Pons is the largest component of the brainstem located distal to the midbrain and proximal to the medulla oblongata. Any obstruction of blood supply to the pons, whether acute or chronic, causes pontine infarction, a type of ischemic stroke. Clinical presentation of a pontine infarction can vary, ranging from the classical crossed syndrome (ipsilateral cranial nerve palsy and contralateral motor and/or sensory impairment) to the less common pure motor hemiparesis or hemiplegia or pure sensory stroke. Clinical presentation is primarily determined by the anatomical boundaries of the infarcted region within the pons and the blood vessels involved.
The most common causes for pontine infarction include - small artery disease, large artery atherosclerosis, and cardiogenic emboli, with the latter two being less frequent causes. The majority of the pons’ blood supply is from the paramedian perforating arteries and the short circumferential arteries which arise from the basilar artery of the posterior circulation. Other sources of supply include the anterior inferior cerebellar artery and the superior cerebellar artery. The primary lesion can be unilateral or bilateral, anterior or posterior, medial, or lateral or, more commonly, a combination of these regions. The established risk factors for ischemic stroke, hypertension, and diabetes are also the leading risk factors for pontine infarction. Long-standing hypertension or diabetes can lead to lipohyalinosis of the small perforating arteries of the pons, leading to chronic ischemia and eventual infarction. Infarction can also result from atheromatous plaques in the larger arteries (vertebral or basilar artery), which in turn can obstruct blood flow to the smaller perforating arteries of pons (microatheromas). Other risk factors postulated include-smoking, hypercholesterolemia, history of ischemic heart disease, hypercoagulable states, and vasculitis. However, the risk factors that increase the risk of infarction, specifically in the pons, are unclear.
Epidemiological studies investigating particularly pontine infarctions are lacking. While pontine infarctions are relatively common, they generally occur as a part of larger posterior circulation stroke. Within pons, presentation further varies depending on the arterial territory involved: 1) the anteromedial and anterolateral region supplied by the basilar artery is the most commonly affected, 2) lateral region supplied by the basilar artery and anterior inferior cerebellar artery, 3) posterior/dorsal region supplied by the superior cerebellar region. Ischemic stroke incidence overall is higher among men than women and Black and Hispanic adults compared to their White counterparts, with some geographic variability. However, studies examining pontine infarctions exclusively are lacking.
Ischemic stroke risk increases with age, and hence a typical presentation of a pontine infarction would be an elderly individual with a history of chronic conditions like hypertension, diabetes, dyslipidemia, or history of heart disease. However, pontine infarction can also occur in younger individuals with vascular disorders like CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), hypercoagulable states, vertebral artery dissections et cetera. Establishing the time of onset of stroke symptoms heavily determines the treatment strategy (thrombolytics vs. thrombectomy). The clinical presentation of a pontine infarct depends on the anatomical/arterial territories involved and are clinically classified as below.
Few distinguishing features that can be used to identify the anatomical location of the pontine infarction include:
Initial assessment of an individual presenting with stroke symptoms should include blood pressure and heart rate measurement along with respiratory function assessment (respiratory rate and pulse oximetry). As pons houses the respiratory centers, large pontine infarctions can compromise respiratory function and may warrant intubation and mechanical ventilation. If hemodynamically stable, a complete neurological examination in addition to routine history taking and physical examination is conducted. While the neurological exam assists in localizing the anatomical region affected and the type of stroke (ischemic vs. hemorrhagic), relevant history and vitals can point to the predisposing conditions (e.g., hypertension). After proper stabilization, a complete neurological examination including an assessment of consciousness, cognition, gait, coordination, reflexes, cranial nerve examination, and sensory and the motor system should be performed. Followed by physical examination, neuroimaging is urgently indicated in all suspected stroke cases, and the timing of the imaging determines the treatment modality and its success. Computed tomography (CT) scan due to its availability and ability to detect hemorrhages is used to triage a stroke patient. However, magnetic resonance imaging (MRI) remains the mainstay of diagnosis for ischemic strokes due to its ability to detect acute ischemia within minutes of onset (diffusion-weighted MRI). Neurovascular imaging (CT or MR angiography) is performed in those with large artery obstruction (e.g., basilar artery) as they might have to undergo mechanical thrombectomy. In cases where an embolus is suspected, imaging studies like carotid doppler or transthoracic echocardiography may be required to identify the degree of stenosis or the source of embolus. Basic investigations like complete blood count, serum glucose, serum electrolytes, renal and liver function tests, lipid profile, and a 12-lead electrocardiogram are routinely ordered. Various other biomarkers (e.g., c-Fn, MMP-9) are being investigated as possible predictors of stroke outcomes and can very well be recommended as routine tests for all stroke patients in the future.
Pontine infarction treatment is akin to other types of ischemic stroke with some variability considering the lack of strong clinical evidence in posterior circulation stroke treatment compared to anterior circulation. This is especially true in patients with a large vessel occlusion, causing a pontine stroke. In general, as with any patient with ischemic stroke, immediately after identifying the subtype of stroke, treatment should be targeted to 1) reverse the extent of ischemic penumbra-tissue adjacent to the infarcted region 2) prevent complications, and 3) facilitate early improvement in functional status. However, this comes secondary to the initial stabilization of airway, breathing, and circulation. Intravenous alteplase is the thrombolytic of choice for those presenting within 4.5 hours of symptom onset and without any absolute contraindications to thrombolytic therapy. Mechanical thrombectomy is the procedure of choice for those with large artery occlusion presenting within 24 hours of symptoms onset. Blood pressure is generally elevated in acute stroke patients, and this works in favor as the cerebral autoregulation of blood pressures is impaired, especially in patients with large vessel occlusion. In patients receiving thrombolytics, it is recommended that the pressure is maintained below 180/105 mmHg for at least 24 hours following thrombolytic administration to limit reperfusion injury. In patients not receiving thrombolytic therapy, hypertension is not treated unless severe (>220/120 mmHg) to facilitate cerebral perfusion in the setting of ischemia. In addition to the above steps, aspirin, clopidogrel, or similar antiplatelet agents or anticoagulants like warfarin, apixaban, dabigatran, etc. are used in secondary prevention based on the etiology of the ischemic stroke. Lipid-lowering therapy is also initiated to prevent recurrence with high-intensity statins. Antihypertensives are added to the treatment regimen at discharge for those with elevated blood pressure. Lastly, but most importantly, lifestyle modifications such as exercise, smoking cessation, dietary changes, and weight loss are strongly recommended.
Isolated pontine infarction is a less frequent occurrence than a larger brainstem infarction.
A few of the many predisposing conditions are hypertension, diabetes, basilar artery atherosclerosis, and vertebrobasilar insufficiency. Clinical presentation may include many signs and symptoms due to the underlying condition making it even more essential to rule out a multitude of diseases like:
Initial neuroimaging would aid in evaluating any other intracranial pathologies. CT imaging delineates hemorrhagic lesions well, while MRI imaging is better suited for mass lesions, abscesses, infectious issues, and other etiologies. High index suspicion should be used for the less common differential diagnoses.
The overall prognosis of those with unilateral pontine infarction is good. Infarctions, especially lacunar in nature, involving the lateral or rostral to mid pons, are associated with more favorable outcomes. On the other hand, bilateral and caudal pontine infarctions have a worse prognosis. Progressive neurological deficit following isolated pontine infarction has also been reported. Long term prognosis is considered good based on a single study with a 4 to 9 year follow-up time. However, Kumral et al. observed the long-term risk of recurrent stroke to be high in those with pontine infarction. Prognosis of isolated pontine infarction in comparison to the other posterior circulation stroke syndromes or any non-pontine infarctions is yet to be determined.
The common medical complications of pontine infarction include 1) aspiration pneumonia secondary to pseudobulbar palsy or locked-in syndrome is the most severe one, 2) dysphagia warranting tube feeding, 3) urinary incontinence requiring catheterization which in turn increases the risk of urinary tract infections, 4) remnant motor weakness resulting in falls, 5) post-stroke depression, 6) complications due to prolonged immobilization (e.g., pressure ulcers, deep venous thrombosis, pulmonary embolism). Long-term disability is also common following pontine infarction and is assessed using various scales like the Barthel Index, the Glasgow Outcome Scale, and the modified Rankin Scale (mRS). Neurological complications of pontine infarction include cerebral edema, hemorrhagic transformation of the infarcted region, palatal myoclonus, and neurological deterioration despite treatment.
Rehabilitation for pontine infarction can include sensory reeducation, physical therapy, speech therapy, and occupational therapy.
Primary prevention of stroke calls for aggressive risk factor control in individuals with high risk. The most important modifiable risk factors are high blood pressure (not necessarily a diagnosis of hypertension), diabetes, dyslipidemia, and smoking. However, the non-modifiable risk factors like age, race, sex, and family history of stroke should also be considered in the prevention efforts. The most recent American Heart Association/American Stroke Association guidelines  for primary prevention of stroke suggested for the general population include:
Educational programs about stroke, its traditional risk factors, and behavioral modifications to reduce stroke risk, have shown to be effective in increasing the knowledge and risk perception among individuals receiving them. Though individuals prefer to know their risk of stroke, the tools used to assess the risk may not have any additional effect on the individual’s behavior than the routine risk factor education.
Proper identification of stroke symptoms by the patients themselves or by individuals witnessing the patient’s symptoms is vital for timely initiation of the emergency medical system (EMS). Stroke education campaigns targeting communities could influence the timely recognition of symptom onset. Once the EMS is triggered, healthcare professionals managing the patient should be well trained to identify stroke and manage accordingly. Stroke care, when strategically organized, can decrease stroke burden considerably. Such organized stroke units can include, stroke units (separate wards), stroke teams (groups of readily available stroke specialists), stroke rehabilitation units (for after stroke care), and comprehensive units for both acute care and rehabilitation services. In addition to recanalization of the affected pontine artery, proper care in the acute stroke unit to prevent complications and appropriate measures in the rehabilitation units are much needed for optimum stroke outcomes.
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