A 52-year-man is brought to the physician because of a 2-week history of memory loss. Three weeks ago, he had a cardiac arrest that required cardiopulmonary resuscitation and intravenous epinephrine. On mental status examination, he cannot recall objects shown to him 20 minutes earlier but vividly recalls memories from before the incident. The remainder of the examination shows no abnormalities. Which of the following structures of the brain is most likely affected?
Q42
A 54-year-old man is brought to the emergency department 30 minutes after being hit by a car while crossing the street. He had a left-sided tonic-clonic seizure and one episode of vomiting while being transported to the hospital. On arrival, he is not oriented to person, place, or time. Physical examination shows flaccid paralysis of all extremities. A CT scan of the head is shown. This patient's symptoms are most likely the result of a hemorrhage in which of the following structures?
Q43
A 54-year-old man is referred to a tertiary care hospital with a history of 5 months of progressive difficulty in walking and left leg numbness. He first noticed mild gait unsteadiness and later developed gradual right leg weakness. His left leg developed progressive numbness and tingling. His blood pressure is 138/88 mm Hg, the heart rate is 72/min, and the temperature is 36.7°C (98.2°F). On physical examination, he is alert and oriented to person, place, and time. Cranial nerves are intact. Muscle strength is 5/5 in both upper extremities and left lower extremity, but 3/5 in the right leg with increased tone. The plantar reflex is extensor on the right. Pinprick sensation is decreased on the left side below the umbilicus. Vibration and joint position senses are decreased in the right foot and leg. All sensations are normal in the upper extremities. Finger-to-nose and heel-to-shin testing are normal. This patient’s lesion is most likely located in which of the following parts of the nervous system?
Q44
A 67-year-old female patient is brought to the emergency department after her daughter noticed she has been having meaningless speech. When assessing the patient, she calls the chair a table, and at times would make up new words. She does not appear to be aware of her deficit, and is carrying on an empty conversation. Her speech is fluent, but with paraphasic errors. Her repetition is impaired. On physical examination, a right upper quadrant field-cut is appreciated, with impairment in comprehension and repetition. Which of the following structures is most likely involved in this patient’s presentation?
Q45
A 67-year-old man is brought to the physician by his daughter because he frequently misplaces his personal belongings and becomes easily confused. His daughter mentions that his symptoms have progressively worsened for the past one year. On mental status examination, he is oriented to person, place, and time. He vividly recalls memories from his childhood but can only recall one of three objects presented to him after 5 minutes. His affect is normal. This patients' symptoms are most likely caused by damage to which of the following?
Q46
A 72-year-old man presents to his primary care physician due to worsening headache and double vision. His headache began several months ago, and he describes them as sharp and localized to the left side of the head. His double vision began one week prior to presentation. Medical history is significant for hypertension and type II diabetes mellitus, which is treated with lisinopril and metformin. He smokes a pack of cigarettes a day for the last 40 years. His temperature is 98.3°F (37°C), blood pressure is 148/84 mmHg, pulse is 60/min, and respirations are 14/min. On physical exam, a mild head turning towards the left is appreciated. Pupils are equal, round, and reactive to light, with a more pronounced esotropia on left-lateral gaze. The rest of the neurologic exam is otherwise normal. Magnetic resonance imaging (MRI) of the head and MR angiography shows a left-sided intracavernous carotid aneurysm. Which of the following nerves is most likely compressed by the aneurysm in this patient?
Q47
A 35-year-old man who suffered a motor vehicle accident 3 months ago presents to the office for a neurological evaluation. He has no significant past medical history and takes no current medications. He has a family history of coronary artery disease in his father and Alzheimer’s disease in his mother. On physical examination, his blood pressure is 110/60 mm Hg, the pulse is 85/min, the temperature is 37.0°C (98.6°F), and the respiratory rate is 20/min. Neurological examination is suggestive of a lesion in the anterior spinal artery that affects the anterior two-thirds of the spinal cord, which is later confirmed with angiography. Which of the following exam findings would have suggested this diagnosis?
Q48
A 73-year-old man presents to your office accompanied by his wife. He has been experiencing a tremor in his right hand for the last several months that seems to be worsening. He does not have any other complaints and says he’s “fine.” His wife thinks that he has also had more difficulty walking. His history is significant for hypertension and an ischemic stroke of the right middle cerebral artery 2 years ago. His medications include hydrochlorothiazide and daily aspirin. On physical exam you note that the patient speaks with a soft voice and has decreased facial expressions. He has a resting tremor that is worse on the right side. He has increased resistance to passive movement when you flex and extend his relaxed wrist. He has 5/5 strength bilaterally. Neuronal degeneration in which of the following locations is most likely responsible for the progression of this disease?
Q49
A 27-year-old man is brought to the emergency department because of a knife wound to his back. His pulse is 110/min, respirations are 14/min, and blood pressure is 125/78 mm Hg. Examination shows a 5-cm deep stab wound at the level of T9. He withdraws the right foot to pain but is unable to sense vibration or whether his right toe is flexed or extended. Sensation in the left leg is normal. Motor strength is 5/5 in all extremities. Rectal tone is normal. Which of the following spinal column structures was most likely affected?
Q50
A 60-year-old man is brought to the emergency department because of a 1-hour history of disorientation and slurred speech. He has a 10-year history of hypertension and hypercholesterolemia. His blood pressure is 210/110 mm Hg, and pulse is 90/min. Once the patient is stabilized, an MRI of the brain is performed, which shows an infarct of the left precentral gyrus involving the facial motor cortex. Given the MRI findings, which of the following neurological findings would most be expected?
Neuroanatomy US Medical PG Practice Questions and MCQs
Question 41: A 52-year-man is brought to the physician because of a 2-week history of memory loss. Three weeks ago, he had a cardiac arrest that required cardiopulmonary resuscitation and intravenous epinephrine. On mental status examination, he cannot recall objects shown to him 20 minutes earlier but vividly recalls memories from before the incident. The remainder of the examination shows no abnormalities. Which of the following structures of the brain is most likely affected?
A. Internal pyramidal layer of the amygdala
B. Microglial cells of dorsal midbrain
C. Purkinje cells of the cerebellum
D. Pyramidal cells of the hippocampus (Correct Answer)
E. Astroglial cells of the putamen
Explanation: ***Pyramidal cells of the hippocampus***
- The patient's inability to form new memories (anterograde amnesia) following a period of **hypoxia** suggests damage to the **hippocampus**, specifically its pyramidal cells.
- The **hippocampus** is highly vulnerable to **ischemic injury** due to the metabolic demands of its pyramidal cells.
*Internal pyramidal layer of the amygdala*
- The amygdala is primarily involved in **emotional processing**, particularly fear and anxiety, not memory encoding directly.
- Damage to the amygdala would likely manifest as altered emotional responses, rather than isolated memory loss.
*Microglial cells of dorsal midbrain*
- Microglial cells are the brain's resident immune cells and proliferate in response to injury, they are not the primary site of memory formation.
- The dorsal midbrain contains structures involved in visual and auditory reflexes, not directly memory consolidation.
*Purkinje cells of the cerebellum*
- Purkinje cells are specialized neurons in the **cerebellum** responsible for **motor coordination** and balance.
- Damage to these cells would result in ataxia and motor dysfunction, not memory deficits.
*Astroglial cells of the putamen*
- Astroglial cells are supportive cells throughout the brain; the putamen is involved in **motor control** and **procedural learning**.
- Dysfunction of the putamen typically leads to movement disorders like Parkinsonism, not specific memory loss.
Question 42: A 54-year-old man is brought to the emergency department 30 minutes after being hit by a car while crossing the street. He had a left-sided tonic-clonic seizure and one episode of vomiting while being transported to the hospital. On arrival, he is not oriented to person, place, or time. Physical examination shows flaccid paralysis of all extremities. A CT scan of the head is shown. This patient's symptoms are most likely the result of a hemorrhage in which of the following structures?
A. Between the dura mater and the arachnoid mater
B. Into the cerebral parenchyma
C. Between the skull and the dura mater
D. Between the arachnoid mater and the pia mater (Correct Answer)
E. Into the ventricular system
Explanation: ***Between the arachnoid mater and the pia mater (Correct)***
- The CT scan demonstrates diffuse high-density (white) material within the sulci and basal cisterns, indicative of a **subarachnoid hemorrhage**. This space is located between the arachnoid mater and the pia mater.
- The patient's presentation with altered mental status, seizures, vomiting, and flaccid paralysis following trauma is consistent with the severe neurological impact of a **traumatic subarachnoid hemorrhage**.
*Between the dura mater and the arachnoid mater (Incorrect)*
- Hemorrhage in this location is known as a **subdural hematoma**, which typically appears as a crescent-shaped collection of blood.
- While possible in trauma, the CT image shows blood primarily filling the sulci, not a subdural collection.
*Into the cerebral parenchyma (Incorrect)*
- This would be an **intraparenchymal hemorrhage**, appearing as a focal area of high density within the brain tissue itself.
- Although there might be some associated parenchymal injury in severe trauma, the predominant pattern seen on the CT is diffuse blood in the subarachnoid space.
*Between the skull and the dura mater (Incorrect)*
- This describes an **epidural hematoma**, often characterized by a lenticular (lens-shaped) collection of blood due to its confinement by dural attachments.
- The CT image does not show a lenticular collection of blood in this space.
*Into the ventricular system (Incorrect)*
- **Intraventricular hemorrhage** would show blood filling the cerebral ventricles.
- While subarachnoid hemorrhage can sometimes extend into the ventricles, the primary finding on this CT is diffuse blood in the subarachnoid space, not isolated ventricular blood.
Question 43: A 54-year-old man is referred to a tertiary care hospital with a history of 5 months of progressive difficulty in walking and left leg numbness. He first noticed mild gait unsteadiness and later developed gradual right leg weakness. His left leg developed progressive numbness and tingling. His blood pressure is 138/88 mm Hg, the heart rate is 72/min, and the temperature is 36.7°C (98.2°F). On physical examination, he is alert and oriented to person, place, and time. Cranial nerves are intact. Muscle strength is 5/5 in both upper extremities and left lower extremity, but 3/5 in the right leg with increased tone. The plantar reflex is extensor on the right. Pinprick sensation is decreased on the left side below the umbilicus. Vibration and joint position senses are decreased in the right foot and leg. All sensations are normal in the upper extremities. Finger-to-nose and heel-to-shin testing are normal. This patient’s lesion is most likely located in which of the following parts of the nervous system?
A. Right hemi-spinal cord (Correct Answer)
B. Right frontal lobe
C. Left frontal lobe
D. Left hemi-spinal cord
E. Right pons
Explanation: ***Right hemi-spinal cord***
- The patient presents with **ipsilateral motor weakness** (right leg 3/5 with increased tone and extensor plantar reflex) and **ipsilateral dorsal column deficits** (decreased vibration and joint position senses in the right foot and leg) along with **contralateral spinothalamic loss** (decreased pinprick sensation on the left side below the umbilicus). This classic combination of symptoms is known as **Brown-Séquard syndrome**, which results from a lesion affecting one half of the spinal cord.
- The specific pattern of deficits—motor and proprioceptive loss on the same side as the lesion, and pain/temperature loss on the opposite side—localizes the lesion to the **right half of the spinal cord**.
*Right frontal lobe*
- A lesion in the right frontal lobe would typically cause **contralateral motor weakness** (left-sided) and potentially cognitive or behavioral changes, without the specific sensory dissociation seen in this patient.
- It would not explain the **ipsilateral proprioceptive loss** or the **contralateral pain/temperature loss** at different levels as observed in this case.
*Left frontal lobe*
- A lesion in the left frontal lobe would primarily result in **contralateral motor weakness** (right-sided), similar to the right leg weakness observed, but it would not explain the other sensory deficits, particularly the **contralateral pain/temperature loss** (right-sided in this scenario) and the **ipsilateral proprioceptive loss**.
- **Speech disturbances** (aphasia) are also common with left frontal lobe lesions, depending on the exact location, which are not mentioned here.
*Left hemi-spinal cord*
- A lesion in the left hemi-spinal cord would cause **ipsilateral motor weakness** (left leg weakness) and **ipsilateral dorsal column deficits** (decreased vibration and joint position senses in the left foot and leg), along with **contralateral spinothalamic loss** (decreased pinprick sensation on the right side).
- This pattern is the opposite of the patient's symptoms, which show right-sided weakness and proprioceptive loss, and left-sided pain/temperature loss.
*Right pons*
- A lesion in the pons would typically present with a **combination of cranial nerve deficits** (e.g., facial sensory or motor abnormalities, gaze palsies) **and long tract signs**, often affecting both sides of the body due to the compact nature of the brainstem.
- While it could cause long tract signs, the specific pattern of **dissociated ipsilateral and contralateral sensory/motor deficits** observed below the umbilical level is highly characteristic of a spinal cord lesion and less so of a pontine lesion.
Question 44: A 67-year-old female patient is brought to the emergency department after her daughter noticed she has been having meaningless speech. When assessing the patient, she calls the chair a table, and at times would make up new words. She does not appear to be aware of her deficit, and is carrying on an empty conversation. Her speech is fluent, but with paraphasic errors. Her repetition is impaired. On physical examination, a right upper quadrant field-cut is appreciated, with impairment in comprehension and repetition. Which of the following structures is most likely involved in this patient’s presentation?
A. Superior temporal gyrus (Correct Answer)
B. Arcuate fasciculus
C. Inferior frontal gyrus
D. Frontal lobe, sparing Brodmann's area 44 and 45
E. Arcuate fasciculus, inferior frontal gyrus, and superior temporal gyrus
Explanation: ***Superior temporal gyrus***
- The patient's presentation of **fluent aphasia** with **paraphasic errors**, **impaired comprehension**, **impaired repetition**, and **lack of awareness** of the deficit is classic for **Wernicke's aphasia**.
- **Wernicke's area**, located in the posterior part of the **superior temporal gyrus** (Brodmann area 22) in the dominant hemisphere, is responsible for language comprehension.
*Arcuate fasciculus*
- Damage to the **arcuate fasciculus** typically causes **conduction aphasia**, characterized by **impaired repetition** with relatively preserved comprehension and fluent speech.
- However, it does not explain the significant comprehension deficits and paraphasic errors seen in this patient to the same extent as a Wernicke's lesion.
*Inferior frontal gyrus*
- The **inferior frontal gyrus** (Brodmann areas 44 and 45) is commonly associated with **Broca's area**, responsible for language production.
- Damage here would result in **non-fluent aphasia** with effortful speech and relatively preserved comprehension, which is contrary to the patient's fluent speech.
*Frontal lobe, sparing Brodmann's area 44 and 45*
- While damage to other parts of the **frontal lobe** can cause various cognitive deficits, sparing Broca's area (44 and 45) would generally not result in the specific pattern of **fluent aphasia** with severe comprehension and repetition impairment seen here.
- This option does not precisely localize the critical language areas affected.
*Arcuate fasciculus, inferior frontal gyrus, and superior temporal gyrus*
- While damage to all these areas would certainly cause severe aphasia, the specific constellation of symptoms—**fluent speech**, **poor comprehension**, **poor repetition**, and **paraphasic errors**—points most directly and primarily to involvement of the **superior temporal gyrus** (Wernicke's area).
- While some level of repetition impairment (seen in Wernicke's aphasia) implies some involvement in the broader language network, a lesion centered in the superior temporal gyrus is the most parsimonious explanation for this classic presentation.
Question 45: A 67-year-old man is brought to the physician by his daughter because he frequently misplaces his personal belongings and becomes easily confused. His daughter mentions that his symptoms have progressively worsened for the past one year. On mental status examination, he is oriented to person, place, and time. He vividly recalls memories from his childhood but can only recall one of three objects presented to him after 5 minutes. His affect is normal. This patients' symptoms are most likely caused by damage to which of the following?
A. Amygdala
B. Superior temporal gyrus
C. Hippocampus (Correct Answer)
D. Ventral posterolateral nucleus
E. Substantia nigra
Explanation: ***Hippocampus***
- The patient's inability to recall new information (only one of three objects after 5 minutes) despite intact long-term memory suggests **anterograde amnesia**, which is characteristic of hippocampal damage.
- The hippocampus is crucial for the **formation of new declarative memories**, such as facts and events. Progressive decline in this function over a year is consistent with neurodegenerative conditions affecting the hippocampus, such as **Alzheimer's disease**.
*Amygdala*
- The amygdala is primarily involved in **processing emotions** and fear, as well as emotional memory.
- Damage to the amygdala would typically manifest as deficits in recognizing or expressing emotions, or in forming emotional memories, which are not the primary symptoms described here.
*Superior temporal gyrus*
- The superior temporal gyrus contains the **primary auditory cortex** and is involved in processing auditory information and language comprehension (Wernicke's area).
- Damage to this area would primarily cause auditory processing difficulties, such as **Wernicke's aphasia**, rather than memory problems for new information.
*Ventral posterolateral nucleus*
- The ventral posterolateral (VPL) nucleus of the thalamus is a key relay station for **somatosensory information** (touch, pain, temperature) from the body to the cerebral cortex.
- Damage to the VPL nucleus would lead to sensory deficits on the contralateral side of the body, not issues with memory formation.
*Substantia nigra*
- The substantia nigra is part of the basal ganglia and is crucial for **motor control**, producing dopamine that projects to the striatum.
- Damage to the substantia nigra is characteristic of **Parkinson's disease**, leading to motor symptoms like tremor, rigidity, bradykinesia, and postural instability, which are not described in this patient.
Question 46: A 72-year-old man presents to his primary care physician due to worsening headache and double vision. His headache began several months ago, and he describes them as sharp and localized to the left side of the head. His double vision began one week prior to presentation. Medical history is significant for hypertension and type II diabetes mellitus, which is treated with lisinopril and metformin. He smokes a pack of cigarettes a day for the last 40 years. His temperature is 98.3°F (37°C), blood pressure is 148/84 mmHg, pulse is 60/min, and respirations are 14/min. On physical exam, a mild head turning towards the left is appreciated. Pupils are equal, round, and reactive to light, with a more pronounced esotropia on left-lateral gaze. The rest of the neurologic exam is otherwise normal. Magnetic resonance imaging (MRI) of the head and MR angiography shows a left-sided intracavernous carotid aneurysm. Which of the following nerves is most likely compressed by the aneurysm in this patient?
A. Optic
B. Abducens (Correct Answer)
C. Oculomotor
D. Trochlear
E. Ophthalmic
Explanation: ***Abducens***
- An intracavernous carotid aneurysm can compress the **abducens nerve (CN VI)** as it runs through the cavernous sinus, leading to **isolated lateral rectus palsy**.
- **Lateral rectus palsy** manifests as **esotropia**, particularly on attempted lateral gaze toward the affected side (left-lateral gaze in this case), causing **diplopia**.
*Optic*
- The **optic nerve (CN II)** is located anterior to the cavernous sinus and typically not affected by an intracavernous aneurysm.
- Optic nerve compression would cause **visual field defects** or **vision loss**, not double vision or ocular misalignment.
*Oculomotor*
- The **oculomotor nerve (CN III)** passes through the cavernous sinus but its compression typically causes a wider range of symptoms, including **ptosis**, **mydriasis**, and impairment of **superior, inferior, and medial rectus muscles**, leading to a **"down and out"** gaze, which is not described.
- While it can cause diplopia, the specific presentation of **esotropia** on lateral gaze points away from an isolated CN III palsy.
*Trochlear*
- The **trochlear nerve (CN IV)** also travels through the cavernous sinus, but its compression would primarily affect the **superior oblique muscle**, leading to vertical or torsional diplopia that is often worse when looking down and in, and sometimes compensated by a head tilt.
- The isolated **esotropia** with left-lateral gaze abnormality is not consistent with trochlear nerve palsy.
*Ophthalmic*
- The **ophthalmic division of the trigeminal nerve (V1)** passes through the cavernous sinus and its compression would result in **sensory loss** over the forehead, upper eyelid, and nose, and potentially **corneal reflex abnormalities**.
- It does not cause motor deficits affecting eye movements or double vision.
Question 47: A 35-year-old man who suffered a motor vehicle accident 3 months ago presents to the office for a neurological evaluation. He has no significant past medical history and takes no current medications. He has a family history of coronary artery disease in his father and Alzheimer’s disease in his mother. On physical examination, his blood pressure is 110/60 mm Hg, the pulse is 85/min, the temperature is 37.0°C (98.6°F), and the respiratory rate is 20/min. Neurological examination is suggestive of a lesion in the anterior spinal artery that affects the anterior two-thirds of the spinal cord, which is later confirmed with angiography. Which of the following exam findings would have suggested this diagnosis?
A. Loss of vibratory sense below the level of the lesion
B. Loss of pain and temperature sensation above the level of the lesion
C. Negative plantar extensor response in his lower limbs
D. Flaccid paralysis on the right side
E. Preserved pressure sensation (Correct Answer)
Explanation: ***Preserved pressure sensation***
- **Anterior spinal artery** occlusion affects the **spinothalamic tracts** (pain and temperature) and **corticospinal tracts** (motor function), but spares the **dorsal columns**.
- The **dorsal columns** carry **vibration, proprioception, and discriminative (fine) touch and pressure sensation**, which would therefore be preserved.
- While crude touch/pressure via the anterior spinothalamic tract may be impaired, the preservation of dorsal column function allows for intact discriminative pressure sensation, distinguishing this from other cord syndromes.
*Loss of vibratory sense below the level of the lesion*
- **Vibratory sense** is carried by the **dorsal columns**, which are typically spared in **anterior spinal artery syndromes** as they are supplied by the posterior spinal arteries.
- Loss of vibratory sense would suggest involvement of the posterior part of the spinal cord, inconsistent with an anterior spinal artery lesion.
*Loss of pain and temperature sensation above the level of the lesion*
- **Anterior spinal artery syndrome** causes loss of **pain and temperature sensation** *below* the level of the lesion, as the spinothalamic tracts are affected in the anterior cord.
- Sensation *above* the lesion level should be intact, as those pathways have already ascended past the lesion.
*Negative plantar extensor response in his lower limbs*
- A **negative plantar extensor response** (normal plantar reflex) indicates the toes curl downwards, which is the normal response.
- Lesions of the **corticospinal tract**, such as in anterior spinal artery syndrome, typically cause a **positive Babinski sign** (extensor plantar response), where the big toe extends upwards, indicating upper motor neuron damage.
*Flaccid paralysis on the right side*
- **Anterior spinal artery syndrome** causes **bilateral motor deficits** due to involvement of both **corticospinal tracts** in the anterior cord.
- While initial presentation can be **flaccid paralysis** due to spinal shock below the level of the lesion, it is typically **bilateral**, not unilateral, and evolves to **spastic paralysis** over time.
Question 48: A 73-year-old man presents to your office accompanied by his wife. He has been experiencing a tremor in his right hand for the last several months that seems to be worsening. He does not have any other complaints and says he’s “fine.” His wife thinks that he has also had more difficulty walking. His history is significant for hypertension and an ischemic stroke of the right middle cerebral artery 2 years ago. His medications include hydrochlorothiazide and daily aspirin. On physical exam you note that the patient speaks with a soft voice and has decreased facial expressions. He has a resting tremor that is worse on the right side. He has increased resistance to passive movement when you flex and extend his relaxed wrist. He has 5/5 strength bilaterally. Neuronal degeneration in which of the following locations is most likely responsible for the progression of this disease?
A. Vermis
B. Substantia nigra pars compacta (Correct Answer)
C. Frontotemporal lobe
D. Caudate and putamen
E. Subthalamic nucleus
Explanation: ***Substantia nigra pars compacta***
- The patient's symptoms, including **resting tremor**, **bradykinesia** (soft voice, decreased facial expressions, difficulty walking), and **rigidity** (increased resistance to passive movement), are classic signs of **Parkinson's disease**.
- Parkinson's disease is primarily caused by the degeneration of **dopaminergic neurons** in the **substantia nigra pars compacta**, leading to a lack of dopamine in the basal ganglia.
*Vermis*
- The **vermis** is a part of the cerebellum primarily involved in coordinating **truncal movements** and maintaining **posture**.
- Damage to the vermis typically causes **ataxia**, truncal instability, and gait disturbances, which are not the primary features described here.
*Frontotemporal lobe*
- The **frontotemporal lobe** is associated with cognitive functions, personality, and language.
- Degeneration in this area is characteristic of **frontotemporal dementia**, presenting with prominent behavioral changes, language difficulties, or progressive memory loss, which are not the main symptoms in this patient.
*Caudate and putamen*
- The **caudate and putamen** are components of the **striatum**, which receives dopaminergic input from the substantia nigra.
- While the lack of dopamine in the striatum contributes to Parkinsonian symptoms, the primary neuronal degeneration occurs *before* this in the substantia nigra pars compacta, which *projects* to the striatum.
*Subthalamic nucleus*
- The **subthalamic nucleus** is part of the basal ganglia circuit, and its overactivity can contribute to motor symptoms in Parkinson's disease.
- **Deep brain stimulation (DBS)** targeting the subthalamic nucleus is a treatment for Parkinson's, but the primary site of neuronal degeneration in the disease itself is not the subthalamic nucleus.
Question 49: A 27-year-old man is brought to the emergency department because of a knife wound to his back. His pulse is 110/min, respirations are 14/min, and blood pressure is 125/78 mm Hg. Examination shows a 5-cm deep stab wound at the level of T9. He withdraws the right foot to pain but is unable to sense vibration or whether his right toe is flexed or extended. Sensation in the left leg is normal. Motor strength is 5/5 in all extremities. Rectal tone is normal. Which of the following spinal column structures was most likely affected?
A. Central spinal cord grey matter
B. Lateral corticospinal tract
C. Dorsal root (Correct Answer)
D. Artery of Adamkiewicz
E. Posterior spinal artery
Explanation: ***Dorsal root***
- The patient's inability to sense **vibration** or **proprioception** (flexed/extended toe) on the right side, with intact motor strength, strongly implicates damage to the **dorsal columns** or the **dorsal root** carrying these afferent fibers.
- The dorsal root transmits **sensory** (afferent) information from the periphery to the spinal cord, and injury would selectively impair these specific sensory modalities without affecting motor function.
*Central spinal cord grey matter*
- Damage to the central gray matter, as seen in conditions like **syringomyelia**, typically affects the **spinothalamic tracts** first, leading to a "cape-like" distribution of bilateral loss of **pain** and **temperature sensation**.
- It would not primarily cause isolated **proprioceptive** or **vibration** loss with preserved motor function.
*Lateral corticospinal tract*
- Injury to the **lateral corticospinal tract** results in **motor deficits**, specifically **weakness** or paralysis, usually on the same side or contralateral depending on the location of the lesion (above or below decussation).
- The patient exhibits normal motor strength (5/5), indicating this tract is likely intact.
*Artery of Adamkiewicz*
- Occlusion or injury to the **Artery of Adamkiewicz** typically causes **anterior spinal artery syndrome**, affecting the **anterior two-thirds of the spinal cord**.
- This leads to bilateral loss of **motor function** (corticospinal tracts) and **pain/temperature sensation** (spinothalamic tracts), with preservation of dorsal column functions (vibration, proprioception).
*Posterior spinal artery*
- The **posterior spinal arteries** supply the **dorsal columns**, and their occlusion would lead to bilateral loss of **vibration** and **proprioception**.
- However, the patient's symptoms are **unilateral** on the right side, suggesting a more localized injury to the dorsal root or dorsal column on that side rather than a bilateral vascular event.
Question 50: A 60-year-old man is brought to the emergency department because of a 1-hour history of disorientation and slurred speech. He has a 10-year history of hypertension and hypercholesterolemia. His blood pressure is 210/110 mm Hg, and pulse is 90/min. Once the patient is stabilized, an MRI of the brain is performed, which shows an infarct of the left precentral gyrus involving the facial motor cortex. Given the MRI findings, which of the following neurological findings would most be expected?
A. Inability to raise the right eyebrow
B. Drooping of the left eyelid
C. Loss of taste in the posterior third of the right half of the tongue
D. Decreased lacrimation of the left eye
E. Flattening of the right nasolabial fold (Correct Answer)
Explanation: ***Flattening of the right nasolabial fold***
- An infarct in the **left precentral gyrus** affecting the facial nerve region impacts the **contralateral lower face** due to the nature of upper motor neuron innervation.
- This typically results in **weakness or paralysis of the muscles of facial expression** on the right side, manifest as a flattened nasolabial fold.
*Inability to raise the right eyebrow*
- The muscles of the **upper face** (e.g., forehead, eyebrow) receive **bilateral innervation** from the motor cortex.
- Therefore, an upper motor neuron lesion in one hemisphere, such as the left precentral gyrus infarct, usually **does not cause significant weakness** in raising the contralateral eyebrow.
*Drooping of the left eyelid*
- Drooping of the left eyelid (**ptosis**) is often associated with dysfunction of the **oculomotor nerve (CN III)** or **sympathetic pathway** (Horner's syndrome).
- It is not a direct consequence of a precentral gyrus infarct affecting facial nerve motor control.
*Loss of taste in the posterior third of the right half of the tongue*
- Taste sensation from the posterior third of the tongue is primarily mediated by the **glossopharyngeal nerve (CN IX)**.
- An infarct in the precentral gyrus, which is part of the motor cortex, would not directly affect taste sensation.
*Decreased lacrimation of the left eye*
- Lacrimation is controlled by parasympathetic fibers traveling with the **facial nerve (CN VII)**, but these fibers typically originate from the brainstem, not directly from the precentral gyrus.
- A cortical infarct primarily affects **motor control of facial muscles**, not autonomic functions like tearing.
