Transperineal versus hydrogen peroxide-enhanced endoanal ultrasonography in never operated and recurrent cryptogenic fistula-in-ano: A pilot study

Background: Accurate delineation of anal fistula anatomy in recurrent cases will assist in surgical fistula eradication whilst preserving continence. Recently, transperineal ultrasonography (TPUS) has been used in perirectal inflammation where there may be advantage over endoanal ultrasonography (EAUS) in complex fistulae-in-ano which lie outside the focal range of the endoanal probe. We assessed the sensitivity of these two imaging modalities to characterize fistula-in-ano, compared to surgical findings. Methods: Hand-held 7.5 MHz TPUS was performed in the axial and sagittal planes in never-operated (Group 1, n=10) and recurrent (Group 2, n=10) cryptogenic fistulae where the ultrasonographer was blinded to the initial operative findings. This was compared with hydrogen peroxide-enhanced EAUS using a 7.5 MHz rotating probe, assessing the fistula anatomy, site of the internal opening, confirmation of Goodsall's rule and the presence of secondary tracks, abscess collections and significant horsehoeing of the track. Results: Overall sensitivity for the detection of trans-sphincteric and extrasphincteric fistulae was 100% using both techniques with a 90% sensitivity for TPUS and an 85% sensitivity for EAUS in the prediction of the internal fistula opening site. The TPUS sensitivity for horseshoeing was poor (28.6%) as was the detection of ancillary abscesses confirmed at surgery (63.6%) but TPUS demonstrated rectovaginal fistulae. Conclusion: TPUS is a novel technique for use in perirectal infection which has a significant learning curve but which is highly accurate for prediction of the anatomy of complex recurrent as well as simple anal fistulae.