You are asked to evaluate a patient in the neurology clinic. Your neurological examination reveals the following symptoms: 1) Loss of pain and temperature sensation over the left side of the face2) Loss of pain and temperature sensation in the right arm and leg and3) Normal tactile and vibratory sensations on the face, body and extremities Where is the lesion?

Lesions (usually vascular in nature) that involve the dorsolateral medulla produce the classic signs of the lateral medullary syndrome (Wallenberg syndrome), which include a loss of pain and temperature sensibility over the ipsilateral face and the contralateral side of the body. Unilateral lesions that involve somatosensory pathways coursing through either the mesencephalon, diencephalon, or the posterior limb of the internal capsule will give rise to a loss of all or some somatosensation over the contralateral face and the contralateral body surface. Unilateral lesions (hemi sections) that interrupt somatosensory pathways in the spinal cord cervical enlargement are likely to produce bilateral somatosensory deficits (mainly ipsilateral tactile and proprioceptive, contralateral pain and temperature) that do not involve the face.