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.
Highlights
Basilar invagination (BI) is an important occipitocervical malformation characterized by odontoid apophysis displacement of the axis inwards towards the foramen magnum and posterior displacement of the bulb; cerebellar BI is generally a congenital pathology, but it can be acquired in rare cases [1,2,3]
This malformation was first described by Ackermann [4] in studies on cretinism performed in the Andes, but this description was subsequently rejected by Virchow [5], who referred to the malformation as basilar impression malformation, thoroughly described the bone changes observed in odontoid process invagination at the base of the skull, and was the first author to accept a congenital origin for the pathological and clinical characteristics
The upper spinal canal >5 mm; this condition is currently known as Chiari malformation type I (CM-I)
Summary
Basilar invagination (BI) is an important occipitocervical malformation characterized by odontoid apophysis displacement of the axis inwards towards the foramen magnum and posterior displacement of the bulb; cerebellar BI is generally a congenital pathology, but it can be acquired in rare cases [1,2,3] This malformation was first described by Ackermann [4] in studies on cretinism performed in the Andes, but this description was subsequently rejected by Virchow [5], who referred to the malformation as basilar impression malformation, thoroughly described the bone changes observed in odontoid process invagination at the base of the skull, and was the first author to accept a congenital origin for the pathological and clinical characteristics. CM-I is complicated by associations with other malformations of the craniocervical junction, including mainly BI [1,8,9]
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