Lateral medullary syndrome
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"lateral medullary syndrome" OR "Wallenberg syndrome"
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Lateral Medullary Syndrome (Wallenberg Syndrome)
Definition & Eponym
Lateral medullary syndrome (LMS), also called Wallenberg syndrome (first described by Adolf Wallenberg in 1895), results from infarction of a wedge-shaped area of the dorsolateral medulla oblongata, lying posterior to the inferior olivary nucleus. It is one of the most clinically distinctive brainstem stroke syndromes in neurology.
Vascular Anatomy
The lateral medulla is supplied by:
- Posterior inferior cerebellar artery (PICA) - classically implicated
- Vertebral artery (VA) - most commonly responsible in practice
Studies of 130 consecutive patients with pure lateral medullary infarction show:
- Large vessel atherosclerosis: 50%
- Arterial dissection: 15%
- Small vessel disease: 13%
- Cardioembolism: 5%
Despite historical attribution to PICA occlusion, careful imaging studies confirm that vertebral artery occlusion (atherothrombotic) accounts for the majority of cases. PICA embolism is less frequent. When an embolus travels distally past the medullary branches of PICA, it can cause isolated cerebellar infarction without the full LMS features.
- Localization in Clinical Neurology, 8e, p. 921
- Adams and Victor's Principles of Neurology, 12th Ed., p. 816
Structures Damaged & Resulting Deficits
The classic "PICA stroke" involves a wedge of lateral medulla. The key structures and their clinical correlates:
| Structure Damaged | Clinical Feature |
|---|---|
| Spinal trigeminal nucleus & tract | Ipsilateral facial pain/temperature loss (+ facial pain) |
| Spinothalamic tract | Contralateral body pain/temperature loss |
| Nucleus ambiguus (CN IX, X) | Ipsilateral palatal, pharyngeal, vocal cord paralysis - dysphagia, dysarthria, hoarseness, decreased gag reflex |
| Descending sympathetic fibers | Ipsilateral Horner syndrome (ptosis, miosis, anhidrosis) |
| Vestibular nuclei | Vertigo, nausea, vomiting, nystagmus |
| Inferior cerebellar peduncle / restiform body | Ipsilateral limb ataxia, gait instability, lateropulsion |
| Nucleus & tractus solitarius | Loss of taste (ipsilateral) |
| Utricular nucleus | Vertical diplopia, ocular tilt, illusion of environmental tilt |
Note: The medial medulla is spared (pyramids, medial lemniscus, hypoglossal nucleus), so motor weakness, vibration/position sense loss, and tongue deviation are absent - a key distinguishing feature.
Classic Presentation - Mnemonic Approach
The hallmark triad that most reliably identifies LMS:
Ipsilateral Horner + Ipsilateral ataxia + Contralateral hypoalgesia (body)
Full syndrome features:
Ipsilateral side:
- Facial hypoalgesia/thermoanesthesia (CN V spinal nucleus)
- Horner syndrome (miosis, ptosis, anhidrosis)
- Palatal/pharyngeal/vocal cord paralysis (hoarseness, dysphagia)
- Cerebellar ataxia and lateropulsion (falls toward lesion side)
- Decreased corneal reflex
Contralateral side:
- Limb and trunk hypoalgesia/thermoanesthesia (spinothalamic tract)
Bilateral:
- Vertigo, nausea, vomiting (vestibular nuclei)
- Nystagmus (often direction-changing - a useful brainstem localizer)
- Hiccups (singultus)
Sensory Dissociation - "Crossed" Pattern
This is the pathognomonic sensory finding: pain/temperature is impaired on the ipsilateral face (spinal trigeminal tract) and the contralateral body (spinothalamic tract), creating a crossed pattern. The "stocking-glove" modalities (vibration, position) are normal because the medial lemniscus is not involved.
Ocular Motor Abnormalities
LMS produces a rich variety of eye signs (Localization in Clinical Neurology, 8e):
- Nystagmus: nearly invariable; horizontal, torsional, or mixed; direction-changing with gaze
- Skew deviation: hypotropia ipsilateral to lesion
- Ocular tilt reaction
- Lateropulsion of saccades: hypometric toward the lesion, hypermetric away from it
- See-saw nystagmus
- Environmental tilt / "floor-on-ceiling" phenomenon
- Occasionally internuclear ophthalmoplegia (INO) fragment
Additional / Less Common Features
From Localization in Clinical Neurology, 8e:
- Lateropulsion - axial tilting toward lesion side (can occur without limb ataxia - due to vestibulospinal tract involvement)
- Ondine's curse (failure of automatic breathing) - discrete lesions of nucleus ambiguus + adjacent reticular formation
- Central hypoventilation with vasomotor instability
- Ipsilateral hemiparesis when lesion extends to the lowermost caudal medulla below the pyramidal decussation = Opalski syndrome (submedullary syndrome)
- Poststroke central facial pain - common long-term sequel from involvement of primary afferents in the spinal trigeminal tract
- Transient urinary retention - interruption of descending fibers from pontine micturition center
- Ipsilateral upper extremity sensory symptoms - from caudal lesions involving dorsal columns or decussating lemniscal fibers
Lesion Localization by Level
| Lesion Level | Prominent Features |
|---|---|
| Rostral lateral medulla | Severe dysphagia, hoarseness, facial paresis |
| Caudal lateral medulla | Marked vertigo, nystagmus, gait ataxia |
| Ventromedial extension | Contralateral (rather than ipsilateral) facial sensory changes |
Horner syndrome, nausea, and vomiting occur regardless of lesion level within the lateral medulla.
Etiology
- Vertebral artery atherothrombosis (most common)
- Vertebral artery dissection (especially in young patients; associated with neck manipulation/trauma; more common with caudal lesions)
- Cardiac embolism to PICA
- Vertebral dissection red flags: young age, posterior neck pain, recent chiropractic manipulation
- Less common: cocaine abuse, medullary neoplasms (metastases), abscess, demyelination (MS), radionecrosis, vascular malformation rupture, trauma
Imaging
- DWI (diffusion-weighted MRI) is the diagnostic standard - shows restricted diffusion in the lateral medulla acutely (may be negative on initial T2 but visible within hours on DWI)
- MRA can demonstrate vertebral artery occlusion or loss of flow signal
- T1-weighted axial MRI through the vertebral arteries shows intramural bright signal ("crescent sign") in dissection, indicating intramural hematoma
Differential Diagnosis
Key mimics of LMS:
- AICA syndrome (anterior inferior cerebellar artery): similar crossed sensory pattern and vertigo, but adds ipsilateral hearing loss (labyrinthine artery involvement) and INO - absence of hoarseness/taste loss helps distinguish from LMS
- SCA syndrome (superior cerebellar artery): predominantly cerebellar features
- Medullary tumor or abscess: slower onset
- MS plaque in lateral medulla
"The presence of hoarseness or loss of taste sensation helps localize the syndrome to the medulla rather than the pons. The presence of ipsilateral hearing loss suggests AICA involvement rather than lateral medullary syndrome." - Neuroanatomy through Clinical Cases, 3rd Ed., p. 685
Prognosis & Complications
- Recovery is often good in the first days-weeks, particularly for vertigo and nystagmus
- Dysphagia can be persistent and requires speech therapy evaluation; aspiration risk is high
- Horner syndrome may persist long term
- Sudden death from respiratory or cardiac arrest has been reported even after initial recovery (without cerebellar swelling or basilar thrombosis) - Adams and Victor's, p. 816
- Central post-stroke pain (deafferentation pain in face/body) is a significant long-term sequel
- Ondine's curse (loss of automatic respiratory drive) is rare but life-threatening; requires ventilatory support
Treatment
- Acute ischemic stroke protocol: IV tPA if within 4.5 hours and eligible; mechanical thrombectomy considerations for large vessel occlusion
- Vertebral artery dissection: antiplatelet therapy (e.g., aspirin) is recommended; anticoagulation remains controversial
- Dysphagia management: nasogastric or PEG tube if severe; swallowing rehabilitation
- Symptomatic: antihistamines/antiemetics for vertigo; vestibular rehabilitation
- Central pain: tricyclics, gabapentinoids, pregabalin
Recent literature note (PubMed, 2024-2026): A 2024 systematic review (PMID 39096581) examined Opalski syndrome, the rare variant of LMS with ipsilateral hemiplegia, confirming it as a distinct clinico-anatomical entity worth differentiating from classic LMS.
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