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?
Q32
A 38-year-old man comes to the physician for a follow-up examination. He has quadriparesis as a result of a burst fracture of the cervical spine that occurred after a fall from his roof 1 month ago. He has urinary and bowel incontinence. He appears malnourished. His temperature is 37.1°C (98.8°F), pulse is 88/min, and blood pressure is 104/60 mm Hg. Examination shows spasticity in all extremities. Muscle strength is decreased in proximal and distal muscle groups bilaterally. Deep tendon reflexes are 4+ bilaterally. Plantar reflex shows extensor response bilaterally. Sensation to pinprick and temperature is absent below the neck. Sensation to vibration, position, and light touch is normal bilaterally. Rectal tone is decreased. There is a 1-cm area of erythema over the sacrum. Which of the following is the most likely cause of this patient's symptoms?
Q33
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?
Q34
An 82-year-old right-handed woman is brought in by ambulance after being found down in her home. On presentation, she is found to be awake but does not follow directions or respond to questions. She is able to speak and produces a fluent string of nonsensical words and sounds. She does not appear to be bothered by her deficits. Subsequent neurologic exam finds that the patient is unable to comprehend any instructions and is also unable to repeat phrases. CT scan reveals an acute stroke to her left hemisphere. Damage to which of the following structures would be most likely to result in this pattern of deficits?
Q35
A 40-year-old man is brought to the emergency department after sustaining multiple lacerations during a bar fight. The patient’s wife says that he has been showing worsening aggression and has been involved in a lot of arguments and fights for the past 2 years. The patient has no significant past medical or psychiatric history and currently takes no medications. The patient cannot provide any relevant family history since he was adopted as an infant. His vitals are within normal limits. On physical examination, the patient looks apathetic and grimaces repeatedly. Suddenly, his arms start to swing by his side in an uncontrolled manner. Which area of the brain is most likely affected in this patient?
Q36
A 75-year-old man comes to the physician because of a 2-week history of sharp, stabbing pain in the lower back that radiates to the back of his left leg. He also has had a loss of sensitivity around his buttocks and inner thighs as well as increased trouble urinating the last week. Two years ago, he was diagnosed with prostate cancer and was treated with radiation therapy. Neurologic examination shows reduced strength and reflexes in the left lower extremity; the right side is normal. The resting anal sphincter tone is normal but the squeeze tone is reduced. Which of the following is the most likely diagnosis?
Q37
A 35-year-old man is transferred to the intensive care unit after a motorcycle accident. He does not open his eyes with painful stimuli. He makes no sounds. He assumes decerebrate posture with sternal rub. His right eye is abnormally positioned downward and outward and has a dilated pupil which is not responsive to light. In contrast to this patient's findings, one would expect a patient with a diabetic mononeuropathy of the oculomotor nerve to present in which fashion?
Q38
A 10-year-old boy is brought to the pediatrician by his mother for evaluation. Last night, he was playing with his younger brother and a hot cup of coffee fell on his left shoulder. Though his skin became red and swollen, he acted as if nothing happened and did not complain of pain or discomfort. He has met all expected developmental milestones, and his vaccinations are up-to-date. Physical examination reveals a normal appearing boy with height and weight in the 56th and 64th percentiles for his age, respectively. The skin over his left shoulder is erythematous and swollen. Sensory examination reveals impaired pain and temperature sensation in a cape-like distribution across both shoulders, arms, and neck. The light touch, vibration, and position senses are preserved. The motor examination is within normal limits, and he has no signs of a cerebellar lesion. His gait is normal. Which of the following disorders is most likely associated with this patient’s condition?
Q39
A 54-year-old woman comes to the physician because of a 1-day history of fever, chills, and double vision. She also has a 2-week history of headache and foul-smelling nasal discharge. Her temperature is 39.4°C (103°F). Examination shows mild swelling around the left eye. Her left eye does not move past midline on far left gaze but moves normally when looking to the right. Without treatment, which of the following findings is most likely to occur in this patient?
Q40
Where does the only cranial nerve without a thalamic relay nucleus enter the skull?
Neuroanatomy US Medical PG Practice Questions and MCQs
Question 31: 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 32: A 38-year-old man comes to the physician for a follow-up examination. He has quadriparesis as a result of a burst fracture of the cervical spine that occurred after a fall from his roof 1 month ago. He has urinary and bowel incontinence. He appears malnourished. His temperature is 37.1°C (98.8°F), pulse is 88/min, and blood pressure is 104/60 mm Hg. Examination shows spasticity in all extremities. Muscle strength is decreased in proximal and distal muscle groups bilaterally. Deep tendon reflexes are 4+ bilaterally. Plantar reflex shows extensor response bilaterally. Sensation to pinprick and temperature is absent below the neck. Sensation to vibration, position, and light touch is normal bilaterally. Rectal tone is decreased. There is a 1-cm area of erythema over the sacrum. Which of the following is the most likely cause of this patient's symptoms?
A. Hemi-transection of the spinal cord
B. Cavitation within the spinal cord
C. Injury to gray matter of the spinal cord
D. Occlusion of the posterior spinal artery
E. Damage to the anterior spinal artery (Correct Answer)
Explanation: ***Damage to the anterior spinal artery***
- This typically results in **anterior cord syndrome**, characterized by bilateral loss of pain and temperature sensation, motor function (quadriparesis), and autonomic dysfunction (bowel/bladder incontinence below the level of injury).
- The **preservation of posterior column functions** (vibration, proprioception, light touch) is a hallmark of anterior spinal artery ischemia, as the posterior columns are supplied by the posterior spinal arteries.
*Hemi-transection of the spinal cord*
- This describes **Brown-Séquard syndrome**, which involves ipsilateral loss of motor function, vibration, and proprioception, and contralateral loss of pain and temperature sensation.
- The patient's symptoms are inconsistent with Brown-Séquard syndrome due to the **bilateral presentation of motor and sensory deficits**.
*Cavitation within the spinal cord*
- This condition, known as **syringomyelia**, typically presents with a **cape-like distribution of pain and temperature loss** (due to central cord involvement affecting the decussating spinothalamic fibers).
- It would usually spare motor function initially and would not explain the sudden, severe quadriparesis and complete sensory loss described.
*Injury to gray matter of the spinal cord*
- Isolated gray matter injury, often seen in conditions like **central cord syndrome**, primarily affects the pain and temperature pathways and may cause upper extremity weakness.
- It would not explain the **complete loss of motor function and pain/temperature sensation below the neck** while preserving posterior column function.
*Occlusion of the posterior spinal artery*
- Occlusion of the posterior spinal artery would primarily affect the **dorsal columns**, leading to loss of vibration, proprioception, and light touch.
- This patient, however, has **preserved sensation to vibration, position, and light touch**, making posterior spinal artery occlusion unlikely.
Question 33: 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.
Question 34: An 82-year-old right-handed woman is brought in by ambulance after being found down in her home. On presentation, she is found to be awake but does not follow directions or respond to questions. She is able to speak and produces a fluent string of nonsensical words and sounds. She does not appear to be bothered by her deficits. Subsequent neurologic exam finds that the patient is unable to comprehend any instructions and is also unable to repeat phrases. CT scan reveals an acute stroke to her left hemisphere. Damage to which of the following structures would be most likely to result in this pattern of deficits?
A. Precentral gyrus
B. Superior temporal gyrus (Correct Answer)
C. Arcuate fasciculus
D. Inferior frontal gyrus
E. Watershed zone
Explanation: ***Superior temporal gyrus***
- This patient presents with **fluent aphasia** (speaking nonsensical words), severely impaired **comprehension**, and impaired **repetition**. This triad is characteristic of **Wernicke's aphasia**.
- **Wernicke's area**, responsible for language comprehension, is located in the **posterior part of the superior temporal gyrus** in the dominant hemisphere (typically left).
*Precentral gyrus*
- The **precentral gyrus** contains the **primary motor cortex** and its damage would primarily cause contralateral motor deficits (e.g., **hemiparesis** or **hemiplegia**).
- This area is not directly involved in language comprehension or production of fluent but nonsensical speech.
*Arcuate fasciculus*
- Damage to the **arcuate fasciculus**, a white matter tract connecting Broca's and Wernicke's areas, results in **conduction aphasia**.
- In **conduction aphasia**, comprehension and fluency are relatively preserved, but **repetition is severely impaired**. This patient also has impaired comprehension.
*Inferior frontal gyrus*
- The **inferior frontal gyrus** houses **Broca's area**, which is responsible for **language production and motor aspects of speech**.
- Damage to this area typically causes **Broca's aphasia**, characterized by **non-fluent speech**, preserved comprehension, and impaired repetition. This patient has fluent speech.
*Watershed zone*
- **Watershed infarcts** occur at the borders between major arterial territories due to hypoperfusion, often leading to **transcortical aphasias**.
- While transcortical sensory aphasia involves impaired comprehension and fluent speech, **repetition is preserved**, which is not the case here.
Question 35: A 40-year-old man is brought to the emergency department after sustaining multiple lacerations during a bar fight. The patient’s wife says that he has been showing worsening aggression and has been involved in a lot of arguments and fights for the past 2 years. The patient has no significant past medical or psychiatric history and currently takes no medications. The patient cannot provide any relevant family history since he was adopted as an infant. His vitals are within normal limits. On physical examination, the patient looks apathetic and grimaces repeatedly. Suddenly, his arms start to swing by his side in an uncontrolled manner. Which area of the brain is most likely affected in this patient?
A. Cerebral cortex
B. Caudate nucleus (Correct Answer)
C. Cerebellum
D. Medulla oblongata
E. Substantia nigra
Explanation: **Caudate nucleus**
- The patient exhibits features like **worsening aggression**, **apathy**, and **uncontrolled, sudden movements** of the limbs, which are characteristic of Huntington's disease, a condition primarily affecting the **caudate nucleus**.
- **Huntington's disease** is an autosomal dominant neurodegenerative disorder linked to a trinucleotide repeat expansion (CAG) on chromosome 4, leading to atrophy of the **caudate and putamen**.
*Cerebral cortex*
- While damage to the cerebral cortex can cause personality changes and motor deficits, the specific combination of **choreiform movements** and progressive cognitive/behavioral decline seen here is more indicative of a basal ganglia disorder like Huntington's.
- Cortical lesions more commonly present with **focal neurological deficits** such as hemiparesis, aphasia, or sensory loss, which are not the primary features described.
*Cerebellum*
- Damage to the cerebellum typically results in **ataxia**, **dysmetria**, **intention tremor**, and problems with balance and coordination.
- The patient's **uncontrolled, sudden limb movements** are characteristic of chorea, not cerebellar dysfunction.
*Medulla oblongata*
- The medulla oblongata is crucial for vital autonomic functions such as **breathing, heart rate, and blood pressure regulation**.
- Lesions in this area would likely cause life-threatening symptoms, including **respiratory failure** or severe cardiovascular instability, which are not present in this patient.
*Substantia nigra*
- Damage or degeneration of the substantia nigra is primarily associated with **Parkinson's disease**, leading to symptoms like **bradykinesia**, **rigidity**, **resting tremor**, and **postural instability**.
- The patient's **hyperkinetic movements** (choreiform movements) are opposite to the hypokinetic presentation of Parkinson's disease.
Question 36: A 75-year-old man comes to the physician because of a 2-week history of sharp, stabbing pain in the lower back that radiates to the back of his left leg. He also has had a loss of sensitivity around his buttocks and inner thighs as well as increased trouble urinating the last week. Two years ago, he was diagnosed with prostate cancer and was treated with radiation therapy. Neurologic examination shows reduced strength and reflexes in the left lower extremity; the right side is normal. The resting anal sphincter tone is normal but the squeeze tone is reduced. Which of the following is the most likely diagnosis?
A. Central cord syndrome
B. Conus medullaris syndrome
C. Anterior spinal cord syndrome
D. Brown-sequard syndrome
E. Cauda equina syndrome (Correct Answer)
Explanation: ***Cauda equina syndrome***
- The patient presents with **bilateral sensory loss in the perineal region** (**saddle anesthesia**) and **new-onset urinary dysfunction** (trouble urinating, reduced squeeze tone), which are classic symptoms of cauda equina syndrome.
- The **sharp, stabbing radicular pain** radiating down the leg indicates nerve root involvement, characteristic of cauda equina rather than conus medullaris.
- The **asymmetric motor weakness** (left leg only) supports cauda equina syndrome, as compression can preferentially affect specific nerve roots, whereas conus medullaris typically causes more symmetric bilateral deficits.
- The history of **prostate cancer** and **radiation therapy** suggests a potential metastatic lesion compressing the cauda equina nerves.
*Central cord syndrome*
- This syndrome primarily affects the **upper extremities more than the lower extremities** and typically results from hyperextension injuries in older individuals.
- It often presents with **dissociated sensory loss** (loss of pain and temperature sensation) below the level of the lesion, which is not the primary complaint here.
*Conus medullaris syndrome*
- Affects the **sacral spinal cord segments (S3-S5)**, leading to **symmetrical motor and sensory deficits**, often with prominent early **bowel and bladder dysfunction**.
- While it causes saddle anesthesia and urinary symptoms, the **asymmetrical motor weakness** (left leg only) and **prominent radicular pain** extending down the leg are more characteristic of cauda equina syndrome.
- Conus lesions typically present with more **symmetric bilateral deficits** rather than the unilateral pattern seen here.
*Anterior spinal cord syndrome*
- Characterized by **bilateral motor paralysis** and **loss of pain and temperature sensation** below the lesion, with **preservation of proprioception and vibratory sensation**.
- It would not typically present with the isolated **saddle anesthesia** and **radicular pain** described in the patient.
*Brown-sequard syndrome*
- Results from a **hemicord lesion**, causing **ipsilateral motor paralysis** and loss of proprioception/vibration below the lesion, and **contralateral loss of pain and temperature sensation**.
- The patient's symptoms of **bilateral saddle anesthesia** and **bowel/bladder dysfunction** do not align with the characteristic unilateral sensory and motor presentation of Brown-Sequard syndrome.
Question 37: A 35-year-old man is transferred to the intensive care unit after a motorcycle accident. He does not open his eyes with painful stimuli. He makes no sounds. He assumes decerebrate posture with sternal rub. His right eye is abnormally positioned downward and outward and has a dilated pupil which is not responsive to light. In contrast to this patient's findings, one would expect a patient with a diabetic mononeuropathy of the oculomotor nerve to present in which fashion?
A. Fixed dilated pupil with normal extraocular movements
B. Downward and outward gaze, ptosis, and a fixed, dilated pupil
C. Ptosis only
D. Downward and outward gaze with ptosis and a responsive pupil (Correct Answer)
E. Inability to abduct the eye
Explanation: ***Downward and outward gaze with ptosis and a responsive pupil***
- **Diabetic mononeuropathy** of the oculomotor nerve (CN III) typically spares the **pupillary fibers** because they are superficial and supplied by pial vessels, which are often unaffected by microvascular ischemia.
- This results in a **"pupil-sparing" CN III palsy**, where extraocular muscles are affected (leading to **downward and outward gaze** and **ptosis**), but the pupil remains reactive.
*Fixed dilated pupil with normal extraocular movements*
- A **fixed dilated pupil** without other extraocular movement deficits is more suggestive of a direct injury to the **iris sphincter** or a lesion affecting the efferent pupillary fibers, not typically isolated diabetic mononeuropathy.
- Normal extraocular movements contradict a significant oculomotor nerve palsy of any etiology.
*Downward and outward gaze, ptosis, and a fixed, dilated pupil*
- This constellation of symptoms, including a **fixed, dilated pupil**, is characteristic of a **compressive lesion** affecting the oculomotor nerve (e.g., aneurysm, tumor), as it damages the superficial pupillary fibers.
- Diabetic neuropathy typically involves the vasa nervorum of the central part of the nerve, sparing the superficial, parasympathetic pupillary fibers.
*Ptosis only*
- While **ptosis** is a component of oculomotor nerve palsy, it typically occurs with other signs like **downward and outward gaze**. Isolated ptosis might suggest a lesion affecting only the efferent fibers to the **levator palpebrae superioris** or a milder, incomplete palsy.
- More commonly, isolated ptosis can be due to conditions like **myasthenia gravis** or Horner's syndrome (which also includes miosis and anhidrosis).
*Inability to abduct the eye*
- **Inability to abduct the eye** (move it laterally) is a classic sign of an **abducens nerve (CN VI) palsy**, not an oculomotor nerve (CN III) palsy.
- The oculomotor nerve is responsible for most other extraocular movements (adduction, elevation, depression).
Question 38: A 10-year-old boy is brought to the pediatrician by his mother for evaluation. Last night, he was playing with his younger brother and a hot cup of coffee fell on his left shoulder. Though his skin became red and swollen, he acted as if nothing happened and did not complain of pain or discomfort. He has met all expected developmental milestones, and his vaccinations are up-to-date. Physical examination reveals a normal appearing boy with height and weight in the 56th and 64th percentiles for his age, respectively. The skin over his left shoulder is erythematous and swollen. Sensory examination reveals impaired pain and temperature sensation in a cape-like distribution across both shoulders, arms, and neck. The light touch, vibration, and position senses are preserved. The motor examination is within normal limits, and he has no signs of a cerebellar lesion. His gait is normal. Which of the following disorders is most likely associated with this patient’s condition?
A. Arnold-Chiari malformation (Correct Answer)
B. Transverse myelitis
C. Spina bifida occulta
D. Leprosy
E. Brown-Séquard syndrome
Explanation: ***Arnold-Chiari malformation***
- The patient presents with **loss of pain and temperature sensation** in a **cape-like distribution** and **preserved light touch**, vibration, and position senses, which is characteristic of **syringomyelia**.
- **Syringomyelia** is commonly associated with **Arnold-Chiari malformations type I**, where cerebellar tonsils extend into the foramen magnum, obstructing CSF flow and leading to syrinx formation.
*Transverse myelitis*
- This condition involves **inflammation across one segment** of the spinal cord, leading to rapid onset of motor, sensory, and autonomic dysfunction.
- It typically causes a **sensory level deficit** (loss of all sensation below a certain spinal level) rather than the dissociated sensory loss seen here.
*Spina bifida occulta*
- This is a **mild form of neural tube defect** where the bony arches of the vertebrae fail to fuse, but the spinal cord and meninges remain within the vertebral canal.
- It is usually **asymptomatic** and not associated with severe neurological deficits like syringomyelia.
*Leprosy*
- This is a **chronic infectious disease** caused by *Mycobacterium leprae* that primarily affects the skin and peripheral nerves.
- It typically causes **patchy sensory loss** and **nerve thickening** in the extremities, not a central cape-like distribution of sensory deficits.
*Brown-Séquard syndrome*
- This is caused by **hemicord lesion** of the spinal cord, resulting in ipsilateral motor paralysis and loss of proprioception/vibration below the lesion.
- It also causes **contralateral loss of pain and temperature sensation**, which is different from the bilateral cape-like distribution observed in this patient.
Question 39: A 54-year-old woman comes to the physician because of a 1-day history of fever, chills, and double vision. She also has a 2-week history of headache and foul-smelling nasal discharge. Her temperature is 39.4°C (103°F). Examination shows mild swelling around the left eye. Her left eye does not move past midline on far left gaze but moves normally when looking to the right. Without treatment, which of the following findings is most likely to occur in this patient?
A. Hemifacial anhidrosis
B. Jaw deviation
C. Absent corneal reflex (Correct Answer)
D. Relative afferent pupillary defect
E. Hypoesthesia of the earlobe
Explanation: ***Absent corneal reflex***
- This patient's symptoms (fever, chills, headache, foul-smelling nasal discharge, periorbital swelling, and ophthalmoplegia) suggest **cavernous sinus thrombosis** secondary to a sinus infection.
- The cavernous sinus contains cranial nerves III, IV, VI, V1, and V2. Untreated, the infection and thrombosis can easily spread to affect **cranial nerve V1 (ophthalmic branch of trigeminal nerve)**, leading to an absent corneal reflex.
*Hemifacial anhidrosis*
- This symptom, along with ptosis and miosis, is indicative of **Horner's syndrome**, which results from damage to the ipsilateral **sympathetic pathway**.
- While cavernous sinus thrombosis can rarely involve sympathetic fibers, it's not the most direct or common neurological sequela compared to trigeminal nerve involvement.
*Jaw deviation*
- **Jaw deviation** typically occurs due to weakness or paralysis of the **motor branch of the trigeminal nerve (V3)**, which innervates the muscles of mastication.
- Cavernous sinus thrombosis primarily affects V1 and V2, and V3 involvement, while possible, is less common and usually presents later than V1 or V2 deficits.
*Relative afferent pupillary defect*
- A relative afferent pupillary defect (RAPD, or Marcus Gunn pupil) indicates a lesion in the **afferent visual pathway** (e.g., optic nerve or retina).
- While vision can be affected in cavernous sinus thrombosis due to optic nerve compression or venous congestion, RAPD is not the most direct or specific neurological complication expected from the provided symptoms.
*Hypoesthesia of the earlobe*
- Sensation to the earlobe is primarily supplied by the **great auricular nerve (C2-C3 cervical spinal nerves)** with minor contribution from the **auricular branch of the vagus nerve (CN X)**.
- Cavernous sinus thrombosis does not involve these nerves, and hypoesthesia of the earlobe is not a characteristic finding.
Question 40: 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.
