Mediastinal invasion. Minimal invasion of mediastinal fat is considered resectable by many surgeons [94]. Contact with the mediastinum is not enough to diagnose mediastinal invasion [17]. In Glazer9s series of 80 CTs considered indeterminate for direct mediastinal invasion, 60% were resectable at thoracotomy with no evidence of mediastinal invasion, 22% did invade the mediastinum but were still technically resectable and only 18% were nonresectable [95]. In fact only one of the 37 masses was not resectable provided that the pre-operative CT demonstrated at least one of the following: 1) 90o contact with the aorta; 3) fat visible between the mass and mediastinal structures. Importantly however, this information does not identify inoperable tumours (thus avoiding unnecessary thoracotomy) because ~50% of the technically resectable tumours had >3 cm of mediastinal contact or loss of the clear fat plane. Artificial pneumothoraces have been used to improve detection of both mediastinal and chest wall invasion by examining whether or not the pleura peels away from the relevant structure. Although one study demonstrated 100% accuracy for chest wall invasion, its accuracy for mediastinal involvement was only 76% [96]. Another study was 100% sensitive for mediastinal and chest wall invasion but only 80% specific [97]. This again indicated that the technique cannot be categorical about the presence of unresectability.