Question:
Monad (Monod) sign is seen in?
Monad (Monod) sign is seen in?
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Radiological Signs of Pulmonary Aspergillosis:
- Monod sign (Air crescent sign): Saprophytic Aspergilloma in a pre-existing cavity.
- Halo sign: Ground-glass opacity surrounding a nodule, indicating hemorrhage in Invasive Pulmonary Aspergillosis (usually in immunocompromised/neutropenic patients).
- Monod sign (Air crescent sign): Saprophytic Aspergilloma in a pre-existing cavity.
- Halo sign: Ground-glass opacity surrounding a nodule, indicating hemorrhage in Invasive Pulmonary Aspergillosis (usually in immunocompromised/neutropenic patients).
Updated On: Sep 3, 2026
- Bronchiectasis
- Aspergilloma cavity lung
- Lung abscess
- Pulmonary sequestration
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The Correct Option is B
Solution and Explanation
Concept:
Eponymous radiological signs are frequently tested. The Monod sign describes a specific imaging artifact created by a mobile mass residing within a pre-existing hollow structure in the lung.
Explanation:
• The Monod sign (often spelled Monad or known as the "air crescent sign") is a classic radiological finding seen on chest X-rays or CT scans.
• It consists of a radiolucent crescent of air partially outlining a solid radiopaque mass within a pulmonary cavity.
• This sign is most characteristically associated with a pulmonary mycetoma, specifically an Aspergilloma (fungal ball).
• Aspergillomas typically form when Aspergillus spores colonize a pre-existing lung cavity, such as those left behind by healed tuberculosis or sarcoidosis.
• The fungal ball (composed of hyphae, mucus, and cellular debris) is separate from the cavity wall. Therefore, as the patient changes position, the fungal ball shifts due to gravity, and the crescent of air is maintained above it.
• While a lung abscess (Option C) is a cavitary lesion, it typically presents with a straight, horizontal air-fluid level rather than an air crescent outlining a solid, mobile mass.
Final Answer:
The Monod sign, characterized by an air crescent surrounding a mobile intracavitary mass, is pathognomonic for an aspergilloma.
Eponymous radiological signs are frequently tested. The Monod sign describes a specific imaging artifact created by a mobile mass residing within a pre-existing hollow structure in the lung.
Explanation:
• The Monod sign (often spelled Monad or known as the "air crescent sign") is a classic radiological finding seen on chest X-rays or CT scans.
• It consists of a radiolucent crescent of air partially outlining a solid radiopaque mass within a pulmonary cavity.
• This sign is most characteristically associated with a pulmonary mycetoma, specifically an Aspergilloma (fungal ball).
• Aspergillomas typically form when Aspergillus spores colonize a pre-existing lung cavity, such as those left behind by healed tuberculosis or sarcoidosis.
• The fungal ball (composed of hyphae, mucus, and cellular debris) is separate from the cavity wall. Therefore, as the patient changes position, the fungal ball shifts due to gravity, and the crescent of air is maintained above it.
• While a lung abscess (Option C) is a cavitary lesion, it typically presents with a straight, horizontal air-fluid level rather than an air crescent outlining a solid, mobile mass.
Final Answer:
The Monod sign, characterized by an air crescent surrounding a mobile intracavitary mass, is pathognomonic for an aspergilloma.
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