An arteriovenous malformation (AVM) in the gastrointestinal tract is an abnormal connection between arteries and veins that bypasses the capillary network. These vascular lesions, often called angiodysplasia when acquired, can occur anywhere along the digestive system. A small intestine AVM is a notable source of internal bleeding because the organ is difficult to access using standard endoscopic procedures. This abnormality creates a direct, high-pressure shunt, making the fragile vessels prone to rupture and hemorrhage.
Understanding Small Intestine AVMs
Vascular lesions in the small intestine are categorized as either true AVMs or angiodysplasia, which differ in origin and structure. True AVMs are generally considered congenital, meaning they are present from birth, though they may not cause problems until later in life. These congenital lesions are less common in the small intestine than in other parts of the body.
The more frequently encountered lesion, especially in older adults, is angiodysplasia, which is an acquired vascular ectasia. Angiodysplasia is characterized by a cluster of dilated, twisted small blood vessels in the mucosal and submucosal layers of the intestinal wall. The small intestine is a long and convoluted organ, making it a uniquely challenging location for the detection and treatment of these lesions.
Etiology and Predisposing Factors
The formation of acquired small intestine AVMs, or angiodysplasia, is thought to be a degenerative process related to chronic mechanical stress on the intestinal wall. One leading theory suggests that intermittent obstruction of the small veins draining the mucosal lining plays a role in their development. Repeated muscular contractions of the intestinal wall may squeeze these draining veins, causing a backlog of pressure in the upstream capillaries.
This chronic back-pressure causes the capillaries to gradually dilate and become tortuous, eventually forming fragile connections between the arteries and veins. This mechanism is believed to occur most often in areas of high wall tension, explaining the prevalence of these lesions in the small intestine. While the exact reason for their formation remains incompletely understood, several specific risk factors increase the likelihood of developing them.
Advanced age is the most significant predisposing factor, with angiodysplasia occurring most often in patients over 50 years old. Chronic kidney disease, especially end-stage renal disease (ESRD), is also a recognized risk factor.
Associated Conditions
A notable association is Heyde’s syndrome, which links aortic stenosis (a narrowing of the aortic heart valve) with gastrointestinal bleeding from angiodysplasia. The high-shear stress caused by the narrowed valve is thought to damage von Willebrand factor, a blood clotting protein, contributing to the bleeding tendency of the fragile vessels. Other conditions, such as von Willebrand disease and the use of left ventricular assist devices (LVADs), also predispose individuals to these lesions due to their effect on blood flow or clotting.
Clinical Presentation and Consequences
The most common presentation of a small intestine AVM is obscure gastrointestinal bleeding (OGIB), meaning the source is not found by standard upper endoscopy or colonoscopy. This bleeding is often slow, chronic, and intermittent, making it difficult to detect immediately. Patients typically experience symptoms related to the resulting blood loss rather than noticing visible blood.
The chronic nature of the bleeding frequently leads to iron-deficiency anemia, the primary consequence of small intestine AVMs. Symptoms of anemia include persistent fatigue, generalized weakness, and pallor. The ongoing blood loss depletes the body’s iron stores, hindering the production of sufficient red blood cells.
While most bleeding is slow, AVMs can occasionally cause acute, overt hemorrhage. This more dramatic presentation can manifest as melena (dark, tarry stools) or hematochezia (bright red or maroon blood in the stool), depending on the location and speed of the bleeding. A severe, rapid bleed can lead to symptoms like lightheadedness, a rapid heart rate, or hypotension.
Diagnosis and Management Approaches
Identifying an AVM in the small intestine is a diagnostic challenge because the small bowel is long and beyond the reach of conventional endoscopes. The initial diagnostic step involves capsule endoscopy, where the patient swallows a small device that captures thousands of images as it travels through the digestive tract. This “pill-cam” is highly effective for visualizing the small bowel mucosa and pinpointing the AVM location.
If a bleeding AVM is found, the next step involves deep enteroscopy, such as balloon-assisted enteroscopy. This specialized procedure uses a flexible scope with an inflatable balloon to advance deep into the small intestine. This allows a physician to directly visualize the lesion and perform therapeutic intervention.
The primary management strategy for bleeding AVMs is endoscopic therapy, which aims to close the fragile vessels and stop the hemorrhage. This is typically achieved using thermal techniques like argon plasma coagulation (APC) or electrocoagulation, which apply heat to the lesion to seal the vessels. Endoscopic treatment is highly effective and minimally invasive, often resolving the immediate bleeding and anemia.
For patients with chronic, recurrent bleeding, medical management is an option. This includes iron supplementation to treat the iron-deficiency anemia. Hormonal therapy, such as estrogen and progesterone, may also help reduce bleeding episodes. Surgical resection, which involves removing the segment of the intestine containing the AVM, is reserved as a last resort for lesions that are refractory to endoscopic and medical therapies.