Frontal sinus infection. Coloured computerized tomography (CT) scan of an axial section of the brain of a 32-year-old patient with a frontal sinus infection. It is a bone window study (grey-level mapping, involving manipulation of the greyscale component of a CT scan to highlight specific structures in the brain), centred on the frontal sinuses. There is an infection of the right frontal sinus, along with a partial filling of the left frontal sinus. The frontal (paranasal) sinuses are airspaces (lined with a mucosal membrane) within the bones of the face and skull. Sinus infection (sinusitis) is where these airspaces become filled with fluid, which leads to bacterial growth and viruses causing infection. This patient is prone to a global sinus infection. This is a CT scan without intravenous iodine injection.