Arteriovenous malformations in the small intestine arise from a mix of causes rather than a single trigger, and in many individual cases the exact origin remains uncertain. Some are driven by inherited genetic mutations that weaken blood vessel walls from birth, while others develop over a lifetime through chronic low-level stress on the gut’s tiny vessels. Age-related degeneration of the intestinal wall, abnormal cardiac conditions, and even mechanical heart-assist devices have all been linked to their formation. The picture is surprisingly layered, and the fact that a diagnosis can still be called “challenging” and “cause unknown” in medical literature tells you how much remains to be sorted out.
How Normal Blood Vessels Go Wrong
In a healthy small intestine, blood flows from tiny arteries into a dense network of capillaries in the gut wall, then drains into small veins. An arteriovenous malformation is essentially a shortcut: blood passes directly from an artery to a vein without traveling through the capillary bed in between. That abnormal connection creates a tangle of fragile, thin-walled vessels that sit close to the inner lining of the intestine. Because these vessels lack the structural reinforcement that normal capillaries and veins have, they are prone to rupturing and bleeding into the gut.
Small bowel vascular lesions, including AVMs, are among the most common causes of obscure gastrointestinal bleeding, the kind of bleeding that standard upper and lower endoscopy cannot easily find. Most small bowel AVMs tend to be relatively large and are prone to re-bleeding, which is why they often end up requiring surgical removal rather than less invasive treatment.1PubMed Central. Diagnosis and therapeutic strategies for small bowel vascular lesions
The Wear-and-Tear Theory
The most common form of intestinal vascular malformation in older adults is thought to be degenerative, meaning it develops gradually over decades. The leading explanation centers on chronic, low-grade obstruction of the small veins in the intestinal wall. Every time the gut contracts during digestion, it temporarily compresses the veins running through its muscular layers. Over many years, that repeated squeezing is thought to cause the veins to dilate. As the veins widen, the capillaries feeding into them lose their normal resistance, and eventually a direct connection forms between the arterial and venous sides.
This process helps explain why acquired intestinal vascular malformations are overwhelmingly a condition of people over 60. The vessels have simply been under mechanical stress for longer. It also explains why lesions tend to cluster in certain segments of the gut where the muscular wall is thickest and the veins are most susceptible to compression during contractions.
Genetic Causes and Hereditary Hemorrhagic Telangiectasia
Not all intestinal AVMs are acquired. Some people are born with a genetic predisposition that makes their blood vessels structurally abnormal from the start. The best-understood genetic cause is hereditary hemorrhagic telangiectasia, also known as Osler-Weber-Rendu syndrome. HHT is an autosomal dominant condition, meaning inheriting just one copy of a mutated gene from either parent is enough to cause it. Its prevalence is estimated at roughly 1.5 to 2 people per 10,000.2PubMed Central. Gastrointestinal Manifestations of Hereditary Hemorrhagic Telangiectasia (HHT): A Systematic Review of the Literature
At the molecular level, HHT involves mutations that disrupt signaling pathways responsible for keeping blood vessels properly formed and resilient. Histological examination of AVMs in HHT patients shows an irregular inner lining, abnormal collagen and actin buildup, and a distorted basement membrane. The most frequently implicated mutations occur in genes called ENG, ACVRL1 (also known as ALK1), and SMAD4, all of which encode proteins involved in controlling how new blood vessels grow and remodel.3PubMed Central. Diagnostic yield of capsule endoscopy for small bowel arteriovenous malformations in patients with hereditary hemorrhagic telangiectasia When these pathways malfunction, the result is extreme vessel fragility. People with HHT can develop AVMs in the lungs, liver, and brain as well, but the small intestine is a particularly common site of bleeding.
HHT is worth knowing about because it can masquerade as ordinary gastrointestinal bleeding for years before anyone considers a genetic diagnosis. A person with recurrent, unexplained intestinal bleeding and a family history of frequent nosebleeds or visible red spots on the lips and fingers should raise the suspicion of HHT.
Aortic Stenosis and Heyde’s Syndrome
One of the more counterintuitive causes of intestinal vascular malformations involves a heart valve problem. Heyde’s syndrome describes a triad: aortic stenosis (a narrowed aortic valve), intestinal angiodysplasia with bleeding, and an acquired deficiency in a clotting protein called von Willebrand factor. The syndrome tends to appear in older adults and is considered significantly underreported.4PubMed Central. Aortic stenosis and Heyde’s syndrome: A comprehensive review
The connection works like this: when blood is forced through a tightly narrowed aortic valve at high speed, the physical shear stress chews up large von Willebrand factor molecules in the bloodstream. These large molecules are exactly the ones the body relies on for sealing small vascular injuries. Without them, even minor fragile-vessel bleeding in the gut becomes difficult to stop. At the same time, the abnormal blood flow dynamics downstream of the narrowed valve appear to promote the formation or enlargement of vascular malformations in the intestine. Replacing the aortic valve often resolves both the clotting problem and the bleeding, which is strong indirect evidence that the valve disease is genuinely driving the intestinal lesions rather than just coincidentally appearing alongside them.
Mechanical Heart Pumps and New-Onset AVMs
Perhaps the most striking modern evidence that abnormal blood flow can directly cause intestinal AVMs comes from patients with continuous-flow left ventricular assist devices. These pumps are implanted in people with severe heart failure to help the heart push blood through the body. Unlike a natural heartbeat, which produces a pulsing flow, many of these devices generate a smooth, continuous stream. That difference turns out to matter enormously for the gut.
Research in humans and large animals has shown that continuous-flow LVAD support causes measurable changes in the blood vessels of the small intestine. In one study, intestinal vascularity in the jejunum was significantly higher after LVAD support compared to controls. The same study found that LVAD support caused substantial degradation of high-molecular-weight von Willebrand factor molecules and a large accumulation of smaller, less functional fragments. The authors described these findings as the first direct evidence that LVAD support itself causes gastrointestinal angiodysplasia, with abnormal von Willebrand factor metabolism serving as a likely mechanistic link between the device, abnormal vessel growth, and bleeding.5PubMed. Continuous-Flow LVAD Support Causes a Distinct Form of Intestinal Angiodysplasia
Clinically, GI bleeding is a common complication in LVAD patients. In one series of patients with the HeartMate II device, AVMs were identified as the bleeding source in roughly a third of those who bled, and these patients were significantly older on average than the broader LVAD population. Bleeding tended to originate in the proximal small intestine, particularly the jejunum, and recurrence at different sites was common.6The Journal of Heart and Lung Transplantation. Arteriovenous malformation and gastrointestinal bleeding in patients with the HeartMate II left ventricular assist device The LVAD story is instructive because it demonstrates that mechanical disruption of normal pulsatile blood flow and von Willebrand factor integrity can produce new vascular malformations even in people who had none before surgery.
The Role of Oxygen Deprivation
A thread running through several of these causes is tissue-level oxygen deprivation. When parts of the intestinal wall do not get enough oxygen, cells activate a molecular alarm system centered on a protein complex called hypoxia-inducible factor, or HIF. Under normal conditions, HIF is quickly broken down. Under low-oxygen conditions, it accumulates and switches on genes that promote the growth of new blood vessels, a process called angiogenesis.
This response is meant to be a short-term rescue: grow new vessels to restore blood supply. But when it becomes chronic or is triggered inappropriately, it can drive the formation of abnormal, poorly structured vessels. Increased activation of the HIF pathway causes aberrant expression of the growth signals that contribute to the formation and persistence of vascular malformations.7PubMed. Hypoxia-inducible factor pathway and diseases of the vascular wall This mechanism helps explain why conditions that reduce blood flow to the gut wall, whether from chronic heart failure, low cardiac output, or localized venous congestion, tend to promote AVM development. The intestine is trying to compensate, but the compensation itself produces fragile, malformed vessels.
Portal Hypertension and Liver Disease
When the liver becomes scarred or otherwise obstructed, pressure builds in the portal venous system, the network of veins that carries blood from the intestines to the liver. That elevated pressure transmits backward into the veins of the gut wall. The resulting condition, portal hypertensive enteropathy, can produce a range of vascular abnormalities in the small intestine, from subtle mucosal changes that cause no symptoms to lesions capable of life-threatening hemorrhage.8PubMed Central. Portal hypertensive enteropathy
The mechanism overlaps with the degenerative theory described earlier but operates on a faster timeline. Rather than decades of normal digestive contractions gradually dilating veins, portal hypertension imposes a constant, abnormally high pressure that distends the intestinal vasculature more aggressively. This makes AVM-like lesions more likely to develop in younger patients than the typical age-related form, particularly those with advanced liver cirrhosis. Patients with portal hypertension who develop GI bleeding are often assumed to be bleeding from esophageal varices, but the small intestine can be a hidden source.
Chronic Kidney Disease
Intestinal vascular malformations show up at a disproportionate rate in people on long-term dialysis or with end-stage kidney disease. The exact mechanism is not fully understood. Uremia, the buildup of waste products in the blood when the kidneys fail, appears to impair normal blood vessel maintenance and repair. There may also be a platelet-function component, since uremia is well known to interfere with how platelets stick together and form clots. The medical literature has acknowledged the association for decades while noting that the diagnosis remains challenging because the cause is still unclear and the clinical presentation varies widely from patient to patient.9PubMed. Gastrointestinal angiodysplasia in chronic renal failure
Chronic kidney disease may also contribute through its cardiovascular effects. Patients with advanced renal failure frequently develop aortic calcification and stiff blood vessels, creating hemodynamic conditions somewhat analogous to aortic stenosis. Whether these cardiac changes independently promote intestinal AVMs in the same way Heyde’s syndrome does is an area of ongoing investigation.
What Treatments Reveal About Causes
Sometimes the therapies that work against intestinal AVM bleeding tell you something about what is driving the malformations in the first place. Two treatments in particular offer mechanistic clues.
Octreotide, a synthetic hormone analogue, has been used to manage bleeding from small bowel vascular lesions. It works by boosting platelet clumping, reducing blood flow to the gut, and directly opposing the growth of new blood vessels.10PubMed Central. Role of octreotide in small bowel bleeding The fact that an anti-angiogenic drug helps control AVM bleeding reinforces the idea that ongoing, abnormal vessel growth is part of what sustains these lesions. They are not just static structural defects; they are actively maintained by pro-growth signals that can be interrupted.
Hormonal therapy with combined estrogen and progesterone has also been studied. There is considerable evidence that this combination significantly reduces bleeding frequency, intensity, and transfusion needs in patients with high transfusion requirements from intestinal AVMs.11PubMed. Pharmacologic therapy of arteriovenous malformations Why sex hormones would affect vascular malformations is not entirely settled, but estrogen is known to influence the integrity of blood vessel walls and the expression of clotting factors. The responsiveness of intestinal AVMs to hormonal manipulation suggests that the vessels’ structural weakness is partly modulated by hormonal signaling, which could also help explain why the prevalence and bleeding behavior of these lesions sometimes differ between men and women.
Why the Cause Often Remains Unknown
Despite all these identified pathways, a large proportion of intestinal AVMs are diagnosed without a clear explanation for why they formed. A patient over 70 with no history of liver disease, no genetic syndrome, and a normal heart valve can still develop bleeding small bowel AVMs. In these cases, the degenerative theory is usually invoked as the default explanation, but “decades of wear on blood vessel walls” is more of a description than a mechanistic cause.
Part of the difficulty is that the small intestine is the hardest segment of the GI tract to examine. It is too far from either end for standard endoscopes to reach easily, and its length (roughly 20 feet in most adults) means that even capsule endoscopy can miss small lesions. Many AVMs are only found after they bleed significantly, which means the early stages of their development are almost never observed in living patients. Researchers have mostly had to work backward from the finished lesion, inferring what went wrong from the final anatomy rather than watching the malformation grow. Until better imaging or molecular markers allow earlier detection, the formation of many small intestinal AVMs will remain a partly open question.
When Multiple Causes Overlap
In real patients, these causes rarely operate in isolation. An older adult with mild aortic stenosis, early chronic kidney disease, and age-related venous dilation in the intestinal wall may be experiencing three separate pressures on their gut vasculature simultaneously. A patient with HHT who also develops liver cirrhosis faces both a genetic defect in vessel formation and the hemodynamic stress of portal hypertension. The clinical challenge is figuring out which factors are contributing most in a given person, since the treatment approach differs. Valve replacement helps in Heyde’s syndrome. Genetic counseling and screening matter in HHT. Managing portal pressure is the priority in liver disease. And in the patient with LVAD-related AVMs, the best intervention might ultimately be a heart transplant that restores normal pulsatile flow.
This overlap also complicates research. Studies of intestinal AVMs inevitably include patients whose lesions arose through different mechanisms, making it hard to draw clean conclusions about any single pathway. Until the field develops better ways to subtype these malformations based on their molecular or histological features, the category “intestinal AVM” will continue to lump together what are likely several distinct diseases sharing a similar final appearance.