What physical deficits are expected with small acute infarcts in the right paramedian pons and possible right lateral medulla?

Expected Physical Deficits from Right Paramedian Pontine and Possible Right Lateral Medullary Infarcts

You should expect left-sided hemiparesis (contralateral motor weakness) as the primary deficit, potentially accompanied by right-sided facial weakness, right abducens nerve palsy causing horizontal gaze limitation, and if the lateral medullary involvement is confirmed, possible dysphagia, dysarthria, and sensory disturbances. 1

Primary Motor Deficits

The right paramedian pontine infarcts extending to the midline will produce contralateral (left-sided) motor weakness because the corticospinal tracts descend through the ventral pons before decussating in the medulla. 1

• Left hemiparesis is the most common and prominent finding in ventral pontine infarcts, with severity varying from mild to severe depending on infarct size 1
• Motor involvement in ventromedial pontine syndrome can range from isolated weakness to severe hemiparesis with bilateral ataxia and dysarthria 1
• Approximately three-fourths of patients with ventral pontine infarcts show clinical evidence of tegmental dysfunction, even when the primary lesion appears ventral 1

Cranial Nerve Deficits (Ipsilateral to Lesion)

The paramedian location affecting the right pons creates risk for ipsilateral cranial nerve palsies, particularly CN VI and CN VII, because these nerves course through the pontine tegmentum. 2

Right Abducens Nerve (CN VI) Palsy

• Right lateral gaze palsy or inability to abduct the right eye is expected, as CN VI originates in the pontine tegmentum and courses through the corticospinal tracts 2
• The sixth nerve nucleus is located approximately 4.4 mm from midline in the pons 3

Right Facial Nerve (CN VII) Palsy

• Right facial weakness is frequently present because CN VII curves over the CN VI nucleus in the pons 2
• This produces ipsilateral facial droop, inability to close the right eye, and loss of facial expression on the right side 2
• Ischemic and hemorrhagic infarcts are the most frequent cause of acute brainstem syndromes affecting CNs V-VIII 4

Potential Lateral Medullary Involvement

The possible tiny right lateral medullary infarct raises concern for additional deficits beyond the pontine syndrome. 5, 6

Sensory Disturbances

• Contralateral (left-sided) diminished pain and temperature sensation affecting the body
• Ipsilateral (right-sided) facial sensory loss if the spinal trigeminal nucleus is involved
• Diminished contralateral superficial sensation is more common than vibratory sensation loss in medullary infarcts 6

Bulbar Symptoms

• Dysphagia (difficulty swallowing) and dysarthria (slurred speech) may occur if CN IX and X nuclei are affected 4
• The glossopharyngeal nerve (CN IX) arises in the medulla and is responsible for elevation of the palate; its involvement causes dysphagia 4
• Lateral medullary lesions can affect vestibular structures, potentially causing vertigo, nystagmus, and ataxia 4

Important Clinical Considerations

Classic Syndromes May Not Apply

• Only 4 of 36 patients with isolated pontine infarcts demonstrated true alternating deficits, and these never corresponded to classic named pontine syndromes like Millard-Gubler or Foville 1
• The clinical presentation is more predictable based on anatomic territories of intrinsic pontine vessels rather than eponymous syndromes 1

Imaging Limitations

• Small brainstem infarcts can have normal initial MRI, particularly in the midbrain and caudal pontine tegmentum 7
• False-negative DWI occurs with very small ischemic brainstem infarcts, with thin-section coronal DWI detecting nearly 25% more acute brainstem infarcts than standard axial DWI 4
• The presence of visible acute infarcts on this MRI suggests the lesions are of sufficient size to produce clinical symptoms

Prognosis

• Recovery is typically good in two-thirds of patients with isolated pontine infarcts 1
• Worse outcomes are associated with large ventral infarcts 1
• The small size of these infarcts and lack of hemorrhagic transformation suggest favorable prognosis

Vascular Etiology Considerations

• Basilar artery branch disease is the most common cause (44%) of isolated pontine infarcts and is associated with progressive or fluctuating course 1
• Large-artery atherosclerosis of the vertebral arteries is the predominant vascular pathology in medullary infarcts 5
• The old right paramedian pontine infarct indicates chronic vascular disease and risk for recurrence