1. VASCULAR - OCCLUSION OF THE MIDDLE CEREBRAL ARTERY
A Sample Case: A 60 yr old anatomist was demonstrating a dissection when he suddenly dropped the forceps from his left hand. At the same time his speech became slurred and as he left the room he dragged his left foot.
In the emergency room his wife related his history which included high blood pressure which was elevated; other vital signs were normal. He was alert and well oriented with respect to time and place and his comprehension was good. In spite of some slurring of speech he was coherent and the content was good. On examining the cranial nerves it was obvious that his eyes were consistently directed to the right and when asked to look to the left his eyes would not pass the midline. The visual exam showed a left homonymous hemianopsia. He could wrinkle his brow on both sides but in attempting to blow out his cheeks only the right side responded. There was a spastic paresis of the left arm and leg. Pain, temperature, and light touch were preserved over the body and face on both sides but but discriminative touch and proprioception were impaired on the left and he was unable identify objects placed in his left hand.
Left spastic hemiparesis of the arms and legs indicates an upper motor neuron lesion at least above the mid-cervical cord; weakness of the left lower face rules out the cord and suggests a lesion above mid-pons on the right side involving the corticospinals and corticobulbar fibers. Left-side loss of proprioception and astereognosis with sparing of pain and temperature can occur with right-sided sensory pathway lesions above the thalamus because although discriminative touch and proprioception is recognized only at cortical levels pain and temperature can be appreciated by the thalamus.
Frontal eye fields (area 8) of the cortex are located just anterior to the area controlling muscles of the face in area 4. Both areas project through the genu of the internal capsule. Destructive lesions of area 8 on the right cause the eyes at rest to deviate to the right due to the activity of area 8 on the left and the eyes cannot be deviated past midline to the left upon command. To account for facial and leg paresis might require postulating a broad lesion of the cerebral cortex including the medial side of the hemisphere (for the foot-knee paresis) and the frontal motor cortex laterally down to the lateral fissure (for facial weakness) - this would be unlikely. However, motor and sensory fibers implicated are compacted in the genu and posterior limb of the internal capsule so this is a more reasonable site.
Left homonymous hemianopsia occurs with lesions of the right visual pathways behind the optic chiasm. Optic radiations form the most posterior fibers of the internal capsule; optic radiations also run deep to the cortex of the parietal and temporal lobes. The abrupt onset of symptoms and history of high blood pressure suggested a vascular event. Neither the anterior nor posterior cerebral arteries supply all of the involved fibers implicated in this case. However, the middle cerebral artery supplies the lateral aspect of the cerebrum and the much of the deeper lying white matter, injury to which can explain all the symptoms.