Purpose. To evaluate the diagnostic informativeness of 3D ТRUS in the diagnosis of rectal fistulas of cryptogenic origin in the absence or obliteration of the external fistula opening.

Materials and methods. 111 patients with rectal fistulas with missing or obliterated external fistulas were examined and operated on. All patients underwent 2D and 3D TRUS at the preoperative stage, and 44 (67.7%) of them were performed twice for the purpose of dynamic control. The 2D and 3D TRUS data were compared with the results of intraoperative revision.

Results. The detection of the fistulous 2D TRUS sensitivity was 98.1%, the 3D TRUS – 100%. Both methods demonstrated similar diagnostic information for different types of fistula (p>0.05). A higher sensitivity of 3D TRUS was detected in determining the lesion of the subcutaneous portion of the external sphincter (2D:70.5% vs 3D: 100% p=0.002). The frequency of correct determination of the localization of the internal fistula hole was 95.4% in 3D and 86.9% in 2D, the differences are statistically significant (p=0.025). During the intraoperative revision, 97 occlusions were diagnosed in 75 (67.6%) patients, 90 occlusions in 64 (57.6%) patients with 2D TRUS, and 101 purulent cavities in 72 (64.9%) patients with 3D TRUS. Differences in the sensitivity of detection of abscesses, calculated for the total number of them (2D:82.5% vs 3D:96.9%; p=0.001). Abscesses were correctly localized in a 2D study in 71(88.8%) of 80 cases, and in a 3D study in 91 (96.8%) of 94 cases (differences are statistically significant, p=0.037).

Conclusions. Endorectal ultrasound with three-dimensional image reconstruction is a visual method for preoperative diagnosis of rectal fistulas, has no absolute contraindications, can be performed an unlimited number of times, has a high diagnostic efficiency and can be recommended for use in the diagnosis of rectal fistulas of cryptogenic origin, including those with a missing or obliterated external fistula opening.