Pulmonary abscess is a localized area of liquefactive necrosis of the lung.

The abscess is characterized by destruction of lung tissue forming a cavity. The cavity is filled with pus (necrotic debris/liquid) or pus and gas (air). The content of the abscess is extremely foul smelling. The abscess may be large or small, single or multiple. The abscess(s) may occur in any part of the lung. Refer to Figure 15-22 in your textbook.
Clinical Note:An abscess which follows aspiration occurs more often in the right lung. Why?

A variety of microorganisms may cause a lung abscess, but more than 60% of cases are associated with anaerobic organisms found normally in the oral cavity. There are many mechanisms for the development of a lung abscess but the most frequent mechanism is aspiration of infective (contaminated with microorganisms) material.

Fever, cough producing large quantity of foul-smelling, purulent sputum; weight loss, chest pain and clubbing. Rule out carcinoma.