A 65-year-old man comes to the emergency department due to acute-onset slurred speech. He also has right-sided weakness but denies any trauma, headache, or loss of consciousness. His medical problems include hypertension and type 2 diabetes mellitus. The patient has smoked 1 pack of cigarettes daily for 20 years. Neurologic examination shows right-sided lower facial droop with sparing of the forehead muscles. Motor strength is 3/5 on the right and 5/5 on the left with a Babinski response on the right. There is also dysmetria and dysdiadochokinesia involving his right upper and lower extremities. MRI of the brain reveals an acute lacunar infarct in the brainstem, as shown in the image below. Which of the following cranial nerves exits the brainstem closest to the level affected by this patient's stroke?

Question

A 65-year-old man comes to the emergency department due to acute-onset slurred speech.  He also has right-sided weakness but denies any trauma, headache, or loss of consciousness.  His medical problems include hypertension and type 2 diabetes mellitus.  The patient has smoked 1 pack of cigarettes daily for 20 years.  Neurologic examination shows right-sided lower facial droop with sparing of the forehead muscles.  Motor strength is 3/5 on the right and 5/5 on the left with a Babinski response on the right.  There is also dysmetria and dysdiadochokinesia involving his right upper and lower extremities.  MRI of the brain reveals an acute lacunar infarct in the brainstem, as shown in the image below.  Which of the following cranial nerves exits the brainstem closest to the level affected by this patient's stroke?

Quizplus · Accepted Answer

11ec160b_35cc_5ece_9249_9f4fc4e5b4c6_MD0001_00 This patient has an acute lacunar ischemic stroke affecting the left medial pons at the level of the middle cerebellar peduncle. The trigeminal nerve (CN V) exits the brainstem at the lateral aspect of the mid-pons at the level of the middle cerebellar peduncles (a key neuroanatomic landmark for locating the nerve). The trigeminal sensory nuclei (eg, principal sensory, spinal, mesencephalic) run from the midbrain to the upper cervical spine and receive afferent signals for facial sensation via all 3 nerve branches (ophthalmic, maxillary, and mandibular). The motor nucleus is located in the lateral mid-pons and sends efferent signals to the muscles of mastication (eg, temporalis, masseter, pterygoids) via the mandibular branch. Infarcts involving the anterior pons can affect the corticospinal tract (contralateral hemiparesis, Babinski sign) and corticobulbar tract (contralateral lower facial palsy, dysarthria). Disruption of the corticopontine fibers that convey motor information from the cortex to the ipsilateral pontine gray matter may also result in contralateral dysmetria and dysdiadochokinesia (ataxic hemiparesis). The cerebellar deficits are contralateral to the lesion as the pontocerebellar fibers arising from the pontine gray matter decussate and enter the cerebellum through the contralateral middle cerebellar peduncle. (Choice A) The facial nucleus is located in the dorsolateral aspect of the caudal pons, and the nerve exits at the ventrolateral pontomedullary junction (below the middle cerebellar peduncles). This patient has sparing of the forehead muscles, which indicates that his facial weakness is a result of a central lesion affecting the corticobulbar tract and is not due to direct damage to the facial nucleus/nerve. (Choice B) The hypoglossal nucleus is located medially on the floor of the fourth ventricle at the level of the medulla, and the nerve exits at the rostral end of the preolivary sulcus. (Choice C) The oculomotor nucleus is located in the rostral midbrain at the level of the superior colliculus and red nucleus, and the nerve exits at the interpeduncular fossa. (Choice E) The trochlear nucleus is located in the caudal midbrain, and the nerve exits the dorsal midbrain just below the inferior colliculus (below the red nucleus). The trochlear nerve is the only cranial nerve to decussate before innervating its target (superior oblique muscle). Educational objective: Infarcts involving the anterior portion of the medial pons can produce dysarthria and contralateral hemiparesis/lower facial palsy due to disruption of the ipsilateral corticospinal and corticobulbar tracts. The trigeminal nerve arises at the level of the middle cerebellar peduncle at the lateral aspect of the mid-pons. __________ References: Ataxic hemiparesis: critical appraisal of a lacunar syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/9836766) The trigeminal (V) and facial (VII) cranial nerves: head and face sensation and movement. (http://www.ncbi.nlm.nih.gov/pubmed/20386632) Cranial nerves IX, X, XI, and XII. (http://www.ncbi.nlm.nih.gov/pubmed/20532157)

A 65-Year-Old Man Comes to the Emergency Department Due to Acute-Onset