Final answer:
Damage at thoracic level T12 that causes the loss of pain and temperature sensation on the left side of the body indicates a hemisection of the spinal cord, leading to a condition known as Brown-Séquard syndrome.
Step-by-step explanation:
Spinal Cord Hemisection and Sensory Deficit
Damage at the thoracic level T12 of the spinal cord that causes loss of pain and temperature sensation on the left side would indicate a disruption of the spinothalamic tract, which carries pain and temperature sensations. In this scenario, the right leg's motor function is intact suggesting that the motor tracts on the right side of the spinal cord are unaffected. However, because pain and temperature sensations cross over to the opposite side of the body shortly after entering the spinal cord, a hemisection at T12 would lead to a loss of these sensations on the left side from T12 and below. This is known as Brown-Séquard syndrome, a condition where damage to one side of the spinal cord results in ipsilateral motor dysfunction and contralateral sensory loss. This sensory discrimination aids in pinpointing the level of trauma using clinical examination techniques or imaging technologies like MRI or CT scans.