Craniospinal space reduction and malalignment due to atlas assimilation in Basilar Invagination-A case-control study

Area of Science:

• Neurosurgery
• Radiology
• Orthopedics

Background:

• Type I Basilar invagination (BI) is characterized by the assimilation of the anterior arch of the atlas (AOA).
• AOA is thought to impede normal development of the space between the skull and the first cervical vertebra (C1).
• This can lead to posterior displacement of the high cervical spine, impacting neural structures.

Purpose of the Study:

• To evaluate and compare craniospinal alignment in patients with Type I Basilar invagination and AOA against normal subjects.
• To assess the positional relationship of the atlas and odontoid process relative to the basion and foramen magnum.

Main Methods:

• Retrospective analysis of MRI and/or CT scans with midline reconstructions (T1/T2 weighted images).
• Evaluation of 30 normal subjects and 27 patients with Type I BI.
• Comparison of key measurements: anterior arch of atlas position, odontoid process position, and distances between C1-C2 and the anterior foramen magnum border.

Main Results:

• Patients with BI and AOA exhibited a significantly greater C2-Basion distance compared to controls (t-test: t=4.18; p=0).
• The space between the skull and atlas was significantly reduced in the BI group.
• Normal subjects consistently showed anterior positioning of the atlas relative to the basion, while BI patients displayed atlas alignment or posterior dislocation, with the odontoid process encroaching on the foramen magnum.

Conclusions:

• Atlas assimilation in Type I Basilar invagination prevents normal skull-to-atlas positioning.
• This condition is associated with a presumed "slip-back" craniospinal displacement during development.
• Findings highlight the significant impact of AOA on craniocervical biomechanics and alignment.