A 32-year-old previously healthy female presents to her primary care physician with double vision. She first noted the double vision yesterday and saw no improvement this morning. She does not think it is worsening. She has not had any changes in her normal routine though she recalls one episode of right arm weakness 2 months ago. She did not seek treatment and the weakness subsided after several days. She does not have a history of head trauma. She denies headache, fever, chills, nausea, vomiting, paresthesias, extremity pain, or weakness. On exam she has right adduction palsy on leftward gaze. She has no focal weakness. Which of the following additional physical exam findings is associated with the lesion responsible for her ocular findings?
Q62
A 78-year-old right-handed male is brought in by ambulance after being found down in his home. After being aroused, the patient has difficulty answering questions and appears to be frustrated by his inability to communicate. He is able to speak his name and a few other words but his speech is not fluent. Subsequent neurologic exam finds that the patient is able to comprehend both one and two step instructions; however, he is unable to repeat phrases despite being able to understand them. He also has difficulty writing despite retaining fine motor control. CT reveals an acute stroke to his left hemisphere. Damage to which of the following sets of structures would be most likely to result in this pattern of deficits?
Q63
A 23-year-old man presents to the emergency room following a stab wound to the back. He was in a bar when he got into an argument with another man who proceeded to stab him slightly right of the midline of his back. He is otherwise healthy and does not take any medications. He has one previous admission to the hospital for a stab wound to the leg from another bar fight 2 years ago. His temperature is 99°F (37.2°C), blood pressure is 115/80 mmHg, pulse is 100/min, and pulse oximetry is 99% on room air. Cardiopulmonary and abdominal exams are unremarkable; however, he has an abnormal neurologic exam. If this wound entered his spinal cord but did not cross the midline, which of the following would most likely be seen in this patient?
Q64
A 63-year-old man is brought to the emergency department by his wife because she is concerned he is having another stroke. The patient says he woke up with right-sided facial weakness and drooping. Past medical history is significant for a recent case of shingles treated with acyclovir, and a stroke, diagnosed 10 years ago, from which he recovered with no residual functional deficits. On physical examination, there is weakness and drooping of the entire right side of the face. Sensation is intact. The remainder of the physical examination is unremarkable. Which of the following additional findings would also most likely be seen in this patient?
Q65
A 25-year-old previously healthy woman presents to her PCP reporting cessation of menses for the past 6 months. Previously, her period occurred regularly, every 30 days. She also complains of decreased peripheral vision, most noticeably when she is driving her car. She denies any recent sexual activity and a pregnancy test is negative. Upon further work-up, what physical exam finding is most likely to be identified?
Q66
A 4-year-old boy is brought to the physician because of a progressive headache and neck pain for 2 weeks. During this period, he has had multiple episodes of dizziness and tingling sensations in his arms and hands. A year ago, he underwent closed reduction of a dislocated shoulder that he suffered after a fall. He underwent surgical removal of a sac-like protuberance on his lower back, soon after being born. His temperature is 36.7°C (98°F), pulse is 80/min, and blood pressure is 100/80 mm Hg. His neck is supple. Neurological examination shows sensorineural hearing loss bilaterally and normal gross motor function. Fundoscopy reveals bilateral optic disk swelling. An MRI of the brain is shown. Which of the following is the most likely cause of this patient's symptoms?
Q67
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?
Q68
A 64-year-old man presents to his primary care clinic for a regular checkup. He reports feeling depressed since his wife left him 6 months prior and is unable to recall why she left him. He denies any sleep disturbance, change in his eating habits, guilt, or suicidal ideation. His past medical history is notable for hypertension, gout, and a myocardial infarction five years ago. He takes lisinopril, aspirin, metoprolol, and allopurinol. He has a 50 pack-year smoking history and was previously a heroin addict but has not used in over 20 years. He drinks at least 6 beers per day. His temperature is 98.6°F (37°C), blood pressure is 155/95 mmHg, pulse is 100/min, and respirations are 18/min. He appears somewhat disheveled, inattentive, and smells of alcohol. During his prior visits, he has been well-groomed and attentive. When asked what year it is and who the president is, he confidently replies “1999” and “Jimmy Carter.” He says his son’s name is “Peter” when it is actually “Jake.” This patient likely has a lesion in which of the following brain regions?
Q69
A 58-year-old man comes to the physician because of burning pain in his neck and arms for a year. He has also had paresthesias in his hands during this period. He has had increasing weakness in both hands during the past 3 months. He has type 2 diabetes mellitus, hypercholesterolemia, and hypertension. He was involved in a motor vehicle collision 3 years ago. Current medications include metformin, sitagliptin, enalapril, atorvastatin, and aspirin. He has had 7 sexual partners in his lifetime; he uses condoms inconsistently. He is oriented to time, place, and person. Vital signs are within normal limits. The pupils are equal and reactive to light. Examination of the upper extremities shows decreased muscle strength, absent reflexes, and decreased hand grip with fasciculations bilaterally. Sensation to temperature and pain is absent over the chest and bilateral upper arms. Vibration and joint position sensations are present in the upper limbs. Cranial nerve examination shows no focal findings. Examination of the lower extremities show no abnormalities. Which of the following is the most likely diagnosis?
Q70
A 26-year-old man comes to the physician for a follow-up examination. Two weeks ago, he was treated in the emergency department for head trauma after being hit by a bicycle while crossing the street. Neurological examination shows decreased taste on the right anterior tongue. This patient's condition is most likely caused by damage to a cranial nerve that is also responsible for which of the following?
Neuroanatomy US Medical PG Practice Questions and MCQs
Question 61: A 32-year-old previously healthy female presents to her primary care physician with double vision. She first noted the double vision yesterday and saw no improvement this morning. She does not think it is worsening. She has not had any changes in her normal routine though she recalls one episode of right arm weakness 2 months ago. She did not seek treatment and the weakness subsided after several days. She does not have a history of head trauma. She denies headache, fever, chills, nausea, vomiting, paresthesias, extremity pain, or weakness. On exam she has right adduction palsy on leftward gaze. She has no focal weakness. Which of the following additional physical exam findings is associated with the lesion responsible for her ocular findings?
A. Afferent pupillary defect in the left eye
B. Horizontal nystagmus in the left eye on leftward gaze (Correct Answer)
C. Ptosis on the right
D. Left abduction palsy on leftward gaze
E. Proptosis of the right eye
Explanation: **Horizontal nystagmus in the left eye on leftward gaze**
- The patient presents with **double vision** and **right adduction palsy on leftward gaze**, indicative of an **internuclear ophthalmoplegia (INO)**, highly suggestive of **multiple sclerosis (MS)** in a young adult with a history of transient neurological symptoms (right arm weakness).
- In INO, the eye attempting to adduct (in this case, the right eye on leftward gaze) has impaired movement, while the contralateral abducting eye (left eye on leftward gaze) often exhibits **horizontal nystagmus**.
*Afferent pupillary defect in the left eye*
- An **afferent pupillary defect (APD)**, also known as a **Marcus Gunn pupil**, indicates a lesion to the **afferent visual pathway** (retina, optic nerve, or optic chiasm).
- While MS can cause optic neuritis leading to APD, it is not a direct consequence or associated finding of an INO itself.
*Ptosis on the right*
- **Ptosis** (drooping eyelid) is typically caused by dysfunction of the **oculomotor nerve (cranial nerve III)** or the **sympathetic pathway (Horner's syndrome)**.
- While MS can affect cranial nerves, ptosis is not a characteristic finding specifically associated with INO.
*Left abduction palsy on leftward gaze*
- A **left abduction palsy on leftward gaze** would mean the left eye is unable to fully abduct, indicating a problem with the **left abducens nerve (cranial nerve VI)** or its nucleus.
- In INO, it is the **adduction** of the ipsilateral eye that is impaired, and the contralateral eye typically **abducts normally** but with nystagmus.
*Proptosis of the right eye*
- **Proptosis** (exophthalmos) is the bulging of the eye from the orbit, usually caused by retro-orbital mass lesions (e.g., **thyroid eye disease**, orbital tumors) or inflammation.
- This finding is unrelated to the neurological lesion causing an INO.
Question 62: A 78-year-old right-handed male is brought in by ambulance after being found down in his home. After being aroused, the patient has difficulty answering questions and appears to be frustrated by his inability to communicate. He is able to speak his name and a few other words but his speech is not fluent. Subsequent neurologic exam finds that the patient is able to comprehend both one and two step instructions; however, he is unable to repeat phrases despite being able to understand them. He also has difficulty writing despite retaining fine motor control. CT reveals an acute stroke to his left hemisphere. Damage to which of the following sets of structures would be most likely to result in this pattern of deficits?
A. Superior temporal gyrus
B. Watershed zone
C. Inferior frontal gyrus (Correct Answer)
D. Arcuate fasciculus
E. Precentral gyrus
Explanation: ***Inferior frontal gyrus***
- Damage to the **inferior frontal gyrus** (Broca's area) typically causes **non-fluent aphasia** (Broca's aphasia), characterized by difficulty with speech production and writing, while **comprehension remains relatively intact**.
- The patient's inability to communicate fluently, frustration, difficulty writing, and preserved comprehension align with the clinical features of **Broca's aphasia**.
*Superior temporal gyrus*
- The **superior temporal gyrus** (Wernicke's area) is primarily involved in **language comprehension**.
- Damage to this area results in **fluent aphasia** (Wernicke's aphasia), where speech is fluent but incomprehensible, and comprehension is severely impaired, which is inconsistent with the patient's presentation.
*Watershed zone*
- A stroke in the **watershed zone** (border zones between major cerebral arteries) can lead to **transcortical aphasias**, where the ability to repeat is often preserved.
- The patient's inability to repeat phrases rules out a typical transcortical aphasia.
*Arcuate fasciculus*
- The **arcuate fasciculus** connects Broca's and Wernicke's areas and is crucial for **repetition**.
- Damage to this structure primarily causes **conduction aphasia**, characterized by impaired repetition despite relatively preserved comprehension and fluent speech, which does not match the patient's non-fluent speech.
*Precentral gyrus*
- The **precentral gyrus** is the primary motor cortex, responsible for initiating voluntary movements.
- Damage here would primarily cause **contralateral motor deficits** (e.g., hemiparesis or hemiplegia), not the specific language deficits described, although motor weakness can coexist with aphasia due to larger lesion size.
Question 63: A 23-year-old man presents to the emergency room following a stab wound to the back. He was in a bar when he got into an argument with another man who proceeded to stab him slightly right of the midline of his back. He is otherwise healthy and does not take any medications. He has one previous admission to the hospital for a stab wound to the leg from another bar fight 2 years ago. His temperature is 99°F (37.2°C), blood pressure is 115/80 mmHg, pulse is 100/min, and pulse oximetry is 99% on room air. Cardiopulmonary and abdominal exams are unremarkable; however, he has an abnormal neurologic exam. If this wound entered his spinal cord but did not cross the midline, which of the following would most likely be seen in this patient?
A. Contralateral spasticity below the level of the lesion
B. Ipsilateral flaccid paralysis at the level of the lesion (Correct Answer)
C. Ipsilateral loss of pain and temperature sensation below the lesion
D. Contralateral loss of tactile, vibration, and proprioception below the lesion
E. Contralateral loss of sensation at the level of the lesion
Explanation: ***Ipsilateral flaccid paralysis at the level of the lesion***
- A stab wound indicates an acute lesion, which often results in **spinal shock** at the level of the injury, leading to **flaccid paralysis** due to damage to the lower motor neurons or their axons.
- If the transection affects nerve roots or the ventral horn at the level of the lesion, it would specifically cause **ipsilateral flaccid paralysis** due to interruption of the efferent motor pathways before decussation.
*Contralateral spasticity below the level of the lesion*
- **Spasticity** (upper motor neuron signs) would occur **ipsilaterally** below the level of the lesion due to damage to the **corticospinal tracts** before their decussation in the medulla.
- This symptom takes time to develop following an acute injury, as the initial phase is often characterized by **spinal shock** and flaccid paralysis.
*Ipsilateral loss of pain and temperature sensation below the lesion*
- The **spinothalamic tracts**, responsible for pain and temperature sensation, **decussate (cross over)** almost immediately upon entering the spinal cord.
- Therefore, a lesion on one side of the spinal cord would cause **contralateral loss of pain and temperature** sensation below the level of the lesion.
*Contralateral loss of tactile, vibration, and proprioception below the lesion*
- The **dorsal columns**, which carry tactile, vibration, and proprioception information, **decussate in the medulla** oblongata, not in the spinal cord.
- Thus, a lesion on one side of the spinal cord would result in **ipsilateral loss of these sensations** below the level of the lesion.
*Contralateral loss of sensation at the level of the lesion*
- Sensation loss at the level of the lesion would involve the disruption of nerve roots or segmental grey matter, which primarily causes **ipsilateral sensory deficits** corresponding to the affected dermatome, not contralateral.
- Contralateral loss occurs for specific tracts (like spinothalamic) **below** the lesion, not typically at the level itself for all sensations.
Question 64: A 63-year-old man is brought to the emergency department by his wife because she is concerned he is having another stroke. The patient says he woke up with right-sided facial weakness and drooping. Past medical history is significant for a recent case of shingles treated with acyclovir, and a stroke, diagnosed 10 years ago, from which he recovered with no residual functional deficits. On physical examination, there is weakness and drooping of the entire right side of the face. Sensation is intact. The remainder of the physical examination is unremarkable. Which of the following additional findings would also most likely be seen in this patient?
A. Decreased salivation (Correct Answer)
B. Wrinkled forehead
C. Expressive aphasia
D. Complete loss of taste to the tongue
E. Partial hearing loss
Explanation: ***Decreased salivation***
- This is the **correct answer** for a patient with **Bell's palsy** (peripheral facial nerve palsy)
- The **facial nerve (CN VII)** carries **parasympathetic fibers** via the **chorda tympani** to innervate the **submandibular and sublingual salivary glands**
- A **lower motor neuron lesion** affecting CN VII results in **decreased salivation** on the affected side
- The clinical presentation of **complete facial weakness** (entire right side) with **recent shingles** strongly suggests **peripheral facial nerve palsy**, potentially **Ramsay Hunt syndrome** (VZV reactivation affecting CN VII)
*Wrinkled forehead*
- This finding would **NOT** be seen in this patient
- A **lower motor neuron (LMN) lesion** of CN VII causes **complete ipsilateral facial paralysis**, including **inability to wrinkle the forehead** on the affected side
- **Forehead sparing** (preserved ability to wrinkle forehead) indicates an **upper motor neuron (UMN) lesion** due to bilateral cortical innervation of the frontalis muscle
- Since this patient has **complete facial weakness** including the forehead, he would be **unable to wrinkle his forehead**
*Expressive aphasia*
- **Expressive aphasia (Broca's aphasia)** results from damage to the **dominant frontal lobe** (Broca's area)
- This represents a **cortical lesion**, typically from stroke affecting the middle cerebral artery territory
- The patient's symptoms are isolated to **CN VII dysfunction** without evidence of cortical involvement
- No language, motor, or sensory deficits outside the facial nerve distribution are present
*Complete loss of taste to the tongue*
- While **partial taste loss** can occur in Bell's palsy, **complete loss of taste to the entire tongue** would not be expected
- The **facial nerve (CN VII)** carries taste from the **anterior two-thirds of the tongue** via the **chorda tympani**
- The **glossopharyngeal nerve (CN IX)** innervates taste from the **posterior one-third of the tongue**
- Complete taste loss would require involvement of both CN VII and CN IX, which is not typical for Bell's palsy
*Partial hearing loss*
- The facial nerve innervates the **stapedius muscle**, and CN VII palsy can cause **hyperacusis** (increased sensitivity to sound) due to loss of the acoustic reflex
- **Hearing loss** itself is mediated by the **vestibulocochlear nerve (CN VIII)**, not CN VII
- While **Ramsay Hunt syndrome** can sometimes involve CN VIII, the primary finding would be **hyperacusis**, not hearing loss
Question 65: A 25-year-old previously healthy woman presents to her PCP reporting cessation of menses for the past 6 months. Previously, her period occurred regularly, every 30 days. She also complains of decreased peripheral vision, most noticeably when she is driving her car. She denies any recent sexual activity and a pregnancy test is negative. Upon further work-up, what physical exam finding is most likely to be identified?
A. Breast mass
B. Enlarged thyroid
C. Bitemporal hemianopsia (Correct Answer)
D. Renal failure
E. Pregnancy
Explanation: ***Bitemporal hemianopsia***
- The patient's symptoms of **amenorrhea** and **decreased peripheral vision** are highly suggestive of a **pituitary adenoma**, specifically one that causes mass effect on the optic chiasm.
- A pituitary adenoma can compress the **optic chiasm**, leading to the classic visual field defect known as **bitemporal hemianopsia**, where the temporal (peripheral) vision in both eyes is lost.
*Breast mass*
- While breast masses are common, they are generally **not associated** with amenorrhea or peripheral vision loss.
- A breast mass would typically present with a palpable lump or imaging abnormality of the breast.
*Enlarged thyroid*
- An enlarged thyroid (goiter) can be associated with thyroid dysfunction, which can cause menstrual irregularities, but it typically **does not cause peripheral vision loss**.
- Visual field defects point towards a problem with the **optic pathways**, not thyroid pathology.
*Renal failure*
- **Chronic renal failure** can cause menstrual irregularities due to hormonal imbalances, but it is **not directly linked** to visual field defects like bitemporal hemianopsia.
- Renal failure would present with symptoms like edema, fatigue, and changes in urination.
*Pregnancy*
- Although amenorrhea is a hallmark of pregnancy, the patient has explicitly **denied recent sexual activity** and a **negative pregnancy test** rules this out.
- Pregnancy does not cause **bitemporal hemianopsia** as a primary symptom.
Question 66: A 4-year-old boy is brought to the physician because of a progressive headache and neck pain for 2 weeks. During this period, he has had multiple episodes of dizziness and tingling sensations in his arms and hands. A year ago, he underwent closed reduction of a dislocated shoulder that he suffered after a fall. He underwent surgical removal of a sac-like protuberance on his lower back, soon after being born. His temperature is 36.7°C (98°F), pulse is 80/min, and blood pressure is 100/80 mm Hg. His neck is supple. Neurological examination shows sensorineural hearing loss bilaterally and normal gross motor function. Fundoscopy reveals bilateral optic disk swelling. An MRI of the brain is shown. Which of the following is the most likely cause of this patient's symptoms?
A. Brachial plexus injury
B. Vestibular schwannoma
C. Chiari II malformation (Correct Answer)
D. Medulloblastoma
E. Intraventricular hemorrhage
Explanation: ***Chiari II malformation***
- The patient's history of surgical removal of a "sac-like protuberance" on his lower back soon after birth suggests a **myelomeningocele**, which is strongly associated with Chiari II malformation.
- Symptoms like progressive headache, neck pain, dizziness, tingling in arms/hands, bilateral optic disk swelling (indicating **increased intracranial pressure**), and sensorineural hearing loss are consistent with brainstem and cranial nerve compression common in Chiari II.
*Brachial plexus injury*
- This typically presents with acute, localized weakness, numbness, or pain in the arm and hand **due to nerve damage**, often following trauma like a dislocated shoulder.
- It would not explain the **progressive headache**, optic disc swelling, or the patient's congenital history of a lower back malformation.
*Vestibular schwannoma*
- This tumor primarily affects the **vestibulocochlear nerve (CN VIII)**, causing **unilateral hearing loss**, tinnitus, and balance issues.
- It would not typically present with bilateral hearing loss, increased intracranial pressure symptoms (like optic disc swelling), or be linked to a congenital spinal defect.
*Medulloblastoma*
- While a **medulloblastoma** can cause symptoms of increased intracranial pressure (headache, optic disc swelling) and sometimes dizziness, it is a **malignant brain tumor**.
- It does not explain the patient's history of a congenital spinal defect (myelomeningocele) or the specific tingling sensations in the arms and hands in the context of brainstem compression.
*Intraventricular hemorrhage*
- This usually occurs in **neonates, especially premature infants**, and presents with acute neurological deficits, apnea, bradycardia, or seizures.
- It is unlikely to present as progressive headache and neck pain in a 4-year-old and does not account for the congenital spinal defect or chronic symptoms.
Question 67: 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 68: A 64-year-old man presents to his primary care clinic for a regular checkup. He reports feeling depressed since his wife left him 6 months prior and is unable to recall why she left him. He denies any sleep disturbance, change in his eating habits, guilt, or suicidal ideation. His past medical history is notable for hypertension, gout, and a myocardial infarction five years ago. He takes lisinopril, aspirin, metoprolol, and allopurinol. He has a 50 pack-year smoking history and was previously a heroin addict but has not used in over 20 years. He drinks at least 6 beers per day. His temperature is 98.6°F (37°C), blood pressure is 155/95 mmHg, pulse is 100/min, and respirations are 18/min. He appears somewhat disheveled, inattentive, and smells of alcohol. During his prior visits, he has been well-groomed and attentive. When asked what year it is and who the president is, he confidently replies “1999” and “Jimmy Carter.” He says his son’s name is “Peter” when it is actually “Jake.” This patient likely has a lesion in which of the following brain regions?
A. Anterior pillars of the fornix (Correct Answer)
B. Posterior pillars of the fornix
C. Parahippocampal gyrus
D. Arcuate fasciculus
E. Dorsal hippocampus
Explanation: ***Anterior pillars of the fornix***
- This patient presents with **confabulation** (stating "1999," "Jimmy Carter," calling his son "Peter" instead of "Jake") and **anterograde amnesia** (unable to recall why his wife left 6 months ago), classic features of **Korsakoff syndrome** in a chronic alcoholic with **thiamine (vitamin B1) deficiency**.
- Korsakoff syndrome classically involves lesions of the **mammillary bodies** and the **dorsomedial nucleus of the thalamus**. These structures are functionally connected via the **mammillothalamic tract** and are part of the **Papez circuit** for memory.
- The **fornix** is a white matter tract connecting the hippocampus to the mammillary bodies and septal nuclei. While the fornix itself is not typically the primary site of pathology in Korsakoff syndrome, damage to the **anterior pillars of the fornix** can disrupt the hippocampal-mammillary body pathway, producing similar memory deficits including anterograde amnesia and confabulation.
- Among the given options, this is the structure most closely associated with the memory circuitry disrupted in Korsakoff syndrome.
*Posterior pillars of the fornix*
- The posterior pillars (crura) of the fornix carry fibers from the hippocampus toward the mammillary bodies but are more posteriorly located.
- While theoretically damage here could affect memory circuits, it is less specifically associated with the diencephalic amnesia pattern seen in Korsakoff syndrome compared to anterior connections.
*Parahippocampal gyrus*
- The parahippocampal gyrus is involved in **memory encoding and retrieval**, particularly recognition memory and spatial context.
- Damage here causes memory deficits but does not produce the characteristic **confabulation** and diencephalic amnesia pattern of Korsakoff syndrome, which primarily affects midline diencephalic structures.
*Arcuate fasciculus*
- The **arcuate fasciculus** connects **Broca's area** (frontal lobe) and **Wernicke's area** (temporal lobe), serving language functions, particularly repetition.
- Damage causes **conduction aphasia** (impaired repetition with relatively preserved comprehension and fluency), not memory dysfunction or confabulation.
*Dorsal hippocampus*
- The hippocampus is essential for **encoding new episodic memories** and would cause severe **anterograde amnesia** if damaged.
- However, Korsakoff syndrome primarily involves **diencephalic structures** (mammillary bodies and dorsomedial thalamus) rather than the hippocampus itself. Additionally, hippocampal damage alone typically does not produce the prominent **confabulation** characteristic of Korsakoff syndrome.
Question 69: A 58-year-old man comes to the physician because of burning pain in his neck and arms for a year. He has also had paresthesias in his hands during this period. He has had increasing weakness in both hands during the past 3 months. He has type 2 diabetes mellitus, hypercholesterolemia, and hypertension. He was involved in a motor vehicle collision 3 years ago. Current medications include metformin, sitagliptin, enalapril, atorvastatin, and aspirin. He has had 7 sexual partners in his lifetime; he uses condoms inconsistently. He is oriented to time, place, and person. Vital signs are within normal limits. The pupils are equal and reactive to light. Examination of the upper extremities shows decreased muscle strength, absent reflexes, and decreased hand grip with fasciculations bilaterally. Sensation to temperature and pain is absent over the chest and bilateral upper arms. Vibration and joint position sensations are present in the upper limbs. Cranial nerve examination shows no focal findings. Examination of the lower extremities show no abnormalities. Which of the following is the most likely diagnosis?
A. Brown-Séquard syndrome
B. Tabes dorsalis
C. Multiple sclerosis
D. Syringomyelia (Correct Answer)
E. Cervical disk prolapse
Explanation: ***Syringomyelia***
- This condition is characterized by a central canal cavitation (syrinx) in the spinal cord, leading to damage to the **spinothalamic tracts** (loss of pain and temperature sensation) and anterior horn cells (weakness, fasciculations, absent reflexes). The **'cape-like' distribution** of sensory loss over the chest and arms, along with hand weakness, is classic.
- The sensation loss to temperature and pain over the chest and bilateral upper arms with preserved vibration and joint position sensation in upper limbs is a **dissociated sensory loss**, a hallmark of syringomyelia, as the dorsal columns (responsible for vibration and proprioception) are typically spared.
*Brown-Séquard syndrome*
- This syndrome results from **hemitransaction of the spinal cord**, causing ipsilateral loss of motor function and proprioception/vibration sensation, and contralateral loss of pain and temperature sensation below the lesion.
- The patient's symptoms of **bilateral sensory loss** and **bilateral weakness** do not fit this unilateral lesion pattern.
*Tabes dorsalis*
- This is a late manifestation of **syphilis**, primarily affecting the posterior columns of the spinal cord (dorsal columns), leading to loss of **proprioception and vibration sensation**, along with ataxia and shooting pains.
- The patient presents with loss of pain and temperature sensation, not primarily proprioception and vibration, and has **motor weakness with fasciculations**, which are not typical for tabes dorsalis.
*Multiple sclerosis*
- MS is characterized by **demyelination in the central nervous system**, presenting with diverse neurological symptoms that often wax and wane, affecting multiple areas of the brain and spinal cord.
- While it can cause sensory and motor deficits, the **dissociated sensory loss** (pain/temperature vs. vibration/proprioception) in a "cape-like" distribution with prominent fasciculations points away from MS.
*Cervical disk prolapse*
- A cervical disk prolapse typically causes **radicular pain and neurological deficits** (motor weakness, sensory loss, reflex changes) in a dermatomal or myotomal distribution corresponding to the compressed nerve root.
- While it can cause arm pain and weakness, the **bilateral, "cape-like" dissociated sensory loss** over the chest and arms is not characteristic of a single or multiple cervical nerve root compressions.
Question 70: A 26-year-old man comes to the physician for a follow-up examination. Two weeks ago, he was treated in the emergency department for head trauma after being hit by a bicycle while crossing the street. Neurological examination shows decreased taste on the right anterior tongue. This patient's condition is most likely caused by damage to a cranial nerve that is also responsible for which of the following?
A. Facial sensation
B. Parotid gland salivation
C. Uvula movement
D. Tongue protrusion
E. Eyelid closure (Correct Answer)
Explanation: ***Eyelid closure***
- The patient's **decreased taste on the right anterior tongue** indicates damage to the **facial nerve (CN VII)**, specifically the chorda tympani branch.
- The facial nerve is also responsible for innervating the muscles of **facial expression**, including the **orbicularis oculi** which closes the eyelid.
*Facial sensation*
- **Facial sensation** (touch, pain, temperature) is primarily mediated by the **trigeminal nerve (CN V)**, not the facial nerve.
- Damage to the trigeminal nerve would result in sensory deficits, not taste disturbances on the anterior tongue.
*Parotid gland salivation*
- **Parotid gland salivation** is primarily controlled by the **glossopharyngeal nerve (CN IX)** via the otic ganglion.
- The facial nerve (CN VII) innervates the **submandibular and sublingual glands**, but not the parotid gland.
*Uvula movement*
- **Uvula movement** and elevation of the soft palate are primarily controlled by the **vagus nerve (CN X)**, specifically through the pharyngeal plexus.
- Damage to CN X would typically lead to deviation of the uvula away from the paralyzed side.
*Tongue protrusion*
- **Tongue protrusion** (moving the tongue out) is the primary function of the **hypoglossal nerve (CN XII)**.
- Damage to the hypoglossal nerve would cause the tongue to deviate towards the lesioned side upon protrusion due to unopposed action of the healthy genioglossus muscle.