platybasia

A developmental anomaly of the skull or an acquired softening of the skull bones so that the floor of the posterior cranial fossa bulges upward in the region about the foramen magnum. SYN: basilar invagination. [platy- + G. basis, ground]

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platy·ba·sia .plat-i-'bā-sē-ə n a developmental deformity of the base of the skull in which the lower occiput is pushed by the upper cervical spine into the cranial fossa

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platy·ba·sia (plat″ĭ-baґse-ə) [platy- + bas- + -ia] bulging upwards of the floor of the posterior cranial fossa adjacent to the foramen magnum due to softening of skull bones or a developmental anomaly; see also basilar invagination, under invagination. Called also basilar impression.