In a patient with decreased pain and temperature sensation in the left lower extremity, which structure is likely damaged?

In this scenario, the patient exhibits decreased pain and temperature sensation in the left lower extremity, which suggests a disruption in the pathways responsible for transmitting these modalities. The spinothalamic tract is primarily responsible for conveying sensations of pain and temperature from the body to the brain.

For the spinothalamic tract, fibers originating from regions of the body cross over to the opposite side at the level of the spinal cord before ascending to the thalamus. When damage occurs in the spinothalamic tract, the loss of pain and temperature sensation occurs contralaterally to the site of the lesion. Thus, if the right spinothalamic tract is injured, it would result in loss of pain and temperature sensation on the left side of the body.

In this specific case, if the right spinothalamic tract is damaged, it aligns with the presentation of decreased pain and temperature sensation in the left lower extremity, as the right side of the tract is responsible for conveying sensations from the left side of the body. This pathway's function and the contralateral organization are crucial in understanding how sensory deficits manifest based on the location of the injury.