tract, the nucleus ambiguus, the vestibular nuclei, the inferior cerebellar peduncle, and the descending sympathetic fibres.
1:04Two territories: ASA and PICA
Two territories, two arteries. The medial strip is supplied by the anterior spinal artery. The lateral part is supplied by the posterior inferior cerebellar artery, or the vertebral artery.
1:19Lateral (Wallenberg) syndrome, sign by sign
Lateral first, structure by structure. The spinal trigeminal nucleus carries pain and temperature from the face on the same side, so that side of the face goes numb to pain and temperature. The spinothalamic tract has already crossed, so pain and temperature are lost on the opposite side of the body. The nucleus ambiguus supplies cranial nerves 9 and 10, so the voice is hoarse and swallowing is difficult. The descending sympathetic fibres give a Horner syndrome on the same side: ptosis, a small pupil and reduced sweating. The vestibular nuclei give vertigo, nystagmus and vomiting, and the inferior cerebellar peduncle gives ataxia on the same side. Face on one side, body on the other, and classically no weakness, because the pyramid lies medially. That is lateral medullary, or Wallenberg, syndrome.
2:15Our patient: signs to structures
Now our man. Hoarseness and choking: nucleus ambiguus. Left face pain loss: left spinal trigeminal. Right body pain loss: left spinothalamic. Left Horner syndrome, strong limbs. Everything is lateral and on the left: a left lateral medullary infarct.
2:37Medial (Dejerine) syndrome
Now the medial syndrome. Three structures, three signs. The pyramid: the opposite arm and leg are weak, and the face is spared, because the facial nucleus and its upper motor neuron input lie in the pons, above the lesion. The medial lemniscus: vibration and position sense are lost in the opposite arm and leg. The hypoglossal nucleus: the tongue is weak on the same side, so it deviates toward the lesion. Pain and temperature are spared, because the spinothalamic tract is lateral. That is medial medullary syndrome, from the anterior spinal artery.
3:17Practice question
Your turn. A 63-year-old woman with hypertension and diabetes has sudden weakness of her left arm and leg. Her tongue deviates to the right when she sticks it out, and vibration and position sense are reduced in the left arm and leg. Pain and temperature sensation are intact, and her face and voice are normal. Occlusion of which vessel is most likely? A, the anterior inferior cerebellar artery. B, the anterior spinal artery. C, the posterior cerebral artery. D, the posterior inferior cerebellar artery. E, the superior cerebellar artery. Pause here and decide.
4:04Wrong options
A is out: that artery supplies the anterior cerebellum, not the medial strip of the medulla. C is out: the posterior cerebral artery supplies the occipital lobe, the medial temporal lobe and the thalamus. D is out: that artery produces the lateral syndrome, and none of its signs is present. E is out: the superior cerebellar artery supplies the upper cerebellum and the tectum of the midbrain.
4:32Answer and explanation
So the answer is B. A tongue deviating right, a weak left side and lost left vibration sense mean a right medial medullary infarct: the anterior spinal artery.
4:46Recap
Three things to keep. One: medial medullary syndrome is the anterior spinal artery: opposite weakness, opposite loss of vibration, and a tongue that deviates toward the lesion. Two: lateral medullary syndrome is the posterior inferior cerebellar or vertebral artery: face pain on the same side, body pain on the opposite side, hoarseness, Horner syndrome and ataxia. Three: the two mirror each other. Medial spares pain and temperature, and lateral classically spares strength. Next, facial nerve lesions: upper versus lower motor neuron.
Sources
Numbers in the text, e.g. [1], point here- StatPearls. Lateral Medullary Syndrome (2026), abstract via Europe PMC (EXT_ID 31869134). ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:31869134&resultType=core&format=json
- TeachMeAnatomy. The Medulla Oblongata. teachmeanatomy.info/neuroanatomy/brainstem/medulla-oblongata/
- TeachMeAnatomy. The Hypoglossal Nerve. teachmeanatomy.info/head/cranial-nerves/hypoglossal/
- Frontiers in Neurology (2026). Medullary infarction syndromes. PMC13053248. pmc.ncbi.nlm.nih.gov/articles/PMC13053248/
- PMC11744032, Opalski syndrome case report (rare weakness in a lateral medullary infarct). pmc.ncbi.nlm.nih.gov/articles/PMC11744032/
- Wikipedia (secondary, cross-checked only): en.wikipedia.org/wiki/Lateral_medullary_syndrome · en.wikipedia.org/wiki/Medial_medullary_syndrome
- StatPearls. Medial Medullary Syndrome (2026), via Europe PMC (EXT_ID 32809425). ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:32809425&resultType=core&format=json
- StatPearls. Brainstem Stroke Syndromes (EXT_ID 32809731), via Europe PMC. ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:32809731&resultType=core&format=json
- StatPearls. Vertebrobasilar Stroke (EXT_ID 32310544), via Europe PMC. ebi.ac.uk/europepmc/webservices/rest/search?query=EXT_ID:32310544&resultType=core&format=json
- MSD Manual Professional. Overview of Stroke. msdmanuals.com/professional/neurologic-disorders/stroke/overview-of-stroke
- TeachMeAnatomy. The Pons. teachmeanatomy.info/neuroanatomy/brainstem/pons/
The patients on screen are teaching vignettes, not real cases. Anterior spinal artery and PICA supply follow the standard convention; AICA supplies the outer part at higher levels.
The practice question is original and its patient is synthetic. Every fact is checked against the sources above in independent accuracy reviews. Always follow your local guidelines and your own laboratory’s ranges.
Image credits. Illustrations: Gray's Anatomy (1918), plates 695 and 519, public domain, via Wikimedia Commons, recoloured and outlined; the PCA, SCA, AICA, PICA and ASA labels are added in code. The cross-section schematics, patient sketches and all handwriting are drawn in code (original).
Corrections. None so far. Spotted an error? Email info@medservatory.com with the lesson code MS-S1-NEURO-001.
For exam study only, not medical advice. Read the medical disclaimer.
In this series
Playlist on YouTube- EP 01Upper vs lower motor neuron lesions: signs and localisation5:08
- EP 02Dorsal column vs spinothalamic tract: where each pathway crosses5:01
- EP 03Spinal cord syndromes compared: rebuild each from three tracts5:06
- EP 04Cranial nerve nuclei: a brainstem map by level and position5:10
- EP 05Brainstem crossed findings: the localisation rule4:50
- EP 06Medial vs lateral medullary syndrome: artery, structures and signs5:30
- EP 07Facial nerve palsy: why the forehead tells you the lesion4:59
- EP 08Stroke syndromes by artery: ACA, MCA and PCA4:41
- EP 09Lacunar stroke syndromes: pure motor, pure sensory and more4:54
- EP 10Visual pathway lesions and field defects4:42
- EP 11Basal ganglia direct and indirect pathways: D1, D2 and movement5:19
- EP 12Cerebellar lesion localisation: vermis vs hemisphere4:42
- EP 13Brain herniation syndromes: what is squeezed, and where4:56
- EP 14CSF flow and hydrocephalus: where the flow fails5:12
- EP 15Corticospinal tract: from cortex to anterior horn4:59
- EP 16Hypothalamic nuclei and their functions5:24