Basilar invagination associated with chiari malformation type I: A literature review

Abstract

Basilar invagination (BI) and Chiari malformation type I (CM-I) are very important anomalies that introduce instability and compression in the occipitocervical transition region and have complex clinical characteristics. These anomalies vary according to the affected structures. The present study revises current knowledge regarding the anatomy, anatomo-physiology, clinical manifestations, and radiological findings of these entities and the associated surgical treatment approaches. A bibliographic survey was performed through a search in the Medline, PubMed, SciELO, Science and LILACS databases. When associated, these craniovertebral malformations result in neurological deficits due to neural parenchyma compression; however, the presence of microtraumas due to repetitive lesions caused by the bulb and cervical marrow instability has been highlighted as a determinant dysfunction. Surgical treatment is controversial and has many technical variations. Surgery is also challenging due to the complex anatomical characteristics and biomechanics of this region. Nevertheless, advances have been achieved in our understanding of related mechanisms, and compression and atlantoaxial instability are considered key elements when selecting the surgical approach.

Figure 1. The odontoid process crosses the Chamberlain line for 18.5 mm and compresses the pons anteriorly.

Figure 2. The odontoid process crosses the Chamberlain line for 19.1 mm (basilar invagination) and is associated with the clivus, compressing the pons and bulb anteriorly.

Figure 3. The clivus is shortened, and the upper extremity of the odontoid process lies 26.5 mm across the Chamberlain line, consistent with basilar invagination, and compresses the pons anteriorly.

Figure 4. The cerebellar tonsils migrated 12.1 mm towards the foramen magnum and compressed the bulb posteriorly, consistent with Chiari type I malformation.