At a glance
Most anal fissures occur at the posterior midline (the back) or, less commonly, at the anterior midline (the front). When a fissure occurs on the side of the anal canal — a lateral fissure — it is considered atypical. This does not mean it is dangerous, but it does mean your clinician may want to investigate further.
This guide explains what a lateral location means and why it prompts additional attention.
Why location matters
The anal canal has predictable points of vulnerability. The posterior midline has the poorest blood supply, which is why most fissures occur there. The anterior midline is the next most common site, particularly in women. These locations have known anatomical explanations.
A fissure on the side of the anal canal does not fit these patterns. It suggests that something other than simple blood supply vulnerability may be involved. This is why lateral fissures prompt investigation — not because they are inherently dangerous, but because they may have a different underlying cause.
What your clinician may consider
When a fissure is in a lateral position, your clinician may investigate:
Crohn’s disease
Crohn’s disease can affect the perianal area and is associated with fissures in atypical locations. If Crohn’s is suspected, your clinician may recommend blood tests, stool tests, or imaging to investigate further.
Infections
Certain infections — including sexually transmitted infections and tuberculosis in some regions — can cause fissures in unusual locations. Testing for these may be recommended depending on your history and risk factors.
Other inflammatory conditions
Conditions that cause inflammation of the bowel or perianal area can sometimes present with atypical fissures.
Previous surgery or trauma
Prior surgery in the anal area can alter the anatomy and create vulnerability points that are not in the typical midline positions.
Idiopathic (no identified cause)
In many cases, investigation reveals no underlying condition. The fissure is atypical in location but has no sinister cause. This is a valid and common outcome.
What happens during investigation
If your clinician decides to investigate further, this may include:
- Thorough physical examination — looking for other signs of inflammatory conditions
- Blood tests — to check for markers of inflammation or infection
- Stool tests — particularly for inflammatory markers
- Colonoscopy or flexible sigmoidoscopy — if bowel disease is suspected
- Biopsy of the fissure — in some cases, a small tissue sample may be taken
This sounds extensive, but the investigation is systematic and each step has a clear purpose. Your clinician will explain what they are looking for and why.
Treatment
Treatment of a lateral fissure depends on what investigation reveals:
- If no underlying cause is found: standard fissure treatment applies — stool management, sitz baths, topical treatments, and escalation to procedures if needed
- If an underlying condition is identified: treatment of that condition becomes part of the plan alongside fissure management
The fissure itself is treated similarly regardless of location. The difference is in the investigation, not the treatment approach.
What this means for you
If you have been told your fissure is in a lateral or atypical position:
- This is not a diagnosis of any serious condition
- Investigation is a precaution, not an alarm
- Many people with lateral fissures have no underlying condition
- The fissure is still treatable
- Your clinician is being thorough, which is a good thing