Ultrasound assessment of low type intersphincteric perianal fistulas in Yemen

Abstract

A perianal fistula is an abnormal tract connection between the anal canal and the surrounding skin of the perineum, with underdiagnosis in specific populations. The aim of this study was to diagnose and describe the intersphincteric perianal fistulas (number, site, number of internal and external openings, and length) using transcutaneous ultrasound (TCUS) imaging. This was a retrospective study included patients who underwent TCUS for clinically diagnosed of low-type intersphincteric perianal fistulas during April 2017-December 2022. A total of 581 perianal fistulas from 549 patients were included in this study. The mean age of the patients was 36.14 ± 13.37-year (range from 1 to 80 years). The majority were in the young adult age group, from 21 to 40 years (56.47%), 84% were male and 16% female. The patients predominantly had one fistula (94.35%) with one external opening (EO) (79.10%), and one internal opening (IO) (99.65%). The left quadrants (1-6 O'clock around the anus) were the most common sites of the EO (60.5%). The IO was 11-20 mm above the anal verge in 58.5% of fistulas and ≤ 10 mm in 27.4%. The length of the fistular tract was 21-30 mm in 30.1%, 11-20 mm in 27.4%, and 31-40 mm in 25.0%. The perianal fistulas in the left posterior quadrant had a significantly shorter fistular tract compared to those in the other three quadrants. There was no significant variation in the IO distance from anal verge between fistulas in the different anal quadrants. The solitary tract, IO and EO with the short length, and small distance of IO from the anal verge improve surgical outcomes and decrease complications and recurrence of the perianal fistulas. TCUS, when performed by an experienced operator, can be effectively utilized for the diagnosis and surgical planning of low-type perianal fistulas, with the offer of that it is a non-invasive, well-tolerated, and radiation-free imaging method.

Keywords: Anal canal; Intersphincteric; Low-type perianal fistula; Transperineal ultrasonography.

Fig. 1

The diagram shows the anatomy of the anus (A), anal canal (from the skin to the dentate line (D), rectum (R), internal anal sphincter (IS), external anal sphincter (ES), and the different types of the perianal fistula including the inter-sphincteric fistula (1), trans-sphincteric fistula (2), supra-sphincteric fistula (3), and extra-sphincteric fistula (4).

Fig. 2

The diagram indicates the perianal region in the knee-chest position divided in clockwise direction into four quadrants, and 12 h. LAQ, left anterior quadrant, LPQ, left posterior quadrant, RPQ, right posterior quadrant, and RAQ, right anterior quadrant.

Fig. 3

An ultrasound image was taken by using a superficial linear probe (7.5 MHz) showing low type right sided perianal fistula, the right image shows the tract of the fistula (Thick white line), external opening (EO), Internal opening (IO), of the tract, around the anus (A), and anal canal (AC). Left image is the same clear image.

Fig. 4

An ultrasound image was taken by using a superficial linear probe (7.5 MHz) showing the low type right sided branching perianal fistula, the right image shows the tract of the fistula (Thick white line), Internal opening (IO), first external opening (EO1), and second external opening (EO2) of the tract, around the anus (A), and anal canal (AC). The left image is the same clear image.

Fig. 5

An ultrasound image was taken by using a superficial linear probe (7.5 MHz) showing a low type left sided perianal abscess. The right image displays the abscess (Filled with white color), Internal opening (IO) around the anus (A), and anal canal (AC). The left image is the same clear image.