The mural nodule in cavitary opportunistic pulmonary aspergillosis.

A common radiographic feature of opportunistic pulmonary aspergillosis is a rounded, cavitary lesion with a nodule projecting into it. This appearance has been given a variety of names, including "air crescent," "meniscus," "target," "bull's-eye," and "peninsula." These signs merely represent different radiographic projections of the cavitary lesion and mural nodule. Similar lesions may also be encountered in other conditions.