WBR0614: Difference between revisions

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|MainCategory=Anatomy, Pathophysiology
|MainCategory=Anatomy, Pathophysiology
|SubCategory=Neurology
|SubCategory=Neurology
|Prompt=A 72-year-old male patient with previous medical history of diabetes and hypertension presents to the emergency department for an acute onset of left leg paralysis.  The patient tells the physician that he woke up in the morning and was not able to lift his left leg up. Physical exam reveals paralysis and loss of sensation in the left leg with intact motion and sensation in the upper extremities and right lower leg. The cranial nerves and cerebellar exam are normal.  Stroke in which of the following areas may explain the symptoms of the patient?
|Prompt=A 72-year-old man with history significant for diabetes and hypertension presents to the emergency department for acute onset left leg paralysis.  The patient explains that he was feeling well yesterday night, but woke up unable to move his right arm and leg. He also noticed that he was unable to control the right side of his face. Physical examination reveals paralysis of both right extremities with no loss of sensation. Cranial nerve exam reveals central facial nerve paralysis. Cerebellar exam is within normal limits.  Following an contrast-enhanced MRI, the physician determines that the patient suffered a lacunar stroke at the level of the internal capsule. Nerve fibers from which of the following regions are likely to be involved?


[[Image:WBR0614.png|600px]]
[[Image:WBR0614.jpg|600px]]
|Explanation=[[Image:Regions_of_the_brain.png|600px]]
|Explanation=[[Image:Regions_of_the_brain.png|600px]]
The functions of the cerebral cortex are specific to each area of the cortex. The [[primary motor cortex]] is located in the posterior portion of the frontal lobe. It works in association with other motor areas including premotor cortex, the supplementary motor area, posterior parietal cortex, and several subcortical brain regions, to plan and execute movements. There is a map of motor space in the primary motor cortex corresponding to the motor homunculus. Branches of the [[middle cerebral artery]] (MCA) provide most of the arterial blood supply for the primary motor cortex.  The medial aspect that controls the lower extremities is supplied by branches of the [[anterior cerebral artery]] (ACA). The patient in the question is unable to move his left leg; hence, the most likely area affected is the primary motor cortex on the medial side of the right lobe.
Lacunar strokes are are caused by occlusion of the small penetrating arteries of the brain. The two main proposed mechanism of these strokes are small artery lipohyalinolysis and microemboli. Lipohyalinolysis is characterized by vessel wall thickening and narrowing of the lumen and is strongly associated with hypertension. Despite popular belief, new evidence points to microemboli as the cause of lacunes. However, lipohyalinolysis remains a correct answer  on the USMLEs. One form of lacunar strokes is the pure motor stroke that affect the internal capsule particularly the posterior limb. This stroke interrupts descending corticospinal tracts from the primary motor cortex leading to contralateral paralysis. Pure motor stroke is the most common lacunar syndrome.
|AnswerA=A
|AnswerA=A
|AnswerAExp=A represents the [[primary motor cortex]] on the lateral side of the brain.  This area is supplied by the [[middle cerebral artery]] and its function is to control the motor activity of the upper extremities, hands and face but not the motor activity of the lower extremities.
|AnswerAExp=A represents the primary motor cortex.  This area is primarily responsible for the descending corticospinal tracts that control voluntary movement.  
|AnswerB=B
|AnswerB=B
|AnswerBExp=B represents the [[somatosensory cortex]] which is the main sensory receptive area for the sense of touch. Like other sensory areas, there is a map of sensory space in this location corresponding to the sensory homunculus.
|AnswerBExp=B represents the [[somatosensory cortex]] which is the main sensory receptive area for the sense of touch. It receives ascending fibers from the thalamus.
|AnswerC=C
|AnswerC=C
|AnswerCExp=C represents the [[prefrontal cortex]] is the anterior part of the frontal lobes of the brain.  This area is responsible cognitive behavior, personality expression, decision making, and moderating social behavior. Lesions in this area lead to personality changes and disinhibitory behaviors.
|AnswerCExp=C represents the [[prefrontal cortex]] is the anterior part of the frontal lobes of the brain.  This area is responsible cognitive behavior, personality expression, decision making, and moderating social behavior. Lesions in this area lead to personality changes and disinhibition.
|AnswerD=D
|AnswerD=D
|AnswerDExp=D represents the [[primary motor cortex]] on the medial side of the [[brain]]. This area is supplied by the [[anterior cerebral artery]] and its function is to control the motor activity of the lower extremities.
|AnswerDExp=D represents the primary visual cortex responsible for vision. [[Posterior cerebral artery]] (PCA) lesions lead to visual field defects.
|AnswerE=E
|AnswerE=E
|AnswerEExp=E represents the primary visual cortex which is supplied by the [[posterior cerebral artery]] (PCA) and is responsible for vision.
|AnswerEExp=E represents the primary auditory cortex. Strokes affecting this area lead to hearing impairment. True cortical hearing loss is rare and requires loss of bilateral auditory cortices.
|EducationalObjectives=The primary motor cortex controls motor activity, the lateral area supplied by the MCA controls the upper extremities, while the medial area supplied by the ACA controls the motor activity of the lower extremities.
|EducationalObjectives=The primary motor cortex controls motor activity, the lateral area supplied by the MCA controls the upper extremities, while the medial area supplied by the ACA controls the motor activity of the lower extremities.
|References=Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. '''(Image)'''<br>
|References=Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. '''(Image)'''<br>
First Aid 2014 page 458
First Aid 2014 page 458
|RightAnswer=D
|RightAnswer=D

Revision as of 22:22, 9 October 2014
Author [[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Anatomy, MainCategory::Pathophysiology
Sub Category SubCategory::Neurology
Prompt [[Prompt::A 72-year-old man with history significant for diabetes and hypertension presents to the emergency department for acute onset left leg paralysis. The patient explains that he was feeling well yesterday night, but woke up unable to move his right arm and leg. He also noticed that he was unable to control the right side of his face. Physical examination reveals paralysis of both right extremities with no loss of sensation. Cranial nerve exam reveals central facial nerve paralysis. Cerebellar exam is within normal limits. Following an contrast-enhanced MRI, the physician determines that the patient suffered a lacunar stroke at the level of the internal capsule. Nerve fibers from which of the following regions are likely to be involved?

]]

Answer A AnswerA::A
Answer A Explanation AnswerAExp::A represents the primary motor cortex. This area is primarily responsible for the descending corticospinal tracts that control voluntary movement.
Answer B AnswerB::B
Answer B Explanation [[AnswerBExp::B represents the somatosensory cortex which is the main sensory receptive area for the sense of touch. It receives ascending fibers from the thalamus.]]
Answer C AnswerC::C
Answer C Explanation [[AnswerCExp::C represents the prefrontal cortex is the anterior part of the frontal lobes of the brain. This area is responsible cognitive behavior, personality expression, decision making, and moderating social behavior. Lesions in this area lead to personality changes and disinhibition.]]
Answer D AnswerD::D
Answer D Explanation [[AnswerDExp::D represents the primary visual cortex responsible for vision. Posterior cerebral artery (PCA) lesions lead to visual field defects.]]
Answer E AnswerE::E
Answer E Explanation AnswerEExp::E represents the primary auditory cortex. Strokes affecting this area lead to hearing impairment. True cortical hearing loss is rare and requires loss of bilateral auditory cortices.
Right Answer RightAnswer::D
Explanation [[Explanation::

Lacunar strokes are are caused by occlusion of the small penetrating arteries of the brain. The two main proposed mechanism of these strokes are small artery lipohyalinolysis and microemboli. Lipohyalinolysis is characterized by vessel wall thickening and narrowing of the lumen and is strongly associated with hypertension. Despite popular belief, new evidence points to microemboli as the cause of lacunes. However, lipohyalinolysis remains a correct answer on the USMLEs. One form of lacunar strokes is the pure motor stroke that affect the internal capsule particularly the posterior limb. This stroke interrupts descending corticospinal tracts from the primary motor cortex leading to contralateral paralysis. Pure motor stroke is the most common lacunar syndrome.
Educational Objective: The primary motor cortex controls motor activity, the lateral area supplied by the MCA controls the upper extremities, while the medial area supplied by the ACA controls the motor activity of the lower extremities.
References: Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. (Image)
First Aid 2014 page 458]]

Approved Approved::No
Keyword WBRKeyword::Primary motor cortex, WBRKeyword::ACA, WBRKeyword::hemiplegia
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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