A pneumonectomy (or pneumectomy) is a surgical procedure to remove a lung. Removal of just one lobe of the lung is specifically referred to as a lobectomy, and that of a segment of the lung as a wedge resection (or segmentectomy).

The most common cause for a pneumonectomy is to excise tumourous tissue arising from lung cancer. Other indications for lobectomy include a solitary pulmonary nodule (the possibility of undiagnosed small-cell cancer in this instance is not necessarily a reason for avoiding thoracotomy), or bronchiectasis where other forms of treatment have failed, particularly if it is localised and recurrent hemoptysis is present. In the days prior to the use of antibiotics in tuberculosis treatment, tuberculosis was sometimes treated surgically by pneumonectomy.

From http://en.wikipedia.org/wiki/Pneumonectomy