Cutting Seton Fistula: Key Points and Placement Steps

A cutting seton is a surgical tool used to treat complex anal fistulas while minimizing the risk of incontinence. It gradually cuts through tissue while allowing fibrosis and healing to occur. This approach is often used for high or complicated fistulas where direct surgical division could damage the sphincter muscles.

Understanding how cutting setons work, their types, and proper placement techniques is essential for effective treatment with minimal complications.

Anatomy Of The Anal Fistula

An anal fistula is an abnormal tunnel between the anal canal and the perianal skin, usually resulting from an infected anal gland. These glands, located in the intersphincteric space, can become obstructed, leading to abscess formation. If the abscess does not drain completely, a persistent tract may develop.

The classification of anal fistulas is based on their relationship to the sphincter muscles. The Parks classification system categorizes them into four main types: intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric. Intersphincteric fistulas remain between the internal and external sphincters, while transsphincteric fistulas penetrate both. Suprasphincteric fistulas bypass the external sphincter, and extrasphincteric fistulas originate from the rectum and extend downward, often due to trauma or surgical complications.

Fistula complexity is influenced by secondary tracts, abscess cavities, and granulation tissue. Chronic inflammation can lead to fibrosis, making spontaneous closure unlikely. The extent of sphincter involvement is a key factor in treatment decisions, as aggressive surgical intervention risks impairing continence. High fistulas, which traverse more of the external sphincter, present greater challenges than low fistulas near the anal verge.

Mechanism Of The Cutting Seton

A cutting seton exerts controlled pressure on the fistulous tract, gradually transecting tissue while allowing fibrosis to stabilize surrounding structures. This staged division minimizes the risk of sudden disruption that could cause incontinence. The gradual process enables collagen deposition and scar formation to reinforce tissue as the seton advances.

Periodic tightening increases tension, leading to ischemic necrosis and gradual separation of tissue. This controlled approach prevents excessive trauma to the sphincter complex, as healing occurs in stages. Adjustments are typically performed every one to two weeks to balance effective cutting with healing.

As the seton progresses, the fistulous tract is replaced by fibrotic tissue, reducing recurrence risk. The inflammatory response promotes granulation tissue formation, which serves as a scaffold for new connective tissue. Optimizing seton tension is critical—excessive force may cause premature muscle division, while insufficient pressure can prolong treatment.

Types Of Cutting Setons

Cutting setons come in various materials, each with distinct properties affecting effectiveness and patient comfort. The choice depends on fistula complexity, sphincter involvement, and surgeon preference. While all cutting setons gradually divide tissue, differences in elasticity, tensile strength, and biocompatibility impact healing and tolerance.

Rubber Band

Rubber band setons are widely used due to their elasticity, which allows gradual tightening without frequent manual adjustments. The continuous pressure facilitates steady cutting, reducing the need for repeated clinical interventions.

Their ability to conform to the fistulous tract while maintaining pressure is a key advantage. However, their elasticity can lead to unpredictable cutting rates, as variations in tissue resistance may alter progression speed. Some patients experience discomfort from constant tension, particularly in high transsphincteric fistulas requiring prolonged treatment. Despite these factors, rubber band setons remain a common choice for a self-regulating approach.

Suture-Based

Suture-based cutting setons, made from non-absorbable materials like silk or polypropylene, offer precise control over the cutting process. Unlike rubber bands, these setons require manual tightening at regular intervals, allowing adjustments based on healing progress.

Their main advantage is consistent and predictable cutting rates. Surgeons can modify the frequency and degree of tightening to optimize healing while minimizing discomfort. However, repeated clinical visits for adjustments can prolong treatment and increase patient burden. Additionally, suture materials may cause localized irritation or foreign body reactions, necessitating monitoring. Despite these challenges, suture-based setons are preferred in complex cases requiring controlled tissue division.

Synthetic Threads

Synthetic thread setons, including nylon and polyester, offer a balance between elasticity and tensile strength. These materials provide controlled pressure while minimizing irritation and excessive inflammation. Their smooth surface reduces friction, preventing unnecessary trauma to surrounding tissues.

A key advantage is durability, as synthetic threads resist degradation, ensuring consistent performance throughout treatment. Their non-absorbable nature allows prolonged use without premature breakdown. However, they require more frequent tightening than rubber bands, necessitating regular follow-ups to maintain optimal tension. Despite this, synthetic thread setons are valued for their reliability and controlled cutting with minimal adverse effects.

Key Steps In Seton Placement

Accurate placement of a cutting seton is essential for effective fistula management and minimal tissue disruption. The procedure begins with identifying the fistulous tract, often using digital rectal examination and imaging such as endoanal ultrasound or MRI. These tools confirm the tract’s course, sphincter involvement, and any secondary extensions or abscesses.

A probe is introduced through the external opening and guided along the tract until it emerges at the internal opening. The selected seton material is then threaded through using the probe as a guide. Smooth passage without excessive force is crucial to prevent tissue trauma.

The seton is secured by tying its ends together with appropriate tension. Rubber band setons provide continuous pressure, while suture- or thread-based setons require periodic tightening. Initial tension must balance effective cutting with patient comfort, as excessive tightness can cause pain or premature sphincter disruption.

Sphincter Preservation Factors

Preserving sphincter function is critical when treating complex anal fistulas, as excessive muscle damage can lead to incontinence. High transsphincteric and suprasphincteric fistulas pose the greatest challenge, requiring fine adjustments in seton tension and placement. Gradual division with a cutting seton, rather than immediate surgical transection, reduces the risk of sphincter dysfunction by allowing fibrosis to reinforce tissue as the seton progresses.

Seton material also affects sphincter preservation. Elastic materials like rubber bands apply continuous pressure, which may lead to uncontrolled cutting if not carefully monitored. Suture-based or synthetic thread setons provide greater control, enabling regulated cutting through periodic tightening. The frequency of adjustments is crucial, as overly aggressive tightening can accelerate muscle division beyond the body’s capacity to heal.

Patient-specific factors, including baseline sphincter tone and prior anorectal surgeries, should be considered when determining the best approach. By balancing controlled tissue division with ongoing fibrosis, cutting setons offer a structured method for resolving complex fistulas while minimizing long-term functional impairment.