Positional headache that worsens when upright (sometimes after being upright for a prolonged amount of time) and gain relief when lying down.
Also see: Intracranial Hypotension, CSF Leaks
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Atlantoaxial Instability [AAI]
A ligamentous defect in which there is excessive movement between the C1 and C2 vertebrae (usually rotational) and can result in neurological symptoms and deficits.
Etiological Cofactors: Heritable Disorders of Connective Tissue (HDCT), such as Ehlers-Danlos Syndrome (EDS).
Basilar Invagination [BI]
A congenital or aquired, cranio-cervical junction abnormality involving cranial settling, where the tip of the 2nd cervical vertebra (axis, odontoid process) is displaced upward and posteriorly (backward) into the intracranial space projecting above the foramen magnum. Basilar Invagnation is caused by this deformation with normal bone (as opposed to Basilar Impression that results from softening of the bone). Basilar Invagnation and Basilar Impression both can cause potential compression of the brainstem.
