From the Guidelines
The crescent sign is a critical radiological finding that necessitates prompt antifungal treatment, typically with voriconazole, in patients with fungal infections of the lungs, particularly invasive aspergillosis, to improve outcomes and prevent potentially fatal hemoptysis. This sign is characterized by a crescent-shaped area of air or fluid within a cavity, typically seen in fungal infections of the lungs, particularly invasive aspergillosis, as described in the European Respiratory Journal study 1. The crescent sign appears when fungal infection causes necrosis of lung tissue, creating a space between the necrotic tissue and the cavity wall, and is most commonly observed in immunocompromised patients, such as those with neutropenia, hematologic malignancies, or those on long-term immunosuppressive therapy. Some key points to consider when identifying the crescent sign include:
- The sign is often associated with a poor prognosis and may precede potentially fatal hemoptysis as the fungal infection can erode into blood vessels 1.
- Early recognition and aggressive treatment are essential to improve outcomes in these high-risk patients.
- The presence of the crescent sign warrants prompt antifungal treatment, typically with voriconazole as first-line therapy at a loading dose of 6 mg/kg IV every 12 hours for two doses, followed by 4 mg/kg IV every 12 hours, as described in the study 1.
- Alternative options include liposomal amphotericin B or isavuconazole, which can be considered based on the patient's specific condition and medical history. It is essential to note that the crescent sign is a late manifestation of chronic pulmonary aspergillosis (CPA), and additional information is required to classify the disease and decide on therapy, as highlighted in the study 1.
From the Research
Definition and Association of Crescent Sign
- The "crescent sign" is a hyperattenuating crescent-shaped region on CT within the mural thrombus or wall of an aortic aneurysm 2.
- It has previously been associated with aneurysm instability or impending rupture, but the literature is largely based on retrospective analyses of urgently repaired aneurysms 2.
- The crescent sign can also be found in the lungs, and is discussed in several studies as a radiologic sign that can be useful in narrowing the differential diagnosis 3, 4, 5.
Clinical Relevance of Crescent Sign
- The finding of an isolated radiographic "crescent sign" without other signs of definitive aortic rupture is not necessarily an indicator of impending aortic rupture, but may be found in the setting of rapid aneurysm growth 2.
- In patients with invasive pulmonary aspergillosis, the crescent sign was seen in 48% of patients on follow-up radiographic examinations, and was more commonly seen in patients with initially large parenchymal lesions on CT scans 6.
- The appearance of the crescent sign was correlated with the pattern of parenchymal lesions on initial CT scans, the presence and duration of neutropenia, and underlying diseases 6.
Imaging Findings and Crescent Sign
- The crescent sign can be seen on CT scans of the chest, and is one of several metaphoric chest CT scan signs that have been described in the literature 3, 4, 5.
- The sign is often associated with other imaging findings, such as periaortic fat stranding, and can be useful in guiding aneurysm management in patients with aortic aneurysms 2.
- In patients with invasive pulmonary aspergillosis, the crescent sign was seen in patients with consolidation or mass on CT scans, and appeared after recovery from neutropenia or treatment with amphotericin B 6.