A 64-year-old male presented with vomiting, and was ventilated for two days after an acute aspiration episode. Two days after extubation, he is noted to freely aspirate oral fluids without a resultant cough. His left pupil is constricted, and he appears clumsy with his left hand. On further examination you find no weakness, but he has past pointing in the left arm. There is nystagmus on looking to the left.

a)    Where is the likely neurologic lesion?    (15% marks)

b)    What is the most common pathology?    (10% marks)

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College answer

a)    Lateral part of medulla (Lateral Medullary Syndrome acceptable)
b)    Occlusion of PICA branch


Important features here are:

  • History of nausea
  • Clearly some sort of serious swallowing dysfunction
  • Left sided miosis
  • Left sided incoordination (obviously cerebellar)
  • Left sided nystagmus

So, to localise this, it is clear something must be going on at the level of the cerebellum. However, an isolated cerebellar lesion would not be producing that miosis. That would require a lesion which interrupts descending sympathetic fibres, leaving behind the parasympathetic stimulus from the midbrain. The combination of the two leads you to the lateral medulla. 

In summary, the features of lateral medullary syndrome are:

  • On the side of the lesion:
    • Facial sensory loss
    • Nystagmus
    • Horner's syndrome
    • Loss of gag reflex
    • Ipsilateral ataxia with a tendency to fall to the ipsilateral side
  • On the contralateral side:
    • Pain and temperature sensory loss in the extremities
  • Generally:
    • Vertigo
    • Nausea
    • Dysphagia

The most likely culprit is the PICA, but a lateral medullary syndrome can also develop due to a large number of different lesions, likely accounting for the wide variation in individual brainstem vascularity. Anatomically, the damaged territory is supplied by the PICA, but PICA-specific occlusions are  apparently in the minority; about 80% of lateral medullary strokes happen because the vertebral artery is occluded (Kim et al, 2016)



Oh's Intensive Care manual: Chapter   51   (pp. 568)  Acute  cerebrovascular  complications by Bernard  Riley  and  Thearina  de  Beer. This chapter of Oh's has the distinction of having very few tables in it - there are only two, for an extremely long block of text.

Qureshi, Adnan I., et al. "Spontaneous intracerebral hemorrhage." New England Journal of Medicine 344.19 (2001): 1450-1460.

Caplan, L. R. "Basic Pathology, Anatomy, and Pathophysiology of Stroke." Caplan’s Stroke A Clinical Approach (2009): 23-4.

Hong, Yuehui, et al. "Lesion Topography and Its Correlation With Etiology in Medullary Infarction: Analysis From a Multi-Center Stroke Study in China." Frontiers in neurology 9 (2018): 813.

Kim, Jong S., and Louis R. Caplan. "Clinical stroke syndromes." Intracranial Atherosclerosis: Pathophysiology, Diagnosis and Treatment. Vol. 40. Karger Publishers, 2016. 72-92.

Lui, Forshing, and Steve S. Bhimji. "Wallenberg syndrome." StatPearls [Internet]. StatPearls Publishing, 2018.