Demonstration of a Tubercular Fistula-in-Ano on F-18 FDG PET/CT

A 53-year-old man diagnosed as a case of adenocarcinoma of the colon, was referred for a FDG-PET/CT after receiving 6 cycles of chemotherapy. On the maximum intensity projection image, a striking curvilinear pattern of FDG accumulation was seen extending postero-inferiorly in the pelvic region to the right side of the midline. This was localized to a curvilinear track of soft tissue attenuation arising from the anal canal, traversing through the right ischio-rectal fossa into the overlying skin in the natal cleft on the fused PET/CT image. On being questioned the patient confirmed of having a history of recurrent fistula-in-ano and had been operated twice for the same. The polymerase chain reaction for TB was positive and the patient was taking antitubercular treatment. In patients being evaluated for malignancies it is important to identify such benign, infective but clinically consequential lesions and the key to correct interpretation in such cases is a detailed history of the patient.