Cogwheel Sign: Cross-sectional ultrasound appearance of an inflamed fallopian tube with echogenic mucosal folds projecting inward, characteristic of pyosalpinx in PID.
The cogwheel sign is a sonographic finding seen in pelvic inflammatory disease (PID) on transvaginal ultrasound in which the inflamed fallopian tube appears as a circular structure with internal echogenic projections (incomplete septa or mucosal folds) resembling a gear wheel when viewed in cross-section. It is a characteristic finding of pyosalpinx and early tubo-ovarian complex formation.