Histologically, it resembles telangiectasia and development is related to age and strain on the bowel wall. It is a degenerative lesion, acquired, probably resulting from chronic and intermittent contraction of the colon that is obstructing the venous drainage of the mucosa. As time goes by the veins become more and more tortuous, while the capillaries of the mucosa gradually dilate and precapillary sphincter becomes incompetent. Thus is formed an arteriovenous malformation characterized by a small tuft of dilated vessels.

Although angiodysplasia is probably quite common, the risk of bleeding is increased in disorders of coagulation. A classic association is Heyde's syndrome (coincidence of aortic valve stenosis and bleeding from angiodysplasia).

In this disorder, von Willebrand factor (vWF) is proteolysed due to high shear stress in the highly turbulent blood flow around the aortic valve. vWF is most active in vascular beds with high shear stress, including angiodysplasias, and deficiency of vWF increases the bleeding risk from such lesions.

Warkentin "et al." argue that apart from aortic valve stenosis, some other conditions that feature high shear stress might also increase the risk of bleeding from angiodysplasia.

In medicine (gastroenterology), angiodysplasia is a small vascular malformation of the gut. It is a common cause of otherwise unexplained gastrointestinal bleeding and anemia. Lesions are often multiple, and frequently involve the cecum or ascending colon, although they can occur at other places. Treatment may be with colonoscopic interventions, angiography and embolization, medication, or occasionally surgery.

Safety regulations from US accreditor the Joint Commission may have unintentionally decreased digital rectal examination and FOBT in hospital settings such as Emergency Departments.

Conditions such as ulcerative colitis or certain types of relapsing infectious diarrhea can vary in severity over time, and FOBT may assist in assessing the severity of the disease. Medications associated with gastrointestinal bleeding such as Bortezomib are sometimes monitored by FOBT.

The exact prevalence of the syndrome is unknown, because both aortic stenosis and angiodysplasia are common diseases in the elderly. A retrospective chart review of 3.8 million people in Northern Ireland found that the incidence of gastrointestinal bleeding in people with any diagnosis of aortic stenosis (they did not subgroup people by severity) was just 0.9%. They also found that the reverse correlation—the incidence of aortic stenosis in people with gastrointestinal bleeding—was 1.5%. However, in 2003 a study of 50 people with aortic stenosis severe enough to warrant immediate valve replacement found GI bleeding in 21% of people, and another study done in the USA looking at angiodysplasia rather than GI bleeding found that the prevalence of aortic stenosis was 31% compared to 14% in the control group.

It is difficult to determine how common hemorrhoids are as many people with the condition do not see a healthcare provider. However, symptomatic hemorrhoids are thought to affect at least 50% of the US population at some time during their lives, and around 5% of the population is affected at any given time. Both sexes experience about the same incidence of the condition, with rates peaking between 45 and 65 years. They are more common in Caucasians and those of higher socioeconomic status.

Long-term outcomes are generally good, though some people may have recurrent symptomatic episodes. Only a small proportion of persons end up needing surgery.

Heyde's syndrome is a syndrome of gastrointestinal bleeding from angiodysplasia in the presence of aortic stenosis.

It is named after Edward C. Heyde, MD who first noted the association in 1958. It is caused by the induction of Von Willebrand disease type IIA (vWD-2A) by a depletion of Von Willebrand factor (vWF) in blood flowing through the narrowed valvular stenosis.

A number of preventative measures are recommended, including avoiding straining while attempting to defecate, avoiding constipation and diarrhea either by eating a high-fiber diet and drinking plenty of fluid or by taking fiber supplements, and getting sufficient exercise. Spending less time attempting to defecate, avoiding reading while on the toilet, and losing weight for overweight persons and avoiding heavy lifting are also recommended.

The prevalence of vWD is about one in 100 individuals. However, the majority of these people do not have symptoms. The prevalence of clinically significant cases is one per 10,000. Because most forms are rather mild, they are detected more often in women, whose bleeding tendency shows during menstruation. It may be more severe or apparent in people with blood type O.

The vWF gene is located on the short arm "p" of chromosome 12 (12p13.2). It has 52 exons spanning 178kbp. Types 1 and 2 are inherited as autosomal dominant traits and type 3 is inherited as autosomal recessive. Occasionally, type 2 also inherits recessively. vWD occurs in approximately 1% of the population and affects men and women equally.

If untreated, severe symptomatic aortic stenosis carries a poor prognosis with a 2-year mortality rate of 50-60% and a 3-year survival rate of less than 30%. Prognosis after aortic valve replacement for people who are younger than 65 is about five years less than that of the general population; for people older than 65 it is about the same.

Approximately 2% of people over the age of 65, 3% of people over age 75, and 4% percent of people over age 85 have aortic valve stenosis. The prevalence is increasing with the aging population in North America and Europe.

Risk factors known to influence disease progression of AS include lifestyle habits similar to those of coronary artery disease such as hypertension, advanced age, being male, hyperlipidemia, diabetes mellitus, cigarette smoking, metabolic syndrome, and end-stage kidney disease.

The body normally gets the iron it requires from foods. If a person consumes too little iron, or iron that is poorly absorbed (non-heme iron), they can become iron deficient over time. Examples of iron-rich foods include meat, eggs, leafy green vegetables and iron-fortified foods. For proper growth and development, infants and children need iron from their diet. A high intake of cow’s milk is associated with an increased risk of iron-deficiency anemia. Other risk factors for iron-deficiency anemia include low meat intake and low intake of iron-fortified products.

Blood contains iron within red blood cells, so blood loss leads to a loss of iron. There are several common causes of blood loss. Women with menorrhagia (heavy menstrual periods) are at risk of iron-deficiency anemia because they are at higher-than-normal risk of losing a larger amount blood during menstruation than is replaced in their diet. Slow, chronic blood loss within the body — such as from a peptic ulcer, angiodysplasia, a colon polyp or gastrointestinal cancer, or excessively heavy periods — can cause iron-deficiency anemia. Gastrointestinal bleeding can result from regular use of some groups of medication, such as NSAIDs (e.g. aspirin), as well as anticoagulants such as clopidogrel and warfarin; however, these are required in some patients, especially those with states causing thrombophilia.