Utility of transperineal and anal ultrasonography in the diagnostics of hidradenitis suppurativa and its differentiation from a rectal fistula.

INTRODUCTION The pathogenesis of hidradenitis suppurativa (HS) is not fully understood. There exist several theories, in which mechanical factors, genetic factors, as well as immunological dysfunction of lymphocytes are suspected. Clinically, this entity is frequently mistaken for anal fistula with consequently wrong treatment. We aim to determine the utility of transperineal ultrasound (TPUS) and anal ultrasound (AUS) in the diagnosis of HS and its differentiation from an anal fistula. MATERIAL/METHODS Retrospective analysis was performed on 51 patients (5 females, 46 males) aged 20-71 years (mean age 47.5), who were operated on in the years 2006-2011 for HS in the area of the anus and perineum, and pre-operatively had been imaged with TPUS and AUS. Sixty-seven operations were analyzed, as 11 patients were operated on more than once due to HS recurrence. RESULTS In 66 out of 67 cases (98.5%), the pre-operative TPUS and AUS were in accordance with the intraoperative findings. Only in 1 patient was a pilonidal cyst diagnosed intraoperatively. In all 67 patients, the TPUS showed typical fluid-solid changes localized in the subcutaneous adipose tissue. In 6 out of 67 cases of HS (8.9%) AUS showed an anal fistula coexisting with the HS. In 2 cases (2.9%) a skin malignancy coexisting with HS was found. DISCUSSION TPUS is an accessible imaging method, which confirms the typical localization of changes of HS, and together with AUS it allows for the proper differentiation of HS from an anal fistula or an abscess.