An arteriovenous malformation (AVM) is an unusual connection between arteries and veins, bypassing the typical capillary network. While AVMs can occur throughout the body, those in the stomach require specific attention due to potential health implications. Understanding their causes is important for recognition and management.
Understanding Stomach AVMs
The body’s circulatory system normally involves arteries carrying oxygen-rich blood away from the heart. These branch into smaller arterioles, which narrow into capillaries where oxygen and nutrients are exchanged with tissues. Blood then flows from capillaries into venules, which merge to form veins returning oxygen-depleted blood to the heart.
In a stomach AVM, this normal pathway is disrupted. A direct, abnormal connection, or “shunt,” forms between an artery and a vein. This bypass allows high-pressure arterial blood to flow directly into the lower-pressure venous system, bypassing capillaries. This direct flow can weaken vessel walls, making them prone to rupture and bleeding within the stomach.
Primary Mechanisms of AVM Formation
Stomach AVMs arise through two main mechanisms: congenital or acquired. Congenital AVMs are present from birth, resulting from errors in blood vessel development during fetal growth. These abnormal vascular structures may not cause symptoms until much later in life.
Many stomach AVMs are acquired, developing over a person’s lifetime. Their formation can stem from the degeneration of normal blood vessels over time. Chronic stress on vessel walls, such as from persistent elevated pressure, can contribute to their development. Localized inflammatory processes within the stomach lining may also play a role, leading to the abnormal formation of new blood vessels that bypass the capillary network.
Associated Medical Conditions and Risk Factors
Several medical conditions and factors increase the likelihood of developing acquired stomach AVMs. Liver cirrhosis, which involves scarring of the liver, can cause portal hypertension (elevated pressure in the portal vein system). This increased pressure can contribute to AVM formation in the gastrointestinal tract as the body seeks alternative blood flow routes.
Chronic kidney disease is another associated condition, possibly due to systemic changes like chronic inflammation. Heart failure, particularly high-output heart failure, can also be a factor, as altered blood flow dynamics may stress blood vessels. Aging is a general risk factor, with stomach AVMs becoming more common in older adults due to natural vessel wall degeneration.
Radiation therapy to the abdominal region can damage existing blood vessels, potentially leading to AVM formation as the body repairs irradiated tissue. While rare, certain genetic syndromes are also associated with AVMs. Hereditary Hemorrhagic Telangiectasia (HHT), also known as Osler-Weber-Rendu syndrome, is a genetic disorder characterized by abnormal blood vessel formation, including AVMs, in various organs like the gastrointestinal tract. These genetic predispositions result in abnormal blood vessel development and maintenance.