Cogwheel sign

The cogwheel sign refers to an imaging appearance in pelvic imaging of thickening loops of the Fallopian tube seen on cross-section. There are infolding projections (sometimes looking like nodules) into the Fallopian tube lumen which is likened to that of a cogwheel. The sign is typically described on ultrasound and is indicative of tubal inflammation in pelvic inflammatory disease with a pyosalpinx or a hydrosalpinx.