Basilar invagination: a study based on 190 surgically treated patients

The authors analyzed the cases of 190 patients with basilar invagination that was diagnosed on the basis of criteria laid down in 1939 by Chamberlain to assess the appropriate surgical procedure.Depending on the association with Chiari malformation, the anomaly of basilar invagination was classified into two groups. Eighty-eight patients who had basilar invagination but no associated Chiari malformation were assigned to Group I; the remainder of the patients, who had both basilar invagination and Chiari malformation, were assigned to Group II. The principal pathological characteristic was observed to be direct brainstem compression due to odontoid process indentation in Group I and a reduction in posterior cranial fossa volume in Group II.Despite the anterior concavity of the brainstem in both groups, transoral surgery was the most suitable procedure for those patients in Group I and decompression of the foramen magnum was found to be appropriate for patients in Group II. After surgical decompression, a fixation procedure was found to be necessary in most Group I cases, but only in a small minority of Group II cases.