Peroxide-enhanced endoanal ultrasound in preoperative assessment of complex fistula-in-ano

In complex fistula-in-ano, preoperative imaging can help identify secondary tracts and abscesses that can be missed, leading to recurrence. We evaluated hydrogen peroxide-enhanced endoanal ultrasound (PEEUS) in the characterization of fistula compared with standard clinical and operative assessment.

Patients with complex fistula-in-ano treated between February 2008 and May 2009 at our institution were prospectively evaluated by PEEUS with recording of the preoperative clinical examination and intraoperative details of the fistula. Of the 135 patients with fistula-in-ano, 68 met the inclusion criteria for complex fistula-in-ano. Correlation of clinical findings and PEEUS to the gold standard intraoperative findings was assessed in characterizing the fistula. The percent agreement between the clinical and PEEUS findings against the gold standard was derived, and the kappa statistic for agreement was determined.

The mean age of the cohort was 42.54 ± 10.86 years. The fistula tracts were curvilinear, high, and transsphincteric in 16 (23.53%), 8 (11.76%), and 42 (61.76%) patients, respectively. Secondary tracts and associated abscess cavities were seen in 28 (33.82%) and 35 (51.47%) patients, respectively. PEEUS correlated better than clinical examination with regard to site (92.65 vs 79.41%; p < 0.001) and course (91.18 vs 77.94%; p < 0.001) of secondary tract and associated abscesses (89.71 vs 80.88%; p = 0.02). There was a trend of better correlation of PEEUS compared to clinical examination in classifying the primary tract as per Park's system (88.24 vs 79.41%; p = 0.06), but it did not reach statistical significance. PEEUS and clinical examination were comparable in correlation of the level of the primary tract (kappa: 0.86 vs 0.78; p = 0.22) and the site of internal opening (kappa: 0.97 vs 0.89; p = 0.22). The operative decision was changed in 13 (19.12%) subjects based on PEEUS findings.

PEEUS is a feasible and efficient tool in the routine preoperative assessment of complex fistula-in-ano.