In chest roentgenograms, the pulmonary meniscus sign is a crescent-shaped inclusion of air surrounded by consolidated lung tissue. The common cause is aspergilloma. A hydatid cyst is, however, the most common cause in endemic areas. Cyst growth produces erosions in the bronchioles that are included in the pericyst, and, as a result, air is introduced between the pericyst and exocyst, producing the crescent or meniscus sign. Air penetrating the interior of the cyst may outline the inner surface of the exocyst, producing parallel arches of air that are referred to as Cumbo's sign with an “onion peel” appearance.
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