Romanowski C A J, Hutton M, Rowe J, Yianni J, Warren D, Bigley J, Wilkinson I D
Department of Neuroradiology, Royal Hallamshire Hospital; Sheffield -
Neuroradiol J. 2011 May 15;24(2):171-6. doi: 10.1177/197140091102400202. Epub 2011 May 11.
The medial lemniscus is part of the main somatosensory pathways ascending within the brainstem. It is formed by the heavily myelinated axons of the second order neurones of the dorsal column nuclei. This pathway ascends through the rostral medulla, pons and mesencephalon to finally terminate by synapsing with third order neurones in the ventral posterior nucleus of the thalamus. The medial lemniscus conveys proprioception and fine tactile discrimination as part of the somatosensory system. Conventional MRI studies of the brainstem have been relatively poor in demonstrating these fibre pathways. Diffusion tensor imaging and tractography may demostrated fibre pathways in the brainstem. These techniques do however suffer from relatively poor spatial resolution and some degree of image distortion - especially if based on echo planar imaging techniques. Knowledge of the anatomical relationships of the medial lemniscus is important for the understanding of clinical manifestations of disease processes affecting the somatosensory pathways and also to demonstrate important adjacent structures. Specifically, the pedunculopontine nucleus (PPN) lies in close anatomical relationship to the medial lemniscus and the decussation of the superior cerebellar peduncle. This nucleus is a promising target for deep brain stimulator placement for alleviation of non-dopamine responsive dystonias. Six healthy male volunteers (mean age 33 years) were imaged at 3 Tesla. Imaging protocols consisted of thin section, high resolution, fat suppressed T1-weighted sequences as well as thin section, high isotropic resolution diffusion tensor imaging (DTI), which was analysed to generate colour fractional anisotropy (FA) maps. These were correlated with the fat suppressed T1 weighted images. In all volunteers the medial lemniscus was seen as a pair of bands of low signal on axial, high resolution, fat suppressed T1-weighted images. They were indentified through the upper medulla, pons and mesencephalon. They correlated well with the head to foot orientated fibres on the colour FA maps generated from the DTI data. This study of normal volunteers has illustrated the value of high resolution, fat suppressed T1-weighted images in demonstrating the anatomy of the heavily myelinated medial lemniscus within the brainstem. These high resolution images with good spatial accuracy can potentially be used to aid the localisation of other nuclei, such as the PPN.
内侧丘系是脑干内主要的躯体感觉传导通路的一部分。它由薄束核二级神经元的有髓鞘轴突形成。该通路向上穿过延髓嘴侧、脑桥和中脑，最终通过与丘脑腹后核的三级神经元形成突触而终止。内侧丘系作为躯体感觉系统的一部分，传递本体感觉和精细触觉辨别。传统的脑干MRI研究在显示这些纤维通路方面相对较差。扩散张量成像和纤维束成像可能显示脑干中的纤维通路。然而，这些技术的空间分辨率相对较差，并且存在一定程度的图像失真——特别是基于回波平面成像技术时。了解内侧丘系的解剖关系对于理解影响躯体感觉传导通路的疾病过程的临床表现以及显示重要的相邻结构非常重要。具体而言，脚桥核（PPN）与内侧丘系和小脑上脚交叉在解剖位置上关系密切。该核是用于缓解非多巴胺反应性肌张力障碍的深部脑刺激器植入的一个有前景的靶点。对6名健康男性志愿者（平均年龄33岁）进行了3特斯拉的成像。成像方案包括薄层、高分辨率、脂肪抑制T1加权序列以及薄层、高各向同性分辨率扩散张量成像（DTI），对其进行分析以生成彩色分数各向异性（FA）图。这些图与脂肪抑制T1加权图像相关。在所有志愿者中，内侧丘系在轴向、高分辨率、脂肪抑制T1加权图像上表现为一对低信号带。它们可通过上延髓、脑桥和中脑识别出来。它们与由DTI数据生成的彩色FA图上从头到脚排列的纤维相关性良好。这项对正常志愿者的研究说明了高分辨率、脂肪抑制T1加权图像在显示脑干内有髓鞘的内侧丘系解剖结构方面的价值。这些具有良好空间准确性的高分辨率图像可能潜在地用于辅助其他核团（如PPN）的定位。
