<unk>  may be classified according to the etiology, anatomical location, and pathological course of the disease. Primary thoracic<unk>  occurs most commonly as iatrogenic<unk>  without associated pneumonia whereas secondary<unk>  occurs more commonly secondary to pneumonia.<unk>  necessitans is a spontaneous  discharge of an<unk>  that has burrowed through the parietal pleura into the chest wall to form a subcutaneous abscess that may eventually rupture through the skin.  On the basis of anatomical location,<unk>  may be classified depending on the affected organ including the following: gallbladder<unk> , subdural<unk> , joint<unk> , and<unk>  cystitis.<unk>  is most frequently caused by bacteria. Causes may be tuberculous or nontuberculous. Tuberculous<unk>  is the most common cause of<unk>  necessitans with majority of affected patients immunocompromised. There are 3 stages of<unk>  which are important in terms of the laboratory findings. These are exudative, fibrinopurulent, and organizing.
Empyema
Emphysema
Atypical pneumonia
Chronic bronchitis
Pleurisy
Bronchiolitis
Acute bronchitis
Eosinophilic pneumonia