This document discusses the meniscus sign seen on medical imaging. The meniscus sign appears as a crescent-shaped air space that separates a solid mass, such as a fungus ball or hydatid cyst, from the wall of a cavity in the lungs. Examples are given of the meniscus sign appearing on CT scans and x-rays of patients with conditions like aspergillosis or a hydatid cyst. The meniscus sign indicates the presence of a solid mass within a lung cavity that is separated from the cavity wall by a crescent of air.

1. 22Meniscus (Air-Crescent) Sign*

2. CLINICAL IMAGAGING
AN ATLAS OF DIFFERENTIAL DAIGNOSIS
EISENBERG
DR. Muhammad Bin Zulfiqar
PGR-FCPS III SIMS/SHL

3. • Fig C 22-1 Aspergillosis. A mycetoma (solid arrow) appears as a
homogeneous rounded mass that is separated from the thick wall
of the cavity by a crescent-shaped air space (open arrows).

4. • Fig C 22-2 Aspergillosis. Multiple cavities of various sizes are
superimposed on a diffuse pulmonary infiltrate. A fungus
ball almost fills the large cavity in the right upper lobe
(arrows). A right pleural effusion is also seen in this patient
with chronic lymphocytic leukemia.

5. • Fig C 22-3 Aspergillosis. Bilateral aspergillomas
in an elderly man with residual tuberculosis.
CT scan shows large cavities in the upper lobes
containing fungus balls of different sizes.41

6. • Fig C 22-4 Hydatid cyst. A crescent of air
(arrows) is seen about the periphery of the
echinococcal cyst.