The thyroid is normally very resistant to infection. Due to a relatively high amount of iodine in the tissue, as well as high vascularity and lymphatic drainage to the region, it is difficult for pathogens to infect the thyroid tissue. Despite all this, a persistent fistula from the piriform sinus may make the left lobe of the thyroid susceptible to infection and abscess formation.

AIT is most often caused by a bacterial infection but can also be caused by a fungal or parasitic infection, most commonly in an immunocompromised host.

We decided to practise a barium esophagram in our case eventually, in order to demonstrate this abnormality. However we could not conclude anything because of the procedure´s difficulty and the lack of help of our patient. The upper GI series were normal till the duodenum but the clinical suspicion was high.

Another way to diagnose this pathology may be using a fibroendoscopy. 

Finally, our patient underwent surgery and with the use of direct endoscopy the suspected fistula was founded in the left piriform sinus and it was treated with cauterization.