An anal fissure and an anal fistula

These are descriptions from public pages opened October 27, 2026. A matching sentence does not identify the problem. ahem has not examined anyone.

Mayo Clinic's fissure page, dated December 31, 2024, calls an anal fissure a small tear in the thin, moist tissue that lines the anus. On that copy it lists pain during a bowel movement, pain afterward that can last up to several hours, bright red blood on the stool or toilet paper, a visible crack in the skin around the anus, and a small lump or skin tag near the tear. It also describes spasm in the anal sphincter, the ring of muscle at the end of the anus.

Mayo Clinic's fistula page, dated July 2, 2024, calls an anal fistula, also fistula-in-ano, a tunnel between the inside of the anus and the skin around it. Most start as an infection in an anal gland. The infection causes an abscess that drains on its own or is drained through the skin. The drainage tunnel stays open. Mayo Clinic says surgery is usually needed, and that nonsurgical treatments are sometimes an option.

On the fistula symptoms page checked October 27, 2026, Mayo Clinic lists an opening on the skin around the anus, a red inflamed area around that opening, oozing of pus, blood, or stool, pain in the rectum and anus especially when sitting or passing stool, and fever.

Cleveland Clinic last updated its fistula page on July 11, 2023. Opened October 27, 2026, it calls the common symptoms intense, throbbing anal pain, worse with a bowel movement, coughing, or sitting; swelling and redness; and fluid from somewhere around the anus that may include pus, stool, or blood. Less common symptoms on that page are fever, pain when urinating, and difficulty holding stool. It says the opening can look like a hole in the skin near the anus, and that a person may or may not be able to see it.

• A fissure, on Mayo Clinic's fissure page: pain with a bowel movement, a visible crack, and bright red blood on stool or paper.
• A fistula, on both fistula pages: a tunnel or skin opening, drainage that can include pus, and pain that can include sitting.
• Fever is on the fistula symptom lists. It is not on Mayo Clinic's fissure symptom list.

Cleveland Clinic's fistula page, checked October 27, 2026, answers the comparison directly. A fissure is a split or tear in the lining of the anal canal. It can cause similar symptoms, and it is a superficial wound. It does not tunnel through the anal wall to the skin. The same page says an infected fissure can form an abscess, and that abscess can create a fistula when it drains.

The counts on that Cleveland Clinic page stay with that page. It says a fistula is twice as common in males, that about half of people who get an infected anal gland will develop a fistula, and that an infected gland that forms an abscess causes 75 percent of anal fistulas. Mayo Clinic's fistula page, dated July 2, 2024, says fistulas occur most often in adults around age 40, may occur younger especially with Crohn's disease, and occur more often in males than in females. It does not print the half or the 75 percent.

Mayo Clinic's fissure page lists constipation, straining, hard or large stools, long-lasting diarrhea, anal intercourse, and childbirth as common causes. Less common causes there include Crohn's disease or another inflammatory bowel disease, anal cancer, HIV, tuberculosis, and syphilis. Its fistula page lists a previously drained anal abscess, Crohn's disease or other inflammatory bowel disease, trauma, infections, and surgery or radiation for anal cancer. Shared ground is an infection or Crohn's disease can sit near either finding. The tear and the tunnel are still different descriptions.

Mayo Clinic's fistula treatment page, also dated July 2, 2024 and opened October 27, 2026, says a clinician asks about symptoms and looks around and inside the anus. The outside opening is usually easy to see. The inside opening is harder, and the path of the tunnel matters for treatment. Tests it names include MRI, endoscopic ultrasound, fistulography, an exam under anesthesia, a fistula probe, an anoscope, and a flexible sigmoidoscopy or colonoscopy, especially if ulcerative colitis or Crohn's disease is suspected.

Cleveland Clinic says most fistulas are found on a physical exam, sometimes under sedation if the exam is too painful, and that imaging can map the path. It classifies fistulas by how they relate to the sphincter muscles. The names it prints are intersphincteric, transsphincteric, suprasphincteric, extrasphincteric, and superficial. Mayo Clinic says the sphincter classification helps the surgeon choose treatment, and it does not print that five-name list. Operations that follow the exam are on surgery for an anal fistula.

A swollen vein is a different finding from either of these. That comparison is on hemorrhoids and anal fissures. How long Mayo Clinic gives a fissure to heal is on how long an anal fissure takes to heal.