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  • Position of Cerebellar Tonsil and Brainstem in Chiari Malformations Type 1: A Difference Between 3 mm and 5 mm

    Final Number:

    Tomohiro Murakami MD, PhD; Michio Inoue MD, PhD; Shuko Inoue; Shigeki Matsumura MD

    Study Design:

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2015 Annual Meeting

    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 neuroradiologically for any doctors, but it is obscure which is 3 or 5 mm of the tonsillar herniation. The purpose of this study is to analyze the differences of their clinical symptoms and radiological features using the position of tonsillar herniation and brainstem.

    Methods: Thirty-one new outpatients diagnosed CM-1 between 2013 and 2014 were studied retrospectively. 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 clivo-axial angle, and the length of the clivus using T1-weighted sagittal images.

    Results: There were 7 men and 24 women aged from 10 to 78 years (mean: 37.6 years). All patients had no syringomyelia. In whom 19 patients with tonsillar herniation of less than 5 mm were determined as T-3 group (T-3) and remained 12 patients as T-5 group (T-5). Headache was the most common symptom (74.2%). Two patients after head injury and a patient with memory disturbance were diagnosed CM-1 incidentally in T-3 group. All measurements except the position of cerebellar tonsil had no significant differences between both groups.

    Conclusions: The patients in both groups had similar sympotms and posterior cranial fossa structures. Chiari malformation type 1 should be diagnosed based on the position of the cerebellar tonsil associated with clinical symptoms and other MRI findings such as brainstem ptosis using pontomedullary junction.

    Patient Care: We can have a precise diagnosis of chiari malformation type 1 and select preferred treatment for chiari malformation.

    Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of the position of the cerebellar tonsil and clinical symptoms in chiari malformation type 1, 2) Discuss, in small groups, the definition of chiari malformation type 1, 3) Identify an effective treatment for chiari malformation type 1


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