1. VASCULAR - OCCLUSION OF THE ANTERIOR BRANCH OF THE MIDDLE CEREBRAL ARTERY
A Sample Case: A 55 yr old woman awoke but couldn’t get out of bed due weakness of the right arm and leg. Her husband spoke to her and she understood him but she was unable to speak in response.
The patient was alert and oriented and followed commands well. She had bruits in both carotid arteries but otherwise the cardiovascular system was normal. Past medical history was unrelated to the present condition. There was no papilledema. The doctor found that the patient had a flattened nasolabial fold on the right and was unable to smile or show her teeth on the right; the brows could be wrinkled symmetrically upon command. When she was asked to protrude her tongue it deviated to the right. Other cranial nerve functions were unaffected. The upper right extremity was very weak, with spasticity and hyperreflexia. The lower limb was less weak with mild hypertonia, hyperreflexia, and a positive Babinski sign. Cerebellar function was unaffected. The sensory exam was normal.
Her speech was very halting. Its content was appropriate but she had difficulty finding the right words and her sentences were short and incomplete. When asked direct questions she would answer appropriately but only with a yes or no response or she would correctly point to an object. Her speech was also slurred making words difficult to understand.
Spastic paralysis (on the right side) was more severe in the arms than the legs. This is suggestive of a left upper motor neuron lesion (corticospinals) at cortical levels rather than in the internal capsule where the fibers of both limbs are compact and so the weakness of upper and lower extremities is more likely to be of equal severity. Slurred, poorly articulated speech (dysarthria) and a tongue which deviated to the right upon protrusion suggests that corticobulbars on the left are also involved. Right-sided paralysis of the lower face indicates corticobulbar involvement on the left.
In addition to slurring of speech, which has to do with the mechanics of sound production, she had trouble with language itself (aphasia), i.e., there were problems in finding the right words to define objects and forming words into sentences. There was no indication of problems with comprehension of language but rather its expression, i.e., motor aphasia. Language functions are usually represented in the left hemisphere.
(In addition to paresis and paralysis of the right limbs, due to the left sided lesion, the patient had an apraxia of the left limbs. Apraxia is the inability to carry out a command for a motor act even though the patient understands the command and has no weakness or incoordination. This patient was asked to scratch her left knee with her left hand, which had no signs of weakness; she made a vague gesture toward her knee, demonstrating comprehension, but didn’t complete the task. Later she used her left hand to adjust the hem on her skirt to cover her left knee. This apraxia is explained by the lesion to the motor cortices including Broca’s motor speech area. The command to scratch is first comprehended in the Wernicke’s speech area in the left temporal lobe. Connections exist (arcuate fasciculus) from Wernicke’s area to Broca’s area and the left motor cortex. The left arm responds to the command when the right motor cortex is activated by crossing fibers coming from the left motor cortex via the corpus callosum. In this case injury to the left motor cortex injures those crossing fibers and so the command is poorly executed.)
The suddenness of the onset of the symptoms suggests that a vascular event has occurred rather than a slowly growing mass. The symptoms suggest that the most severely affected area is the lateral surface of the frontal lobe, i.e., the precentral gyrus (areas 4,6) containing the motor cortex serving the head, arms (and to a lesser extent the legs) and in addition, Broca’s motor speech area (area 44,45). These areas are served by branches of the middle cerebral artery. An angiogram confirmed an occlusion in anterior branches of the middle cerebral artery.