The wandering broncholith.
In a patient with "stone asthma" the obstructing broncholith moved from one lung to the other and was later spontaneously expectorated.
D001982:Bronchial Diseases / Q000000981:diagnostic imaging*; D002137:Calculi / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008172:Lung Diseases, Fungal / Q000000981:diagnostic imaging*; D008173:Lung Diseases, Obstructive / Q000000981:diagnostic imaging; D008875:Middle Aged; D011859:Radiography