Platybasia

What it means

A developmental malformation of the occipital bone and upper end of the cervical spine, in which the latter appears to have pushed the floor of the occipital bone upward such that there is an abnormal flattening of the skull base.

Platybasia is malformation of the base of the skull due to softening of skull bones or a developmental anomaly, with bulging upwards of the floor of the posterior cranial fossa, upward displacement of the upper cervical vertebrae, and bony impingement on the brainstem. It results in abnormal obtuseness of the basal angle that can be demonstrated radiographically. If platybasia is associated with basilar invagination, compression of the brainstem and upper cervical cord can result. Basal Angle formed by: line joining the nasion with the center of the pituitary fossa line joining the anterior border of the foramen magnum with the center of the pituitary fossa normal: 125 degrees-143 degrees platybasia: > 143 degrees basilar kyphosis: < 125 degrees. {xref="https://orcid.org/0000-0001-5889-4463"}

Rare diseases that can present with this6

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Flattening of the skull base · Increased basal angle of skull base · Obtuse basal angle of skull base