Thrombosed Hemorrhoid

What Is It, Causes, Diagnosis, Treatment, and More

Author: Anna Hernández Castillo, MD

Editors: Antonella Melani, MD, Lisa Miklush, PhD, RN, CNS

Illustrator: Abbey Richard


What is a thrombosed hemorrhoid?

Hemorrhoidal disease (most commonly known as hemorrhoids), arises from an abnormal distension of the hemorrhoidal veins that lie underneath the mucosa of the lower rectum and anus. Although the word “hemorrhoids” is frequently used to refer to hemorrhoidal disease, hemorrhoids are actually normal clusters of highly vascular structures, smooth muscle, and elastic connective tissue that form the anal cushions. Their main function is to protect the anal sphincter and help prevent incontinence when the abdominal pressure increases, such as when sneezing or coughing. 

In some individuals, these anal cushions can become swollen or protrude through the anal canal, leading to what is commonly known as hemorrhoids or piles. A thrombosed hemorrhoid occurs when a blood clot forms inside a hemorrhoidal vein, obstructing blood flow and causing a painful swelling of the anal tissues. Thrombosed hemorrhoids are not dangerous, but they can be very painful and cause rectal bleeding if they become ulcerated.

There are two kinds of hemorrhoids, internal hemorrhoids, which develop in the lower rectum, above the dentate line, and external hemorrhoids, which develop on the verge of the anal canal, below the dentate line. Almost all thrombosed hemorrhoids are external, but thrombosis of internal hemorrhoids is also possible.

What does a thrombosed hemorrhoid look like?

Acutely thrombosed external hemorrhoids typically appear as a painful dark bluish lump at the verge of the anal canal. In some cases, the increased pressure within the hemorrhoid can lead to necrosis and ulceration of the skin on top of it, causing rectal bleeding. On the other hand, thrombosed internal hemorrhoids are far less common and may not be visible from the outside unless they protrude from the anal canal.

Will a thrombosed hemorrhoid go away on its own?

Many thrombosed hemorrhoids go away on their own after a few weeks, even without treatment. The severity of pain is most intense in the first day or two from the onset. After that, the blood clot will most likely be reabsorbed and the pain will decrease within the next few days. Sometimes, resolved thrombosed hemorrhoids can leave behind a residual skin tag due to excessive stretching of the skin around the anus.

What causes thrombosed hemorrhoids?

Initially, hemorrhoidal disease can develop as a result of a combination of factors, including the weakening of the supportive connective tissue within the anal cushions, reduced blood flow to the perianal area, and increased intra-abdominal pressure. Risk factors associated with the development of hemorrhoids include a history of constipation, prolonged straining during bowel movements, heavy lifting, sitting for a long period of time, obesity, and pregnancy. Once hemorrhoids have developed, blood pooling within the blood vessels can contribute to the formation of a blood clot, resulting in thrombosis.

How do you diagnose a thrombosed hemorrhoid?

Diagnosis of thrombosed external hemorrhoids can be suspected in individuals with a history of sudden intense pain in the anal region, along with the detection upon physical examination of a painful lump or swelling of the perianal tissues. Inspection of the anus will exclude the presence of a prolapsing internal hemorrhoid. A digital rectal exam may be performed to check for blood in the stool, as well as exclude the presence of a rectal mass or internal hemorrhoids. If the digital exam is inconclusive, the anal canal can be examined with the help of an anoscope, which is an illuminated speculum that can be used to visualize the lower rectum. Finally, if there’s clinical evidence of rectal bleeding, a colonoscopy or sigmoidoscopy may be performed to rule out other causes of bleeding, such as inflammatory bowel disease, colorectal polyps, or cancer.

How do I know if my hemorrhoid is thrombosed?

Hemorrhoids are otherwise painless unless they are thrombosed, prolapsed, or strangulated, meaning their blood supply has been cut-off. Thus, significant pain in the perineal area, as well as feeling a painful lump near the anus can be signs of thrombosed hemorrhoids.

How do you treat a thrombosed hemorrhoid?

Treatment of thrombosed hemorrhoids is aimed at relieving the pain and speeding recovery time, as the body is generally able to reabsorb the blood clot even without treatment. In individuals with severe pain, surgical excision of the blood clot is recommended within the first 24–48 hours from onset. If more than 24–48 hours have passed, individuals are usually treated with conservative measures, such as oral or topical pain relievers and warm water sitz baths several times a day. In addition, constipation or straining can be relieved by increasing fluid and dietary fiber intake, as well as taking fiber supplements and stool softeners, thus reducing the chance of developing hemorrhoids in the future.

Can I drain a thrombosed hemorrhoid myself?

Surgical excision or drainage of the blood clot is a procedure that can entail significant risks, such as incomplete removal of the blood clot, uncontrollable bleeding and infection of the perianal tissues, which is why it should always be performed by a trained physician. Surgical excision or drainage of the blood clot begins by numbing the affected area with local anesthesia, and then performing a circumferential incision to remove the clot.

What are the most important facts to know about thrombosed hemorrhoids?

Thrombosed hemorrhoids occur when a blood clot forms inside a hemorrhoidal vein, obstructing blood flow and causing a painful swelling of the perianal tissues. Most thrombosed hemorrhoids are external, meaning they occur below the dentate line, but thrombosis of internal hemorrhoids is also possible. Although thrombosed hemorrhoids are not dangerous, they can cause intense pain and rectal bleeding when ulcerated. Diagnosis of thrombosed hemorrhoids can be made through clinical history and physical examination, including inspection of the anus and a digital rectal exam. If there’s evidence of blood in the anal canal, further tests may be necessary to rule out other causes of rectal bleeding, such as colorectal cancer. Treatment of thrombosed hemorrhoids may include surgical excision of the blood clot or conservative measures, including pain relievers, having a warm bath or sitz bath, and relieving constipation.

Related links

Clinical Reasoning: Anal conditions
Hemorrhoid
High Yield: Gastrointestinal bleeding

Resources for research and reference

Lohsiriwat, V. (2015). Treatment of hemorrhoids: A coloproctologist's view. World Journal of Gastroenterology, 21(31): 9245–9252. DOI: 10.3748/wjg.v21.i31.9245

Sanchez, C. & Chinn, B. T. (2011). Hemorrhoids. Clinics in Colon and Rectal Surgery, 24(1): 5–13. DOI: 10.1055/s-0031-1272818

Sugerman, D. T. (2014). Hemorrhoids. JAMA, 312(24): 2698. DOI: 10.1001/jama.2014.281