Lateral medulla strokes occur when the vertebral artery and/or posterior inferior cerebellar artery become occluded. With occlusion, blood, and along with it, oxygen and nutrients fail to reach the brainstem. If blood flow is not restored quickly the affected brain tissue dies leading to permanent neurological injury.
Risk factors for medulla strokes are the same for other strokes. They include hypertension, diabetes, smoking, atrial fibrillation, and a whole slew of hypercoagulable states (ie: pathologic increases in the bodies' propensity to form blood clots).
The blood supply to the medulla is from branches of the vertebral arteries. One of the main branches of the vertebral artery - the posterior inferior cerebellar artery (PICA) - courses around the brainstem towards the cerebellum. During its course it sends small branches that supply the lateral medulla with blood.
The medulla oblongata (typically referred to as just the "medulla") is the lowest (ie: most inferior or caudal) portion of the brainstem. It contains neurons that compose the nuclei of the 8th, 9th, 10th, 11th, and 12th cranial nerves. It also contains all of the information tracts that pass between the spinal cord and brain.
The lateral medulla, which is what is affected in Wallenberg syndrome, contains many important structures. They include the anteromedial (spinothalamic) fibers, the spinal trigeminal tract and nucleus, the sympathetic fiber tract, the nucleus ambiguus, the vestibular nuclei, and finally tracts destined for the cerebellum.
Each structure in the preceding paragraph serves an important neurological function. The spinothalamic fibers relay pain and temperature information from the opposite side of the body to the brain. Similarly, the spinal trigeminal nuclei and tract send pain and temperature information from the face to the brain (note: the same side of the face, not the opposite side).
The sympathetic fibers send information to the thoracic spinal cord and control the "fight or flight" response of numerous organ systems.
The nucleus ambiguus is a scattered collection of neurons (hence the name "ambiguus") that send information via the 9th and 10th cranial nerves to the muscles in the pharynx and larynx (ie: voice box).
The vestibular nuclei receive information from the middle ear (ie: the otolith organs and semicircular canals) about the position of the head in space. Similarly, the cerebellar tracts originating from the spinal cord are responsible for relaying position information about the bodies limbs and trunk to the cerebellum.
A stroke of the lateral medulla occurs when blood flow is interrupted in either the vertebral artery or posterior inferior cerebellar artery. With a lack of blood flow, the neurons and tracts that compose the lateral medulla die and give rise to the signs and symptoms discussed below.
Lateral medulla strokes give rise to a stereotyped pattern of symptoms known collectively as Wallenberg syndrome. These symptoms are based on the anatomical structures housed in this area of the brainstem.
Pain and temperature sensation from the opposite side of the body, and the same side of the face are affected. This is secondary to interruption of the spinothalamic and spinal trigeminal tracts.
The descending sympathetic fibers, which are in close proximity to the spinothalamic tract, are also interrupted. This leads to a "Horner's syndrome", which is composed of an abnormally small pupil (miosis), decreased facial sweating (anhydrosis), and slight drooping of the eyelid (ptosis) on the affected side.
Patient's also present with ataxia (ie: a loss of muscle coordination) because the cerebellar connections from the spinal cord are destroyed.
Nausea, vomiting, vertigo, and nystagmus are also commonly seen. These symptoms are attributable to the death of neurons in the vestibular nuclei.
Injury to the neurons that compose the nucleus ambiguus leads to difficulty swallowing (secondary to paralysis of the pharyngeal muscles) and difficulty speaking (secondary to paralysis of the muscles that control the larynx).
Diagnosis of lateral medulla strokes are based on symptoms, CT scans, and MRI images. CT and MR angiograms can sometimes show the blocked blood vessel causing the stroke. Formal catheter angiograms may be performed for both diagnostic and therapeutic purposes.
Treatment depends on the timing of the stroke. If the patient presents within 3 hours of symptom onset, and the head CT reveals no bleeding, than intravenous tissue plasminogen activator (tPA) may be given to help "break" up the blood clot causing the stroke.
Other treatments using catheter based approaches are frequently used in patients who are unable to receive tPA. Such treatments include mechanical clot removal with special catheter and wire devices. In addition, in patients more than 3 hours, but less than 6 hours out from symptom onset intra-arterial (not to be confused with intravenous) tPA may be used.
As for all strokes, the underlying cause of the stroke should also be addressed. Patients with atrial fibrillation should be started on blood thinners. If high blood pressure is to blame, then medications to control blood pressure can be used. Patients with atherosclerotic disease should be started on a statin.
In fact, sometimes preventing a second stroke, by modifying risk factors, is unfortunately all that can be done for some patients.
Lateral medulla strokes give rise to a constellation of signs and symptoms known as Wallenberg syndrome. The signs and symptoms are due to disruption of cranial nerve nuclei, as well as ascending and descending fiber tracts. The most frequently blocked blood vessel is the vertebral artery followed by the posterior inferior cerebellar artery. In the setting of the right clinical exam findings, the diagnosis can be made using various neuroimaging modalities. Treatment is based on the time from symptom onset and consists of both medicines and/or mechanical means of re-opening the occluded artery.Monro-Kellie doctrine
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