Vascular supply (Circle of Willis) — MCQs

Q: 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?

Left posterior inferior cerebellar artery. ***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.

Q: A 34-year-old woman presents with thunderclap headache and is found to have subarachnoid hemorrhage. Angiography reveals an anterior communicating artery aneurysm. During surgical clipping, the surgeon must be most cautious about preserving which small perforating vessels that arise from this region?

Recurrent artery of Heubner. ***Recurrent artery of Heubner*** - This vessel, also known as the **medial striate artery**, typically arises from the distal **A1 or proximal A2 segment** of the anterior cerebral artery, very close to the **anterior communicating artery (ACoA)**. - It supplies critical structures including the **caudate nucleus head**, **anterior limb of the internal capsule**, and putamen; injury during clipping can lead to **contralateral hemiparesis** and cognitive deficits. *Thalamoperforating arteries* - These small vessels primarily arise from the **P1 segment** of the **posterior cerebral artery** and the posterior communicating artery. - They supply the **thalamus** and midbrain, areas distal to the location of an **ACoA aneurysm**. *Anterior choroidal artery* - This artery usually branches directly from the **internal carotid artery (ICA)** before it bifurcates into the MCA and ACA. - It supplies the **optic tract**, posterior limb of the internal capsule, and the **choroid plexus**, making it distinct from the ACoA region. *Medullary perforating arteries* - These vessels arise from the **basilar artery** or **vertebral arteries** to supply the brainstem (medulla). - They are located in the **posterior circulation** and are not at risk during surgery for an anterior communicating artery aneurysm. *Lenticulostriate arteries* - These are lateral striate arteries that characteristically arise from the **M1 segment** of the **middle cerebral artery (MCA)**. - They supply the **basal ganglia** and internal capsule but are located more laterally than the medial striate branches involved in ACoA surgery.

Q: A 45-year-old man undergoes cerebral angiography that reveals hypoplasia of the right posterior communicating artery. During the procedure, the left vertebral artery is inadvertently occluded. Which vascular territory is most at risk for ischemia given this anatomical variant?

Right occipital lobe and thalamus. ***Right occipital lobe and thalamus*** - The right **Posterior Cerebral Artery (PCA)** typically supplies the **occipital lobe** and **thalamus**; with a hypoplastic **right posterior communicating artery (PCoA)**, this region cannot receive collateral flow from the anterior circulation. - Occlusion of a vertebral artery compromises the **vertebrobasilar system**, leaving the right PCA territory ischemic as it lacks a compensatory connection to the **internal carotid artery**. *Left frontal lobe* - The **frontal lobe** is primarily supplied by the **Anterior Cerebral Artery (ACA)** and **Middle Cerebral Artery (MCA)** from the anterior circulation. - Since the anterior circulation is fed by the **carotid arteries**, it is not directly threatened by an occlusion in the **vertebrobasilar system**. *Right temporal lobe* - While the **medial temporal lobe** is supplied by the PCA, the right **PCoA hypoplasia** specifically isolates the whole PCA territory from the carotid supply. - However, the lateral temporal lobe is predominantly supplied by the **Middle Cerebral Artery (MCA)**, which remains patent via the right carotid system. *Bilateral basal ganglia* - The **basal ganglia** are primarily supplied by **lenticulostriate arteries** arising from the **Middle Cerebral Artery (MCA)**. - These vessels are part of the **anterior circulation** and would not be the primary site of ischemia following a vertebral artery occlusion. *Left cerebellar hemisphere* - The cerebellum is supplied by the **PICA**, **AICA**, and **SCA**, which originate from the vertebral and **basilar arteries**. - While the left side might see reduced flow, the **contralateral (right) vertebral artery** usually provides sufficient collateral flow to the brainstem and cerebellum compared to the distal PCA territory isolated by a hypoplastic PCoA.

Q: A 58-year-old woman presents to the emergency department with sudden onset of severe headache, vomiting, and loss of consciousness. CT angiography reveals a saccular aneurysm at the junction of the posterior communicating artery and internal carotid artery. Which nerve structure is most likely to be compressed by this aneurysm if it expands?

Oculomotor nerve (CN III). ***Oculomotor nerve (CN III)*** - The **oculomotor nerve** passes directly lateral to the junction of the **internal carotid artery** and the **posterior communicating artery**, making it highly susceptible to compression by aneurysms in this region. - Compression typically leads to **ipsilateral pupil dilation** (mydriasis) due to parasympathetic fiber involvement, followed by **ptosis** and a **"down and out"** eye position. *Trigeminal nerve (CN V1)* - The **ophthalmic division (V1)** of the trigeminal nerve is located within the **cavernous sinus**, but it is inferior to the typical site of a **PCoA aneurysm**. - Compression would result in **sensory loss** over the forehead or loss of the **corneal reflex**, rather than the oculomotor deficits described. *Optic nerve (CN II)* - **CN II** is located more medially and anteriorly to the PCoA-ICA junction, near the **optic chiasm**. - It is more commonly compressed by aneurysms of the **anterior communicating artery** or large ophthalmic artery aneurysms, leading to **visual field defects**. *Trochlear nerve (CN IV)* - **CN IV** has a long intracranial course but is situated further from the PCoA-ICA junction compared to **CN III**. - It is rarely the primary nerve affected by PCoA aneurysms; its dysfunction would cause **vertical diplopia** and difficulty looking down and in. *Abducens nerve (CN VI)* - **CN VI** runs more medially and inferiorly within the **cavernous sinus**, adjacent to the **cavernous portion** of the internal carotid artery. - It is more likely to be affected by **cavernous sinus thrombosis** or aneurysms involving the **intracavernous ICA**, causing inability to abduct the eye.

Vascular supply (Circle of Willis) — MCQs

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.

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 34-year-old woman presents with thunderclap headache and is found to have subarachnoid hemorrhage. Angiography reveals an anterior communicating artery aneurysm. During surgical clipping, the surgeon must be most cautious about preserving which small perforating vessels that arise from this region?

A 45-year-old man undergoes cerebral angiography that reveals hypoplasia of the right posterior communicating artery. During the procedure, the left vertebral artery is inadvertently occluded. Which vascular territory is most at risk for ischemia given this anatomical variant?

A 72-year-old man with atrial fibrillation presents with sudden onset right-sided weakness and aphasia. MRI reveals an acute infarct in the left middle cerebral artery territory. Given the Circle of Willis anatomy, which collateral pathway would most likely provide blood flow to the affected territory if the left internal carotid artery were severely stenotic?

Q10

A 58-year-old woman presents to the emergency department with sudden onset of severe headache, vomiting, and loss of consciousness. CT angiography reveals a saccular aneurysm at the junction of the posterior communicating artery and internal carotid artery. Which nerve structure is most likely to be compressed by this aneurysm if it expands?

Vascular supply (Circle of Willis) US Medical PG Practice Questions and MCQs

Question 1: 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 2: 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 3: 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 4: 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 5: 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 6: 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.

Question 7: A 34-year-old woman presents with thunderclap headache and is found to have subarachnoid hemorrhage. Angiography reveals an anterior communicating artery aneurysm. During surgical clipping, the surgeon must be most cautious about preserving which small perforating vessels that arise from this region?

A. Thalamoperforating arteries
B. Anterior choroidal artery
C. Medullary perforating arteries
D. Lenticulostriate arteries
E. Recurrent artery of Heubner (Correct Answer)

Explanation: ***Recurrent artery of Heubner*** - This vessel, also known as the **medial striate artery**, typically arises from the distal **A1 or proximal A2 segment** of the anterior cerebral artery, very close to the **anterior communicating artery (ACoA)**. - It supplies critical structures including the **caudate nucleus head**, **anterior limb of the internal capsule**, and putamen; injury during clipping can lead to **contralateral hemiparesis** and cognitive deficits. *Thalamoperforating arteries* - These small vessels primarily arise from the **P1 segment** of the **posterior cerebral artery** and the posterior communicating artery. - They supply the **thalamus** and midbrain, areas distal to the location of an **ACoA aneurysm**. *Anterior choroidal artery* - This artery usually branches directly from the **internal carotid artery (ICA)** before it bifurcates into the MCA and ACA. - It supplies the **optic tract**, posterior limb of the internal capsule, and the **choroid plexus**, making it distinct from the ACoA region. *Medullary perforating arteries* - These vessels arise from the **basilar artery** or **vertebral arteries** to supply the brainstem (medulla). - They are located in the **posterior circulation** and are not at risk during surgery for an anterior communicating artery aneurysm. *Lenticulostriate arteries* - These are lateral striate arteries that characteristically arise from the **M1 segment** of the **middle cerebral artery (MCA)**. - They supply the **basal ganglia** and internal capsule but are located more laterally than the medial striate branches involved in ACoA surgery.

Question 8: A 45-year-old man undergoes cerebral angiography that reveals hypoplasia of the right posterior communicating artery. During the procedure, the left vertebral artery is inadvertently occluded. Which vascular territory is most at risk for ischemia given this anatomical variant?

A. Left frontal lobe
B. Right temporal lobe
C. Bilateral basal ganglia
D. Left cerebellar hemisphere
E. Right occipital lobe and thalamus (Correct Answer)

Explanation: ***Right occipital lobe and thalamus*** - The right **Posterior Cerebral Artery (PCA)** typically supplies the **occipital lobe** and **thalamus**; with a hypoplastic **right posterior communicating artery (PCoA)**, this region cannot receive collateral flow from the anterior circulation. - Occlusion of a vertebral artery compromises the **vertebrobasilar system**, leaving the right PCA territory ischemic as it lacks a compensatory connection to the **internal carotid artery**. *Left frontal lobe* - The **frontal lobe** is primarily supplied by the **Anterior Cerebral Artery (ACA)** and **Middle Cerebral Artery (MCA)** from the anterior circulation. - Since the anterior circulation is fed by the **carotid arteries**, it is not directly threatened by an occlusion in the **vertebrobasilar system**. *Right temporal lobe* - While the **medial temporal lobe** is supplied by the PCA, the right **PCoA hypoplasia** specifically isolates the whole PCA territory from the carotid supply. - However, the lateral temporal lobe is predominantly supplied by the **Middle Cerebral Artery (MCA)**, which remains patent via the right carotid system. *Bilateral basal ganglia* - The **basal ganglia** are primarily supplied by **lenticulostriate arteries** arising from the **Middle Cerebral Artery (MCA)**. - These vessels are part of the **anterior circulation** and would not be the primary site of ischemia following a vertebral artery occlusion. *Left cerebellar hemisphere* - The cerebellum is supplied by the **PICA**, **AICA**, and **SCA**, which originate from the vertebral and **basilar arteries**. - While the left side might see reduced flow, the **contralateral (right) vertebral artery** usually provides sufficient collateral flow to the brainstem and cerebellum compared to the distal PCA territory isolated by a hypoplastic PCoA.

Question 9: A 72-year-old man with atrial fibrillation presents with sudden onset right-sided weakness and aphasia. MRI reveals an acute infarct in the left middle cerebral artery territory. Given the Circle of Willis anatomy, which collateral pathway would most likely provide blood flow to the affected territory if the left internal carotid artery were severely stenotic?

A. Basilar artery via superior cerebellar arteries
B. Right internal carotid artery via anterior communicating artery (Correct Answer)
C. Vertebral arteries via posterior inferior cerebellar arteries
D. External carotid artery via ophthalmic artery anastomoses
E. Right middle cerebral artery via leptomeningeal collaterals

Explanation: ***Right internal carotid artery via anterior communicating artery*** - The **anterior communicating artery (ACoA)** facilitates cross-flow between the right and left internal carotid artery (ICA) systems, serving as the primary **anterior collateral** pathway. - In the event of left ICA compromise, blood enters the left circulation from the right ICA through the **right anterior cerebral artery (ACA)** and crosses the ACoA to reach the left ACA and **middle cerebral artery (MCA)**. *Basilar artery via superior cerebellar arteries* - The **superior cerebellar arteries** are terminal branches of the basilar artery that supply the cerebellum and midbrain, not the cerebral hemispheres. - Collateral flow from the posterior to anterior circulation typically occurs through the **posterior communicating arteries (PCoA)**, not the cerebellar branches. *Vertebral arteries via posterior inferior cerebellar arteries* - The **posterior inferior cerebellar artery (PICA)** is a branch of the vertebral artery that supplies the medulla and inferior cerebellum. - These vessels are part of the **posterior circulation** and do not have a direct anatomical connection to provide significant collateral flow to the MCA territory. *External carotid artery via ophthalmic artery anastomoses* - This represents a secondary collateral pathway where the **external carotid artery (ECA)** provides retrograde flow to the ICA via the **ophthalmic artery**. - While clinically significant, it is typically less efficient and slower to recruit than the primary **Circle of Willis** pathways like the ACoA. *Right middle cerebral artery via leptomeningeal collaterals* - **Leptomeningeal collaterals** (pial synangiosis) are small distal anastomoses between major cerebral arteries on the brain surface. - While they can provide localized flow during ischemia, they connect adjacent territories within the same hemisphere or distal branches, rather than bridging major arterial systems as effectively as the **Circle of Willis**.

Question 10: A 58-year-old woman presents to the emergency department with sudden onset of severe headache, vomiting, and loss of consciousness. CT angiography reveals a saccular aneurysm at the junction of the posterior communicating artery and internal carotid artery. Which nerve structure is most likely to be compressed by this aneurysm if it expands?

A. Trigeminal nerve (CN V1)
B. Optic nerve (CN II)
C. Oculomotor nerve (CN III) (Correct Answer)
D. Trochlear nerve (CN IV)
E. Abducens nerve (CN VI)

Explanation: ***Oculomotor nerve (CN III)*** - The **oculomotor nerve** passes directly lateral to the junction of the **internal carotid artery** and the **posterior communicating artery**, making it highly susceptible to compression by aneurysms in this region. - Compression typically leads to **ipsilateral pupil dilation** (mydriasis) due to parasympathetic fiber involvement, followed by **ptosis** and a **"down and out"** eye position. *Trigeminal nerve (CN V1)* - The **ophthalmic division (V1)** of the trigeminal nerve is located within the **cavernous sinus**, but it is inferior to the typical site of a **PCoA aneurysm**. - Compression would result in **sensory loss** over the forehead or loss of the **corneal reflex**, rather than the oculomotor deficits described. *Optic nerve (CN II)* - **CN II** is located more medially and anteriorly to the PCoA-ICA junction, near the **optic chiasm**. - It is more commonly compressed by aneurysms of the **anterior communicating artery** or large ophthalmic artery aneurysms, leading to **visual field defects**. *Trochlear nerve (CN IV)* - **CN IV** has a long intracranial course but is situated further from the PCoA-ICA junction compared to **CN III**. - It is rarely the primary nerve affected by PCoA aneurysms; its dysfunction would cause **vertical diplopia** and difficulty looking down and in. *Abducens nerve (CN VI)* - **CN VI** runs more medially and inferiorly within the **cavernous sinus**, adjacent to the **cavernous portion** of the internal carotid artery. - It is more likely to be affected by **cavernous sinus thrombosis** or aneurysms involving the **intracavernous ICA**, causing inability to abduct the eye.

Question 11: A 36-year-old woman, gravida 1, para 1, has back pain and numbness in her lower extremities after an emergency cesarean delivery of a healthy 3856-g (8-lb, 8-oz) newborn male. She had a placental abruption and lost approximately 2000 ml of blood. During the procedure, she received two units of packed red blood cells and intravenous fluids. She has no history of serious illness and takes no medications. She is sexually active with one male partner, and they use condoms inconsistently. She is alert and oriented to person, place, and time. Her temperature is 37.2°C (98.9°F), pulse is 90/min, respirations are 15/min, and blood pressure is 94/58 mm Hg. Examination shows decreased sensation to temperature and pinprick below her waist and 0/5 muscle strength in her lower extremities. She feels the vibrations of a tuning fork placed on both of her great toes. Deep tendon reflexes are absent in the lower extremities and 2+ in the upper extremities. Which of the following is the most likely diagnosis?

A. Posterior spinal artery syndrome
B. Brown-Séquard syndrome
C. Anterior spinal artery syndrome (Correct Answer)
D. Guillain-Barré Syndrome
E. Tabes dorsalis

Explanation: ***Anterior spinal artery syndrome*** - This syndrome is characterized by the sudden onset of **bilateral motor paralysis** below the level of the lesion, accompanied by a dissociated sensory loss (**loss of pain and temperature sensation**) while **proprioception and vibratory sensation are preserved**. - The patient's history of **significant blood loss** and hypotension during delivery makes her susceptible to spinal cord ischemia, particularly in the anterior spinal artery territory, which supplies the anterior two-thirds of the spinal cord. *Posterior spinal artery syndrome* - This syndrome primarily affects the **dorsal columns**, leading to a loss of **proprioception and vibratory sensation**, with preservation of motor function and pain/temperature sensation. - The patient's preserved vibratory sensation and significant motor deficits rule out posterior spinal artery syndrome. *Brown-Séquard syndrome* - This syndrome results from **hemitransverse lesion of the spinal cord**, causing **ipsilateral motor paralysis** and loss of proprioception/vibration below the lesion, and **contralateral loss of pain and temperature sensation**. - The patient's **bilateral motor and sensory deficits** are inconsistent with the unilateral presentation of Brown-Séquard syndrome. *Guillain-Barré Syndrome* - GBS typically presents as an **ascending paralysis** with **areflexia**, but sensory loss is usually stocking-glove distribution and often involves proprioception, and it is a **peripheral neuropathy** not a spinal cord infarction. - The acute, localized nature of the sensory and motor loss below the waist, along with preserved vibratory sensation, differentiates it from the more diffuse presentation of GBS. *Tabes dorsalis* - This is a late manifestation of **syphilis** affecting the **dorsal columns** and dorsal roots, characterized by ataxia, lancinating pains, and loss of proprioception and vibration sense. - The acute onset of symptoms following a hypotensive episode, along with motor paralysis and preserved vibratory sensation, does not fit the chronic, dorsal column pathology of tabes dorsalis.

Question 12: A 61-year-old man is brought to the emergency room with slurred speech. According to the patient's wife, they were watching a movie together when he developed a minor headache. He soon developed difficulty speaking in complete sentences, at which point she decided to take him to the emergency room. His past medical history is notable for hypertension and hyperlipidemia. He takes aspirin, lisinopril, rosuvastatin. The patient is a retired lawyer. He has a 25-pack-year smoking history and drinks 4-5 beers per day. His father died of a myocardial infarction, and his mother died of breast cancer. His temperature is 98.6°F (37°C), blood pressure is 143/81 mmHg, pulse is 88/min, and respirations are 21/min. On exam, he can understand everything that is being said to him and is able to repeat statements without difficulty. However, when asked to speak freely, he hesitates with every word and takes 30 seconds to finish a short sentence. This patient most likely has an infarct in which of the following vascular distributions?

A. Proximal middle cerebral artery
B. Inferior division of the middle cerebral artery
C. Middle cerebral artery and posterior cerebral artery watershed area
D. Superior division of the middle cerebral artery (Correct Answer)
E. Anterior cerebral artery and middle cerebral artery watershed area

Explanation: ***Superior division of the middle cerebral artery*** - The patient's inability to speak spontaneously coupled with intact comprehension and repetition is characteristic of **Broca's aphasia**, which results from damage to **Broca's area** in the dominant frontal lobe. - Broca's area is supplied by the **superior division of the middle cerebral artery (MCA)**. *Proximal middle cerebral artery* - An infarct in the proximal MCA, or the main stem, would typically lead to global aphasia if the dominant hemisphere is affected, characterized by **severe deficits in comprehension, repetition, and speech production**. - This presentation does not align with the patient's ability to understand and repeat statements. *Inferior division of the middle cerebral artery* - The inferior division of the MCA supplies Wernicke's area in the dominant hemisphere. - Damage here causes **Wernicke's aphasia**, characterized by **fluent but nonsensical speech** with **impaired comprehension** and **repetition**, which is contrary to the patient's symptoms. *Middle cerebral artery and posterior cerebral artery watershed area* - Watershed infarcts, especially between the MCA and posterior cerebral artery (PCA), can cause **transcortical sensory aphasia** if in the dominant hemisphere. - This type of aphasia involves impaired comprehension but **intact repetition**, which differs from Broca's aphasia where spontaneous speech is the main deficit. *Anterior cerebral artery and middle cerebral artery watershed area* - Infarcts in the watershed area between the anterior cerebral artery (ACA) and MCA can result in **transcortical motor aphasia** if in the dominant hemisphere. - This condition presents with **non-fluent speech** and **intact repetition**, similar to Broca's aphasia, but Broca's area itself is located specifically within the MCA superior division territory.

Question 13: A 78-year-old left-handed woman with hypertension and hyperlipidemia is brought to the emergency room because of sudden-onset right leg weakness and urinary incontinence. Neurologic examination shows decreased sensation over the right thigh. Muscle strength is 2/5 in the right lower extremity and 4/5 in the right upper extremity. Strength and sensation in the face are normal but she has difficulty initiating sentences and she is unable to write her name. The most likely cause of this patient’s condition is an occlusion of which of the following vessels?

A. Right vertebrobasilar artery
B. Right middle cerebral artery
C. Left posterior cerebral artery
D. Left anterior cerebral artery (Correct Answer)
E. Right anterior cerebral artery

Explanation: ***Left anterior cerebral artery*** - Stroke in the **left anterior cerebral artery (ACA)** territory typically causes **contralateral leg weakness** (right leg in this case) and **urinary incontinence** due to involvement of the paracentral lobule. - The patient's difficulty writing her name (agraphia) and initiating sentences (transcortical motor aphasia, which can manifest as difficulty initiating speech) is consistent with damage to the supplemental motor area in the dominant (left) hemisphere, provided by the ACA. *Right vertebrobasilar artery* - Occlusion of the vertebrobasilar artery typically presents with a wide range of symptoms including **vertigo**, **ataxia**, **dysarthria**, and bilateral or alternating sensory/motor deficits. - It would not selectively cause isolated right leg weakness, urinary incontinence, and dominant hemisphere language difficulties without other brainstem or cerebellar signs. *Right middle cerebral artery* - A stroke in the **right middle cerebral artery (MCA)** would cause **left-sided deficit**, not right-sided. - Although it can cause motor and sensory deficits, it typically affects the arm and face more than the leg, and would not cause the specific language deficits of the dominant hemisphere seen here. *Left posterior cerebral artery* - Occlusion of the **left posterior cerebral artery (PCA)** typically leads to issues like **contralateral homonymous hemianopia**, visual field defects, and potentially memory impairment or alexia without agraphia if the splenium of the corpus callosum is involved. - It directly affects posterior brain regions, so it would not cause the anterior cerebral artery specific symptoms such as prominent contralateral leg weakness, urinary incontinence, or the described language difficulties. *Right anterior cerebral artery* - Occlusion of the **right anterior cerebral artery (ACA)** would cause **left leg weakness** and **left-sided sensory deficits**, not the right-sided deficits observed in this patient. - While it could cause urinary incontinence, the combination of right-sided weakness and dominant hemisphere language deficits points against a right ACA occlusion.

Question 14: A 65-year-old male presents to the emergency room complaining of a severe headache. He developed a sudden-onset severe throbbing headache while watching a football game on television. His past medical history is significant for migraines and hypertension; however, he states that this headache is different from his normal migraine headaches. He has a 30 pack-year smoking history. His family history is notable for stroke in his mother and father. His temperature is 98.9°F (37.2°C), blood pressure is 150/90 mmHg, pulse is 100/min, and respirations are 14/min. On examination, he is oriented to person, place, and time. Neck motion is limited due to pain. Strength is 5/5 bilaterally in both the upper and the lower extremities and sensation is grossly intact across all the dermatomal distributions. Patellar, brachioradialis, and Achilles reflexes are 2+ bilaterally. The vessel that is most commonly involved in this patient's likely condition directly branches off which of the following vessels?

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

Explanation: ***Internal carotid artery*** - The patient's presentation with a **sudden-onset, severe "thunderclap" headache**, cervical pain, and normal neurologic examination, particularly in the context of **hypertension and smoking history**, is highly suggestive of a **subarachnoid hemorrhage (SAH)**. SAH is most commonly caused by rupture of a **saccular (berry) aneurysm**. - Approximately 85% of SAHs result from the rupture of an aneurysm in the **anterior circulation**. The most common site for these aneurysms is the **anterior communicating artery**, which directly branches off the **anterior cerebral artery**. However, the **anterior cerebral artery (ACA)**, the **middle cerebral artery (MCA)**, and the **posterior communicating artery (PCoA)** (which is commonly involved in berry aneurysms) all originate directly or indirectly, through the ACA, from the **internal carotid artery (ICA)**. Therefore, the ICA is the most encompassing and correct option from which the most common aneurysm sites ultimately branch. *Middle cerebral artery* - While the **middle cerebral artery (MCA)** is a common location for aneurysms, particularly at its bifurcation, it is generally less common than the anterior communicating artery or the posterior communicating artery. - Aneurysms of the MCA are also branches of the internal carotid artery. *Maxillary artery* - The **maxillary artery** is primarily involved in supplying blood to structures in the deep face, maxilla, and mandible. - It is not a significant location for intracranial berry aneurysms that lead to subarachnoid hemorrhage. *Anterior cerebral artery* - While the **anterior cerebral artery (ACA)** itself can be a site for aneurysms, particularly the **anterior communicating artery** (AComA) which connects the two ACAs, it is a branch off the internal carotid artery. - The AComA is the single most common site for berry aneurysms; however, the question asks for the vessel from which the commonly involved vessel *directly branches off*. The ACA itself directly branches off the ICA. *Posterior cerebral artery* - The **posterior cerebral artery (PCA)** is part of the posterior circulation, originating from the basilar artery. - Aneurysms in the posterior circulation (vertebrobasilar system) are less common causes of SAH than those in the anterior circulation.

Question 15: A 55-year-old man comes to the emergency department because of left-sided chest pain and difficulty breathing for the past 30 minutes. His pulse is 88/min. He is pale and anxious. Serum studies show increased cardiac enzymes. An ECG shows ST-elevations in leads I, aVL, and V5-V6. A percutaneous coronary intervention is performed. In order to localize the site of the lesion, the catheter must pass through which of the following structures?

A. Left coronary artery → left circumflex artery (Correct Answer)
B. Right coronary artery → posterior descending artery
C. Left coronary artery → left anterior descending artery
D. Right coronary artery → right marginal artery
E. Left coronary artery → posterior descending artery

Explanation: ***Left coronary artery → left circumflex artery*** - **ST-elevations** in leads I, aVL, and V5-V6 are indicative of a **lateral myocardial infarction**. - The **left circumflex artery** primarily supplies the lateral wall of the left ventricle. *Right coronary artery → posterior descending artery* - The **posterior descending artery** (PDA) typically supplies the inferior wall and posterior interventricular septum. - An occlusion here would cause **ST-elevations** in leads II, III, and aVF, which is not seen in this case. *Left coronary artery → left anterior descending artery* - The **left anterior descending** (LAD) artery supplies the anterior wall and apex of the left ventricle. - Occlusion of the LAD would typically cause **ST-elevations** in leads V1-V4, indicating an anterior MI. *Right coronary artery → right marginal artery* - The **right marginal artery** is a branch of the right coronary artery and supplies part of the right ventricle. - Occlusion here would primarily affect the **right ventricle**, and is not typically associated with the given ECG changes. *Left coronary artery → posterior descending artery* - While the **posterior descending artery** can sometimes originate from the left circumflex artery (**left dominant circulation**), it primarily supplies the inferior wall. - The observed ECG changes in leads I, aVL, and V5-V6 are characteristic of a **lateral wall infarct**, which is supplied by the left circumflex artery.

Practice by Chapter

Internal carotid artery anatomy

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Vertebrobasilar system

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Anterior cerebral artery territory

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Middle cerebral artery territory

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Posterior cerebral artery territory

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Communicating arteries

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Variations in circle of Willis

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Venous drainage of brain

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Stroke syndromes by vascular territory

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Collateral circulation

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