WBR0614

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Serge Korjian M.D.)]]
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 right sided paralysis. The patient explains that he was feeling well yesterday night, but he 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 is remarkable 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 a 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::A
Explanation	[[Explanation:: Lacunar strokes 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. Although lipohyalinosis is thought to be involved in the pathogenesis of lacunes, new evidence suggests that microemboli are the main cause. 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 mainly controls the upper extremities, while the medial area supplied by the ACA mainly 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 2015 page 464]]
Approved	Approved::Yes
Keyword	WBRKeyword::Primary motor cortex, WBRKeyword::ACA, WBRKeyword::Hemiplegia, WBRKeyword::Paralysis, WBRKeyword::Stroke, WBRKeyword::Lacunar stroke, WBRKeyword::Neuroanatomy, WBRKeyword::Neurovasculature
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::