Medial pontine syndrome

Overview

Medial pontine syndrome, also known as Foville syndrome (when involving specific structures), is a rare brainstem stroke syndrome that affects the medial portion of the pons. It results from a lesion in the ventromedial pons and causes a characteristic constellation of neurological deficits. These typically include contralateral hemiparesis (weakness of the body opposite the lesion), contralateral loss of vibration and proprioception, and ipsilateral facial or ocular motor deficits due to involvement of cranial nerves or their nuclei.

This syndrome is considered a type of crossed or alternating hemiplegia, where cranial nerve signs are on one side of the body and long tract signs (motor or sensory) are on the other. The syndrome is most often caused by an infarction due to occlusion of perforating branches of the basilar artery, which supplies the medial pons.

Causes

The primary cause of medial pontine syndrome is an ischemic stroke involving the paramedian branches of the basilar artery, which supply the medial region of the pons. Specific causes include:

• Atherosclerosis: Narrowing of the basilar artery due to plaque buildup is the most common cause in older adults.

• Embolism: Clots originating from the heart (e.g., in atrial fibrillation) or large arteries can lodge in the basilar artery.

• Small vessel disease: Particularly in patients with chronic hypertension or diabetes.

• Vertebrobasilar insufficiency: Reduced blood flow in the posterior circulation due to vascular anomalies or low blood pressure.

• Brainstem hemorrhage or demyelinating disease: Rare non-ischemic causes that may mimic the clinical features.

Symptoms

Symptoms of medial pontine syndrome vary based on the extent of the lesion but typically follow a classic pattern. The hallmark is a combination of ipsilateral cranial nerve deficits and contralateral motor or sensory impairments. Common features include:

1. Contralateral Hemiparesis

• Weakness or paralysis of the limbs on the side opposite the lesion

• Due to involvement of the corticospinal tract

2. Contralateral Loss of Vibration and Proprioception

• Impairment of position sense and fine touch on the opposite side

• Due to damage to the medial lemniscus

3. Ipsilateral Cranial Nerve VI and/or VII Deficits

• Abducens nerve (CN VI) palsy:

  • Inability to abduct the eye on the side of the lesion, causing horizontal diplopia

• Facial nerve (CN VII) involvement:

  • Facial weakness or paralysis on the same side of the lesion (if lesion extends laterally)

Other Possible Symptoms

• Dysarthria: Slurred speech due to impaired motor control

• Ataxia: Uncoordinated movement if adjacent cerebellar pathways are involved

• Gaze palsy: In some cases, involvement of gaze centers leads to conjugate gaze abnormalities

Symptoms usually have a sudden onset and may worsen over hours to days depending on the underlying vascular event.

Diagnosis

Diagnosis of medial pontine syndrome relies on a detailed neurological examination and neuroimaging to confirm the location and cause of the lesion. Diagnostic workup includes:

• Clinical examination:

  • Localization based on crossed findings (ipsilateral cranial nerve deficits with contralateral motor/sensory loss)

• Magnetic Resonance Imaging (MRI):

  • The most sensitive test to detect infarcts or hemorrhages in the brainstem

  • Diffusion-weighted imaging (DWI) helps identify acute ischemic stroke

• Magnetic Resonance Angiography (MRA) or CT Angiography:

  • Used to evaluate basilar artery and vertebral artery patency

• Electrocardiogram and Echocardiography:

  • To assess for cardiac sources of embolism

• Laboratory work-up:

  • Assessment of vascular risk factors such as hypertension, diabetes, and hyperlipidemia

Differential diagnoses include lateral pontine syndrome, medial medullary syndrome, and brainstem tumors or demyelinating lesions.

Treatment

Treatment of medial pontine syndrome centers around managing the acute stroke, preventing recurrence, and supporting neurological recovery.

Acute Management

• Thrombolytic therapy (tPA):

  • Considered if the patient presents within the appropriate time window (usually within 4.5 hours of onset) and has no contraindications

• Antiplatelet therapy:

  • Aspirin or dual antiplatelet therapy to prevent further clot formation

• Blood pressure control:

  • Careful management to maintain cerebral perfusion while preventing further damage

• Management of risk factors:

  • Treat underlying conditions like diabetes, atrial fibrillation, and hyperlipidemia

Supportive and Rehabilitative Care

• Physical therapy: To improve strength and motor control

• Speech therapy: For dysarthria and facial weakness

• Occupational therapy: To regain independence in daily living activities

• Nutritional support: May be necessary if swallowing is impaired

Prognosis

The prognosis of medial pontine syndrome depends on the size and location of the lesion, the speed of treatment, and the presence of complications. Key factors influencing outcome include:

• Severity of the stroke: Larger infarcts affecting multiple pathways may result in more significant and lasting deficits

• Timing of treatment: Early intervention with thrombolytics or supportive care improves outcomes

• Rehabilitation potential: With intensive therapy, many patients regain some or most motor function

In some cases, patients may be left with persistent weakness, facial asymmetry, or coordination issues. However, with aggressive rehabilitation and long-term care, quality of life can improve considerably.