Perioperative management - Seton drainage for high transsphincteric anal fistula

• intermediate transsphincteric fistulas
• high transsphincteric fistulas
• suprasphincteric fistulas
• acute abscesses with an existing fistula that cannot be primarily split

Etiologyof cryptoglandular anal fistulas

The cryptoglandular hypothesis by Parks is generally accepted as an explanation for the development of perianal abscesses and fistulas. According to this, a perianal abscess initially results from the obstruction of a proctodeal gland or its duct, followed by infection. The fistula represents the abscess drainage channel, which forms as a result of chronic inflammation and epithelialization. The internal opening of all cryptoglandular anal fistulas is located—in accordance with the proctodeal gland opening—in an anal crypt at the dentate line, whereas the external fistula opening is in the perianal skin.

The classification of cryptoglandular anal fistulas is based on their course in relation to the anal sphincter apparatus. They are distinguished as

·       Subanodermal/subcutaneous anal fistula

·       Intersphincteric anal fistula

·       Transsphincteric anal fistula

Note: In the case of a transsphincteric anal fistula, the fistula tract penetrates the external anal sphincter and enters the ischioanal fossa. Depending on whether the external anal sphincter is perforated by the fistula tract in its cranial or caudal part, it is referred to as a "high" or "low" transsphincteric anal fistula. The high transsphincteric fistula is not clearly defined. Usually, a high transsphincteric anal fistula is referred to when >30% of the external anal sphincter is affected, i.e., the fistula traverses the muscle in its upper two-thirds.

• Inoperability of the patient

Note: Chronic inflammatory bowel diseases do not constitute a contraindication for this surgical method.

• The necessary diagnostics depend on the underlying problem and the urgency of the acute inflammation. Generally, no specific examination methods are required. In special cases, an endosonography, CT, or MRI may be helpful.

The medical history should include the following aspects: duration of symptoms, course (acute or chronic recurrent), indications of IBD (e.g., diarrhea, perianal bleeding, or abdominal pain), previous surgeries possibly even decades ago, childbirths and possible birth injuries, pre-existing continence limitations.

Symptoms

Perianal fistula disease typically manifests through pain, perianal discharge, or secretion.

Proctological Examination

During the inspection of the anal region, the distance of the external fistula opening from the linea anocutanea provides an indication of the fistula course – the further away the external fistula opening can be depicted, the more likely a high fistula course is. 

Part of the fistula course can sometimes be palpated as a scarred strand. A proctoscopy can be performed to visualize the internal fistula opening. Orientation by the Goodsall's rule facilitates the search for the internal fistula opening.

Goodsall's Rule: If the external anal fistula opening is in the dorsal perianal circumference, the fistula tract usually runs in an arc with an internal opening at the 6 o'clock lithotomy position. Anal fistulas with an external opening in the ventral perianal circumference usually run straight towards the dentate line.

Endosonography

Endoanal sonography, where available, is a minimally invasive and cost-effective method for diagnosing perianal fistulas and abscesses, but requires appropriate experience in interpreting findings.

Magnetic Resonance Imaging

MRI (Magnetic Resonance Imaging) examination is particularly indicated for complex fistulas, in IBD, or recurrence.

Computed Tomography

If endosonography and MRI are unavailable and there is a high suspicion of an abscess, a CT (Computed Tomography) scan can be used to exclude or confirm a supralevator abscess.

• Preoperative bowel evacuation the evening before the surgery with enema or suppository

General:

• Bleeding
• Thrombosis
• Embolism, etc.

Specific:

• Persistent secretion
• Prolonged healing
• Re-abscess
• Usually further surgeries necessary