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Question:

A 76-year-old woman is brought to the emergency department due to sudden-onset vertigo and difficulty swallowing for an hour.  Her only other medical condition is hypertension.  Blood pressure is 160/90 mm Hg and pulse is 80/min and regular.  The patient is alert, awake, and oriented.  Examination shows decreased pain and temperature sensation on the left side of the face and right side of the body.  The gag reflex is absent on the left side.  Muscle strength is 5/5 in all 4 extremities.  This patient's lesion is most likely located in which of the following areas?

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Explanation:

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This patient's stroke has resulted in vertigo and bulbar weakness (eg, difficulty swallowing), in addition to loss of pain and temperature sensation on the left side of the face and right side of the body.  Because most cranial nerves (other than CN II & IV) do not decussate while most of the body's motor and sensory fibers cross the midline in the medulla, brainstem strokes characteristically lead to ipsilateral cranial nerve deficits and contralateral deficits of the body (ie, crossed signs).  Therefore, this patient's stroke likely impacted the left brainstem.  Specifically, this patient has the following:

  • Vertigo without hearing loss, suggesting a lesion impacting the vestibular nucleus rather than the peripheral CN VIII (which would likely result in hearing loss as well).

  • Loss of pain and temperature sensation on the left (ipsilateral) side of the face with neuropathic pain in that area, suggesting involvement of the spinal trigeminal nucleus

  • Loss of pain and temperature sensation on the right (contralateral) side of the body, which suggests dysfunction of the spinothalamic tract

These areas are all located in the left lateral medulla.  This constellation of symptoms is consistent with lateral medullary (Wallenberg) syndrome.  Horner syndrome is also common due to damage of the descending sympathetic nervous system fibers that travel very close to the spinothalamic tract.

(Choices B and E)  Ischemia impacting the medial medulla can damage the pyramidal tract (contralateral hemiparesis), medial lemniscus (contralateral loss of tactile, vibratory & position sense), and hypoglossal nucleus, which causes tongue deviation toward the lesion due to ipsilateral hypoglossal nerve (CN XII) palsy.  The strong side "pushes" the tongue toward the weak side when it is protruded.

(Choices C and F)  Strokes in the midbrain can damage the red nucleus (ataxia), cerebral peduncle (contralateral hemiparesis), and, often, oculomotor nerve fascicles (ipsilateral CN III palsy).

(Choice D)  A lesion in the right lateral medulla would cause decreased pain and temperature in the right side of the face (ipsilateral) and left side of the body (contralateral).

Educational objective:
A lateral medullary infarct (Wallenberg syndrome) leads to vertigo (vestibular nucleus), loss of pain/temperature sensation on the ipsilateral face (trigeminal nucleus) and contralateral body (spinothalamic tract), bulbar weakness (lower cranial nerves), and ipsilateral Horner syndrome (descending sympathetic nervous system fibers).