A patient with a right posterior inferior cerebellar artery (PICA) infarct has ipsilateral Horner syndrome, loss of pain and temperature over the right face, and contralateral loss of pain and temperature over the body. Which nucleus is responsible for the ipsilateral facial sensory loss?
- A Chief (principal) sensory nucleus of trigeminal
- B Spinal trigeminal nucleus (nucleus spinalis V) ✓
- C Mesencephalic nucleus of trigeminal
- D Motor nucleus of trigeminal
Correct answer: B. Spinal trigeminal nucleus (nucleus spinalis V)
Explanation
In the lateral medullary (Wallenberg) syndrome caused by PICA occlusion, the spinal trigeminal nucleus is infarcted. This nucleus descends from the pons into the medulla and receives pain and temperature fibres from the ipsilateral face; its injury produces ipsilateral facial thermo-analgesia. The chief sensory nucleus subserves discriminative touch and lies in the pons, not the medulla. The mesencephalic nucleus carries proprioceptive input from masticatory muscles. The contralateral body sensory loss results from involvement of the spinothalamic tract before it has decussated.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.