Lateral Medullary Syndrome (Wallenberg Syndrome)

Lateral medullary syndrome (also known as Wallenberg syndrome, posterior inferior cerebellar artery (PICA) syndrome, and vertebral artery syndrome) is a neurological constellation of symptoms and signs due to obstruction in vessels supplying the medulla, resulting in brainstem ischemia or infarction. The most common cause is atherosclerosis in the posterior cerebral circulation, and the most reported symptom is a transient ischemic attack (TIA) with dizziness or vertigo. With stroke/infarction, patients also present with nausea and vomiting, loss of balance with gait, instability, hoarseness, and difficulty in swallowing. The signs are dependent on the specific nuclei and fibers affected. Diagnosis is made by clinical exam and imaging with CT/MRI. Management is mostly supportive, including speech and occupational therapy after acute intervention, as well as risk factor reduction for future ischemic events.

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Lateral medullary infarction (also known as Wallenberg syndrome, posterior inferior cerebellar artery (PICA) syndrome, and vertebral artery syndrome) is a neurological constellation of symptoms and signs due to decreased blood flow in vessels supplying the medulla, resulting in brainstem ischemia or infarction.


Components of the lateral medulla:

  • Inferior cerebellar peduncle
  • Vestibular nuclei
  • Trigeminal nucleus and tract
  • Spinothalamic tract
  • Descending sympathetic fibers
  • Nucleus ambiguus
  • Nucleus solitarius
Brain and brainstem - cerebellum

Location of cerebellum in relation to the other brainstem structures

Image by Lecturio.

Blood supply:

  • Left and right vertebral arteries → ventrolateral aspect of the brainstem 
  • Left and right PICAs → lateral medulla 
    • Arise from the vertebral arteries 
    • PICA supplies the vestibular nucleus, spinothalamic tract, trigeminal nucleus, and nucleus ambiguus.


  • Most prevalent ischemic stroke syndrome: in the US, > 60,000 new cases/year 
  • More common in men
  • Most commonly arises in the 6th decade of life


  • Ischemic stroke of 
    • Vertebral arteries
    • Posterior inferior cerebellar arteries
  • Risk factors:
    • Hypertension (most important)
    • Large artery atherosclerosis
    • Diabetes mellitus
    • Smoking
    • Hyperlipidemia
    • Older age


A complete reduction in cerebellar blood flow involving the PICA results in lateral medullary syndrome.

  1. Occlusion of intracranial artery
  2. Reduction in blood flow to the region the vessel supplies 
  3. Cerebral tissue starts to undergo ischemia as neurons are deprived of glucose and oxygen → failure of mitochondria to produce ATP
  4. Membrane ion pumps stop functioning due to lack of ATP and neurons depolarize → intracellular calcium increases, and glutamate is released from presynaptic terminals
  5. Excess extracellular glutamate induces greater uptake of calcium by neurons → neurotoxicity 
  6. Free radicals are produced and accumulated within neurons → catalytic destruction of membranes
  7. If blood flow is not restored within a few minutes, infarction or necrosis of brain tissue will occur.
  8. Clinical neurological symptoms become apparent.

Clinical Presentation and Diagnosis

Clinical presentation

Wallenberg syndrome causes abnormalities in the vestibulocerebellar, sensory, bulbar, respiratory, and autonomic systems. 

  • Most common symptoms are vestibulocerebellar:
    • Vertigo, dizziness, feeling off-balance
    • Difficulty sitting up
    • Blurred vision or diplopia
    • Gait instability
  • Sensory symptoms:
    • Facial pain
    • Loss of pain and temperature sensation in the contralateral trunk and limbs
  • Other symptoms:
    • Nausea and vomiting
    • Hiccups
  • Bulbar muscle weakness
    • Hoarseness 
    • Dysphagia
  • Respiratory symptoms: Ondine’s curse = failure to initiate respiration 
  • Autonomic: 
    • Horner syndrome
      • Miosis
      • Ptosis
      • Anhidrosis
    • Cardiovascular
      • Orthostatic hypotension
      • Tachycardia
  • Signs:
    • Nystagmus
    • Limb ataxia/past-pointing
    • Hypotonia of the ipsilateral arm
    • Ipsilateral decreased pain and temperature sensation in the face
    • Contralateral loss of pain and temperature sensation in the body and limbs on exam
    • Decreased corneal reflex in the ipsilateral eye
Table: Clinical features (depending on the specific nuclei and fibers affected)
Structure affectedPresenting symptoms
Spinothalamic tractContralateral loss of pain and temperature sensation in the trunk and limbs
Spinal trigeminal nucleusIpsilateral loss of pain and temperature in the face
Nucleus ambiguusDysphagia, dysphonia, and diminished gag reflex (supply to the vagus and glossopharyngeal nerves is affected)
Inferior vestibular nucleusVertigo (same direction as the lesion), diplopia, nystagmus, vomiting
Sympathetic fibersHorner syndrome = miosis, ptosis, anhidrosis
Inferior cerebellar peduncleAtaxia, dysmetria, dysdiadochokinesia


  • Clinical exam as above
  • Test to distinguish vertigo of brainstem and cerebellar ischemia from peripheral causes:
    • Head impulse, nystagmus, test of skew (HINTS) test assesses vestibulo-ocular function:
      • HI = head impulse: The examiner turns the patient’s head quickly about 15º while the patient’s gaze is fixed on a distant target; a normal response is that the eyes remain on the target, while an abnormal response is that the eyes are dragged off of the target by the head turn, followed by a saccade back to the target after the head turn.
      • N = nystagmus that changes direction with different gaze positions (peripheral vestibular lesions have nystagmus that is always in the same direction)
      • TS = test of skew: examiner observes for a vertical shift in the patient’s eye when covered → uncovered.
    • These findings suggest a brainstem or cerebellar lesion:
      • Normal head impulse test on both sides
      • Direction-changing nystagmus
      • Skew deviation
  • Imaging: CT and/or MRI to pinpoint the exact location of the infarct
Lateral medullary syndrome

Lateral medullary syndrome: MRI showing an acute infarct in the left dorsolateral medulla

Image: “Lateral medullary syndrome” by John S. To, M.D. License: Public Domain


Rapid intervention and treatment are necessary to manage Wallenberg syndrome similar to the management of ischemic stroke. The goals are to reduce the size of the infarction and prevent medical complications.

  • Maintain:
    • Volume status
    • Oxygenation
    • Normal blood glucose levels (BGLs)
    • Body temperature
  • Control blood pressure: systolic < 220 and diastolic < 120
  • Antiplatelet drugs (e.g., aspirin)
  • Anticoagulants may be needed with ischemic stroke.
  • Supportive therapy for speech and swallowing should be provided.

Secondary prevention of future strokes with risk factor reduction:

  • Anticoagulation if atrial fibrillation is present
  • Antiplatelet therapy 
  • Control of atherosclerotic risk factors:
    • Hypertension
    • Diabetes
    • Hyperlipidemia
  • Smoking cessation


  • Aspiration due to bulbar muscle weakness and pooling of secretions in the pharynx
  • Pneumonia
  • Hiccups
  • Locked-in syndrome
  • Palatal myoclonus
  • Clonic jaw movements
  • Pseudobulbar affect:  
    • Emotional lability
    • Exaggerated crying and laughing spells with infarction at the base of the pons

Prognosis depends on the size and location of the area of the stroke (extent of the medulla damaged by the occlusion of the PICA).

Differential Diagnosis

  • Chronic pain syndrome: a poorly defined condition with the characteristic feature being pain lasting longer than 6 months. The syndrome may be due to physical and/or psychological trauma, infections, chronic underlying diseases, or autoimmune conditions. Diagnosis is based on history and clinical findings. Management is with a combination of medication and therapy. 
  • Middle cerebral artery (MCA) stroke: a sudden onset of focal neurologic deficit arising from ischemic damage to areas of the brain supplied by the MCA. Patients present with weakness, dizziness, numbness, issues with speech, or visual changes. Diagnosis and evaluation are done with the help of CT or MRI imaging. Intravenous tissue plasminogen activator (TPa) and thrombectomy are used for acute intervention. Antiplatelet or anticoagulant drugs can be used to prevent secondary occurrence as well as aggressive treatment of cardiovascular risk factors.
  • Multiple sclerosis (MS): an autoimmune disease of the central nervous system characterized by chronic inflammation, demyelination, gliosis, and neuronal loss. Patients present with visual disturbances, vertigo, gait imbalance, dysarthria, dysphagia, tremor, and loss of sensation. Patients are diagnosed by history and clinical findings, and an MRI is done to confirm findings. Treatment includes disease-modifying drugs. 
  • Subarachnoid hemorrhage (SAH): extravasation of blood into the subarachnoid space between the pia and arachnoid membranes. Trauma, ruptured berry aneurysm, and rupture of arteriovenous (AV) malformations are the most common causes. Patients present with headache, dizziness, visual disturbances, sensory or motor disturbances, and seizures. Diagnosis is made by clinical examination, contrast CT, and lumbar puncture. Treatment is with osmotic agents, loop diuretics, steroids, and surgery. 


  1. Caplan, LR. (2021). Posterior circulation cerebrovascular syndromes. UpToDate. Retrieved August 11, 2021, from
  2. National Institute of Neurological Disorders and Stroke. Wallenberg’s Syndrome Information Page. Retrieved August 11, 2021, from
  3. Saleem, F, & Das, JM. (2021). Lateral medullary syndrome. StatPearls, StatPearls Publishing. PubMed. Retrieved August 11, 2021, from
  4. Lui, F, et al. (2021). Wallenberg’s syndrome. StatPearls, StatPearls Publishing. PubMed. Retrieved August 11, 2021, from

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