When the blood supply to tissue is suddenly cut off, the resulting lack of oxygen and nutrients is called ischemia. If this deprivation is prolonged, the affected cells begin to die, a process known as an infarction. An infarct represents the death of tissue due to blocked blood flow and is a serious medical event that most commonly affects the heart or the brain. The term “lateral” specifies the anatomical location of this tissue death, indicating that the damage occurred on the side of the affected organ. This specific location holds significant implications for the symptoms and diagnostic methods required to confirm the condition.
Defining the Lateral Infarct
The term “lateral” means “to the side,” and a lateral infarct is most frequently discussed in the context of the heart and the brain. In the heart, a Lateral Wall Myocardial Infarction (LMI) involves the side wall of the left ventricle, the heart’s main pumping chamber. This area is typically supplied by the left circumflex coronary artery (LCx) or a diagonal branch of the left anterior descending artery (LAD).
Damage to this lateral region is classified based on which part of the wall is affected, such as high lateral or inferolateral, depending on the specific coronary artery branch that is blocked. The left ventricle’s lateral wall is a component of the larger muscle mass that controls the force of the heart’s contraction. Damage here can impact overall cardiac function.
In the brain, a lateral infarct usually refers to a stroke affecting the lateral portion of the medulla oblongata, a region in the brainstem. This condition is often referred to as Lateral Medullary Syndrome, or Wallenberg Syndrome. The area is supplied by the posterior inferior cerebellar artery (PICA) or the vertebral artery.
The medulla oblongata relays signals between the brain and the spinal cord, controlling many involuntary functions. An infarct in this specific lateral region disrupts multiple nerve pathways and nuclei, leading to a unique collection of neurological deficits. Identifying the lateral location is important because the consequences of tissue death are tied directly to the function of the compromised anatomical site.
The Primary Causes of Tissue Death
The mechanism leading to a lateral infarct, whether in the heart or the brain, involves the abrupt cessation of blood flow due to an obstruction within an artery. Most of these events are caused by atherosclerosis, a condition where fatty deposits, or plaque, build up inside the artery walls. While this plaque can remain stable, a sudden rupture of the plaque cap initiates the acute event.
Once the plaque ruptures, the body’s clotting system is triggered to seal the injury, resulting in the rapid formation of a blood clot, or thrombus, at the site of the tear. This thrombus grows quickly, completely blocking the artery and preventing oxygenated blood from reaching the downstream tissue.
In the heart, a thrombus typically forms in the left circumflex artery or its branches, cutting off the blood supply to the lateral wall of the left ventricle. In the brain, a clot most often lodges in the vertebral artery or the posterior inferior cerebellar artery, leading to the infarct in the lateral medulla. Less common causes include coronary artery spasms, or an embolism, which is a clot that travels from another part of the body and becomes lodged in a smaller artery.
Symptoms Related to Lateral Infarction Location
The symptoms of a lateral infarct vary depending on whether the heart or the brain is affected, though both require immediate medical attention. A Lateral Wall Myocardial Infarction (LMI) may present with chest discomfort, often described as pressure, squeezing, or tightness in the center or left side of the chest. However, LMI is often associated with more subtle or atypical presentations compared to infarcts in other areas of the heart.
A person may instead experience pain radiating to the jaw, neck, back, or left arm, or suffer from shortness of breath, fatigue, or a cold sweat. Nausea and vomiting are also common symptoms that can occur with LMI. Because the symptoms can be less pronounced than other types of heart attacks, LMI can sometimes be more challenging to recognize quickly.
A lateral infarct in the brain, which leads to Lateral Medullary Syndrome, produces a distinctive set of neurological symptoms due to damage to the brainstem. One of the hallmark signs is “crossed” sensory loss, where a person loses pain and temperature sensation on one side of the face and the opposite side of the body. Damage to the nerve centers in this region can also cause severe difficulty swallowing (dysphagia) and slurred speech (dysarthria).
Other symptoms include vertigo, loss of coordination (ataxia) leading to difficulty walking, and persistent nausea or vomiting. Damage to sympathetic nerve fibers may also result in Horner syndrome, which involves a drooping eyelid, a smaller pupil, and a lack of sweating on the same side of the face as the lesion.
How Lateral Infarcts Are Identified
The identification of a lateral infarct relies on patient history, laboratory tests, and specialized imaging to confirm tissue death and locate the damage. For a suspected Lateral Wall Myocardial Infarction, the primary diagnostic tool is the electrocardiogram (ECG). The ECG measures the electrical activity of the heart and looks for specific patterns that indicate damage to the lateral wall, such as changes in the ST-segment or the presence of pathological Q waves in the lateral leads (I, aVL, V5, and V6).
Confirmation of heart muscle injury is achieved by measuring cardiac biomarkers in the blood, most notably the protein troponin. Troponin is released into the bloodstream when heart cells are damaged or die, and a rise or fall in its level above a certain threshold provides definitive evidence of an infarction. Additional imaging, such as an echocardiogram, may be used to visualize the heart muscle and detect a new abnormality in the movement of the lateral wall.
When a lateral infarct is suspected in the brain, imaging technology is the most important method for diagnosis. A Computed Tomography (CT) scan may be performed initially to quickly rule out a hemorrhagic stroke, which involves bleeding in the brain. However, Magnetic Resonance Imaging (MRI), particularly with diffusion-weighted sequences, is the preferred method for confirming an acute ischemic stroke.
The MRI provides detailed images that can visualize the area of dead tissue in the lateral medulla oblongata and confirm the location of the infarct. The combination of the patient’s unique neurological symptoms and the location of the infarct on the brain scan allows for a definitive diagnosis of Lateral Medullary Syndrome.