Platybasia is an abnormality of the base of the skull, literally flattening of the skull base. It may be developmental in origin or due to softening of the skull base bone, allowing it to be pushed upward (see Basilar Invagination). The developmental variant is the result of a wider (flatter) angle between the skull base of the frontal or anterior fossa and the clivus, which defines the anterior wall of the posterior fossa. It is sometimes associated with other congenital abnormalities of the bone structure, such as fusion of the first cervical vertebrae to the skull (atlas assimilation).
In the absence of neural compression, pain at the back of the skull and upper part of the neck is the most common symptom. Neural compression may affect the medulla and nerve roots from the lower brainstem, particularly those that might affect swallowing and the cough reflex.
Skull x-rays, MRI and CT scans are all helpful in reducing misdiagnosis and MRI in assessing the severity of neural impingement.
Unless there is impingement or compression of nerve roots or other neural tissue, no treatment is specifically indicated for platybasia; however, neural compression requires optimal treatment. In some patients, posterior decompression usually in conjunction with fusion of the skull to the upper cervical spine suffices. When the odontoid process of the second cervical vertebra indents, the brainstem and reduction by traction is not successful, odontoid resection, followed by posterior fusion, may be necessary.