Cranial nerves and brainstem practice quiz

A. Midbrain This question is asking you to localize the location of the lesion based on the finding of paraylsis in the lower quarter of the left face, double vision (diplopia), right ptosis (a drooping eyelid) and loss/absence of the pupillary light reflex on the right. If we attempt to attribute each of the findings to a specific pathway or cranial nerve the answer will become evident. Because cranial nerve findings related to a lesion readily localize a lesion to a specific side of the body and level of the brainstem, unlike symptoms associated with lesions to long tract pathways, it is best to start with the cranial nerve related findings. Cranial nerve III, the oculomotor nerve (CN III), is responsible for maintaining the eyelid open and thus lesions to CN III result in ptosis or a drooping eyelid. The ptosis is on the right suggesting a lesion to the CN III on the right. The pupillary light reflex is associated with CN II (afferent/sensory limb) and CN III (the efferent/motor limb), supporting involvement of CN III on the right. Finally, CN III also innervates extraocular muscles. When there is paralysis of extraocular muscles, a patient can present with double vision. CN III innervates muscles that adduct, elevate, and depress the eye. A unilateral lesion to CN III can therefore result in double vision. Unilateral lesions to CN IV and VI can also result in double vision, though they would not result in the other cranial nerve findings, thus CN III is most likely the lesioned nerve. The findings associated with CN III suggest a lesion to the midbrain, but to confirm this we have to reconcile the paralysis of the left lower face. Initially this might cause one to think the lesion is in facial nerve or facial motor nucleus and therefore is in the pons. A lesion to the facial nerve or nucleus would result in paralysis of the ipsilateral half of the face, not just the lower quarter. A lesion to the left lower quarter of the face suggests an UMN lesion to the descending corticobulbar fibers on the contralateral side. This could occur in the right crus cerebrus (cerebral peduncle) as the corticobulbar fibers would not yet have decussated on their descent toward the LMNs of the facial motor nucleus. The oculomotor nerves exit the midbrain medial to the crus cerebri. Therefore, we could localize the lesion to this area of the right midbrain.

A man has paralysis of his left lower face, diplopia, ptosis and loss of the pupillary reflex on the right. The lesion is most likely in what anatomic location? A. Midbrain B. Pons C. Medulla

C. The midbrain This question is asking that you relate cortical topography (location of the uncus) and dural partitions (i.e. the tentorium cerebelli) to brainstem anatomy. The uncus is a bump on the medial portion of the parahippocampal gyrus of the temporal lobe. See basal views of the brain from the topography lecture. This is an important structure since swelling or displacement of the brain can produce uncal herniations through the tentorial notch into the posterior cranial fossa. (Review brain herniations in the lecture on Blood Supply and Meninges). The brainstem is connected to the cerebrum through the tentorial notch. This is a critical area for compression resulting from herniation, trauma, or mass lesions. Herniation of the uncus can damage cranial nerve III and compress the upper brainstem (most likely the midbrain) resulting in coma. Interruption of pathways in this narrow region commonly results in conditions in which the cerebral cortex is essentially disconnected from the brainstem and spinal cord.

A protrusion of the uncus into the tentorial notch would most likely compress what structure? A. The pituitary B. The cavernous sinus C. The midbrain D. The pons

A. Trigeminal The trigeminal nerve is the main general sensory innervation for the head. GSA fibers within this nerve carry sensory information pertaining to perception of touch, pain, temperature, vibration, and/or proprioception from areas such as the skin of the face, dura mater in the anterior and middle cranial fossae, the cornea, the nasal cavities, the tongue, the teeth, the lips, the mucosa of the mouth, and the temporomandibular joints of the jaw. Thus altered sensation to the face would most likely result from damage to this nerve. The facial nerve provides motor innervation to the muscles of facial expression via BE fibers.

Altered sensation in the face would most likely result from damage to which cranial nerve? A. Trigeminal B. Facial C. Abducens D. Vagus

D. Cranial nerve X

An absent gag reflex along with failure of the soft palate to elevate upon vocalization would most likely indicate a lesion to which of the following cranial nerves? A. Cranial nerve V B. Cranial nerve VII C. Cranial nerve IX D. Cranial nerve X

A. Basilar Artery The section associated with this question is the rostral pons. Blood supply to the bracketed region is supplied by paramedian and lateral circumfrential branches of the basilar artery

Blood supply to the region indicated by the brackets is supplied by what vessel? A. Basilar Artery B. Internal Carotid Artery C. Anterior inferior cerebellar artery D. Superior cerebellar artery

C. Cranial nerve XI

Difficulty performing a shoulder shrug would most likely result from a lesion to which cranial nerve? A. Cranial nerve IX B. Cranial nerve X C. Cranial nerve XI D. Cranial nerve XII

D. Hoarseness of the voice

In Wallenberg's syndrome (a stroke involving posterior inferior cerebellar artery (PICA) or the vertebral artery) which one of the following symptoms is caused by damage to the Nucleus Ambiguus? A. Vertigo and nystagmus B. Altered sensation in the ipsilateral face C. Paralysis of the ipsilateral half of the face D. Hoarseness of the voice

A. Facial nerve

Motor innervation to muscles of facial expression is conveyed through which cranial nerve? A. Facial nerve B. Trigeminal nerve C. Abducens nerve D. Hypoglossal nerve

C. Trigeminal

The afferent limb of the blink reflex involves which of the following cranial nerves? A. Optic B. Oculomotor C. Trigeminal D. Facial

A. Paralysis of the ipsilateral tongue musculature The region of brainstem in this image is a cross-section of the rostral medulla. The area of the lesion corresponds to the medullary pyramid and the preolivary sulcus where the hypoglossal nerve (CN XII) exits from the brainstem. Included in the lesion is the most ventral aspect of the medial lemniscus. Because CN XII would be impacted in this lesion where it exits the brainstem, the effects in the patient would be paralysis of ipsilateral tongue musculature, making "a' the correct choice. Remember that where tongue musculature is weak, the tongue deviates toward the side of the weakness upon protrusion. In this patient, the tongue would deviate on protrusion toward the side of the lesion. The corticospinal pathway, specifically axons of the UMNs would course through the medullary pyramid and be affected in this lesion. Any effects due to the lesion to the corticospinal pathway here would be observed on the side contralateral to the lesion because the pathway has not yet decussated at the level of the rostral medulla. It decussates in the caudal medulla. That might make "c" seem like a correct choice; however, the corticospinal lesion would result in UMN findings in the patient (e.g. hyperreflexia and spastic paralysis) not a hypoactive knee jerk reflex. The spinothalamic pathway is not implicated in this lesion as it is more laterally located in the medulla, making "b" an incorrect choice. Choice "d" may also seem like a correct choice, because the most ventral aspects of the medial lemniscus would be impacted in this lesion. However, the axons related to the leg not the arm would be traveling through this part of the medial lemniscus making contralateral loss of prioceptove sense in the leg correct, but not the in hand. This may seem like a fine point, but lesions can differentially impact the leg or arm due to the somatotopy of this pathway

The lesion in the associated image would most likely result in which of the following in your patient? A. Paralysis of the ipsilateral tongue musculature B. Ipsilateral loss of pain and temperature sensations in the face C. A contralateral hypoactive knee jerk reflex D. Contralateral loss of proprioceptive sense in the hand

C. Oculomotor 3,7,9,10

Which of the following cranial nerves contains parasympathetic fibers? A. Olfactory B. Optic C. Oculomotor D. Trigeminal

A. Trochlear Any cranial nerve that is associated with movements of the eye may cause double vision (diplopia) when lesioned. This would include CNs (III, IV, and VI). A lesion to the Optic nerve (CN II) would cause blurry vision rather than double vision. The trigeminal nerve (CN V) provides sensory innervation to the cornea and thus is involved in the corneal (blink) reflex but is not associated with eye movements. The facial nerve (CN VII) innervates the muscle responsible for closure of the eyelid and thus is also associated with the blink reflex but not eye movements.

Which of the following cranial nerves, when lesioned, may be associated with double vision? A. Trochlear B. Trigeminal C. Optic D. Facial

C. Left Hypoglossal

You ask your patient to protrude his tongue. Upon protrusion, the tongue deviates to the left. The lesion is most likely affecting which cranial nerve? A. Left glossopharyngeal B. Right glossopharyngeal C. Left Hypoglossal D. Right Hypoglossal

B. Cranial nerve III The patient presents with symptoms consistent with a lesion to cranial nerve III. Ptosis refers to a drooping eyelid. CN III helps elevate the eyelid to keep the eye open through innervation of a muscle called the levator palpebrae. The dilated pupil at rest results from loss of parasympathetic innervation to the pupillary constrictor muscle. Finally, the position of the eye in abduction at rest results from a muscular imbalance. CN III controls adduction (medial rectus muscle) of the eye and CN VI controls abduction (lateral rectus muscle). With a loss of CN III, the eye is pulled into abduction by an unopposed lateral rectus muscle (innervated by CN VI).

Your patient has a profound ptosis, a dilated pupil at rest, and an eye that is deviated at rest into an abducted position. Which of the following cranial nerves has most likely been lesioned? A. Cranial nerve II B. Cranial nerve III C. Cranial nerve IV D. C Cranial nerve VI

E. Left Abducens nerve

Your patient reports double vision when he looks to the left. You notice also that when the patient attempts to look to the left, the left eye does not abduct. Which of the following cranial nerves has most likely been lesioned? A. Left Oculomotor nerve B. Right Oculomotor nerve C. Left Trochlear nerve D. Right Trochlear nerve E. Left Abducens nerve F. Right Abducens nerve