Hollowed chest. Coloured X-ray of a section through the chest of a 57-year-old patient with pectus excavatum (hollowed chest). Also seen is a neurostimulator (oval, far left) implanted under the skin for the treatment of Parkinson's disease. Pectus excavatum is a congenital disorder of the anterior wall of the chest in which several ribs and the sternum (breastbone) grow abnormal, resulting in a caved-in appearance of the chest. Neurostimulators are used to send electrical impulses to electrodes implanted in the brain for the treatment of the motor symptoms of Parkinson's disease.