Sunken chest (pectus excavatum). 3D computed tomography (CT) scan of a frontal view of the rib-cage of a patient with the condition pectus excavatum, a sunken chest. This is a congenital abnormality (present from birth) in which part of the breastbone is concave in shape. The breastbone (sternum) is the bone running down the centre of the front of the chest, to which the ribs are attached. Image obtained using the Vesalius3D scanning technique.