Vascular supply (Circle of Willis)

Vascular supply (Circle of Willis) US Medical PG Question 1: A 52-year-man is brought to the physician because of a 2-week history of memory loss. Three weeks ago, he had a cardiac arrest that required cardiopulmonary resuscitation and intravenous epinephrine. On mental status examination, he cannot recall objects shown to him 20 minutes earlier but vividly recalls memories from before the incident. The remainder of the examination shows no abnormalities. Which of the following structures of the brain is most likely affected?

• A. Internal pyramidal layer of the amygdala
• B. Microglial cells of dorsal midbrain
• C. Purkinje cells of the cerebellum
• D. Pyramidal cells of the hippocampus (Correct Answer)
• E. Astroglial cells of the putamen

Vascular supply (Circle of Willis) Explanation: ***Pyramidal cells of the hippocampus*** - The patient's inability to form new memories (anterograde amnesia) following a period of **hypoxia** suggests damage to the **hippocampus**, specifically its pyramidal cells. - The **hippocampus** is highly vulnerable to **ischemic injury** due to the metabolic demands of its pyramidal cells. *Internal pyramidal layer of the amygdala* - The amygdala is primarily involved in **emotional processing**, particularly fear and anxiety, not memory encoding directly. - Damage to the amygdala would likely manifest as altered emotional responses, rather than isolated memory loss. *Microglial cells of dorsal midbrain* - Microglial cells are the brain's resident immune cells and proliferate in response to injury, they are not the primary site of memory formation. - The dorsal midbrain contains structures involved in visual and auditory reflexes, not directly memory consolidation. *Purkinje cells of the cerebellum* - Purkinje cells are specialized neurons in the **cerebellum** responsible for **motor coordination** and balance. - Damage to these cells would result in ataxia and motor dysfunction, not memory deficits. *Astroglial cells of the putamen* - Astroglial cells are supportive cells throughout the brain; the putamen is involved in **motor control** and **procedural learning**. - Dysfunction of the putamen typically leads to movement disorders like Parkinsonism, not specific memory loss.

Vascular supply (Circle of Willis) US Medical PG Question 2: A 59-year-old man is brought to the emergency department by his wife for a 1-hour history of sudden behavior changes. They were having lunch together when, at 1:07 PM, he suddenly dropped his sandwich on the floor. Since then, he has been unable to use his right arm. She also reports that he is slurring his speech and dragging his right foot when he walks. Nothing like this has ever happened before. The vital signs include: pulse 95/min, blood pressure 160/90 mm Hg, and respiratory rate 14/min. The physical exam is notable for an irregularly irregular rhythm on cardiac auscultation. On neurological exam, he has a facial droop on the right half of his face but is able to elevate his eyebrows symmetrically. He has 0/5 strength in his right arm, 2/5 strength in his right leg, and reports numbness throughout the right side of his body. Angiography of the brain will most likely show a lesion in which of the following vessels?

• A. Posterior cerebral artery
• B. Internal carotid artery
• C. Middle cerebral artery (Correct Answer)
• D. Basilar artery
• E. Anterior cerebral artery

Vascular supply (Circle of Willis) Explanation: ***Middle cerebral artery*** - The patient's symptoms, including **right-sided weakness with arm > leg involvement** (0/5 arm, 2/5 leg), **facial droop** (lower face sparing the forehead), and **slurred speech (dysarthria/aphasia)**, are classic signs of an **MCA stroke**. - The **arm > leg pattern** is the key distinguishing feature of MCA territory infarction, as the MCA supplies the **lateral motor cortex** (which controls arm and face). - The finding of an **irregularly irregular rhythm** suggests **atrial fibrillation**, a common cause of **embolic stroke** to the MCA. *Posterior cerebral artery* - PCA strokes primarily affect the **occipital lobe** and **medial temporal lobe**, leading to **visual field defects** (e.g., homonymous hemianopsia) or memory deficits. - While it can cause sensory loss, it typically does not present with the **prominent motor deficits** and **facial droop** seen in this patient. *Internal carotid artery* - ICA occlusion can cause symptoms similar to MCA stroke, especially if the **MCA is a direct branch of the ICA**, or it can cause both MCA and ACA symptoms simultaneously. - However, the specific constellation of symptoms described (predominant motor and sensory deficits, speech issues) points more directly to the **MCA territory downstream**. *Basilar artery* - Basilar artery strokes affect the **brainstem** and often present with a combination of **cranial nerve palsies**, **ataxia**, bilateral weakness, **vertigo**, and sometimes **"locked-in" syndrome**. - The patient's symptoms are more consistent with a **hemispheric lesion**, not a brainstem lesion. *Anterior cerebral artery* - ACA strokes typically cause **contralateral leg > arm weakness** (opposite pattern from MCA), as the ACA supplies the **medial motor cortex**. - ACA strokes may also present with **behavioral changes** (e.g., abulia, apathy) due to involvement of the frontal lobe. - The patient's prominent **right arm weakness** and **facial droop** are not characteristic of an ACA stroke.

Vascular supply (Circle of Willis) US Medical PG Question 3: A researcher is studying the brains of patients who recently died from stroke-related causes. One specimen has a large thrombus in an area of the brain that is important in relaying many modalities of sensory information from the periphery to the sensory cortex. Which of the following embryologic structures gave rise to the part of the brain in question?

• A. Metencephalon
• B. Diencephalon (Correct Answer)
• C. Mesencephalon
• D. Telencephalon
• E. Myelencephalon

Vascular supply (Circle of Willis) Explanation: ***Diencephalon*** - The **thalamus**, a key relay center for sensory information to the cerebral cortex, develops from the diencephalon. - A thrombus in this area would severely impair the transmission of **sensory modalities** from the periphery. *Metencephalon* - The metencephalon gives rise to the **pons** and the **cerebellum**. - These structures are primarily involved in motor control, coordination, and respiratory regulation, not direct sensory relay to the cortex. *Mesencephalon* - The mesencephalon develops into the **midbrain**. - The midbrain contains structures involved in visual and auditory reflexes, and motor control, but not the primary sensory relay described. *Myelencephalon* - The myelencephalon gives rise to the **medulla oblongata**. - The medulla is crucial for vital autonomic functions (e.g., breathing, heart rate) and connects the brain to the spinal cord. *Telencephalon* - The telencephalon develops into the **cerebral hemispheres** (cerebral cortex, basal ganglia, hippocampus). - While it processes sensory information, it is not the primary relay center from the periphery; that role belongs to the thalamus.

Vascular supply (Circle of Willis) US Medical PG Question 4: A 44-year-old female is admitted to the neurological service. You examine her chart and note that after admission she was started on nimodipine. Which of the following pathologies would benefit from this pharmacologic therapy?

• A. Thromboembolic stroke
• B. Subdural hematoma
• C. Epidural hematoma
• D. Pseudotumor cerebri
• E. Subarachnoid hemorrhage (Correct Answer)

Vascular supply (Circle of Willis) Explanation: ***Subarachnoid hemorrhage*** - Nimodipine is a **calcium channel blocker** specifically used to prevent and treat **cerebral vasospasm** following a subarachnoid hemorrhage. - Vasospasm is a common and often devastating complication that can lead to delayed cerebral ischemia and poor neurological outcomes. *Thromboembolic stroke* - Treatment for thromboembolic stroke focuses on **reperfusion therapies** (e.g., tPA, thrombectomy) and antiplatelet/anticoagulant medications. - Nimodipine does not play a role in the acute management or prevention of tissue damage in ischemic stroke. *Subdural hematoma* - Subdural hematomas are collections of blood between the dura and arachnoid mater, usually resulting from **head trauma**. - Management typically involves **surgical evacuation** if symptomatic, and nimodipine is not indicated. *Epidural hematoma* - Epidural hematomas involve bleeding between the dura mater and the skull, often due to **arterial injury** from head trauma. - These are surgical emergencies, and nimodipine has no therapeutic role. *Pseudotumor cerebri* - Also known as **idiopathic intracranial hypertension**, this condition involves elevated intracranial pressure without a mass lesion. - Treatment focuses on reducing CSF pressure, often with diuretics (e.g., acetazolamide), and nimodipine is not part of the management.

Vascular supply (Circle of Willis) US Medical PG Question 5: A 78-year-old right-handed man with hypertension and hyperlipidemia is brought to the emergency department for sudden onset of nausea and vertigo one hour ago. Physical examination shows 5/5 strength in all extremities. Sensation to light touch and pinprick is decreased in the right arm and leg. A CT scan of the brain shows an acute infarction in the distribution of the left posterior cerebral artery. Further evaluation of this patient is most likely to show which of the following findings?

• A. Right-sided homonymous hemianopia (Correct Answer)
• B. Prosopagnosia
• C. Left-sided gaze deviation
• D. Left-sided hemineglect
• E. Right-sided superior quadrantanopia

Vascular supply (Circle of Willis) Explanation: ***Right-sided homonymous hemianopia*** - A **left PCA infarct** typically affects the **occipital lobe**, specifically the visual cortex or optic radiations, leading to a contralateral visual field deficit. - The **right visual field** from both eyes projects to the left occipital lobe, so infarction here causes a **right homonymous hemianopia**. *Prosopagnosia* - **Prosopagnosia**, the inability to recognize faces, is associated with infarction of the **fusiform gyrus**, often a bilateral PCA territory infarction or an infarct affecting the right occipital or temporal lobe. - This patient has a **left PCA infarct**, so isolated prosopagnosia is less likely. *Left-sided gaze deviation* - **Gaze deviation** usually occurs in lesions of the **frontal eye fields** (Brodmann area 8), which are supplied by the middle cerebral artery, causing the eyes to deviate towards the side of the lesion in acute stages. - A **PCA infarct** typically spares the frontal eye fields and the brainstem gaze centers. *Left-sided hemineglect* - **Hemineglect** is most commonly associated with lesions of the **right parietal lobe** or right frontal lobe, primarily in the territory of the right middle cerebral artery. - With a **left PCA infarct**, left-sided hemineglect is an unexpected finding. *Right-sided superior quadrantanopia* - A **superior quadrantanopia** is caused by damage to the **inferior optic radiations** (Meyer's loop), which typically carry information from the superior visual field. - A complete **homonymous hemianopia** involving the entire right visual field is more characteristic of an occipital lobe lesion due to a PCA infarct, rather than an isolated quadrantanopia.

Vascular supply (Circle of Willis) US Medical PG Question 6: A 61-year-old man is brought to the emergency department by his son after collapsing to the ground while at home. His son immediately performed cardiopulmonary resuscitation and later the patient underwent successful defibrillation after being evaluated by the emergency medical technician. The patient has a medical history of hypertension, hyperlipidemia, and type II diabetes mellitus. He has smoked one-half pack of cigarettes for approximately 30 years. The patient was admitted to the cardiac intensive care unit, and after a few days developed acute onset right upper extremity weakness. His temperature is 99°F (37.2°C), blood pressure is 145/91 mmHg, pulse is 102/min and irregularly irregular, and respirations are 16/min. On physical examination, the patient is alert and orientated to person, place, and time. His language is fluent and he is able to name, repeat, and read. His strength is 5/5 throughout except in the right hand, wrist, and arm, which is 2/5. Based on this patient's clinical presentation, the affected neuronal fibers decussate at which level of the central nervous system?

• A. Caudal medulla (Correct Answer)
• B. Pons
• C. Spinal cord
• D. Primary motor cortex
• E. Thalamus

Vascular supply (Circle of Willis) Explanation: ***Caudal medulla*** - The patient's **acute right upper extremity weakness** following a cardiac event suggests a **stroke** affecting the left motor pathways. - The **pyramidal decussation**, where the vast majority of the **corticospinal tracts** cross to the contralateral side, occurs in the **caudal medulla**. *Pons* - While the corticospinal tracts pass through the pons, they generally do not decussate at this level. - Lesions in the pons often present with **ipsilateral cranial nerve** deficits and **contralateral body weakness**. *Spinal cord* - Only a small percentage (about 10-15%) of the corticospinal fibers decussate in the spinal cord, and these form the **anterior corticospinal tract**, mainly supplying axial muscles. - Significant contralateral upper extremity weakness implies a lesion higher up, before the spinal cord. *Primary motor cortex* - Lesions in the primary motor cortex would cause contralateral weakness, but the decussation itself occurs in the brainstem, not the cortex. - The motor cortex is where the motor commands originate, not where they cross over. *Thalamus* - The thalamus is a major **sensory relay station** and also plays a role in motor control, but it is not the site of decussation for the corticospinal tracts. - Thalamic lesions typically cause **sensory deficits** (e.g., contralateral hemianesthesia) and sometimes ataxia or dyskinesias.

Vascular supply (Circle of Willis) US Medical PG Question 7: A 68-year-old man is brought to the emergency department by ambulance after he was found to be altered at home. Specifically, his wife says that he fell and was unable to get back up while walking to bed. When she approached him, she found that he was unable to move his left leg. His past medical history is significant for hypertension, atrial fibrillation, and diabetes. In addition, he has a 20-pack-year smoking history. On presentation, he is found to still have difficulty moving his left leg though motor function in his left arm is completely intact. The cause of this patient's symptoms most likely occurred in an artery supplying which of the following brain regions?

• A. Motor cortex (ACA) (Correct Answer)
• B. Cerebellum (PICA/SCA)
• C. Occipital cortex (PCA)
• D. Brainstem (Vertebrobasilar)
• E. Motor cortex (MCA)

Vascular supply (Circle of Willis) Explanation: ***Motor cortex (ACA)*** - The patient's inability to move his **left leg** while his **left arm** remains intact points to an injury in the **right cerebral hemisphere** affecting the leg area of the motor cortex. - The leg area of the **primary motor cortex** is primarily supplied by the **anterior cerebral artery (ACA)**, making an ACA stroke the most likely cause. *Motor cortex (MCA)* - The **middle cerebral artery (MCA)** primarily supplies the motor cortex areas responsible for the **face and arm**, not typically isolated leg weakness. - If the MCA were affected, you would expect to see involvement of the face and/or arm on the contralateral side in addition to leg weakness. *Brainstem (Vertebrobasilar)* - A **brainstem stroke** would likely present with more widespread neurological deficits, including **cranial nerve palsies**, ataxia, or altered consciousness. - Isolated contralateral leg weakness without arm involvement is not characteristic of a brainstem lesion. *Cerebellum (PICA/SCA)* - The **cerebellum** is primarily involved in **coordination and balance**, not direct motor strength. - A cerebellar stroke would present with symptoms like **ataxia**, dysarthria, or nystagmus, not isolated paralysis. *Occipital cortex (PCA)* - The **occipital cortex** is primarily responsible for **vision**. - A posterior cerebral artery (PCA) stroke would typically cause **visual field defects** (e.g., contralateral homonymous hemianopia) rather than motor weakness.

Vascular supply (Circle of Willis) US Medical PG Question 8: A 67-year-old female patient is brought to the emergency department after her daughter noticed she has been having meaningless speech. When assessing the patient, she calls the chair a table, and at times would make up new words. She does not appear to be aware of her deficit, and is carrying on an empty conversation. Her speech is fluent, but with paraphasic errors. Her repetition is impaired. On physical examination, a right upper quadrant field-cut is appreciated, with impairment in comprehension and repetition. Which of the following structures is most likely involved in this patient’s presentation?

• A. Superior temporal gyrus (Correct Answer)
• B. Arcuate fasciculus
• C. Inferior frontal gyrus
• D. Frontal lobe, sparing Brodmann's area 44 and 45
• E. Arcuate fasciculus, inferior frontal gyrus, and superior temporal gyrus

Vascular supply (Circle of Willis) Explanation: ***Superior temporal gyrus*** - The patient's presentation of **fluent aphasia** with **paraphasic errors**, **impaired comprehension**, **impaired repetition**, and **lack of awareness** of the deficit is classic for **Wernicke's aphasia**. - **Wernicke's area**, located in the posterior part of the **superior temporal gyrus** (Brodmann area 22) in the dominant hemisphere, is responsible for language comprehension. *Arcuate fasciculus* - Damage to the **arcuate fasciculus** typically causes **conduction aphasia**, characterized by **impaired repetition** with relatively preserved comprehension and fluent speech. - However, it does not explain the significant comprehension deficits and paraphasic errors seen in this patient to the same extent as a Wernicke's lesion. *Inferior frontal gyrus* - The **inferior frontal gyrus** (Brodmann areas 44 and 45) is commonly associated with **Broca's area**, responsible for language production. - Damage here would result in **non-fluent aphasia** with effortful speech and relatively preserved comprehension, which is contrary to the patient's fluent speech. *Frontal lobe, sparing Brodmann's area 44 and 45* - While damage to other parts of the **frontal lobe** can cause various cognitive deficits, sparing Broca's area (44 and 45) would generally not result in the specific pattern of **fluent aphasia** with severe comprehension and repetition impairment seen here. - This option does not precisely localize the critical language areas affected. *Arcuate fasciculus, inferior frontal gyrus, and superior temporal gyrus* - While damage to all these areas would certainly cause severe aphasia, the specific constellation of symptoms—**fluent speech**, **poor comprehension**, **poor repetition**, and **paraphasic errors**—points most directly and primarily to involvement of the **superior temporal gyrus** (Wernicke's area). - While some level of repetition impairment (seen in Wernicke's aphasia) implies some involvement in the broader language network, a lesion centered in the superior temporal gyrus is the most parsimonious explanation for this classic presentation.

Vascular supply (Circle of Willis) US Medical PG Question 9: A 19-year-old man is brought to the emergency department following a high-speed motor vehicle collision in which he was a restrained passenger. He complains of pelvic pain and urinary retention with overflow incontinence, along with associated lower extremity weakness. Examination shows perineal bruising and there is pain with manual compression of the pelvis. Injury to which of the following structures is most likely responsible for this patient's urinary incontinence?

• A. Ilioinguinal nerve
• B. Obturator nerve
• C. Genitofemoral nerve
• D. Pelvic splanchnic nerves (Correct Answer)
• E. Superior gluteal nerve

Vascular supply (Circle of Willis) Explanation: ***Pelvic splanchnic nerves*** - Urinary retention with overflow incontinence and lower extremity weakness following a pelvic trauma suggests damage to the **sacral spinal segments** or the **pelvic splanchnic nerves**. - These nerves carry **parasympathetic fibers** that stimulate bladder contraction (detrusor muscle) and relaxation of the internal urethral sphincter, which are crucial for normal micturition. *Ilioinguinal nerve* - This nerve supplies sensory innervation to the **genitalia** and part of the inner thigh, and motor innervation to the internal oblique and transversus abdominis muscles. - Damage to this nerve would primarily cause sensory deficits or abdominal muscle weakness, not urinary retention or lower extremity weakness. *Obturator nerve* - The obturator nerve primarily innervates the **adductor muscles of the thigh** and provides sensory innervation to the medial thigh. - Injury would result in difficulty with hip adduction and sensory loss in the medial thigh, not bladder dysfunction or diffuse lower extremity weakness. *Genitofemoral nerve* - This nerve provides sensory innervation to the **anterior compartment of the thigh** and the external genitalia, and motor innervation to the cremaster muscle. - Damage would typically manifest as altered sensation in these areas or an absent cremasteric reflex, without directly affecting bladder function. *Superior gluteal nerve* - The superior gluteal nerve innervates the **gluteus medius, gluteus minimus, and tensor fasciae latae muscles**, which are crucial for hip abduction and stabilization during walking. - Injury would lead to a characteristic **Trendelenburg gait**, but would not directly cause urinary incontinence or retention.

Vascular supply (Circle of Willis) US Medical PG Question 10: An 82-year-old right-handed woman is brought in by ambulance after being found down in her home. On presentation, she is found to be awake but does not follow directions or respond to questions. She is able to speak and produces a fluent string of nonsensical words and sounds. She does not appear to be bothered by her deficits. Subsequent neurologic exam finds that the patient is unable to comprehend any instructions and is also unable to repeat phrases. CT scan reveals an acute stroke to her left hemisphere. Damage to which of the following structures would be most likely to result in this pattern of deficits?

• A. Precentral gyrus
• B. Superior temporal gyrus (Correct Answer)
• C. Arcuate fasciculus
• D. Inferior frontal gyrus
• E. Watershed zone

Vascular supply (Circle of Willis) Explanation: ***Superior temporal gyrus*** - This patient presents with **fluent aphasia** (speaking nonsensical words), severely impaired **comprehension**, and impaired **repetition**. This triad is characteristic of **Wernicke's aphasia**. - **Wernicke's area**, responsible for language comprehension, is located in the **posterior part of the superior temporal gyrus** in the dominant hemisphere (typically left). *Precentral gyrus* - The **precentral gyrus** contains the **primary motor cortex** and its damage would primarily cause contralateral motor deficits (e.g., **hemiparesis** or **hemiplegia**). - This area is not directly involved in language comprehension or production of fluent but nonsensical speech. *Arcuate fasciculus* - Damage to the **arcuate fasciculus**, a white matter tract connecting Broca's and Wernicke's areas, results in **conduction aphasia**. - In **conduction aphasia**, comprehension and fluency are relatively preserved, but **repetition is severely impaired**. This patient also has impaired comprehension. *Inferior frontal gyrus* - The **inferior frontal gyrus** houses **Broca's area**, which is responsible for **language production and motor aspects of speech**. - Damage to this area typically causes **Broca's aphasia**, characterized by **non-fluent speech**, preserved comprehension, and impaired repetition. This patient has fluent speech. *Watershed zone* - **Watershed infarcts** occur at the borders between major arterial territories due to hypoperfusion, often leading to **transcortical aphasias**. - While transcortical sensory aphasia involves impaired comprehension and fluent speech, **repetition is preserved**, which is not the case here.

Vascular supply (Circle of Willis) Flashcard 1 of 10

Question: ID Vessel: _____

Answer: Superior cerebellar artery

Vascular supply (Circle of Willis) Flashcard 2 of 10

Question: What artery supplies the medial and lateral midbrain? _____

Answer: Posterior cerebral artery

Vascular supply (Circle of Willis) Flashcard 3 of 10

Question: The _____ branches of the posterior cerebral artery supply the thalamus, splenium, parahippocampal gyrus, and fusiform gyrus

Answer: deep

Vascular supply (Circle of Willis) Flashcard 4 of 10

Question: ID Vessel: _____

Answer: Middle cerebral artery

Vascular supply (Circle of Willis) Flashcard 5 of 10

Question: ID Vessel: _____

Answer: Anterior cerebral artery

Vascular supply (Circle of Willis) Flashcard 6 of 10

Question: The macula is spared during posterior cerebral artery infarct due to collateral circulation with the _____ artery

Answer: middle cerebral

Vascular supply (Circle of Willis) Flashcard 7 of 10

Question: Alexia without Agraphia is a speech deficit associated with _____ artery infarct

Answer: posterior cerebral

Vascular supply (Circle of Willis) Flashcard 8 of 10

Question: anterior communicating artery

Answer: cranial nerves

Extra Information: visual field defects

Vascular supply (Circle of Willis) Flashcard 9 of 10

Question: posterior communicating artery

Answer: CN 3

Extra Information: eye externally and inferiorly rotated, ptosis, pupil dilation

Vascular supply (Circle of Willis) Flashcard 10 of 10

Question: Where do saccular "berry" aneurysms tend to occur?

Answer: bifurcations in Circle of Willis; especially anterior and posterior communicating arteries