An anatomical state in which the angle between the base of the front part of the skull and the front of the posterior fossaThat part of the cranial cavity that lies below the tentorium and which contains the brain stem and the cerebellum. is shallower than normal. It is a feature seen on a skull radiographThe correct name for what is commonly referred to as an X-ray. In fact, X-rays are the energy beams that pass through the body and produce an image, traditionally on a sheet of radiographic film but more often, these days, as a digital image that can be viewed on a computer monitor. , CT scan or magnetic resonance imagingA highly sophisticated form of obtaining images (pictures) of the internal structures of the body. Unlike some other forms of imaging, magnetic resonance imaging does not involve the subject being exposed to ionising radiation, which can be harmful if used to excess. Magnetic resonance imaging can reveal not just structures but information about how well or otherwise body parts are functioning.. It has no significance in its own right but may be associated with other abnormalities, such as basilar invaginationWe can envisage the skull, in simple terms, as ball sitting on top of a pipe, the latter representing the spinal column. We refer to the point where the two join together as the craniovertebral junction. Normally the shape of this junction is like a funnel, with the lower part of the cerebellum sitting in the mouth of the funnel and the cervical part of the spinal cord being in the stem. The term basilar invagination describes an anatomical state where the “pipe” (i.e. the uppermost part of the spinal column) is pushed up into the lower half of the “ball” (i.e. the posterior fossa of the cranial cavity). This results in a distortion of the normal bony anatomy at..., which may be associated with neurological problems.