To explore the value of trans-fistula contrast-enhanced ultrasound (CEUS) using blood pool contrast agent in the preoperative diagnosis of complex fistula-in-ano.

Twenty-four cases of complex fistula-in-ano confirmed by surgery were retrospectively analyzed. Conventional ultrasonography and trans-fistula CEUS were both applied before operation. The internal and external opening of fistula were observed, and the number and tract of primary fistula and secondary fistula were detected. The existence of abscess was also observed. Statistical analysis was performed to compare the diagnostic efficacy between these two methods.

The diagnostic accuracy of internal opening and secondary fistula using conventional ultrasonography combined with CEUS were 83.3%, 86.7%, respectively. They were significantly higher than those of conventional ultrasound (33.3%, 40%, respectively; χ²=12.343, 7.033, all P>0.01). Although the diagnostic accuracy of primary fistula and abscess using conventional ultrasonography combined with CEUS were higher than those of conventional ultrasound (100% vs 87.5%, 100% vs 62.5%, respectively), no significant difference was found (all P>0.05).

Trans-fistula CEUS provides abundant diagnostic information for complex fistula-in-ano, improves the accuracy of preoperative diagnosis, and is beneficial to surgical procedures. The greatest advantage of CEUS is the indication of the internal opening and secondary fistula of complex fistula-in-ano.