The aim of this study is to evaluate the effect of hyperbaric oxygen therapy (HBOT) on patient suffering from residual Crohn's disease related perianal fistulas already treated with TNF alpha blockers

This study is a prospective open-label study that consists three periods: screening, treatment and follow-up. After signing an informed consent, subjects will be assessed by a gastroenterologist, a surgeon (for the diagnosing the perianal disease and assessing the need for surgery) and a HBOT specialist for assessing the capability of the subject to undergo HBOT treatment.After the screening period, eligible subjects will enter an 8 weeks HBOT treatment period, combined with TNFalpha blocker treatment. This period will be followed by a 4 months follow-up period in which treatment with TNFalpha blocker will continue.

All patients will have an MRI and TRUS examinations to assess the fistulas and also blood tests for CBC, chemistry, inflammatory markers and cytokine analysis. Same evaluation will be repeated at the end of the study.

Inclusion Criteria:

patients aged 18 and above that suffer from Crohn's disease one or more perianal draining fistulas for at least 3 months currently receiving a TNFalpha blocker for at least 3 months (without improvement of the perianal disease)

Exclusion Criteria:

Pregnancy or plans to conceive during the next year Inability (such as previous adverse effects, tuberculosis, concurrent infection etc.)or unwillingness to start or continue with TNF alpha blockers treatment.

Any past or current malignancy Treatment with HBOT in the last year Claustrophobia Middle ear problems Inability to equalize pressure in the middle ear Medical status that precludes treatment with HBOT such as chest X-ray abnormality, epilepsy, severe congestive heart failure, uncontrolled diabetes or uncontrolled hypertension Any perianal surgery in the last 6 months Any change in Crohn's disease medications in the last 3 months