A patient presents with loss of pain and temperature sensation in the right upper and lower extremities, with preservation of vibration sense and proprioception on the same side. The lesion is most likely in the:

• A Right dorsal horn and right spinothalamic tract, representing hemicord damage sparing posterior columns
• B Left spinothalamic tract in the lateral funiculus below the level of decussation ✓
• C Right posterior column with intact ipsilateral spinothalamic pathways
• D Bilateral anterior spinal artery occlusion sparing the posterior one-third of the cord

Explanation

The spinothalamic tract crosses at the level of the spinal cord (within 1-2 segments) and then ascends contralaterally. Therefore, a lesion of the left spinothalamic tract causes contralateral (right-sided) loss of pain and temperature. Since posterior columns carrying vibration and proprioception are preserved (they travel ipsilaterally until the medulla), this combination — contralateral pain/temperature loss with ipsilateral preserved proprioception — precisely localizes the lesion to the left lateral funiculus. This is the essence of the Brown-Séquard syndrome pattern on the sensory side.

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

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Written and medically reviewed by the StethoPrep medical team.