Show Explanatory Sources

This patient has had a stroke resulting in the following crossed signs:

• Right hemiparesis:  This is nearly always contralateral to the site of ischemia.

• Leftward tongue deviation and slurred speech:  On tongue protrusion, the strong side "pushes" the tongue toward the weak side, so this patient has a defect of the left hypoglossal nerve (CN XII)

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 are characterized by ipsilateral cranial nerve deficits accompanied by contralateral hemiparesis or hemisensory loss (ie, crossed signs).

The specific cranial nerves impacted can further localize the lesion.  In this case, the hypoglossal nerve (CN XII) originates in the medulla.  This is consistent with left medial medullary syndrome, which is most often caused by occlusion of the paramedian bulbar arteries that impacts the pyramidal tract (contralateral arm and/or leg weakness) and hypoglossal nucleus (ipsilateral tongue weakness).  Paresthesias can occur due to damage of the medial lemniscus, although, typically, there are no objective sensory deficits, as in this patient.

(Choices A and D)  A stroke in the lateral medulla classically results in Wallenberg syndrome.  There is typically no motor weakness.  Instead, it is typified by vertigo/nystagmus (vestibular nucleus), ataxia (inferior cerebellar peduncle), a diminished gag reflex (nucleus ambiguus), and loss of pain and temperature sensation from the ipsilateral face (spinal trigeminal nucleus) and contralateral body (spinothalamic tract).

(Choices C and F)  The primary motor cortex is located in the precentral gyrus.  A stroke impacting the left precentral gyrus could result in right hemiparesis.  However, strokes impacting the cortex often result in cortical signs such as Visual disturbances, Aphasia (in contrast to the dysarthria seen in this patient), Neglect, and/or Sensory disturbances (VANS).  Cranial nerve deficits would not be expected.

(Choice E)  Brainstem strokes result in contralateral hemiparesis and ipsilateral cranial nerve defects.  Therefore, a stroke in the right medulla would lead to left hemiparesis and right tongue weakness (leading to right tongue deviation because the strong side "pushes" the tongue to the weak side as it protrudes).

Educational objective:
Crossed signs (ie, ipsilateral cranial nerve dysfunction with contralateral limb weakness) are typical of a brainstem stroke.  A stroke in the medial medulla often results in contralateral limb weakness with ipsilateral tongue weakness, which causes tongue deviation to the weak side.