The sign implies a freely mobile mass, which moves on mobilizing the patient. This is best demonstrated by acquiring images in a prone position, causing the mass to fall, to a gravity-dependent location and favoring a Monod sign; as compared to an air crescent sign.
In practice, it is likely that the term Monod sign will receive blank stares. The gas around the mycetoma is often crescent-shaped and hence, the term air crescent sign is used interchangeably by many to refer to both pathological processes.
History and etymology
The sign was first described by the French physicians G D Pesle and Olivier Monod in 1954 .