A 42-year-old woman presents to her primary care provider with vision loss. She reports that twice over the last 2 weeks she has had sudden “black out” of the vision in her right eye. She notes that both episodes were painless and self-resolved over approximately a minute. The patient’s past medical history is significant for hypertension, diet-controlled diabetes mellitus, and hypothyroidism. Her family history is notable for coronary artery disease in the patient’s father and multiple sclerosis in her mother. Ophthalmologic and neurologic exam is unremarkable. Which of the following is the best next step in management?
Q2
A 60-year-old male is admitted to the ICU for severe hypertension complicated by a headache. The patient has a past medical history of insulin-controlled diabetes, hypertension, and hyperlipidemia. He smokes 2 packs of cigarettes per day. He states that he forgot to take his medications yesterday and started getting a headache about one hour ago. His vitals on admission are the following: blood pressure of 160/110 mmHg, pulse 95/min, temperature 98.6 deg F (37.2 deg C), and respirations 20/min. On exam, the patient has an audible abdominal bruit. After administration of antihypertensive medications, the patient has a blood pressure of 178/120 mmHg. The patient reports his headache has increased to a 10/10 pain level, that he has trouble seeing, and he can't move his extremities. After stabilizing the patient, what is the best next step to diagnose the patient's condition?
Q3
A 50-year-old man presents to his primary care provider complaining of double vision and trouble seeing out of his right eye. His vision started worsening about 2 months ago and has slowly gotten worse. It is now severely affecting his quality of life. Past medical history is significant for poorly controlled hypertension and hyperlipidemia. He takes amlodipine, atorvastatin, and a baby aspirin every day. He smokes 2–3 cigarettes a day and drinks a glass of wine with dinner every night. Today, his blood pressure is 145/85 mm Hg, heart rate is 90/min, respiratory rate is 14/min, and temperature is 37.0°C (98.6°F). On physical exam, he appears pleasant and talkative. His heart has a regular rate and rhythm and his lungs are clear to auscultation bilaterally. Examination of the eyes reveals a dilated right pupil that is positioned inferolateral with ptosis. An angiogram of the head and neck is performed and he is referred to a neurologist. The angiogram reveals a 1 cm berry aneurysm at the junction of the posterior communicating artery and the posterior cerebral artery compressing the oculomotor nerve. Which of the following statements best describes the mechanism behind the oculomotor findings seen in this patient?
Q4
Where does the only cranial nerve without a thalamic relay nucleus enter the skull?
Q5
A 75-year-old man is brought to the emergency room after being found unresponsive in his home. His medical history is unknown. On physical examination he does not demonstrate any spontaneous movement of his extremities and is unable to respond to voice or painful stimuli. You notice that he is able blink and move his eyes in the vertical plane. Based on these physical exam findings, you expect that magnetic resonance angiogram will most likely reveal an occlusion in which of the following vessels?
Q6
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?
Q7
An 80-year-old woman is brought to the emergency department for left hip pain 30 minutes after she fell while walking around in her room. Examination shows left groin tenderness. The range of motion of the left hip is limited because of pain. An x-ray of the hip shows a linear fracture of the left femoral neck with slight posterior displacement of the femur. Which of the following arteries was most likely damaged in the patient's fall?
Q8
A 71-year-old woman presents to the emergency department with a headache for the past 30 minutes. She says that this is the worst headache of her life and that it came on suddenly after she hit her head. She says that she has also been experiencing visual problems with double vision when she looks to the left or the right. Visual examination reveals that her right eye cannot move right past the midline and her left eye cannot move left past the midline. Which of the following is most likely responsible for this patient's visual defects?
Q9
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?
Q10
A 26-year-old man is brought to the emergency department by ambulance after being involved in a motor vehicle collision. He does not open his eyes on command or respond to verbal cues. A CT scan of the head shows a hyperdense fluid collection in the right medial temporal lobe with medial displacement of the uncus and parahippocampal gyrus of the temporal lobe. Which of the following cranial nerves is most likely to be injured as a result of this patient's lesion?
Internal carotid artery anatomy US Medical PG Practice Questions and MCQs
Question 1: A 42-year-old woman presents to her primary care provider with vision loss. She reports that twice over the last 2 weeks she has had sudden “black out” of the vision in her right eye. She notes that both episodes were painless and self-resolved over approximately a minute. The patient’s past medical history is significant for hypertension, diet-controlled diabetes mellitus, and hypothyroidism. Her family history is notable for coronary artery disease in the patient’s father and multiple sclerosis in her mother. Ophthalmologic and neurologic exam is unremarkable. Which of the following is the best next step in management?
A. Intravenous dexamethasone
B. Emergent referral to ophthalmology
C. Ultrasound of the carotid arteries (Correct Answer)
D. Check serum inflammatory markers
E. MRI of the brain
Explanation: **Ultrasound of the carotid arteries**
- The patient's symptoms of **transient monocular vision loss** ("black out" vision in one eye that self-resolved) are highly suggestive of **amaurosis fugax**.
- Amaurosis fugax is often caused by **atheroembolic disease** originating from the ipsilateral carotid artery, making carotid ultrasound the best next step to assess for **carotid stenosis**.
*Intravenous dexamethasone*
- This treatment is typically used for **acute inflammation** or **autoimmune conditions**, such as optic neuritis related to multiple sclerosis, which is less likely given the painless, transient, and self-resolving nature of the vision loss.
- While the mother has multiple sclerosis, the daughter's symptoms do not align with a typical demyelinating event, and the primary concern is underlying vascular pathology.
*Emergent referral to ophthalmology*
- While an ophthalmology consult may eventually be warranted, the immediate concern is to identify the **underlying systemic cause** of the **embolic event** to prevent future, more severe cerebrovascular events like a stroke.
- The vision loss in amaurosis fugax is usually a symptom of a more serious **systemic vascular problem** originating proximal to the eye.
*Check serum inflammatory markers*
- Inflammatory markers (e.g., ESR, CRP) would be elevated in conditions like **temporal arteritis**, but the patient's vision loss is painless and self-resolving, which is inconsistent with the typical presentation of temporal arteritis.
- Furthermore, temporal arteritis usually presents in older patients (>50 years old), and would cause more persistent vision loss, often accompanied by tenderness over the temporal artery and jaw claudication.
*MRI of the brain*
- An MRI of the brain would be appropriate if there were concerns for a **stroke** or **demyelinating disease** affecting the optic pathways or brain, but the transient monocular vision loss points to an issue with the retinal circulation, not necessarily the brain.
- While a stroke is a concern, the acute vision loss is more indicative of a **retinal event**, which originates from a more proximal arterial source.
Question 2: A 60-year-old male is admitted to the ICU for severe hypertension complicated by a headache. The patient has a past medical history of insulin-controlled diabetes, hypertension, and hyperlipidemia. He smokes 2 packs of cigarettes per day. He states that he forgot to take his medications yesterday and started getting a headache about one hour ago. His vitals on admission are the following: blood pressure of 160/110 mmHg, pulse 95/min, temperature 98.6 deg F (37.2 deg C), and respirations 20/min. On exam, the patient has an audible abdominal bruit. After administration of antihypertensive medications, the patient has a blood pressure of 178/120 mmHg. The patient reports his headache has increased to a 10/10 pain level, that he has trouble seeing, and he can't move his extremities. After stabilizing the patient, what is the best next step to diagnose the patient's condition?
A. Doppler ultrasound of the carotids
B. CT head with intravenous contrast
C. MRI head without intravenous contrast
D. CT head without intravenous contrast (Correct Answer)
E. MRI head with intravenous contrast
Explanation: ***CT head without intravenous contrast***
- The sudden onset of severe headache, visual disturbances, and neurological deficits (inability to move extremities), coupled with uncontrolled severe hypertension despite initial treatment, is highly suggestive of an **intracranial pathology**, most likely a **hemorrhagic stroke**.
- A **non-contrast CT scan of the head** is the **gold standard** for rapidly identifying acute intracranial hemorrhage, as it can be performed quickly and is readily available in emergency settings.
*Doppler ultrasound of the carotids*
- This test is primarily used to evaluate **carotid artery stenosis** due to atherosclerosis, which can lead to ischemic stroke.
- While the patient has risk factors for atherosclerosis, his acute presentation with severe central neurological symptoms points more towards an acute intracranial event rather than carotid disease.
*CT head with intravenous contrast*
- While a contrast CT can be useful for identifying tumors, abscesses, or vascular malformations, it is **contraindicated in the initial assessment of acute stroke** if an intracranial hemorrhage is suspected.
- Contrast can sometimes obscure subtle bleeds or complicate the interpretation of acute hemorrhage, and it also carries a risk of **contrast-induced nephropathy**, especially in a patient with diabetes.
*MRI head without intravenous contrast*
- An MRI provides superior soft tissue resolution compared to CT and is excellent for detecting ischemic strokes in later stages, as well as subtle hemorrhages, tumors, and other conditions.
- However, it is **less available, takes longer to perform**, and is often not the first choice in an acute neurological emergency where time is critical, particularly when differentiating between ischemic and hemorrhagic stroke.
*MRI head with intravenous contrast*
- Similar to a contrast CT, an MRI with contrast is generally **not the initial imaging choice for acute stroke** due to time constraints and the need to quickly rule out hemorrhage before considering contrast administration.
- Contrast agents for MRI, such as gadolinium, have their own risks, including **nephrogenic systemic fibrosis** in patients with renal impairment, which is a concern in a diabetic patient.
Question 3: A 50-year-old man presents to his primary care provider complaining of double vision and trouble seeing out of his right eye. His vision started worsening about 2 months ago and has slowly gotten worse. It is now severely affecting his quality of life. Past medical history is significant for poorly controlled hypertension and hyperlipidemia. He takes amlodipine, atorvastatin, and a baby aspirin every day. He smokes 2–3 cigarettes a day and drinks a glass of wine with dinner every night. Today, his blood pressure is 145/85 mm Hg, heart rate is 90/min, respiratory rate is 14/min, and temperature is 37.0°C (98.6°F). On physical exam, he appears pleasant and talkative. His heart has a regular rate and rhythm and his lungs are clear to auscultation bilaterally. Examination of the eyes reveals a dilated right pupil that is positioned inferolateral with ptosis. An angiogram of the head and neck is performed and he is referred to a neurologist. The angiogram reveals a 1 cm berry aneurysm at the junction of the posterior communicating artery and the posterior cerebral artery compressing the oculomotor nerve. Which of the following statements best describes the mechanism behind the oculomotor findings seen in this patient?
A. The parasympathetic nerve fibers of this patient’s eye are activated.
B. The sympathetic nerve fibers of this patient’s eye are inhibited.
C. The unopposed inferior oblique muscle rotates the eye downward.
D. The unopposed superior oblique muscle rotates the eye downward. (Correct Answer)
E. The unopposed medial rectus muscle rotates the eye in the lateral direction.
Explanation: ***The unopposed superior oblique muscle rotates the eye downward.***
- The **oculomotor nerve** (CN III) innervates most extraocular muscles, including the **superior rectus, inferior rectus, medial rectus, and inferior oblique**, as well as the **levator palpebrae superioris** and **parasympathetic fibers** to the pupillary sphincter.
- With a complete **oculomotor nerve palsy**, the only remaining functional extraocular muscles are the **lateral rectus** (innervated by CN VI) and the **superior oblique** (innervated by CN IV), which causes the eye to be positioned **down and out** due to their unopposed actions.
*The parasympathetic nerve fibers of this patient’s eye are activated.*
- **Parasympathetic fibers** within the oculomotor nerve control **pupillary constriction** and lens accommodation.
- Compression of the oculomotor nerve, especially by an aneurysm, typically affects these superficial parasympathetic fibers first, leading to **pupillary dilation** (mydriasis) due to their impairment, not activation.
*The sympathetic nerve fibers of this patient’s eye are inhibited.*
- **Sympathetic innervation** to the eye controls pupillary dilation, eyelid elevation (via Müller's muscle), and sweat gland function.
- Inhibition of sympathetic fibers would lead to **miosis** (constricted pupil) and **ptosis** (drooping eyelid) as seen in **Horner's syndrome**, which is not the primary presentation of oculomotor nerve compression.
*The unopposed inferior oblique muscle rotates the eye downward.*
- The **inferior oblique muscle** elevates and abducts the eye; it is innervated by the **oculomotor nerve**.
- In an oculomotor nerve palsy, the inferior oblique muscle is **paralyzed**, thus it cannot exert any rotational force on the eye.
*The unopposed medial rectus muscle rotates the eye in the lateral direction.*
- The **medial rectus muscle** adducts the eye (moves it medially); it is innervated by the **oculomotor nerve**.
- In an oculomotor nerve palsy, the medial rectus is paralyzed, and its unopposed action would not cause lateral rotation; rather, the **lateral rectus** (innervated by CN VI) would cause the eye to deviate laterally.
Question 4: Where does the only cranial nerve without a thalamic relay nucleus enter the skull?
A. Superior orbital fissure
B. Internal auditory meatus
C. Foramen rotundum
D. Jugular foramen
E. Cribriform plate (Correct Answer)
Explanation: ***Cribriform plate***
- The **olfactory nerve (CN I)** is the only cranial nerve that does not have a thalamic relay nucleus before reaching the cerebral cortex.
- It passes through the **cribriform plate** of the ethmoid bone to reach the olfactory bulbs.
*Superior orbital fissure*
- This opening transmits the **oculomotor (CN III), trochlear (CN IV), ophthalmic division of trigeminal (CN V1)**, and **abducens (CN VI)** nerves.
- These nerves all have sensory or motor components that relay through the thalamus, directly or indirectly.
*Internal auditory meatus*
- This canal transmits the **facial (CN VII)** and **vestibulocochlear (CN VIII)** nerves.
- The vestibulocochlear nerve's auditory pathway involves a thalamic relay in the **medial geniculate nucleus**.
*Foramen rotundum*
- The **maxillary division of the trigeminal nerve (CN V2)** passes through the foramen rotundum.
- Sensory information carried by CN V2 relays through the **thalamus**.
*Jugular foramen*
- This opening transmits the **glossopharyngeal (CN IX), vagus (CN X)**, and **accessory (CN XI)** nerves.
- Sensory components of these nerves, particularly taste and visceral sensation, involve thalamic nuclei.
Question 5: A 75-year-old man is brought to the emergency room after being found unresponsive in his home. His medical history is unknown. On physical examination he does not demonstrate any spontaneous movement of his extremities and is unable to respond to voice or painful stimuli. You notice that he is able blink and move his eyes in the vertical plane. Based on these physical exam findings, you expect that magnetic resonance angiogram will most likely reveal an occlusion in which of the following vessels?
A. Basilar artery (Correct Answer)
B. Anterior cerebral artery
C. Anterior spinal artery
D. Posterior cerebral artery
E. Anterior inferior cerebellar artery
Explanation: ***Basilar artery***
- The patient's presentation with **quadriplegia**, inability to respond to stimuli, and preserved **vertical eye movements** and blinking is characteristic of **locked-in syndrome**.
- **Locked-in syndrome** is most commonly caused by an **occlusion of the basilar artery**, leading to infarction of the ventral pons while sparing the tegmentum.
*Anterior cerebral artery*
- Occlusion of the **anterior cerebral artery** typically causes **contralateral leg weakness** and sensory loss, and sometimes **abulia** or urinary incontinence.
- It does not explain the widespread motor paralysis affecting all four limbs or the preservation of vertical eye movements in an otherwise unresponsive patient.
*Anterior spinal artery*
- Occlusion of the **anterior spinal artery** causes an **anterior spinal cord syndrome**, characterized by bilateral weakness and loss of pain/temperature sensation below the lesion, with preserved proprioception and vibration sense.
- This presentation does not include the characteristic signs of **brainstem dysfunction** seen in locked-in syndrome.
*Posterior cerebral artery*
- An occlusion in the **posterior cerebral artery** typically leads to **contralateral homonymous hemianopia**, and depending on the branch occluded, can also cause memory deficits or thalamic pain.
- It does not account for the extensive motor paralysis or the pattern of preserved vertical eye movements seen in locked-in syndrome.
*Anterior inferior cerebellar artery*
- Occlusion of the **anterior inferior cerebellar artery (AICA)** typically results in **lateral pontine syndrome**, which includes ipsilateral facial weakness, hearing loss, cerebellar ataxia, and contralateral loss of pain and temperature sensation.
- While it affects the pons, AICA occlusion does not typically cause the complete quadriplegia and preservation of vertical eye movements characteristic of locked-in syndrome.
Question 6: 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 7: An 80-year-old woman is brought to the emergency department for left hip pain 30 minutes after she fell while walking around in her room. Examination shows left groin tenderness. The range of motion of the left hip is limited because of pain. An x-ray of the hip shows a linear fracture of the left femoral neck with slight posterior displacement of the femur. Which of the following arteries was most likely damaged in the patient's fall?
A. Superior gluteal artery
B. Deep circumflex iliac
C. Deep femoral artery
D. Obturator
E. Medial circumflex femoral (Correct Answer)
Explanation: ***Medial circumflex femoral***
- This artery is the **primary blood supply** to the femoral head and neck, making it highly vulnerable to injury in cases of femoral neck fractures.
- Damage to the medial circumflex femoral artery significantly increases the risk of **avascular necrosis** of the femoral head.
*Superior gluteal artery*
- The superior gluteal artery primarily supplies the **gluteus medius** and **minimus muscles**.
- It is **not directly involved** in the primary blood supply to the femoral head and neck.
*Deep circumflex iliac*
- This artery mainly supplies the **iliac fossa** and the **abdominal wall muscles**.
- It does not contribute significantly to the blood supply of the femoral neck.
*Deep femoral artery*
- The deep femoral artery, also known as the **profunda femoris artery**, is the main supply to the **thigh muscles**.
- While it gives rise to the circumflex arteries, it is not the artery directly compromised in a femoral neck fracture.
*Obturator*
- The obturator artery primarily supplies the **adductor muscles** of the thigh and contributes a small branch to the femoral head via the **ligamentum teres**.
- This contribution is **insufficient** to maintain viability of the femoral head, especially in trauma to the femoral neck.
Question 8: A 71-year-old woman presents to the emergency department with a headache for the past 30 minutes. She says that this is the worst headache of her life and that it came on suddenly after she hit her head. She says that she has also been experiencing visual problems with double vision when she looks to the left or the right. Visual examination reveals that her right eye cannot move right past the midline and her left eye cannot move left past the midline. Which of the following is most likely responsible for this patient's visual defects?
A. Bilateral uncal herniation
B. Unilateral uncal herniation
C. Central herniation (Correct Answer)
D. Subfalcine herniation
E. Tonsillar herniation
Explanation: ***Central herniation***
- The sudden onset of severe headache after head trauma with **bilateral lateral rectus palsies** (right eye cannot move right, left eye cannot move left) indicates **bilateral abducens nerve (CN VI) dysfunction**.
- Central herniation involves **downward displacement of the diencephalon and midbrain** through the tentorial notch, which causes **increased intracranial pressure** and **stretching of CN VI bilaterally** as it has the longest intracranial course.
- CN VI is particularly vulnerable to **stretching over the petrous ridge** with increased ICP, and bilateral involvement is characteristic of **diffuse increased pressure** or **rostrocaudal deterioration** seen in central herniation.
- While central herniation can progress to pupillary changes and posturing, **early bilateral CN VI palsies** are a recognized finding with increased ICP.
*Bilateral uncal herniation*
- This is an extremely rare occurrence that would primarily affect **CN III (oculomotor nerve) bilaterally**, causing bilateral pupil dilation and "down and out" eye positioning.
- **Uncal herniation does NOT typically cause CN VI palsy**; it compresses CN III as the uncus herniates over the tentorial edge.
- The described findings (bilateral lateral rectus weakness) are not consistent with uncal herniation.
*Unilateral uncal herniation*
- Causes **ipsilateral CN III palsy** with a dilated pupil and "down and out" eye on one side.
- Would not explain the **bilateral abducens nerve deficits** described in this case.
- This is the classic herniation syndrome from temporal lobe mass effect.
*Subfalcine herniation*
- Involves the **cingulate gyrus** passing beneath the **falx cerebri**.
- Typically affects the **anterior cerebral artery**, leading to leg weakness, but **spares cranial nerves entirely**.
- Would not cause any extraocular movement abnormalities.
*Tonsillar herniation*
- Occurs when **cerebellar tonsils** descend through the **foramen magnum**.
- Presents with **respiratory depression, bradycardia, and cardiovascular instability** due to medullary compression.
- Does not typically affect CN VI or cause isolated extraocular movement deficits.
Question 9: 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 10: A 26-year-old man is brought to the emergency department by ambulance after being involved in a motor vehicle collision. He does not open his eyes on command or respond to verbal cues. A CT scan of the head shows a hyperdense fluid collection in the right medial temporal lobe with medial displacement of the uncus and parahippocampal gyrus of the temporal lobe. Which of the following cranial nerves is most likely to be injured as a result of this patient's lesion?
A. Vagus
B. Facial
C. Oculomotor (Correct Answer)
D. Abducens
E. Trigeminal
Explanation: ***Oculomotor***
- The description of **medial displacement of the uncus and parahippocampal gyrus** (uncus herniation) compresses the **oculomotor nerve (CN III)** as it passes between the posterior cerebral and superior cerebellar arteries.
- Compression of the oculomotor nerve leads to a **dilated pupil** (due to parasympathetic fiber involvement) and **down-and-out deviation of the eye** (due to paralysis of extraocular muscles it innervates).
*Vagus*
- The vagus nerve (CN X) is deep within the skull and brainstem, far from the temporal lobe, and is not directly affected by uncal herniation.
- Injury to the vagus nerve typically presents with dysphagia, hoarseness, or cardiac arrhythmias, symptoms not indicated here.
*Facial*
- The facial nerve (CN VII) exits the brainstem at the pontomedullary junction and is located more superiorly and laterally than the structures involved in uncal herniation.
- Damage to the facial nerve causes facial muscle weakness or paralysis, which is not the primary concern with uncal herniation.
*Abducens*
- The abducens nerve (CN VI) is a long, slender nerve that can be affected by **generalized increases in intracranial pressure**, but is less commonly directly compressed by an uncal herniation itself.
- Injury to the abducens nerve causes **lateral rectus muscle paralysis**, leading to medial deviation of the eye, whereas uncal herniation typically affects the oculomotor nerve.
*Trigeminal*
- The trigeminal nerve (CN V) exits the pons and is located superior to the tentorial notch and medial temporal lobe, making it unlikely to be directly compressed by uncal herniation.
- Injury to the trigeminal nerve causes sensory loss in the face or weakness of the muscles of mastication, which are not consistent with the described lesion.
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