Air crescent sign

Invasive fungus

Air crescent sign is a radiologic sign found on radiographs or more commonly on CT scans of the lungs. It represents a crescent of air in the lung that outlines a mass, typically seen in certain lung infections and conditions. This sign is significant in the diagnosis and management of various pulmonary diseases, particularly in the context of invasive pulmonary aspergillosis, which is a serious infection that primarily affects people with weakened immune systems.

Etiology

The air crescent sign is most commonly associated with the resolution phase of angioinvasive aspergillosis, a fungal infection caused by Aspergillus species. However, it can also be seen in other conditions such as:

• Pulmonary infarction
• Pulmonary hematoma
• Certain types of lung cancer
• Necrotizing pneumonia
• Tuberculosis

Pathophysiology

The air crescent sign indicates the presence of air between the wall of a cavity and a mass within it. In the context of angioinvasive aspergillosis, this sign suggests that the infection has led to the necrosis of lung tissue, and the resultant cavity is beginning to be separated from the surrounding lung parenchyma by a collection of air. This separation typically occurs during the recovery phase of the infection, as the immune system begins to clear the infected tissue and air enters the space.

Clinical Significance

The presence of the air crescent sign is a critical diagnostic clue and can help differentiate between various types of lung lesions. In patients with a compromised immune system, such as those undergoing chemotherapy, with HIV/AIDS, or receiving immunosuppressive therapy for organ transplantation, the detection of the air crescent sign warrants immediate attention. It often prompts further diagnostic testing, including microbiological cultures and histopathological examination, to confirm the presence of fungal infection and to identify the specific pathogen involved.

Diagnosis

Diagnosis of conditions associated with the air crescent sign involves a combination of clinical evaluation, imaging studies, and laboratory tests. CT scans are particularly useful in identifying the air crescent sign and assessing its characteristics. Radiologists play a crucial role in interpreting these imaging findings in the context of the patient's clinical history and symptoms.

Treatment

The treatment of conditions associated with the air crescent sign depends on the underlying cause. In the case of angioinvasive aspergillosis, antifungal therapy with agents such as voriconazole or amphotericin B is typically initiated. The management of other conditions, such as lung cancer or tuberculosis, follows specific guidelines tailored to those diseases.

Conclusion

The air crescent sign is an important radiologic finding that can help in the diagnosis and management of various pulmonary conditions. Its identification requires careful analysis of imaging studies by experienced radiologists, and its presence necessitates a comprehensive approach to patient care, including further diagnostic testing and appropriate treatment.