A 64-year-old man comes to the emergency department due to left lower extremity weakness. The patient was asymptomatic when he went to bed the night before, but he has had difficulty standing after waking up today. He has had no headache, double vision, or back pain. Medical history is significant for hypertension, diabetes mellitus, and myocardial infarction. Temperature is 37 C (98.6 F), blood pressure is 140/90 mm Hg, and pulse is 110/min and irregularly irregular. Left lower extremity examination shows motor power is 0/5, deep tendon reflexes are 3+, and Babinski sign is present. Right lower extremity examination is normal. An abnormality in which of the following structures is the most likely cause of this patient's symptoms?

Question

A 64-year-old man comes to the emergency department due to left lower extremity weakness.  The patient was asymptomatic when he went to bed the night before, but he has had difficulty standing after waking up today.  He has had no headache, double vision, or back pain.  Medical history is significant for hypertension, diabetes mellitus, and myocardial infarction.  Temperature is 37 C (98.6 F), blood pressure is 140/90 mm Hg, and pulse is 110/min and irregularly irregular.  Left lower extremity examination shows motor power is 0/5, deep tendon reflexes are 3+, and Babinski sign is present.  Right lower extremity examination is normal.  An abnormality in which of the following structures is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

11ec160b_35b8_6178_9249_bf97de1f66e8_MD0001_00 This patient with atrial fibrillation (irregularly irregular pulse, tachycardia) has isolated left lower extremity motor deficits, most likely caused by a cardioembolic stroke in the right anterior cerebral artery (ACA) territory. The ACA supplies the medial aspects of the frontal and parietal lobes, a region which contains the upper motor neurons responsible for contralateral lower extremity motor control. Occlusion of the ACA characteristically causes contralateral lower limb weakness with upper motor neuron signs (eg, hyperreflexia, Babinski sign). Contralateral sensory deficits occur in a minority of patients. The most common etiology of ACA stroke is cardiac embolization due to atrial fibrillation, which can cause blood flow stasis resulting in thrombus formation in the left atrial appendage. Atrial thromboemboli frequently travel to and obstruct branches of ACA or middle cerebral artery (MCA), causing cerebral ischemia with associated neurologic defects. (Choice A) An embolic occlusion of the anterior spinal artery in the lumbosacral region would cause bilateral lower extremity weakness with hyporeflexia (ischemia of the anterior horns and corticospinal tracts) and loss of pain and temperature sensation (ischemia of the spinothalamic tracts) below the level of the lesion. (Choice B) Posterior inferior cerebellar artery occlusion characteristically causes ischemia in the lateral medulla (Wallenberg syndrome) and inferior cerebellar peduncle, resulting in dysphagia, hoarseness, and vestibulocerebellar symptoms (eg, ataxia, dizziness, nystagmus). (Choice C) Although lumbosacral neural foraminal stenosis can cause unilateral lower extremity weakness, compression injury of a spinal nerve root (lower motor neuron fibers) at this level would typically result in significant radicular back and leg pain with hyporeflexia. (Choice E) MCA strokes predominantly affect the upper extremity and are often associated with homonymous hemianopia, aphasia, and hemineglect. Although large MCA strokes can also cause lower extremity weakness, the defects in those cases are usually extensive and involve both the upper and lower extremities (hemiparesis). Educational objective: The anterior cerebral artery (ACA) supplies the medial aspects of the frontal and parietal lobes, which contain the upper motor neurons responsible for contralateral lower extremity motor control. Thromboembolic occlusion of the ACA characteristically results in contralateral lower extremity weakness with hyperreflexia. __________ References: Infarction in the territory of the anterior cerebral artery: clinical study of 51 patients (http://www.ncbi.nlm.nih.gov/pubmed/19589132)

A 64-Year-Old Man Comes to the Emergency Department Due to Left