HY lecture notes:
Important locations
Broca area: left inferolateral posterior frontal lobe.
Wernicke area: left posterior temporal lobe (superior temporal gyrus).
Broca aphasia
- Expressive, non-fluent aphasia –> sometimes described as “telegraphic speech” because the patient exhibits forceful effort to produce language (spoken or written) with a propensity to leave out non-essential grammatical words, like prepositions and articles.
- Comprehension remains intact.
- Caused by stroke of superior branch of left middle cerebral artery.
- Repetition usually impaired. –> if vignette sounds like Broca but they explicitly tell you repetition is intact, choose “transcortical motor aphasia,” not Broca.
Wernicke aphasia
- Receptive, fluent aphasia –> patient has difficulty comprehending written or spoken language –> reciprocally, patient also produces language that lacks content or meaning (“word salad”).
- Fluency remains intact in the sense that the patient can produce language effortlessly; but as stated, it just simply lacks content and meaning.
- Caused by stroke of inferior branch of left middle cerebral artery.
- Repetition usually impaired. –> if vignette sounds like Wernicke but they explicitly tell you repetition is intact, choose “transcortical sensory aphasia,” not Wernicke.
Conduction aphasia
- Lesion of arcuate fasciculus.
- Repetition alone is impaired.
Global aphasia
- Lesion of Broca, Wernicke, and arcuate fasciculus.
- Vignette will sound like both Broca + Wernicke together, AND repetition is impaired.
- If repetition, not impaired, choose “mixed transcortical aphasia” instead.
USMLE also loves showing you a gross brain specimen and then asking you where a stroke lesion is (and its blood supply) based on the patient’s signs:
Before you freak out, the starting point is identifying the central sulcus, which is the line running transversely across the brain between points D and E, and then again between C and F.
Anterior to the central sulcus = primary motor cortex. (C and D)
Posterior to the central sulcus = primary sensory cortex. (E and F)
The next step is saying, “Ok, are we medial or lateral on the hemisphere?” As you can see, D and E are clearly medial; C and F are lateral.
If the contralateral legs are affected due to a stroke, that’s medial brain (D and E) supplied by the anterior cerebral artery (ACA).
If the contralateral face and arms are affected, that’s lateral brain (C and F) supplied by the middle cerebral artery (MCA).
So if vignette says, e.g., an 82M with AF has sudden numbness and paresthesias of the right leg and they asked you to choose the letter, what would you say?
Well, we say we’re clearly looking at the left side of the brain, so that makes sense. Second, since it’s the leg, we know we’re dealing with D and E. Finally, because it’s sensory, not motor, we know we’re dealing with posterior to the central sulcus, so we know it’s E as the answer. And if they had asked you for the blood vessel affected by an embolus instead, it would be ACA because it’s medial brain.
Likewise, if they told you a guy with hypertension and a carotid bruit now has right-sided arm weakness + facial droop, which letter would you say corresponds?
Well, we say we’re clearly looking at the left side of the brain, so that makes sense. Second, since it’s the arm + face, we know we’re dealing with C + F. Finally, because it’s motor, not sensory, we know we’re dealing with anterior to the central sulcus, so we know it’s C as the answer. And if they had asked you for the blood vessel affected by an embolus instead, it would be MCA because it’s lateral brain.
