NETs that develop in the lungs. There are two types depending on where they occur. Central bronchial NETs are located in trachea (windpipe) and around the main central area of the lungs. Peripheral bronchial NETs are in the outer areas of the lungs. Bronchial NETs are the second most common cause of carcinoid syndrome. Bronchial NETs may also be referred to as bronchial carcinoids or bronchial carcinoid tumors.