Why would someone need a thoracotomy for pneumothorax?

Prevent recurrence: Usually can be done with a video assisted technique avoiding a true thoracotomy. Recurrence is the usual indication for surgery or job/recreation that involve pressure changes such as scuba diviers and pilots.

Most of the time no.: The majority of cases of pneumothrorax can be treated with what's called a tube thoracostomy, or a chest tube. The only time a video-assisted thoracostomy (vats) or thoracotomy (open procedure) would be required for a pneumothorax is in a situation where the lung is scarred down in a collapsed position, and needs a procedure to free up the lung. This is rare though.

Treatment: It is very uncommon to use thoracotomy approach for a simple pneumothorax. If surgery is indicated, it is most often by minimally invasive technique (vats).