Fistula

A fistula is an abnormal passage or connection between two organs, two vessels, or an organ and the body surface. In sonography, several types of fistulas are commonly encountered. Arteriovenous fistulas, both congenital and surgically created for dialysis, are evaluated with Doppler ultrasound. Enterovesical fistulas between the bowel and bladder may produce gas bubbles visible on bladder ultrasound. Perianal fistulas can be mapped with endoanal or transperineal ultrasound. Bronchopleural fistulas may cause air within a pleural effusion. Identifying a fistula on ultrasound requires recognizing abnormal connections, unusual flow patterns, or the presence of gas where it should not normally be found.