Platybasia

What it is

Platybasia is a flattening of the skull base — an abnormally open angle at the base of the skull (the basal angle). It is a bony feature that can be associated with Chiari malformation, a small posterior fossa, and related craniocervical conditions.

Understanding Platybasia

Platybasia describes a skull base that is abnormally flat, measured by an increased basal angle on imaging. By itself, platybasia may not cause symptoms, but it can contribute to a reduced posterior fossa size and can occur alongside other craniocervical abnormalities, including basilar invagination and Chiari. In the context of complex Chiari, platybasia is one of the bony features that may be present and contribute to crowding at the craniocervical junction. It is assessed as part of the craniometric evaluation of the skull base. Recognizing platybasia helps complete the picture of the bony anatomy in Chiari and related conditions. Understanding platybasia clarifies a skull-base feature that can be associated with Chiari and a small posterior fossa.

Why it matters

Understanding platybasia helps families see how a flattened skull base can contribute to a small posterior fossa and accompany Chiari and related conditions, as part of the bony evaluation.