Timothy C. Hain, MD Page last modified: April 30, 2014
The purpose of this page is to consider the findings in brainstem strokes in detail. More general aspects of brainstem strokes and TIA's related to vertigo are considered elsewhere.
There are a large number of well described brainstem stroke syndromes. Most of these involve ischemia in the distribution of the basilar or vertebral arteries, as shown to the right. Here we will describe the most common syndromes.
Clinically, in localizing strokes to the brainstem one looks for the "cardinal" feature of an ipsilateral peripheral cranial nerve involvement, and a contralateral weakness or sensory deficit. Cerebellar signs, if present, should be ipsilateral. MRI is frequently needed to make a specific diagnosis and to separate vascular etiologies from tumor and other structural injuries. The pattern of sensory disturbance may be helpful. A dissociated sensory deficit over the face or half the body usually indicates a lesion within the brainstem. A hemisensory loss involving all modalities indicates a lesion in the upper brainstem, in the thalamus, or deep in the white matter of the parietal lobe. Bilaterality of both motor and sensory signs is almost certain evidence of a brainstem lesion. When hemiplegia or hemiparesis and sensory loss are coextensive, the lesion usually lies supratentorially.
Vertigo (spinning) is a common early symptom of brainstem strokes. However, because strokes are much less common than other sources of vertigo such as ear disorders, vertigo is only caused by central nervous system problems (including stroke) about 5% of the time. Migraine is a common cause of vascular vertigo.
Hearing disturbance is a much less common symptom of brainstem stroke than vertigo. This may reflect the resilience of the wiring pattern of hearing in the brainstem which includes of both crossed and uncrossed pathways, or factors related to details of the blood supply or resistance of the ear to disturbances in blood supply.
Strokes may be ischemic (lack of blood flow), or hemorrhagic (leakage of blood into the brain). Risk factors for stroke are considered here.
Ischemic strokes are caused by blockage of blood vessels. The blocks may originate from a distant source -- such as a clot from the heart -- then they are called "emboli". The blocks may result from clotting from within - -then they are called "thrombi". Thrombotic strokes are most often attributed to buildup of cholesterol within blood vessel walls, producing a turbulence and roughening of the wall, onto which a clot forms. Another common cause of thrombotic stroke is a sustained drop in blood pressure -- such as might be due to a cardiac arrest for several minutes. There are just occasional sources of ischemic stroke outside these general two categories (emboli and thrombi). For example, strokes can be caused by mechanical obstruction of blood vessels - -which might happen during a high speed chiropractic manipulation of the neck, or some other event that causes a very forceful neck movement. We have encountered patients who have experienced stroke (as an example), after roller coaster rides.
Hemorrhagic strokes -- leakage of blood within the brain - -are most commonly caused by too high blood pressure. Other possible causes include irregularities in blood clotting, damage to blood vessel walls by various processes (including ischemic stroke). In the brainstem, circuitry is tight and hemorrhagic strokes are often devastating.
The PICA syndrome is also known as "lateral medullary syndrome", or "Wallenberg's syndrome", after Wallenberg's description in 1895. This is the most common brainstem stroke. See this link for more detail.
The AICA syndrome is usually accompanied by vertigo and unilateral ipsilateral deafness from labyrinthine artery ischemia. It is a common brainstem stroke. See this link for more detail.
The labyrinthine or internal auditory artery usually takes its origin from AICA, but it can also take origin from PICA or the basilar artery. It supplies the inner ear. In the internal auditory canal or IAC it supplies Scarpa's ganglion. After exiting it divides into the common cochlear artery and anterior vestibular artery. The common cochlear artery further divides into the main cochlear artery and the vestibulocochlear artery, the latter forming the posterior vestibular artery and the vestibular ramus. The main cochlear artery supplies the apical 3/4 of the cochlea, and the cochlear ramus, the basal 1/4 (high frequencies). The posterior vestibular artery supplies the inferior saccule and the ampulla of the posterior SCC. The anterior vestibular artery is a smaller artery that supplies the utricle, superior saccule, and ampulae of the anterior and lateral semicircular canals (Kim et al, 1999). The labyrinthine artery is an end-artery, and as such may be relatively more vulnerable than other circulations.
Diagnosis may be difficult because the brain may show no lesion. This is a small blood vessel and imaging studies such as CT-angiography or MRA may miss it. Contrast is absolutely necessary (during MRA).
Main symptoms are ipsilateral cerebellar ataxias (middle and/or superior cerebellar peduncles), nausea and vomiting, slurred (pseudobulbar) speech, loss of pain and temperature over the opposite side of the body. Partial deafness, tremor of the upper extremity, an ipsilateral Horner syndrome and palatal myoclonus have been reported. Clinically, this stroke may be impossible to distinguish from a partial AICA or PICA territory stroke. It is much rarer than either one. Ocular pulsion away from the side of lesion has been reported in SCA syndrome. Diagnosis of the stroke is via MRI.
In Weber's syndrome, there is damage to the midbrain, including the fascicles of the 3rd nerve within the midbrain and also there is damage to the pyramidal tract prior to it's decussation (cerebral peduncle area). This results in an ipsilateral 3rd nerve palsy combined with a contralateral hemiplegia. This syndrome can arise from damage to the SCA.
|Infarct of the lateral midbrain resulting from an aneurysm of the superior cerebellar artery. The lesion here is just posterior to the cerebral peduncle.|
This is a catastrophic event, typically a hypertensive bleed. It presents with of coma, quadriplegia, small reactive pupils and absent horizontal eye movements. In most quadriplegic patients a hematoma in the middle of the pons is centered at the junction of the tegmentum and basis pontis. Ocular bobbing is a less constant feature. Lateral tegmental hemorrhages present with 1 1/2 syndrome, small reactive pupils, limb ataxia of the cerebellar type, and contralateral hemisensory loss (Caplan and Goodwin, 1982). Those that survive may develop oculopalatal myoclonus. Diagnosis may be made via MRI (best) or CT scan, or a combination of both.
0.5% of all brain infarcts. Contralateral hemiparesis sparing the face, hemisensory loss of the posterior column type (contralateral). Weakness of the tongue is ipsilateral to the infarct. Pathology may be in vertebral artery or mesial limb of vertebral artery after PICA. Upbeat nystagmus may occur. Small vessel disease (diabetes, hypertension, hypercholesterolemia) is the usual cause.
MRI scan of person with central pontine myelinolysis. Sagittal view The dark area inside the circle is the region of damage.
© Timothy C. Hain, M.D.
MRI scan of person with central pontine myelinolysis, axial view. Note the "I" shaped area in the center of the pons.
It is common to encounter areas of increased signal on T2 MRI in the pons in older persons with unsteadiness. These patients often display symptoms of disequilibrium, difficult with speech and swallowing. (Kwa et al, 1998). In the author's experience, these patients often exhibit rebound nystagmus, which is a variant of gaze-evoked nystagmus.
A rare source of pontine hyperintense lesions is central pontine myelinolysis (see above). This is caused by rapid fluctuations in electrolyte status, usually in the context of a hospitalization. The individual shown above had a liver transplant done. After the liver transplant, he was fine for a couple of days but then gradually became comatose. His MRI at that time showed the picture above. Examination nine months later revealed an ambulatory individual with some mild cerebellar signs. About 2% of persons with liver transplant develop central pontine myelinolysis.
Individuals with midline pontine infarcts usually have normal ABR testing (Faught and Oh, 1985).
Decreased blood flow in the vertebrobasilar system is invoked as a potential explanation for a myriad of symptoms possibly attributable to the brainstem.
At this writing (12-2007), CT-angiography is the best way to establish this diagnosis. While MRI technology has advanced greatly, MRA is presently not of high enough resolution to reliably visualize the tiny arteries involved in this area. Conventional angiography is the most reliable way to infer the diagnosis, but is usually unreasonably risky compared to CT-angiography.
|CT angiogram showing a hypoplastic right vertebral, in a person with symptoms of vertebrobasilar insufficiency. Left vertebral (left lower) is large and dominant. Right vertebral (right lower) is small and hypoplastic. This is the same case as shown in the selective vertebral angiogram below.|
Considerable discussion of imaging for the vertebral arteries can be found on the cervical vertigo page.
As the basilar artery supplies most of the brainstem, occlusion is commonly catastrophic resulting in quadriplegia. Death from respiratory failure is common. The "locked in syndrome", denoting a state where the unfortunate patient can think and see but may be unable to respond may occur. Occlusion of the "top" of the basilar artery can result in a large number of complex syndromes that may include visual hallucinations, somnolence, various ocular findings mainly involving vertical gaze and/or convergence/retraction nystagmus. The classic paper is by Kubik and Adams (1946) . Diagnosis is via MRI/MRA.
Usually manifests as PICA territory infarct (see below). Bilateral occlusions are much rarer than unilateral, and have a slowly progressive course and poor prognosis (Caplan, 1983). Ct-angiography combined with MRI is usually the best way to make this diagnosis. Considerable discussion of imaging for the vertebral arteries can be found on the cervical vertigo page.
Carotid disease rarely causes vertigo. This is because the parts of the brain that control motion perception are in the back, and are supplied by different arteries (the vertebral and basilar arteries). When carotid disease is severe, and accompanied by disease in the back arteries, carotid disease can be associated with vertigo, but this is unusual. Diagnosis is via MRA, doppler, or angiography.
The brainstem graphic is courtesy of Northwestern University.
|Eponym||Site||Cranial Nerves||Tracts||Signs||Usual Cause|
|Weber||Base of Midbrain||III||Corticospinal||Oculomotor palsy with crossed hemiplegia||Vascular, tumor|
|Claude||Midbrain tegmentum||III||Red nucleus and Brachium Conjunctivum||Oculomotor palsy with contralateral cerebellar ataxia and tremor||Vascular, tumor|
|Benedict||Midbrain tegmentum||III||Red nucleus, corticospinal tract, brachium conjunctivum||Oculomotor palsy, contralateral cerebellar ataxia, corticospinal signs||Vascular, tuberculoma, tumor|
|Nothnagel||Midbrain tectum||Unilateral or bilateral III||Superior cerebellar peduncles||Ocular palsies, paralysis of gaze, cerebellar ataxia||Tumor|
|Parinaud||Dorsal Midbrain||Paralysis of upward gaze and accommodation, fixed pupils, retraction nystagmus||Pinealoma, hydrocephalus|
|Millard-Gubler and Raymond-Foville||Base of Pons||VII and sometimes VI||Corticospinal tract||Facial and 6th palsy, contralateral hemiplegia, sometimes gaze palsy||Vascular,tumor|
|Avellis||Medulla tegmentum||X||Spinothalamic, sometimes pupillary fibers||Paralysis of soft palate and vocal cord and contralateral hemianesthesia||Infarct or Tumor|
|Jackson||Medulla Tegmentum||X,XII||Corticospinal||Avellis plus ipsilateral tongue||Infarct or Tumor|
|Wallenberg||Medulla, lateral tegmentum||Spinal V,IV,X,XI||Lateral STT,Descending Pupil fibers, Spinocerebellar and olivocerebellar tracts||Ipsi V, IV, X, XI palsy, Horner's, cerebellar ataxia. Contra pain and temp||Vascular - Pica or vertebral|