A 65-year-old man with a history of atrial fibrillation comes to the office due to numbness of his left hand for the past 3 weeks. When the eyes are closed, he is unable to recognize the letters written on his left hand with a stylus. Muscle strength is normal in all extremities. Deep tendon reflexes are 2+. Gait is normal. This patient most likely has a lesion in which of the following locations of the brain?
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This patient has isolated numbness of his left hand and graphesthesia, which are suspicious for a lesion impacting the right somatosensory cortex. A small lesion of the somatosensory cortex leads to contralateral deficits impacting the corresponding area of the body. Higher-level sensory processing (ie, cortical sensory signs) can also be impaired. This may include loss of the following:
The primary somatosensory cortex is located on the postcentral gyrus, which is posterior to the central sulcus and superior to the lateral sulcus.
(Choice B) The area just anterior to the central sulcus (precentral gyrus) is the primary motor cortex. A lesion in this area would lead to weakness according to the somatotopic organization of the cortex.
(Choice C) This area indicates the frontal eye fields, an area that directs gaze to produce conjugate horizontal gaze. An ischemic lesion in this area would lead to gaze deviation toward the side of the lesion (ie, rightward deviation if the right hemisphere is impacted).
(Choice D) This is the occipital cortex, the area of the primary visual cortex. A lesion in this area would cause cortical blindness.
(Choice E) A lesion impacting the cerebellum typically leads to ataxia and vertigo.
Educational objective:
A lesion of the somatosensory cortex, located just posterior to the central sulcus, leads to contralateral sensory deficits and cortical sensory signs.