Case Report

A 70-year-old male with a previous history of hemorrhoidectomy, presented with purulent perianal drainage without pain or rectal bleeding six months after the anal surgery.

On proctologic examination, there was no evidence of external fistulous tracts. Digital rectal examination was painless, with a possible internal opening located in the posterior midline quadrant and resting hypotonia was noted with normal voluntary contraction.

A perianal MRI was inconclusive regarding the presence of a perianal abscess or fistula.

To further investigate, a lower transendoscopic ultrasonography was performed using a radial echoendoscope. Initial assessment identified a suspicious area in the right posterior quadrant, prompting required further characterization.

To enhance diagnostic accuracy, contrast-enhanced ultrasound was performed by instilling 1 mL of Sonovue® through a 20G plastic cannula into the internal fistulous opening, which was located in the posterior quadrant. The following images were acquired after contrast instillation.

What is the most likely diagnosis?

Submeter

Key Findings

Figuere 1. Abscess in the right posterior quadrant, a heterogeneous, predominantly hypoechoic collection with well-defined boundaries measuring 18×26 mm was identified. This collection was located between the muscular wall and submucosa, consistent with a suppurative process

 

Figure 2. Fistula tract: In communication with the collection, a short intersphincteric fistulous tract was identified, with an opening in the right posterior quadrant at the junction of the upper anal canal and middle anal canal (arrow)

 

Figure 3. Anatomical damage: In the middle and upper anal canal, at the right posterior/lateral quadrant, a complete laceration of the internal anal sphincter was observed, with a maximum laceration angle of 118 degrees

Discussion

Precise anatomical mapping of perianal fistulas is essential for effective surgical planning and for minimizing the risks of postoperative incontinence and recurrence. Accurate evaluation of sphincter involvement and secondary tracts, typically guided by Parks’ classification, is a critical component of this process.

Before the introduction of SonoVue®, contrast agents such as hydrogen peroxide and Levovist® were used to enhance the diagnostic capability of endoanal ultrasound. While hydrogen peroxide is still widely used in clinical settings, newer contrast agents like SonoVue® could be an option with possible advantages (1).

In the study by Yang et al., 3D endoanal ultrasound (3D-EAUS) with SonoVue® was compared to standard 3D-EAUS in 60 patients. Although both approaches offered similar accuracy in fistula classification, the use of SonoVue® markedly improved the detection of internal openings, fistula complexity, and secondary tracts — features essential for tailored surgical intervention and recurrence prevention (2).

Another study involving 98 patients compared EAUS with transfistulous SonoVue® injection to MRI. CE-US with SonoVue® demonstrated superior sensitivity in detecting internal openings located within 3 cm of the anal verge, likely due to improved visualization of the lower rectal mucosa and muscularis mucosa, and the contrast’s ability to partially reopen fibrotic or adherent tracts (3).

Furthermore, Gou et al. evaluated 360° 3D transrectal ultrasound with and without CE-US in 156 patients with complex anal fistulas. SonoVue® significantly enhanced the accuracy of identifying primary and secondary tracts, internal openings, and allowed more precise Parks classification. Importantly, patients assessed with CE-US had lower recurrence rates at 6-month follow-up (4).

In summary, contrast-enhanced ultrasound with SonoVue® provides substantial benefits in the assessment of complex perianal fistulas. As demonstrated in the present case, it enhances the visualization of key anatomical features, enabling more accurate diagnosis and more effective surgical planning, ultimately contributing to better clinical outcomes.

References

1. Gaertner WB, Burgess PL, Davids JS, Lightner AL, Shogan BD, Sun MY, et al. The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula. Dis Colon Rectum. 2022 Aug 5;65(8):964–85. 2. Parks AG, Gordon PH, Hardcastle JD. A classification of fistula-in-ano. Journal of British Surgery. 1976 Jan 1;63(1):1–12. 3. Moscowitz I, Baig MK, Nogueras JJ, Ovalioglu E, Weiss EG, Singh JJ, et al. Accuracy of hydrogen peroxide enhanced endoanal ultrasonography in assessment of the internal opening of an anal fistula complex. Tech Coloproctol. 2003 Oct 27;7(3):133–7.
2. Yang J, Li Q, Li H, et al. Preoperative assessment of fistula-in-ano using SonoVue enhancement during three-dimensional transperineal ultrasound. Gastroenterology Report. 2024;12:goae002.
3. Lin T, Ye Z, Hu J, Yin H. A comparison of trans-fistula contrast-enhanced endoanal ultrasound and MRI in the diagnosis of anal fistula. Ann Palliat Med. 2021 Aug;10(8):9165–73.
4. Gou J, et al. Comparison of the diagnostic accuracy of percutaneous fistula contrast-enhanced ultrasound combined with transrectal 360° 3-D imaging and conventional transrectal ultrasound in complex anal fistula. Ultrasound in Medicine and Biology. 2022;48(12):2792–2800.

Authors

Rosa Coelho, Pedro Moutinho Ribeiro, Guilherme Macedo

Gastrenterology Department, Centro Hospitalar de São João

Faculdade de Medicina da Universidade do Porto