F-18 FDG imaging of an asymptomatic sacrococcygeal pilonidal sinus in a patient with malignant disease

This case illustrates a pitfall associated with F-18 FDG imaging. We present the images of a 57-year-old woman with non-Hodgkin's lymphoma that shows intense accumulation of F-18 FDG in a sacrocoecygeal pilonidal sinus that could indicate a lymphomatous involvement from a primary disease. MRI showed a well-defined sinus tract from skin to the sacrococcygeal region corresponding to the F-18 FDG uptake. She did not have any symptoms of a sacrococcygeal pilonidal sinus such as discharge, swelling or pain. There was no visible opening of the sinus tract on the skin. Pilonidal sinus is commonly a hair-containing sinus or abscess in the sacrococcygeal area. Hair acts as a foreign body causing an inflammatory reaction.