Anal vein thrombosis

Anal vein thrombosis is also known as anal thrombosis, anal rim thrombosis or perianal thrombosis. The thrombosis forms in a network of veins at the edge of the anus, typically due to a minor injury to the vessel wall or superficial inflammation of one of these veins. A blood clot (thrombus) forms in the affected vein and the vessel swells. Sufferers suddenly feel a painful swelling in the anus. Although generally harmless, anal vein thrombosis often needs treating because of the intense pain it causes.

Enlarged haemorrhoids are often confused with anal vein thrombosis. Anal vein thrombosis manifests itself as a painful, bluish lump on the anus and develops suddenly, often due to increased pressure in the anus. In contrast, enlarged haemorrhoids develop gradually over an extended period.

The swelling occurs within minutes or hours and often causes severe, persistent pain. The swelling is usually bluish in colour and feels like a firm, slightly elastic bump when touched. It is painful to the touch and cannot be pushed back into the anus. The thrombus can vary in size and may grow as large as a chestnut. If the anal vein thrombosis is severe, it can damage the delicate anal skin so much that blood starts to leak out. If bleeding occurs and the thrombus empties, the pain subsides immediately.

Anal vein thrombosis may not require treatment, as the pain often subsides after a few days by itself, and the condition typically resolves completely after just a few weeks. However, certain ointments can relieve the pain of anal vein thrombosis if they contain anti-inflammatory or anaesthetic ingredients, such as the local anaesthetic lidocaine. Suppositories and sitz baths can also provide relief.

If anal vein thrombosis is very painful, it is advisable to consult a specialist (proctologist).

Short breaks are also beneficial for physically demanding jobs, and strenuous activities like weightlifting should be avoided when experiencing acute anal vein thrombosis.

The exact causes of anal vein thrombosis are still a subject of debate among experts. They often form in veins with very thin walls, in areas of the rectum where there is minor inflammation, or in haemorrhoid sufferers.

Possible triggers:

• Straining when constipated
• Overstraining of the sphincter muscles with diarrhoea
• Over-exertion when weight training, lifting heavy objects and cycling, also during the final stages of pregnancy and childbirth
• Unhealthy eating and drinking habits
• Sitting on cold surfaces
• Hormonal factors
• Surgery on the rectum or anal canal
• Anal intercourse

Excessive cleaning of the anus with soap or shower gel can irritate the sensitive anal skin and increase the risk of discomfort.