Extradural haematoma. This noncontrast CT of a young man who was knocked off his bike shows the typical appearance of an extradural haematoma. It is biconvex or ‘lens’ shaped, and its extension is limited by the coronal and lambdoid sutures anteriorly and posteriorly. There is a scalp haematoma overlying this, related to the direct trauma. A large proportion of these are associated with underlying skull fractures, which can be identified by reviewing the images on bone windows.