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Twenty-four patients with seropositive rheumatoid arthritis, 12 of them with anterior atlanto-axial subluxation alone and 12 with vertical atlanto-axial subluxation, were examined by echo-encephalographic measurement of the width of third and lateral cerebral ventricles. The 12 patients with anterior atlanto-axial subluxation showed normal values for the third and the lateral ventricles. Ten of the 12 patients with vertical atlanto-axial subluxation had increased width of third and lateral ventricles, indicating hydrocephalus.

CT examination of rheumatoid dislocation in the C1-C2 region was performed in 20 patients with advanced disease. The patients were classified in three grades according to the degree of medullary compression caused by the odontoid process in the extended position of the neck. Five patients showed no dural or medullary compression (grade 1), nine dural compression (grade 2), and six medullary compression (grade 3). CT grading was found to correlate best with long tract symptoms. These were present in 4/6 grade 3 and 0/5 grade 1 patients, while 3/9 grade 2 patients had long tract symptoms. Tissue attenuation values over the anterior atlanto-axial joint indicated interposing firm connective tissue in patients showing no reduction of the subluxation on extension of the neck.