A Practical Ultrasound-Based Classification System for Mapping Perianal Fistula

What is it about?

This study evaluated how combined ultrasound techniques can improve the diagnosis and classification of perianal fistulas and abscesses before surgery. Perianal fistulas are abnormal tracts connecting the anal canal to the skin around the anus, often developing after infection or abscess formation. Accurate mapping of these tracts is essential because incomplete assessment may lead to recurrence or fecal incontinence after surgery. The study included 480 patients with suspected perianal infection examined over seven years. Patients underwent a combination of transperineal ultrasound, endoanal ultrasound, and, in female patients, transvaginal ultrasound. Surgical findings and intraoperative probing were used as reference standards. Among the patients, 30 had anal abscesses and 450 had perianal fistulas. The author proposed a broader imaging classification system that assessed not only the sphincteric course of fistulas, as in the traditional Parks classification, but also the etiology, extrasphincteric extensions, internal and external openings, side branches, abscess formation, and predicted postoperative risks. Transsphincteric fistulas were the most common type (70%), followed by intersphincteric fistulas (24%). The combined ultrasound approach showed high diagnostic sensitivity: 97% for assessing extrasphincteric extensions, 93% for detecting internal openings, and up to 100% sensitivity for superficial and low transsphincteric fistulas. Follow-up of 120 operated patients demonstrated low complication rates when surgical planning was guided by the proposed imaging classification. Minor postoperative incontinence occurred in only 2.5% of patients, while recurrence occurred in 5%.

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Photo by Robert Collins on Unsplash

Photo by Robert Collins on Unsplash

Why is it important?

Perianal fistulas are surgically challenging diseases with significant risks of recurrence and fecal incontinence. Traditional classifications mainly focus on the fistula’s relationship to the anal sphincters and may overlook clinically important details such as branching tracts, hidden internal openings, or associated abscesses. This study proposes a more comprehensive imaging-based classification that directly supports surgical decision-making. The work is important because it demonstrates that widely available ultrasound techniques can approach MRI-level diagnostic performance while being cheaper, safer, and more accessible. The classification also links imaging findings to postoperative risk prediction, helping surgeons select safer procedures for complex cases.

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