A 58-year-old man develops sudden onset of right-sided facial pain and temperature loss along with left-sided body pain and temperature loss below the neck, right-sided Horner syndrome, dysphagia, and hoarseness. MRI shows a lesion in the right dorsolateral medulla. Which of the following best explains the ipsilateral facial sensory loss?

• A Involvement of the right main sensory nucleus of trigeminal nerve
• B Involvement of the left spinal trigeminal nucleus crossed fibers
• C Involvement of the right thalamocortical fibers
• D Involvement of the right spinal trigeminal nucleus and tract ✓

Explanation

Lateral medullary (Wallenberg) syndrome involves the dorsolateral medulla. The spinal trigeminal nucleus and tract, which carry ipsilateral facial pain and temperature, lie in the dorsolateral medulla. Injury causes ipsilateral facial loss (spinal trigeminal nucleus) and contralateral body loss (already-crossed spinothalamic tract). The main sensory nucleus in the pons handles discriminative touch. Thalamocortical fibers are supramedullary.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.