4-1-Cavitary lesion

Cavitary lesion of the lung could classified into three main categories:

-Cavity with air-fluid level:

If you find the cavity containing air fluid level, just look to the fluid surface

1-If it is straight, think for acute lung abscess.
Diagnostic signs are presence of air and  enhanced wall.

2-If it is wavy, think for ruptured hydatid cyst.
Diagnostic signs are presence of other lesions and non enhanced wall.

-Cavity containing air only:

If the cavity is containing air only, look to the thickness of its wall

1-If it is thick, look to the type of thickness, is it regular or irregular with mural nodules

If it is of regular thickness, it will be a chronic lung abscess(common cause).

If it is of irregular thickness with mural nodules, it will be a bronchogenic carcinoma(less common).

2-If the wall is thin, look to the site of the lesion in lung parenchyma.

If it is central, think for pneumatocele secondary to pneumonia.

If it is situated peripherally in the lung parenchyma, think for sub pleural emphysematous bulla.

-Cavity containing intra cavitary mass:

-The most common lesion causing this appearance is fungal ball.

-Less commonly, ruptured hydatid cyst and necrotic tumor.

-Rarely, blood clot.
-Look to the wall of the cavity, if it is thick with regular inner margin, it will be a fungal ball. If it is thick with irregular inner margin, it will be a cavitating tumor.
If the wall is thin and regular, it could be ruptured hydatid cyst.