Introduction The incidence of Crohn's disease (CD) is increasing in industrialized societies.1, 2 While CD most commonly affects the ileocaecal region it may secondarily affect the sigmoid as a bystander in up to 40% of patients with the penetrating phenotype.3-7 Many internal fistulas are not diagnosed until surgery, highlighting the limitations of diagnostic modalities and the lack of symptoms exhibited by most patients.3, 8, 9 Diarrhoea may be attributed to the underlying inflammatory...