What condition is caused by a lesion to the posterior portion of the spinal cord?

The condition caused by a lesion to the posterior portion of the spinal cord is posterior cord syndrome. This syndrome results from damage to the dorsal columns, which are responsible for proprioception, vibration sense, and fine touch. When there is a lesion in this area, patients typically present with loss of these sensory modalities below the level of the injury, while maintaining normal motor function and pain/temperature sensations, which are carried by the anterolateral pathways.

This condition contrasts with the other options, which involve different mechanisms of injury or different parts of the spinal cord. For instance, Brown-Sequard syndrome is characterized by hemisection of the spinal cord, leading to ipsilateral motor and proprioceptive loss and contralateral loss of pain and temperature sensation. Cauda equina syndrome is caused by injury to the nerve roots below the level of the spinal cord and typically leads to lower limb weakness and bladder dysfunction. Central cord syndrome involves damage to the central part of the spinal cord, often presenting with upper limb weakness and variable preservation of lower limb function.

Thus, posterior cord syndrome specifically aligns with lesions affecting the dorsal columns and their associated sensory deficits, making it the correct answer to the question regarding the condition resulting from a posterior cord lesion.