Lesions of the Brain Stem

Question 1

The affected structures and resultant deficits in lateral medullary syndrome [i.e., posterior inferior cerebellar artery (PICA) syndrome] include…

Answer 1

1. The vestibular nuclei. Lesions result in nystagmus, nausea, vomiting, and vertigo.
2. The inferior cerebellar peduncle. Lesions result in ipsilateral cerebellar signs [e.g., dystaxia, dysmetria (past pointing), dysdiadochokinesia].
3. The nucleus ambiguus of CN IX, CN X, and CN XI. Lesions result in ipsilateral laryngeal, pharyngeal, and palatal hemiparalysis [i.e., loss of the gag reflex (efferent limb), dysarthria, dysphagia, and dysphonia (hoarseness)].
4. The glossopharyngeal nerve roots. Lesions result in loss of the gag reflex (afferent limb).
5. The vagal nerve roots. Lesions result in the same deficits as seen in lesions involving the nucleus ambiguus.
6. The spinothalamic tracts (spinal lemniscus). Lesions result in contralateral loss of pain and temperature sensation from the trunk and extremities.
7. The spinal trigeminal nucleus and tract. Lesions result in ipsilateral loss of pain and temperature sensation from the face (facial hemianesthesia).
8. The descending sympathetic tract. Lesions result in ipsilateral Horner’s syndrome (i.e., ptosis, miosis, hemianhidrosis, and apparent enophthalmos).

Question 2

Medial inferior pontine syndrome results from occlusion of…

Answer 2

the paramedian branches of the basilar artery.

Question 3

Affected structures and resultant deficits in medial inferior pontine syndrome include…

Answer 3

1. The corticospinal tract. Lesions result in contralateral spastic hemiparesis.
2. The medial lemniscus. Lesions result in contralateral loss of tactile sensation from the trunk and extremities.
3. The abducens nerve roots. Lesions result in ipsilateral lateral rectus paralysis.

Question 4

Affected structures and resultant deficits in lateral inferior pontine syndrome [i.e., anterior inferior cerebellar artery (AICA) syndrome] include…

Answer 4

1. The facial nucleus and intraaxial nerve fibers. Lesions result in: A) ipsilateral facial nerve paralysis, B) ipsilateral loss of taste from the anterior two-thirds of the tongue, C) ipsilateral loss of lacrimation and reduced salivation, D) loss of corneal and stapedial reflexes (efferent limbs).
2. The cochlear nuclei and intraaxial nerve fibers. Lesions result in unilateral central deafness.
3. The vestibular nuclei and intraaxial nerve fibers. Lesions result in nystagmus, nausea, vomiting, and vertigo.
4. The spinal trigeminal nucleus and tract. Lesions result in ipsilateral loss of pain and temperature sensation from the face (facial hemianesthesia).
5. The middle and inferior cerebellar peduncles. Lesions result in ipsilateral limb and gait dystaxia.
6. The spinothalamic tracts (spinal lemniscus). Lesions result in contralateral loss of pain and temperature sensation from the trunk and extremities.
7. The descending sympathetic tract. Lesions result in ipsilateral Horner’s syndrome.

Question 5

Medial longitudinal fasciculus (MLF) syndrome (internuclear ophthalmoplegia) interrupts…

Answer 5

fibers from the contralateral abducens nucleus that project, through the MLF, to the ipsilateral medial rectus subnucleus of CN III.

Question 6

Internuclear ophthalmoplegia presents as…and is often seen in patients with…

Answer 6

medial rectus palsy on attempted lateral conjugate gaze and nystagmus in the abducting eye. Convergence remains intact. This syndrome is often seen in patients with multiple sclerosis.

Question 7

Facial colliculus syndrome usually results from…

Answer 7

a pontine glioma or a vascular accident.

Question 8

Lesions of the internal genu of the facial nerve cause:

Answer 8

1. Ipsilateral facial paralysis

2. Ipsilateral loss of the corneal reflex

Question 9

Lesions of the abducens nucleus cause:

Answer 9

1. Lateral rectus paralysis
2. Medial (convergent) strabismus
3. Horizontal diplopia

Question 10

Dorsal midbrain (Parinaud’s) syndrome is often the result of…

Answer 10

a pinealoma or germinoma of the pineal region.

Question 11

Affected structures and resultant deficits in Parinaud’s syndrome include…

Answer 11

1. The superior colliculus and pretectal area. Lesions cause paralysis of upward and downward gaze, pupillary disturbances, and absence of convergence.
2. The cerebral aqueduct. Compression causes noncommunicating hydrocephalus.

Question 12

Affected structures and resultant deficits in paramedian midbrain (Benedikt) syndrome include…

Answer 12

1. The oculomotor nerve roots (intraaxial fibers). Lesions cause complete ipsilateral oculomotor paralysis. Eye abduction and depression is caused by the intact lateral rectus (CN VI) and superior oblique (CN IV) muscles. Ptosis (paralysis of the levator palpebra muscle) and fixation and dilation of the ipsilateral pupil (complete internal ophthalmoplegia) also occur.
2. The dentatothalamic fibers. Lesions cause contralateral cerebellar dystaxia with intention tremor.
3. The medial lemniscus. Lesions result in contralateral loss of tactile sensation from the trunk and extremities.

Question 13

Affected structures and resultant deficits in medial midbrain (Weber) syndrome include…

Answer 13

1. The oculomotor nerve roots (intraaxial fibers). Lesions cause complete ipsilateral oculomotor paralysis. Eye abduction and depression is caused by intact lateral rectus (CN VI) and superior oblique (CN IV) muscles. Ptosis and fixation and dilation of the ipsilateral pupil also occur.
2. The corticospinal tracts. Lesions result in contralateral spastic hemiparesis.
3. The corticobulbar fibers. Lesions cause contralateral weakness of the lower face (CN VII), tongue (CN XII), and palate (CN X). The upper face division of the facial nucleus receives bilateral corticobulbar input. The uvula and pharyngeal wall are pulled toward the normal side (CN X), and the protruded tongue points to the weak side.

Question 14

A benign tumor of Schwann cells that affects the vestibulocochlear nerve (CN VIII) is…

Answer 14

an acoustic neuroma (or schwannoma), which is a posterior fossa tumor of the internal auditory meatus and cerebellopontine angle. Acoustic neuromas often compress the facial nerve (CN VII), which accompanies CN VIII in the cerebellopontine angle and internal auditory meatus. These tumors may also impinge on the pons and affect the spinal trigeminal tract (CN V).

Question 15

Affected structures and resultant deficits in schwannoma include…

Answer 15

1. The cochlear nerve of CN VIII. Damage results in tinnitus and unilateral nerve deafness.
2. The vestibular nerve of CN VIII. Damage results in vertigo, nystagmus, nausea, vomiting, and unsteadiness of gait.
3. The facial nerve (CN VII). Damage results in facial weakness and loss of the corneal reflex (efferent limb).
4. The spinal trigeminal tract (CN V). Damage results in paresthesia, anesthesia of the ipsilateral face, and loss of the corneal reflex (afferent limb).

Question 16

Bilateral acoustic neuromas are associated with…

Answer 16

neurofibromatosis type 2.

Question 17

Jugular foramen syndrome usually results from…

Answer 17

a posterior fossa tumor (e.g., glomus jugulare tumor, the most common inner ear tumor) that compresses CN IX, X, and XI.

Question 18

Affected structures and resultant deficits in jugular foramen syndrome include…

Answer 18

1. The glossopharyngeal nerve (CN IX). Damage results in A) ipsilateral loss of the gag reflex and B) ipsilateral loss of pain, temperature, and taste in the tongue.
2. The vagus nerve (CN X). Damage results in A) ipsilateral paralysis of the soft palate and larynx and B) ipsilateral loss of the gag reflex.
3. The spinal accessory nerve (CN XI). Damage results in A) paralysis of the sternocleidomastoid muscle (which results in the inability to turn the head to the opposite side) and B) paralysis of the trapezius muscle (which causes shoulder droop and inability to shrug the shoulder).

Question 19

A lesion of the base of the pons (as a result of infarction, trauma, tumor, or demyelination) in which the corticospinal and corticobulbar tracts are affected bilaterally, yet the oculomotor and trochlear nerves are spared.

Answer 19

Locked-in syndrome. Patients are conscious and may communicate through vertical eye movements.

Question 20

A lesion of the base of the pons that affects the corticospinal and corticobulbar tracts. The majority of cases are associated with alcoholism or rapid correction of hyponatremia.

Answer 20

Central pontine myelinolysis. Symptoms include spastic quadriparesis, pseudobulbar palsy, and mental changes. This condition may progress to locked-in syndrome.

Question 21

Neurologic signs of “top of the basilar” syndrome include…

Answer 21

optic ataxia and psychic paralysis of fixation of gaze (Balint’s syndrome), ectopic pupils, somnolence, and cortical blindness, with or without visual anosognosia (Anton’s syndrome). This syndrome results from embolic occlusion of the rostral basilar artery.

Question 22

Long-standing thrombosis of the left subclavian artery proximal to the vertebral artery can manifest clinically as…

Answer 22

subclavian steal syndrome. In this condition, blood is shunted retrograde down the left vertebral artery and into the left subclavian artery.

Question 23

Clinical signs of subclavian steal syndrome include…

Answer 23

transient weakness and claudication of the left arm on exercise and vertebrobasilar insufficiency (i.e., vertigo, dizziness).

Question 24

Affected structures in medial medullary syndrome (i.e., anterior spinal artery syndrome) include…

Answer 24

1. The corticospinal tract (medullary pyramid). Lesions result in contralateral spastic hemiparesis.
2. The medial lemniscus. Lesions result in contralateral loss of tactile and vibration sensation from the trunk and extremities.
3. The hypoglossal nucleus or intraaxial root fibers (CN XII). Lesions result in ipsilateral flaccid hemiparalysis of the tongue. When protruded, the tongue points to the side of the lesion (i.e., the weak side).

Question 25

Five brain tumors, including a cyst, are often located in the cerebellopontine angle cistern. Name them.

Answer 25

1. Schwannoma (75%)
2. Arachnoid cyst (1%)
3. Meningioma (10%)
4. Ependymoma (1%)
5. Epidermoid (5%)

Remember the acronym SAME.