208.Chiari Ｉ Ｍalformation（小脑扁桃体下疝畸形（I型））

IMAGING

General Features

Best diagnostic clue

○ Combination of inferiorly displaced 'pointed' tonsils　with 'crowded' posterior fossa, effaced retrocerebellar　CSF spaces at foramen magnum/upper cervical level

Morphology

○ Low-lying, pointed peg-like tonsils with oblique vertical sulci, elongated but normally located 4th ventricle (normal dorsally-pointed fastigium)

【Chiari Ｉ Ｍalformation 小脑扁桃体下疝畸形（I型）】

影像表现：

最佳诊断线索：小脑扁桃体尖部向下移位，“挤在”后颅窝。移位至枕骨大孔/颈髓平面，导致小脑后脑脊液间隙消失。

形态改变：钉状扁桃体向下移位，伴斜行的脑沟，形态变长但通常位于第四脑室（正常尖部朝向背部）。

MR Findings

· T1WI

○ Pointed (not rounded) tonsils ≥ 5 mm below foramen　magnum

○ 'Tight' foramen magnum with small/absent cisterns

○ ± 4th ventricle elongation, hindbrain anomalies

· T2WI

○ Oblique tonsillar folia (sergeant's stripes like)

○ ± short clivus → apparent descent of 4th ventricle,　medulla

○ ± syringohydromyelia (14-75%)

磁共振表现：

T1WI：尖状扁桃体，位于枕骨大孔下 ≥5mm。枕骨大孔“紧缩”，伴小的/不伴脑池。伴或不伴四脑室的拉长，后脑异常。

T2WI：血型扁桃体条纹（海军条纹征）。伴/不伴斜坡变短，明显降至第四脑室，骨髓。伴/不伴脊髓空洞症（14-75%）

Notes：

1. tonsil [ˈtɑ:nsl] n. 扁桃体

2. fossa ['fɒsə] n. 窝，凹

3. retrocerebellar 小脑后

4. foramen magnum [ˈmæɡnəm] 枕骨大孔

5. medulla [mɪ'dʌlə] n. 骨髓

6. syringohydromyelia 脊髓空洞