From the Guidelines
The crescent sign on a CT chest is indicative of an air crescent sign, most commonly associated with invasive pulmonary aspergillosis. This radiological finding appears as a crescent-shaped area of air that separates a fungal ball or necrotic tissue from the surrounding lung parenchyma. It occurs when the immune system begins to recover and inflammatory cells invade the area of infection, causing the necrotic tissue to separate from the surrounding lung, creating an air-filled space that appears as a crescent on imaging. The air crescent sign is particularly common in immunocompromised patients, such as those with neutropenia, who are recovering from their immunosuppressed state. While aspergillosis is the classic cause, this sign can also be seen in other conditions including tuberculosis, lung abscesses, cavitating lung cancers, and pulmonary infarcts. When this sign is identified, prompt antifungal therapy is often necessary, typically with voriconazole as first-line treatment for invasive aspergillosis, with alternatives including amphotericin B formulations, isavuconazole, or posaconazole depending on patient factors and fungal susceptibilities. However, the provided evidence does not directly support this claim, as it discusses the general approach to patients suspected of having lung cancer and the importance of CT scans in diagnosis and staging 1.
From the Research
Crescent Sign on CT Chest
- The crescent sign is indicative of pulmonary embolism (PE) and is characterized by a crescent-shaped area of oligemia, which is a region of decreased blood flow, surrounding an area of increased attenuation due to the embolus 2.
- However, the crescent sign itself is not explicitly mentioned in the provided studies, but the reverse halo sign, which is also related to pulmonary infarction, is mentioned as a sign of PE in a non-contrast CT scan 2.
- Other signs of PE in a non-contrast CT scan include the hyperdense lumen sign and wedge-shaped sub-pleural opacity surrounded by an air-space consolidation 2.
- The diagnosis of PE is typically determined by chest imaging, and the clinical probability of PE can be assessed using a structured score or clinical gestalt 3.
- Treatment for PE typically involves anticoagulation, with direct oral anticoagulants such as apixaban, edoxaban, rivaroxaban, or dabigatran being noninferior to heparin combined with a vitamin K antagonist for treating PE 3, 4.
- Thrombolytic therapy may be used in patients with clinically serious or massive PE, and has been shown to reduce the odds of death and recurrence of PE, but may also increase the risk of major and minor haemorrhagic events 5, 6.