What causes an anal thrombosis?
There are many possible causes that can lead to a painful blood clot on the anus. In the skin of the perianal area, there are very fine veins; if the natural blood flow in one of these vessels is blocked, the vessel swells and a so-called venous blood clot forms, causing the anal thrombosis.
The exact causes of an anal vein thrombosis are not yet fully clarified; it is assumed to be a combination of several factors. An anal thrombosis basically arises from the formation of one or more blood clots in a vein of the outer anal area. This clot can be triggered by various factors that lead to increased stress or irritation of the vessels. These factors include genetic predisposition, but also hormonal factors that can adversely affect blood flow and thus promote the formation of a blood clot in the anal area.
An anal thrombosis primarily arises due to increased intra-abdominal pressure, that is, elevated pressure in the abdominal and pelvic area. This can be caused by frequent coughing, excessive straining during bowel movements, diarrhea, but also by lifting heavy loads during weight training or generally sitting for long periods in the office, long car rides, and also long-distance flights. Overweight also exerts constant pressure on the anal region while sitting and can cause the bluish, painful nodules on the anus.
Injuries to the blood vessel walls in the anus also play a role here. Tears in the vessel wall at the anus trigger a chain of blood clotting activities, which can also lead to the formation of a thrombus. Such small injuries can be caused by high pressure in the abdominal cavity, primarily due to frequent strong straining during bowel movements, but also by pregnancy or childbirth. Lifting heavy objects or loads can also play a role, as can mechanical influences in the anal area, such as proctological surgery or anal intercourse as possible causes.
Even sitting on cold surfaces leads to a narrowing of the blood vessels and thus increases the risk of developing a perianal vein thrombosis. Here is an overview of the most common causes of anal vein thrombosis:
Increased pressure on the anal veins
Activities and conditions that exert strong pressure on the veins in the anal area can hinder blood circulation and increase the risk of perianal thrombosis. These include straining hard during bowel movements, especially with constipation. Prolonged sitting, for example during office work or long flights, but also certain sports such as strength training, weightlifting, or cycling.
Physical exertion
Intense physical exertion, especially in strength training, can significantly increase the pressure on the anal veins and thus promote the risk of an anal vein thrombosis. Exercises that involve lifting heavy weights often cause a high increase in intra-abdominal pressure. This increased pressure can compress the blood vessels in the anal area and impair venous return, leading to blood congestion. This congestion can in turn promote the formation of blood clots at the anus, which appear as painful, palpable, bluish nodules or lumps in the venous plexus around the anus.
Furthermore, intense training can also lead to injuries in the anal region, whether through sudden movements or lifting heavy loads, which further damages the vessels. Athletes who pay little attention to adequate recovery and stretching are also more prone to muscle tension in the pelvic floor, which can further impair blood flow in the anal region. These factors often make intense physical activity the cause, or at least a potential risk factor, for the development of an anal vein thrombosis. Especially in all those people who regularly expose themselves to the described high stresses as part of their training program.
Pregnancy and childbirth
During pregnancy, the pressure on the abdominal cavity and pelvic veins increases significantly. The birth itself can also be a strain due to pushing, which promotes the formation of an anal thrombosis. Various rectal complaints occur very frequently during pregnancy and after delivery because several risk factors accumulate during pregnancy. Hormonal changes cause constipation in many women. The baby and amniotic fluid put pressure on the intestines and pelvic floor. Pushing during birth is accompanied by a further increase in pressure in the anal veins. The delivery of the baby causes tears in the pelvic floor muscles. This results in a bruise that settles at the lowest point. Therefore, significant swelling around the anus is often found in women after childbirth. These appear as anal thrombosis, combined with swelling due to water retention and a bruise (hematoma).
Trauma or injury to the anal area
Traumatic injuries to the anal area, whether from surgical procedures or mechanical impacts such as anal intercourse, represent a significant risk factor for the development of an anal vein thrombosis. After surgical procedures, for example an operation for hemorrhoids or other surgeries for proctological diseases, injuries to the fine blood vessels in the anal area can occur. These injuries often lead to an inflammatory reaction and increase the likelihood of blood clots forming in the adjacent veins.
In addition, anal intercourse can also lead to micro-injuries of the vessel walls in the anal canal. These anal fissures or micro-injuries in the anal canal can trigger a chain reaction that promotes blood clotting and thus also favors the development of an anal thrombosis. Furthermore, repeated mechanical stress or trauma, whether from frequently lifting heavy objects or sitting for long periods on hard surfaces, can also damage the sensitive vessels in the anal area and thus increase the risk of blood clots. In all these cases, both the acute pressure on the anal veins and the damage to the tissue of the vessels play a decisive role in the development of anal venous thrombosis. Many of the causes mentioned can also cause hemorrhoids. Hemorrhoids can also occur together with anal venous thromboses. Perianal or anal pain in general can also indicate an anal fissure, anal fistulas, or anal abscesses.
Which risk factors can promote the development of anal venous thromboses?
In addition to the direct causes, there are various risk factors that increase the likelihood of developing an anal thrombosis. Generally, men are more frequently affected by anal venous thromboses than women. However, there are also some female-specific risk factors, such as hormone-related vascular dilation during pregnancy or childbirth. We will take a closer look at the most important risk factors here.
Constipation (obstipation)
Chronic constipation often leads to strong straining during bowel movements, which increases the pressure on the anal veins and promotes the risk of a blood clot in the anus.
Genetic predisposition
Some people have a congenital weakness of the connective tissue or a genetic predisposition to vascular diseases. This susceptibility can increase the risk of anal venous thrombosis, especially if there is already a known family history.
Prolonged sitting
People who sit a lot professionally or privately, such as office workers or long-distance drivers, are at higher risk. Reduced blood flow due to sitting can promote the formation of anal thrombosis. Sitting on cold surfaces also has a negative effect, as this leads to a narrowing of the blood vessels in the anal area and thus makes perianal thrombosis more likely. Contact with damp cold during prolonged sitting, for example when surfing or sitting outside on the ground in winter after outdoor sports, can promote the occurrence of anal thrombosis.
Lack of exercise
Those who move little often suffer from restricted blood circulation, which generally promotes the formation of thrombosis, including anal venous thrombosis.
Overweight
An increased BMI leads to additional strain on the venous system, which in turn increases the risk of venous thrombosis, including anal thrombosis.
Anal thrombosis during pregnancy and childbirth
During pregnancy, the pressure on the pelvic floor steadily increases, which can not only impair blood circulation in the abdominal and pelvic area but also promote the development of anal venous thrombosis. The growing baby and the weight of the amniotic fluid exert increased pressure on the veins in the pelvis and anal region. This often leads to blood congestion, as the venous blood return is hindered.
In addition, the hormonal changes during pregnancy, especially the increase in progesterone, make the vessels softer and more elastic, which at the same time promotes the formation of blood clots. Many pregnant women also suffer from constipation due to slowed digestion, which often triggers strong straining during bowel movements. This straining puts additional pressure on the anal veins, further increasing the likelihood of developing anal venous thrombosis. During childbirth, the intense straining significantly increases pressure in the anal region, which can promote the formation of a blood clot. The risk is also elevated after birth, as hormonal changes and physical strain can delay the recovery of the pelvic floor. These factors overall make pregnancy and childbirth significant risk factors for the development of anal venous thrombosis.
Hormonal changes
In addition to pregnancy and taking the pill, there are other hormonal changes that can increase the risk of anal venous thrombosis. These include menopause and also hormone-based therapies that can affect blood flow and vessel elasticity.
Decreasing elasticity of blood vessels with age
With increasing age, the elasticity of blood vessels decreases, which can also increase the risk of anal venous thrombosis. Older people are also more often affected by constipation and other digestive problems, which in turn increases the risk of elevated pressure in the abdominal area.
Consumption of Alcohol and Nicotine
The consumption of alcohol and nicotine can increase the risk of anal venous thrombosis, as both substances negatively affect the blood vessels. Alcohol acts as a vasodilator, which weakens the veins in the anal area and, due to reduced blood flow, promotes the formation of blood clots. Additionally, alcohol often leads to dehydration and constipation, which requires straining during bowel movements and increases pressure on the anal veins. Nicotine, on the other hand, narrows the blood vessels and damages the vessel walls in the long term, further increasing the risk of thrombosis. Both substances also impair the body's healing processes, which can further increase the risk of thrombosis.
Low-fiber dietary habits
A low-fiber diet can lead to constipation, which in turn increases the risk of anal thrombosis. Spicy or heavily seasoned foods can also irritate the anal area. Dehydration due to insufficient fluid intake also seems to promote the development of anal thrombosis.
Psychosocial factors and stress
Stress can contribute as an indirect cause to the development of anal venous thrombosis by negatively affecting several physical mechanisms. Chronic stress often leads to digestive problems such as constipation or diarrhea, which increases pressure on the anal veins. At the same time, many people resort to unhealthy habits like smoking, alcohol consumption, or poor diet under stress, which raises the risk of constipation and vascular damage. Lack of exercise due to a sedentary lifestyle and muscle tension in the abdominal and pelvic area also increase pressure on the anal veins. Additionally, chronic stress weakens the immune system, leading to inflammation and a higher susceptibility to blood clots. All these factors can increase the risk of anal venous thrombosis.
Mechanical overload of the anal canal
Mechanical stress on the anal canal or anus, such as from hard stools or anal intercourse, is another risk factor that plays a role in the development of anal thrombosis.
In summary, anal vein thromboses often arise from a combination of pressure on the anal veins, physical strain, or injuries in the anal area. The mentioned risk factors increase the likelihood of a blood clot forming in the sensitive veins of the anal region. Those who know these risk factors can take targeted measures to minimize the risk and prevent the development of anal thrombosis. Find concrete tips here on what to consider to prevent anal vein thromboses. Especially if an anal vein thrombosis keeps recurring, or if the anal vein thrombosis does not go away, preventive measures play a central role in treatment and aftercare to effectively prevent repeated or recurring anal vein thrombosis. Find various measures here for your daily life regarding the prevention of anal vein thromboses.
If you suffer from symptoms of anal vein thrombosis, a medical evaluation is definitely recommended. To investigate the specific cause in your case and consequently initiate an appropriate, supportive conservative treatment of anal vein thrombosis.
Often, anal vein thromboses heal on their own, but if there is very severe pain and very large lumps or ulcers on the anus, surgery may be necessary. This is also the case if - despite conservative treatment - an anal vein thrombosis does not go away, or if it is a repeatedly recurring anal vein thrombosis. Read more here about CANNEFF® SUP suppositories and the treatment of anal vein thromboses with suppositories.
Even self-healed anal vein thromboses can result in so-called sentinel folds or skin tags, which, if they become sufficiently large and severely impair anal hygiene, may also require treatment. Find here all information about diagnosis, examinations, and the doctor's visit for anal vein thrombosis.
