At a glance
For some people with chronic anal fissures, the underlying problem is clear: their internal anal sphincter has an unusually high resting pressure. This high pressure reduces blood flow to the anal lining, prevents the fissure from healing, and drives the pain-spasm cycle that makes the condition so debilitating.
When manometry (pressure testing) confirms high resting pressure, the treatment conversation often moves toward lateral internal sphincterotomy (LIS) — a surgical procedure that directly addresses the pressure problem. This guide covers what high sphincter pressure means, how it connects to fissure treatment, and what people describe about making the decision to have LIS.
Understanding the connection
The internal anal sphincter maintains a constant resting tone — this is normal and necessary. But in some people, this resting tone is significantly higher than average.
High resting pressure causes problems for fissure healing because:
- Reduced blood supply — the tighter the sphincter, the less blood flow reaches the anal lining
- Increased spasm — the muscle is already tight, so any irritation (like a bowel movement passing the fissure) triggers intense spasm
- Mechanical pressure — high sphincter tone makes the anal canal narrower, increasing the force on the fissure during bowel movements
- Self-perpetuating cycle — pain from the fissure triggers more spasm, which further increases pressure, which further reduces healing
This is why many chronic fissures in people with high sphincter pressure do not respond to conservative measures alone. The underlying pressure problem persists regardless of how soft the stools are or how consistent the sitz bath routine is.
The manometry test
Anorectal manometry is the test used to measure sphincter pressure. People describe the experience as:
- Mildly uncomfortable but generally not painful
- Quick — the measurement itself takes only a few minutes
- Informative — the numbers give both patient and clinician concrete data to guide decisions
- Sometimes surprising — some people’s readings are significantly higher than they or their clinician expected
The results are usually expressed as a resting pressure in millimetres of mercury (mmHg). What constitutes “high” varies by laboratory, but readings above a certain threshold are generally considered relevant to fissure management.
Why this often leads to LIS
When high resting pressure is confirmed, the treatment logic becomes clearer:
- Conservative measures (fibre, sitz baths) support healing but do not reduce sphincter pressure
- Topical treatments (such as GTN or diltiazem) work by temporarily relaxing the sphincter and reducing pressure — but the effect is temporary and may not be sufficient for very high pressure
- Botox provides a temporary reduction in sphincter pressure that can allow healing — but the effect wears off, and for very high pressure, may not reduce it enough
- LIS permanently reduces resting pressure by making a controlled partial cut in the internal sphincter — directly and permanently addressing the root cause
This does not mean LIS is always the immediate next step. Many clinicians trial topical treatments or botox first, even with confirmed high pressure. But the awareness that surgical sphincterotomy may be needed helps people mentally prepare and make informed decisions about their treatment pathway.
The decision process
People describe the decision to proceed with LIS after confirmed high pressure as both difficult and, in some ways, clearer than other surgical decisions:
What makes it clearer:
- The manometry provides objective evidence of the problem
- The logic connecting high pressure to non-healing is straightforward
- LIS directly addresses the measured abnormality
- Success rates for LIS are high
What makes it difficult:
- Surgery carries a small but real risk to continence
- The decision feels permanent — once the sphincter is cut, it cannot be uncut
- People have often been through months or years of conservative treatment and are emotionally exhausted
- Fear of any surgical procedure in this area is understandable
People describe finding it helpful to have specific numbers from their manometry to reference. Knowing that their pressure is genuinely elevated — not just “a bit tight” — provides a concrete rationale for a surgical approach.
After LIS with high pressure
People who had LIS specifically because of confirmed high resting pressure commonly describe:
- An immediate and noticeable change in sphincter tension — the chronic tightness is gone
- The first bowel movement being dramatically different — less spasm, less guarding
- A sense of relief that is partly physical and partly emotional
- Gradual healing of the fissure over the following weeks
- Adjustment to the new “normal” — a sphincter that feels looser than what they were used to
The concern about continence is real but, in most accounts from people with genuinely high pressure, the controlled reduction brought their sphincter toward normal range rather than below it. Most people describe no change in continence. A small number describe temporary difficulty with gas control that resolved within weeks.
The broader picture
High resting sphincter pressure is not something people cause or can fully control through lifestyle changes. It is a physiological characteristic — like having higher or lower blood pressure. Understanding this can help remove the self-blame that many people with chronic fissures carry.
If your clinician has discussed high sphincter pressure with you, or if you are considering manometry testing, this is a sign that your treatment is being approached thoughtfully and with attention to the underlying mechanisms. The data from manometry helps guide decisions, and the decisions it guides — whether that is continued conservative care, botox, or LIS — are made with better information than without it.