A patient with a medullary lesion develops the following deficits: ipsilateral facial numbness (pain and temperature) with contralateral body numbness (pain and temperature), ipsilateral Horner syndrome, hoarseness, and dysphagia. This is Wallenberg (lateral medullary) syndrome. The ipsilateral facial numbness is due to damage to which structure?

• A Medial lemniscus carrying crossed facial tactile afferents from the trigeminal nucleus
• B Trigeminothalamic tract which has already crossed at the level of the pons
• C Nucleus and spinal tract of CN V (descending trigeminal tract) which processes ipsilateral facial pain and temperature before crossing ✓
• D Motor nucleus of CN V causing inability to feel facial muscle tension

Explanation

The spinal (descending) tract of the trigeminal nerve and its nucleus extend from the pons down through the medulla into the upper cervical cord; these process pain and temperature from the ipsilateral face before second-order fibers cross to ascend contralaterally in the anterior trigeminothalamic tract. A lateral medullary infarct (posterior inferior cerebellar artery territory) damages this structure, causing ipsilateral facial pain/temperature loss. Contralateral body pain/temperature loss results from damage to the spinothalamic tract (which has already crossed at spinal cord level). This crossed sensory pattern is pathognomonic of lateral medullary syndrome.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.