The Value of Transrectal Ultrasound in the Preoperative Diagnosis of Complex Anal Fistula (CAF): Based on a Retrospective Cohort Study.

Objective: A case-control study was employed to retrospectively analyze the value of transrectal ultrasound in the preoperative diagnosis of complex anal fistula (CAF). Methods: The clinical data of 128 patients with CAF treated in our hospital from March 2019 to June 2021 were analyzed retrospectively. All patients were examined by transrectal ultrasound and MRI with Hitachi HI Vision Ascendus ultrasound diagnostic apparatus and MRI. The general data of the patients (age, sex, course of disease, complications, and previous operation history) and ultrasonic image characteristics were recorded. The consistency of internal orifice, head, branch/abscess, and abscess detected by ultrasound, MRI, and ultrasound combined with MRI were compared, and the sensitivity, accuracy, and specificity of ultrasound, MRI, and the combination of ultrasound and MRI (ultrasound+MRI) in the diagnosis of different Parks classification of anal fistula (AF) were compared. Results: The ultrasound images of the rectal probe in typical cases were compared with the MRI images. The characteristics of the ultrasound images were as follows: the outer orifice of AF was a thin strip of mixed echo or low echo leading to the skin side, and the inner orifice showed local dilated low echo, mixed echo, or interruption of mucosal continuity. The following are the MRI image features: abnormal long bar signal shadow from the dorsal side of the end of the coccyx to the S5 plane, low signal on T1WI, high signal on T2WI, blurred boundary, uneven signal, bifurcation in the lower end of the tail for "Y" shape, one branch opening at the body surface at about 6 o'clock, the other walking horizontally, passing through the levator ani muscle to the right posterior position of the rectum at about 6:00 o'clock, and penetrating the inner mouth of the rectum at 6 o'clock. The detection of internal orifice, head, branch/abscess, and abscess were compared by three examination methods. There was significant difference in the detection rate of internal orifice and branch/purulent cavity among the three methods ( Conclusion: The sphincter, anorectal, and surrounding tissues were clearly demonstrated by transrectal ultrasound. The internal orifice, head, branch/abscess, abscess, and the relationship between abscess and sphincter in the diagnosis of CAF were in good agreement with the surgical results. Ultrasound+MRI can take into account the advantages of ultrasound and MRI, make up for each other, and improve the detection rate of internal orifice and branch/abscess. It can improve the sensitivity of diagnosis of transsphincter AF and the sensitivity and accuracy of intersphincter AF, which can provide intuitive and valuable imaging information for surgical intervention.