Atlas invagination through the foramen magnum: expanding the spectrum of craniovertebral junction malformations.

Abstract

Malformations of the craniovertebral junction (CVJ) range from mild, asymptomatic conditions to severe forms of instability with basilar invagination. Rarely, there have been accounts of forms of so-called paramedian basilar invagination, with abnormal bone masses invading the lateral portion of the foramen magnum. All these entities have been comprehensively classified both from an anatomical and embryological standpoint. Here, we report a case of a unique CVJ malformation which is not included in any existing classification framework and could represent a novel pathologic entity. We also provide an overview of the pertinent literature. The patient was a 14-year-old boy with a recent onset of spastic tetraparesis. Radiological studies documented a malformation of the atlas which invaginated through the foramen magnum, causing anterolateral medullary incarceration. Surgical treatment involved posterior decompression with resection of the abnormal bone and occipito-cervical fusion. Our report enriches the panorama of CVJ malformations, showing how anatomical knowledge and embryological insights constitute the basis for the correct assessment and treatment of these complex entities.