Abstract
Introduction
Chiari malformation type 1 (CM-1) is diagnosed by more than 3 or 5 mm caudal displacement of the cerebellar tonsils through the foramen magnum. This definition is a simple and easy method neuroradiological, but it is obscure which is 3 or 5 mm. The purpose of this study is to investigate the incidence of new outpatients diagnosed as CM-1 using this definition and to analyze their clinical symptoms and radiological features.
Patients and Methods
We had 3,787 new outpatients in our neurosurgical hospital in 2013. In whom, 3,533 patients examined head CT or MRI, and were studied retrospectively. We diagnosed Chiari malformation type 1 using more than 3-mm tonsillar herniation. Their clinical symptoms and the following measurements were analyzed: the distances from the pontomedullary junction (PMJ) to the basion (PMJ-Ba), PMJ to the basion–opisthion (PMJ–BO), the distances from the basion–opisthion to tip of the cerebellar tonsil, from BO to the obex (BO–obex), and from basion to opisthion, the clivoaxial angle, and the length of the clivus using T1-weighted sagittal images.
Results
There were 19 patients with CM-1 aged from 10 to 54 years (mean: 35.0 years) consisted of 6 men and 13 women. In whom, 10 patients with tonsillar herniation of less than 5 mm were determined as T3 group (T-3) and remaining 9 patients as T5 group (T-5). No patients had syringomyelia. All the patients had clinical symptoms or signs related to CM-1 except two patients in T3 after head injury. Headache was the most common symptom. The distances of PMJ–Ba, PMJ–BO, BO–obex, BO, the clivoaxial angle, and the length of the clivus were similar between both the groups.
Conclusions
The incidence of new diagnosis of CM-1 was 0.53%. Two patients in T3 group without symptoms associated with CM-1 were diagnosed incidentally. Chiari malformation type 1 should be diagnosed based on not only tonsillar herniation but also clinical symptoms and other MRI findings such as brain stem ptosis.