Ishikawa M, Kikuchi H, Fujisawa I, Yonekawa Y
Department of Neurosurgery, Kyoto University, Japan.
Neurosurgery. 1988 Jan;22(1 Pt 1):77-81. doi: 10.1227/00006123-198801010-00012.
To evaluate the risk of tonsillar herniation, the caudal pole of the cerebellar tonsil in posterior fossa mass lesions and anomalies was investigated with magnetic resonance imaging. The cerebellar tonsil was clearly demonstrated in relation to the surrounding structures on T1-weighted images in the paramedian or midline sagittal plane. In 78% of a control group of 50 cases, the tonsil was located just on or close to the upper border of the posterior lip of the foramen magnum. It was close to the line of the foramen magnum in 4 cases (8%), but displacement below this line was not observed in any case. In 18 cases of posterior fossa mass lesions, the tonsil tended to be in a lower position than in the control group, and tonsillar displacement below the foramen magnum was noted in 3 cases. Two of these cases had anterior medullary displacement with loss of the cerebrospinal fluid (CSF) space anterior to the tonsil; these patients had either rapid clinical deterioration or severe papilledema. In the remaining case and in 3 additional cases of Chiari malformation, the tonsils were displaced into the cervical canal with preservation of the CSF space, and the patients showed no signs of rapid clinical deterioration or increased intracranial pressure. The present study suggests that tonsillar displacement through the foramen magnum with associated anterior medullary displacement and loss of the CSF space anterior to the tonsil can be regarded as a sign of tonsillar herniation.
为评估扁桃体疝的风险，我们利用磁共振成像对后颅窝肿块病变及畸形患者小脑扁桃体的尾极进行了研究。在正中旁矢状面或中线矢状面的T1加权图像上，小脑扁桃体与周围结构清晰可辨。在50例对照组中，78%的患者扁桃体恰位于枕骨大孔后唇上缘或其附近。4例（8%）患者扁桃体接近枕骨大孔连线，但无一例扁桃体低于此线。在18例后颅窝肿块病变患者中，扁桃体位置往往低于对照组，3例患者扁桃体低于枕骨大孔。其中2例患者延髓向前移位，扁桃体前方脑脊液（CSF）间隙消失；这些患者临床症状迅速恶化或出现严重视乳头水肿。在其余1例及另外3例Chiari畸形患者中，扁桃体移位至颈椎管内，CSF间隙保留，患者未出现临床症状迅速恶化或颅内压升高的迹象。本研究表明，扁桃体经枕骨大孔移位伴延髓向前移位及扁桃体前方CSF间隙消失可视为扁桃体疝的征象。
