[Atlantoid assimilation: malformation, compensation or deformity. Is it part of basilar invagination?].

Introduction: atlas assimilation can occur alone or in association with other craniocervical junction malformations and deformities. The etiological and pathological mechanisms are not clear.

Case Presentation: patient in her sixth decade of life, who was treated at the "Eugenio Espejo" Hospital, with asymmetric pyramidal symptoms after a low-energy kinetic fall.