Brain stem infarction is a potentially life-threatening condition which develops due to focal ischemia of the midbrain, pons, and medulla oblongata. It results in neurologic deficits involving the respiratory, cardiovascular, speech, swallowing, hearing and ocular movement centers located within the brain stem. Diagnosis is based on clinical presentation with computed tomography and magnetic resonance imaging helping to confirm the extent of the infarct.
The brain stem consists of the midbrain, pons, and medulla. Brain stem infarction commonly occurs due to an embolus occluding large arteries (vertebral or basilar arteries) supplying it or due to an embolus traveling from the heart, or atherosclerotic plaques from the large arteries (vertebral, basilar) . Brainstem infarcts are relatively less common as compared to hemispheric infarcts . The common clinical presentation is sudden onset focal neurological deficits like hemiparesis, vertigo, orthostatic symptoms, diplopia, and lower cranial nerve paralysis with dysphagia, and hoarseness. Vertigo is the cardinal feature of brain stem infarction  followed by ipsilateral cranial nerve symptoms, contralateral hemiplegia, hemianesthesia (crossed motor or sensory signs) with bilateral involvement of the sensory tract or motor tract or both.
A few uncommon clinical features of brain stem infarction include "salt and pepper" facial pain , blepharospasm , palatal myoclonus , hiccough , tinnitus in medullary infarction , bruxism and trismus in basilar artery occlusion , and peduncular hallucinosis in midbrain infarction . If there is total occlusion of the vertebrobasilar system then patients can present with tachycardia, fluctuating blood pressure, ataxia, impaired consciousness, and coma leading to death. Pontine or midbrain infarction can also present as "locked-in syndrome" in which the affected individual has sudden onset vomiting, transient loss of consciousness with quadriplegia, bilateral facial palsy, anarthria (total loss of articulation), and bilateral oculomotor nerve palsy resulting in loss of voluntary eye movements .
Clinical features specific to the ischemic involvement of the different regions of the brainstem are:
Midbrain: ipsilateral oculomotor (3rd cranial nerve) paralysis with contralateral hemiplegia (Weber syndrome)
Pons: 5th, 6th, 7th and 8th cranial nerve involvement, diplopia, dysarthria, vertigo, gait abnormality, and/or sensation of ear canal block, sustained horizontal nystagmus, conjugate eye movements when the gaze is directed towards the side of hemiparesis , ataxic hemiparesis.
Medulla: 9th, 10th, 11th and 12th cranial nerve involvement, pure motor hemiparesis if the medullary pyramid is the site of the infarction; sensory motor hemiplegia if the medial lemniscus is involved; or Dejerine syndrome wherein there is ipsilateral tongue paralysis with contralateral hemiplegia. A patient presenting with acute onset vertigo and then developing sudden respiratory failure is likely to have a medullary infarct.
The aim of the workup is to determine the characteristics of the vascular lesion and the etiology of the brain stem infarction. A detailed history during workup provides clues to the risk factors and etiology of the condition while a thorough neurological, cardiovascular, and bedside glucose testing are mandatory to determine further workup and management.
Computed tomography scanning (CT) is performed first to differentiate between an ischemic infarct and hemorrhagic stroke as it has 95% sensitivity in identifying hemorrhage especially if done within 24 hours of onset of symptoms  . Occluded and dolichoectatic arteries can be identified better with spiral CT angiography  . Magnetic resonance imaging (MRI) has greater sensitivity than CT in the identification of ischemia with small lacunar infarcts being seen only on MRI. Diffusion-weighted MRI is highly sensitive for early ischemia and should be ordered after the CT scan. MRI and magnetic resonance angiography (MRA) are useful in detecting dissection, demyelinating plaques, vertebrobasilar dolichoectasia, and dissection.   .
In addition, other tests are indicated based on the clinical evaluation to detect the etiology and risk factors of the brainstem infarct:
Cardiac factors: electrocardiography (in all cases), telemetry or holter monitoring, serum troponin (in cases suspected to have myocardial ischemia), and echocardiography  especially in patients under 45 years of age or in those with basilar artery occlusion.
Vascular factors: blood tests to rule out thrombotic disorders (homocysteine levels, antiphospholipid antibodies, protein S, protein C, antithrombin III, factor V Leiden) and routine tests like complete blood count, platelet count, PT/PTT, fasting blood glucose, lipid profile, and serology for syphilis.
Autoimmune factors: antinuclear antibodies, rheumatoid factor, erythrocyte sedimentation rate.
Urine toxicology and drug screening for stimulants like cocaine and amphetamines.