Variations in circle of Willis — MCQs

10 questions

A previously healthy 10-year-old boy is brought to the emergency department for the evaluation of one episode of vomiting and severe headache since this morning. His mother says he also had difficulty getting dressed on his own. He has not had any trauma. The patient appears nervous. His temperature is 37°C (98.6°F), pulse is 100/min, and blood pressure is 185/125 mm Hg. He is confused and oriented only to person. Ophthalmic examination shows bilateral optic disc swelling. There is an abdominal bruit that is best heard at the right costovertebral angle. A complete blood count is within normal limits. Which of the following is most likely to confirm the diagnosis?

A 3-year-old boy is brought to the emergency department after losing consciousness. His parents report that he collapsed and then had repetitive, twitching movements of the right side of his body that lasted approximately one minute. He recently started to walk with support. He speaks in bisyllables and has a vocabulary of almost 50 words. Examination shows a large purple-colored patch over the left cheek. One week later, he dies. Which of the following is the most likely finding on autopsy of the brain?

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 72-year-old woman presents to the emergency department for vision loss. She was reading a magazine this afternoon when she started having trouble seeing out of her left eye. Her vision in that eye got progressively darker, eventually becoming completely black over the course of a few minutes. It then returned to normal after about 10 minutes; she reports she can see normally now. She had no pain and no other symptoms then or now. Past medical history is notable for hypertension and hyperlipidemia. A high-pitched sound is heard when the diaphragm of the stethoscope is placed on her left neck, but her physical exam is otherwise unremarkable; vision is currently 20/30 bilaterally. The etiology of her symptoms most likely localizes to which of the following anatomic locations?

A 38-year-old woman with moyamoya disease undergoes cerebral angiography showing bilateral progressive stenosis of distal internal carotid arteries with extensive collateral formation. She has had multiple TIAs despite medical management. CT perfusion shows reduced flow in bilateral MCA territories. The neurosurgery team debates between direct bypass (STA-MCA) versus indirect revascularization (EDAS). Evaluate the optimal approach considering Circle of Willis pathophysiology.

A 70-year-old man undergoes elective clipping of an unruptured basilar tip aneurysm. Preoperative angiography shows bilateral fetal-type posterior cerebral arteries (PCAs arising from internal carotid arteries) with hypoplastic P1 segments. The aneurysm involves both posterior communicating artery origins. Synthesize an approach to surgical planning that optimally preserves cerebral perfusion.

A 42-year-old woman presents with progressive cognitive decline, early-onset dementia, and recurrent subcortical strokes. Genetic testing reveals CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy). MR angiography shows no large vessel abnormalities but extensive white matter changes. Her sister, also affected, is considering pregnancy. Evaluate the counseling regarding Circle of Willis anatomy and implications for disease manifestations.

A 55-year-old man with diabetes and hypertension undergoes carotid endarterectomy for critical left internal carotid stenosis. Postoperatively, he develops right homonymous hemianopia without motor deficits. Intraoperative transcranial Doppler had shown reduced flow in the ipsilateral middle cerebral artery but preserved anterior cerebral artery flow. Analyze the most likely mechanism for this specific deficit pattern.

A 28-year-old woman presents with bilateral lower extremity weakness worse than upper extremity weakness, abulia, and urinary incontinence. MRI reveals bilateral anterior cerebral artery territory infarcts. Angiography shows an azygos anterior cerebral artery variant. Analyze the anatomical basis for this patient's bilateral deficits from a presumed single vascular occlusion.

Q10

A 65-year-old woman with hypertension develops sudden vertigo, dysphagia, and loss of pain and temperature sensation on the left face and right body. MRI shows a left lateral medullary infarct. Analysis of her vascular anatomy reveals an incomplete Circle of Willis. Which specific arterial segment occlusion best explains this clinical presentation?

Variations in circle of Willis US Medical PG Practice Questions and MCQs

Question 1: A previously healthy 10-year-old boy is brought to the emergency department for the evaluation of one episode of vomiting and severe headache since this morning. His mother says he also had difficulty getting dressed on his own. He has not had any trauma. The patient appears nervous. His temperature is 37°C (98.6°F), pulse is 100/min, and blood pressure is 185/125 mm Hg. He is confused and oriented only to person. Ophthalmic examination shows bilateral optic disc swelling. There is an abdominal bruit that is best heard at the right costovertebral angle. A complete blood count is within normal limits. Which of the following is most likely to confirm the diagnosis?

A. Serum IGF-I level
B. Oral sodium loading test
C. Echocardiography
D. CT angiography (Correct Answer)
E. High-dose dexamethasone suppression test

Explanation: ***CT angiography*** - The patient presents with **malignant hypertension** (BP 185/125 mmHg, confusion, optic disc swelling) and an **abdominal bruit** especially at the **right costovertebral angle**, pointing strongly towards **renovascular hypertension** due to **renal artery stenosis**. - **CT angiography** is the most appropriate imaging modality to confirm **renal artery stenosis** by visualizing the renal arteries and identifying any narrowing. *Serum IGF-I level* - This test is used to screen for **growth hormone disorders** like **acromegaly** or **gigantism**, which are not indicated by the patient's symptoms. - The patient's presentation is focused on acute severe hypertension and neurological changes, rather than chronic growth disturbances. *Oral sodium loading test* - This test is used to confirm the diagnosis of **primary aldosteronism**, where **aldosterone levels** fail to suppress after a sodium load. - While primary aldosteronism can cause hypertension, it typically doesn't present with an **abdominal bruit** or the acute, severe neurological symptoms seen here. *Echocardiography* - **Echocardiography** assesses the heart's structure and function, which could show signs of **hypertensive heart disease** (e.g., left ventricular hypertrophy) due to long-standing uncontrolled hypertension. - However, it does not identify the underlying cause of the hypertension in this acute setting, especially when an **abdominal bruit** suggests a vascular origin. *High-dose dexamethasone suppression test* - This test is used to differentiate between **Cushing's disease** (pituitary ACTH-dependent) and other causes of **Cushing's syndrome** (e.g., ectopic ACTH production, adrenal tumor) due to excess cortisol. - The patient's symptoms are inconsistent with Cushing's syndrome, and the **abdominal bruit** points away from this diagnosis.

Question 2: A 3-year-old boy is brought to the emergency department after losing consciousness. His parents report that he collapsed and then had repetitive, twitching movements of the right side of his body that lasted approximately one minute. He recently started to walk with support. He speaks in bisyllables and has a vocabulary of almost 50 words. Examination shows a large purple-colored patch over the left cheek. One week later, he dies. Which of the following is the most likely finding on autopsy of the brain?

A. Subependymal giant cell astrocytoma
B. Periventricular calcification
C. Brainstem glioma
D. Leptomeningeal vascular malformation (Correct Answer)
E. Intraparenchymal cyst

Explanation: ***Leptomeningeal vascular malformation*** - The constellation of **seizures** and a **large purple patch** on the face (**port-wine stain** or nevus flammeus) strongly suggests **Sturge-Weber syndrome**. - **Leptomeningeal angioma** (vascular malformation) is the characteristic brain finding in Sturge-Weber syndrome, often leading to neurological deficits, seizures, and increased intracranial pressure. *Subependymal giant cell astrocytoma* - This tumor is pathognomonic for **tuberous sclerosis complex**, which is typically associated with **facial angiofibromas** (adenoma sebaceum) and other skin lesions like ash-leaf spots. - While tuberous sclerosis can present with seizures, the facial lesion described in the patient (large purple patch, or port-wine stain) is not consistent with the typical skin findings of tuberous sclerosis. *Periventricular calcification* - **Periventricular calcifications** are a hallmark sign of **congenital cytomegalovirus (CMV)** infection. - While CMV can cause neurological sequelae and developmental delay, the clinical presentation with a distinct facial lesion and recent onset seizures is more indicative of Sturge-Weber syndrome. *Brainstem glioma* - **Brainstem gliomas** typically present with **cranial nerve deficits**, **ataxia**, and long tract signs, rather than focal seizures and a port-wine stain. - The sudden onset of seizures and collapse, along with the characteristic facial lesion, points away from a primary brainstem tumor. *Intraparenchymal cyst* - An **intraparenchymal cyst** is a non-specific finding that could result from various causes, such as infection, trauma, or developmental anomalies. - It does not specifically account for the combination of seizures and the facial **port-wine stain** seen in this patient.

Question 3: 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

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.

Question 4: A 72-year-old woman presents to the emergency department for vision loss. She was reading a magazine this afternoon when she started having trouble seeing out of her left eye. Her vision in that eye got progressively darker, eventually becoming completely black over the course of a few minutes. It then returned to normal after about 10 minutes; she reports she can see normally now. She had no pain and no other symptoms then or now. Past medical history is notable for hypertension and hyperlipidemia. A high-pitched sound is heard when the diaphragm of the stethoscope is placed on her left neck, but her physical exam is otherwise unremarkable; vision is currently 20/30 bilaterally. The etiology of her symptoms most likely localizes to which of the following anatomic locations?

A. Left atrium
B. Subclavian artery
C. Temporal artery
D. Carotid artery (Correct Answer)
E. Vertebral artery

Explanation: ***Carotid artery*** - The sudden, temporary vision loss (amaurosis fugax) in one eye, described as a "curtain coming down," is a classic symptom of an **embolus originating from the ipsilateral carotid artery**. - The **bruit** heard in the left neck further points to significant **carotid artery stenosis**, which can be a source of these emboli to the **ophthalmic artery**. *Left atrium* - An embolus from the left atrium (e.g., in atrial fibrillation) would typically cause symptoms of a **cerebral stroke** or vision loss in **both eyes** if it affects a major supplying vessel before the intracranial branches, or could affect the carotid artery system, but the neck bruit directly implicates the carotid. - While a source of emboli, the direct finding of a neck bruit makes the carotid the more immediate and specific localization. *Subclavian artery* - **Subclavian artery** stenosis can cause **subclavian steal syndrome**, leading to vertebrobasilar insufficiency and symptoms like **dizziness** or **syncope**, but generally does not cause unilateral amaurosis fugax. - Its territory primarily supplies the arm and posterior circulation, not the anterior cerebral circulation or ophthalmic artery directly as suggested by amaurosis fugax. *Temporal artery* - **Temporal arteritis** (Giant Cell Arteritis) can cause sudden vision loss, often irreversible, and is usually associated with **headaches**, **jaw claudication**, and a very high **ESR**, none of which are reported here. - While it affects the ophthalmic artery, the absence of pain and the transient nature of the vision loss (amaurosis fugax) make it less likely than an embolic event. *Vertebral artery* - The **vertebral arteries** supply the **posterior circulation** of the brain, leading to symptoms such as **diplopia**, **vertigo**, **ataxia**, or **hemiparesis**, but not isolated unilateral amaurosis fugax. - Problems in this artery typically manifest as **vertebrobasilar insufficiency**, which affects both eyes or causes other brainstem symptoms, not transient unilateral blindness.

Question 5: A 38-year-old woman with moyamoya disease undergoes cerebral angiography showing bilateral progressive stenosis of distal internal carotid arteries with extensive collateral formation. She has had multiple TIAs despite medical management. CT perfusion shows reduced flow in bilateral MCA territories. The neurosurgery team debates between direct bypass (STA-MCA) versus indirect revascularization (EDAS). Evaluate the optimal approach considering Circle of Willis pathophysiology.

A. Indirect revascularization allows gradual angiogenesis; better for incomplete Circle variants
B. Combined direct and indirect approaches optimize collateral development regardless of Circle anatomy (Correct Answer)
C. Circle of Willis anatomy is irrelevant; external to internal carotid bypass is contraindicated in moyamoya
D. Observation only; intact Circle of Willis through ACoA and PCoA provides adequate collaterals
E. Direct bypass provides immediate flow; superior for adults with completed Circle

Explanation: ***Combined direct and indirect approaches optimize collateral development regardless of Circle anatomy*** - In **Moyamoya disease**, the **Circle of Willis** loses its compensatory efficiency due to progressive **internal carotid artery (ICA) stenosis**, necessitating both immediate and long-term revascularization strategies. - A **combined approach** (direct STA-MCA bypass plus indirect EDAS) provides **immediate hemodynamic augmentation** and facilitates **long-term angiogenesis** to counter chronic ischemia. *Indirect revascularization allows gradual angiogenesis; better for incomplete Circle variants* - While **indirect revascularization (EDAS)** promotes gradual **angiogenesis**, it is usually less effective in adults when used alone due to reduced angiogenic potential compared to children. - It does not address the need for **immediate flow restoration** in a patient experiencing recurrent **TIAs** despite medical management. *Direct bypass provides immediate flow; superior for adults with completed Circle* - **Direct bypass** (STA-MCA) does provide **immediate flow**, but relying solely on it ignores the benefit of **indirect synangiosis** in providing wider regional coverage over time. - The status of a "completed" **Circle of Willis** is often irrelevant in advanced disease because the progressive **distal ICA stenosis** prevents effective cross-flow regardless of anatomical completeness. *Circle of Willis anatomy is irrelevant; external to internal carotid bypass is contraindicated in moyamoya* - External to internal carotid bypass is not contraindicated; it is actually a **standard of care** for preventing future **ischemic strokes** in symptomatic Moyamoya patients. - While the disease originates at the **Circle of Willis**, understanding its anatomy is vital for surgical planning and predicting **collateral compensation** patterns. *Observation only; intact Circle of Willis through ACoA and PCoA provides adequate collaterals* - Observation is inappropriate for a patient with **recurrent TIAs** and **reduced CT perfusion**, as it carries a high risk of permanent **ischemic stroke**. - In **Moyamoya disease**, the typical **distal ICA stenosis** frequently involves the origins of the **ACoA and PCoA**, rendering the **Circle of Willis** inadequate for maintaining cerebral perfusion.

Question 6: A 70-year-old man undergoes elective clipping of an unruptured basilar tip aneurysm. Preoperative angiography shows bilateral fetal-type posterior cerebral arteries (PCAs arising from internal carotid arteries) with hypoplastic P1 segments. The aneurysm involves both posterior communicating artery origins. Synthesize an approach to surgical planning that optimally preserves cerebral perfusion.

A. Staged bilateral STA-PCA bypasses followed by aneurysm clipping with PCoA sacrifice
B. Standard clip placement sacrificing one PCoA; contralateral PCoA provides adequate flow
C. Bypass surgery from external carotid to PCA prior to aneurysm clipping
D. Endovascular coiling instead of clipping to preserve both PCoA vessels
E. Clip reconstruction technique preserving both PCoA origins with intraoperative flow assessment (Correct Answer)

Explanation: ***Clip reconstruction technique preserving both PCoA origins with intraoperative flow assessment*** - In patients with **fetal-type posterior cerebral arteries (PCAs)**, the **posterior communicating artery (PCoA)** is the primary supply to the PCA territory because the **P1 segment** of the basilar artery is hypoplastic. - **Clip reconstruction** is the gold standard for maintaining the integrity of these vital vessels, and **intraoperative flow assessment** (like ICG angiography) ensures that perfusion to the occipital and temporal lobes is maintained. *Staged bilateral STA-PCA bypasses followed by aneurysm clipping with PCoA sacrifice* - While **bypass surgery** can provide additional flow, performing staged bilateral procedures is excessively invasive and carries a high risk for an **unruptured aneurysm**. - The goal should be the **anatomic preservation** of the primary vessels rather than replacing them with complex extracranial-to-intracranial bypasses unless necessary. *Standard clip placement sacrificing one PCoA; contralateral PCoA provides adequate flow* - Sacrificing a **fetal-type PCoA** is contraindicated because the **hypoplastic P1** cannot provide compensatory flow, leading to a major **ischaemic stroke** in the PCA territory. - Unlike a typical Circle of Willis, **contralateral flow** cannot cross over to support the deprived PCA territory in this specific anatomical configuration. *Bypass surgery from external carotid to PCA prior to aneurysm clipping* - External carotid-to-PCA bypass is a complex rescue operation and is typically reserved for cases where **direct clip reconstruction** is technically impossible. - In elective surgery for a basilar tip aneurysm, the priority is **microsurgical technique** to save the native **internal carotid-driven** flow. *Endovascular coiling instead of clipping to preserve both PCoA vessels* - While **endovascular coiling** is an alternative, the question specifically asks for a **surgical planning approach** based on the decision to use clipping. - Furthermore, coiling a wide-necked **basilar tip aneurysm** often requires stents or balloons that could still inadvertently compromise the **PCoA origins** if not performed meticulously.

Question 7: A 42-year-old woman presents with progressive cognitive decline, early-onset dementia, and recurrent subcortical strokes. Genetic testing reveals CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy). MR angiography shows no large vessel abnormalities but extensive white matter changes. Her sister, also affected, is considering pregnancy. Evaluate the counseling regarding Circle of Willis anatomy and implications for disease manifestations.

A. Pregnancy increases stroke risk regardless of Circle anatomy; recommend avoiding pregnancy
B. Complete Circle of Willis anatomy predicts milder phenotype due to better collateral flow
C. CADASIL primarily affects perforating arteries; Circle of Willis anatomy has minimal impact on phenotype (Correct Answer)
D. Incomplete Circle increases stroke risk; recommend prophylactic aspirin during pregnancy
E. Circle of Willis variants determine specific infarct patterns; genetic testing can predict locations

Explanation: ***CADASIL primarily affects perforating arteries; Circle of Willis anatomy has minimal impact on phenotype*** - **CADASIL** is caused by **NOTCH3 mutations** that lead to the accumulation of granular osmiophilic material in **small penetrating arteries** and arterioles. - Since the pathology involves **microvasculature** rather than large-caliber vessels, the macrostructure of the **Circle of Willis** does not provide effective collateral flow to the affected deep white matter areas. *Pregnancy increases stroke risk regardless of Circle anatomy; recommend avoiding pregnancy* - While CADASIL patients may have an increased risk of stroke or **migraines with aura** during the postpartum period, CADASIL is not an absolute contraindication to pregnancy. - Genetic counseling should focus on the **50% inheritance risk** (autosomal dominant) rather than suggesting the Circle of Willis anatomy dictates pregnancy outcomes. *Complete Circle of Willis anatomy predicts milder phenotype due to better collateral flow* - The **Circle of Willis** provides collateralization for **large vessel** occlusions; however, CADASIL is a **small vessel disease** where collateral circulation is limited at the capillary level. - Clinical phenotypic severity is more closely linked to **age**, **hypertension**, and the specific **NOTCH3 mutation** site rather than large vessel anatomy. *Incomplete Circle increases stroke risk; recommend prophylactic aspirin during pregnancy* - **Ischemic events** in CADASIL are due to intrinsic degenerative changes in the arterial wall (vasculopathy), not necessarily large-vessel flow dynamics influenced by the **Circle of Willis**. - There is limited evidence to support prophylactic **aspirin** specifically for pregnancy management in CADASIL based solely on vascular variants. *Circle of Willis variants determine specific infarct patterns; genetic testing can predict locations* - **Infarct patterns** in CADASIL are typically localized to the **periventricular white matter**, **basal ganglia**, and **thalamus**, irrespective of large vessel variants. - **Genetic testing** identifies the mutation but cannot accurately predict the exact anatomical location or timing of future **lacunar infarcts**.

Question 8: A 55-year-old man with diabetes and hypertension undergoes carotid endarterectomy for critical left internal carotid stenosis. Postoperatively, he develops right homonymous hemianopia without motor deficits. Intraoperative transcranial Doppler had shown reduced flow in the ipsilateral middle cerebral artery but preserved anterior cerebral artery flow. Analyze the most likely mechanism for this specific deficit pattern.

A. Embolic shower to left middle cerebral artery branches during manipulation
B. Inadequate collateral flow through anterior communicating artery during clamping
C. Watershed infarct between ACA and MCA territories
D. Hypoperfusion of posterior cerebral artery via inadequate posterior communicating artery (Correct Answer)
E. Occlusion of lenticulostriate arteries from perioperative hypotension

Explanation: ***Hypoperfusion of posterior cerebral artery via inadequate posterior communicating artery*** - **Right homonymous hemianopia** without motor deficits localization strongly points to the **left occipital lobe**, which is supplied by the **posterior cerebral artery (PCA)**. - During **carotid endarterectomy**, if the PCA is dependent on the internal carotid artery (ICA) via a dominant **posterior communicating artery (PCoA)**, clamping can lead to isolated visual field loss if collateral flow is insufficient. *Embolic shower to left middle cerebral artery branches during manipulation* - **Emboli** to the **middle cerebral artery (MCA)** typically result in cortical deficits like hemiparesis or aphasia, which are absent in this patient. - Transcranial Doppler noted reduced flow but not the micro-embolic signals characteristic of an **embolic shower**. *Inadequate collateral flow through anterior communicating artery during clamping* - The **anterior communicating artery (ACoA)** primarily supplies the **anterior cerebral artery (ACA)** territory, and flow there was documented as preserved. - Deficits here would typically manifest as **lower limb weakness** rather than a pure homonymous hemianopia. *Watershed infarct between ACA and MCA territories* - **Watershed infarcts** between these territories (the 'man-in-a-barrel' zone) cause **proximal limb weakness**, not isolated visual field defects. - The pattern would not explain a complete **homonymous hemianopia**, which requires damage to the optic radiation or **visual cortex**. *Occlusion of lenticulostriate arteries from perioperative hypotension* - **Lenticulostriate artery** occlusion results in a lacunar stroke of the **internal capsule**, causing dense motor deficits. - This patient specifically had **no motor deficits**, which excludes involvement of the deep perforating branches of the MCA.

Question 9: A 28-year-old woman presents with bilateral lower extremity weakness worse than upper extremity weakness, abulia, and urinary incontinence. MRI reveals bilateral anterior cerebral artery territory infarcts. Angiography shows an azygos anterior cerebral artery variant. Analyze the anatomical basis for this patient's bilateral deficits from a presumed single vascular occlusion.

A. Both A1 segments are hypoplastic with dominant left A2 segment
B. Single midline A2 segment supplies both hemispheres without ACoA (Correct Answer)
C. Bilateral A1 occlusions with isolated posterior circulation
D. ACoA aneurysm with mass effect on both A2 segments
E. Duplicate anterior communicating arteries with bilateral flow restriction

Explanation: ***Single midline A2 segment supplies both hemispheres without ACoA*** - An **azygos anterior cerebral artery (ACA)** is a rare anatomical variant where both A1 segments merge to form a **single midline A2 trunk**, which then supplies the medial aspects of both cerebral hemispheres. - A single embolic or thrombotic occlusion in this **common trunk** results in bilateral infarction, explaining the patient's **bilateral lower extremity weakness**, **abulia**, and **urinary incontinence**. *Both A1 segments are hypoplastic with dominant left A2 segment* - Hypoplasia of both A1 segments would likely lead to recruitment of blood from the **posterior circulation** via the **posterior communicating arteries** rather than a single infarct resulting in bilateral deficits. - A dominant A2 segment usually implies an **unpaired artery of Wilder**, but the classic "azygos" description specifically refers to a **midline shared vessel**. *Bilateral A1 occlusions with isolated posterior circulation* - Simultaneously occurring **bilateral A1 occlusions** are extremely rare and do not represent a single vascular variant as described by the angiography. - This scenario would likely present with more profound global ischemia rather than the specific **azygos ACA** distribution mentioned. *ACoA aneurysm with mass effect on both A2 segments* - While an **anterior communicating artery (ACoA)** aneurysm can cause focal deficits, it typically presents with **subarachnoid hemorrhage** or cranial nerve palsies rather than sudden-onset ischemic infarcts in a specific vascular territory. - Mass effect is a chronic or subacute presentation and does not explain the **angiographic appearance** of an azygos segment. *Duplicate anterior communicating arteries with bilateral flow restriction* - **Duplicate ACoAs** are relatively common variants but would provide **redundant collateral flow**, potentially protecting the brain from bilateral infarction rather than causing it. - Bilateral flow restriction across two separate arteries simultaneously is not a likely outcome of a **single vascular occlusion** event.

Question 10: A 65-year-old woman with hypertension develops sudden vertigo, dysphagia, and loss of pain and temperature sensation on the left face and right body. MRI shows a left lateral medullary infarct. Analysis of her vascular anatomy reveals an incomplete Circle of Willis. Which specific arterial segment occlusion best explains this clinical presentation?

A. Left anterior inferior cerebellar artery
B. Left posterior inferior cerebellar artery (Correct Answer)
C. Left superior cerebellar artery
D. Basilar artery perforators
E. Left anterior spinal artery

Explanation: ***Left posterior inferior cerebellar artery*** - Occlusion of the **PICA** (or vertebral artery) causes **Wallenberg syndrome** (lateral medullary syndrome), which matches the patient's presentation of dysphagia, vertigo, and sensory deficits. - It specifically affects the **nucleus ambiguus** (dysphagia/hoarseness), **vestibular nuclei** (vertigo/nystagmus), and the **spinothalamic tract** (contralateral body sensory loss). *Left anterior inferior cerebellar artery* - **AICA** occlusion causes **lateral pontine syndrome**, which typically includes **ipsilateral facial paralysis** and hearing loss (involvement of CN VII and VIII). - While it can cause vertigo, it does not typically cause the **dysphagia** associated with medullary nucleus ambiguus damage. *Left superior cerebellar artery* - Occlusion of the **SCA** generally leads to **ipsilateral cerebellar ataxia**, nausea, and vomiting without the specific brainstem cranial nerve deficits seen in medullary strokes. - It supplies the **upper pons and cerebellum**, meaning lower brainstem signs like dysphagia and lateral medullary sensory patterns are absent. *Basilar artery perforators* - These vessels primarily supply the **medial pons**, and their occlusion results in **medial pontine syndrome**. - This manifests with **contralateral hemiparesis** and potential gaze palsies, rather than the lateral sensory and lower cranial nerve symptoms identified here. *Left anterior spinal artery* - Occlusion of the **ASA** leads to **medial medullary syndrome**, characterized by **contralateral hemiparesis** and ipsilateral tongue deviation. - It does not cause the lateral medullary features such as **crossed sensory loss** or dysphagia seen in this patient.

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