Q: What is Monod sign?    

Answer:  Monod or Monad sign refers to air that surrounds an aspergilloma in a pre existing pulmonary cavity.This is in contrast to "Air-Crescent" sign which is new crescent shaped air inside aspergilloma cavity and represents recovery. This can also be best described as mobile aspergilloma or gravity-dependent aspergilloma within a pulmonary cystic cavity, and not a good prognostic sign.