A patient with a lateral medullary (Wallenberg) infarction characteristically shows loss of pain and temperature on the ipsilateral face and contralateral body. Which two structures are simultaneously damaged to explain this crossed pattern?
- A Ipsilateral spinal trigeminal nucleus and ipsilateral spinothalamic tract that has already crossed ✓
- B Ipsilateral spinal trigeminal nucleus and contralateral spinothalamic tract — both in the lateral medulla
- C Contralateral trigeminal lemniscus and ipsilateral spinothalamic tract
- D Bilateral trigeminal nuclei at different levels
Correct answer: A. Ipsilateral spinal trigeminal nucleus and ipsilateral spinothalamic tract that has already crossed
Explanation
In Wallenberg syndrome (PICA occlusion), the lateral medullary lesion simultaneously damages: (1) the ipsilateral spinal trigeminal nucleus/tract, which has not yet crossed, causing ipsilateral facial pain/temperature loss; and (2) the ipsilateral spinothalamic tract, which has already crossed in the spinal cord, causing contralateral body pain/temperature loss. This is the anatomical basis of the classic 'crossed' sensory deficit. The medial lemniscus (dorsal column pathway) is spared as it lies medially.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.