Horsburgh Avril, Kirollos Ramez W, Massoud Tarik F
Section of Neuroradiology, Addenbrooke's Hospital, Cambridge, United Kingdom.
Department of Neurosurgery, Addenbrooke's Hospital, Cambridge, United Kingdom.
J Neurol Surg A Cent Eur Neurosurg. 2014 Mar;75(2):98-103. doi: 10.1055/s-0033-1342934. Epub 2013 Jun 24.
An appreciation of normal intracranial anatomy allows optimal planning of trajectories necessary for safe and effective neuroendoscopy. Little information exists on displacement of the caudal brain relative to the skull upon head movement; this could have important implications for planning and performance of neuroendoscopic procedures. We used kinematic magnetic resonance imaging (MRI) studies to examine the morphometric displacement and changing anatomical relationships between the clivus and basal brain structures, intracranial vessels, and subarachnoid spaces.
We retrospectively analyzed 15 patients undergoing sagittal T2 kinematic MRI of the head and neck in modest flexion and extension. The angle between a horizontal axial reference plane and a line between the opisthion and the hard palate defined the degree of flexion and extension. We then measured in flexion and extension (1) the cervicomedullary angle (CMA), (2) displacement of the ventral surface of the brainstem (i.e., depth of the prepontine and premedullary cisterns), (3) total sagittal area of the combined suprasellar and ventral brainstem cisterns, and (4) the basilar tip to tuber cinereum distance.
Relative to neutral head position, a mean extension angle of -15.8 degrees was achieved in all 15 patients, and a mean flexion angle of +9.9 degrees was achieved in 6 patients. The mean CMA was 146 degrees in flexion and 158 degrees in extension. The mean reduction in prepontine and premedullary cistern depth was 0.7 mm and 0.5 mm, respectively, upon flexion from extension. The combined area of suprasellar and ventral brainstem cisterns was minimally reduced from 402 mm2 in flexion to 399 mm(2) in extension. The basilar tip did not move significantly from its position in flexion to extension, 5.3 mm to 5.2 mm respectively from the tuber cinereum.
Kinematic MRI shows minimal brainstem-to-clivus displacement even within minor physiological changes in head flexion. Importantly, these movements are small and there is no significant shift in the position of the basilar tip in modest flexion or extension. These results should be useful for presurgical planning of optimal patient positioning during neuroendoscopic procedures such as third ventriculostomy and the expanded endonasal transsphenoidal approach to the retroclival space.
了解正常颅内解剖结构有助于为安全有效的神经内镜检查所需的手术路径进行优化规划。关于头部运动时尾侧脑相对于颅骨的移位情况，目前所知甚少；这可能对神经内镜手术的规划和实施具有重要意义。我们使用运动磁共振成像（MRI）研究来检查斜坡与基底脑结构、颅内血管及蛛网膜下腔之间的形态计量学移位和解剖关系变化。
我们回顾性分析了15例接受头颈部矢状面T2运动MRI检查的患者，检查时头部进行适度的屈伸运动。水平轴向参考平面与枕骨大孔后缘和硬腭之间连线的夹角定义了屈伸程度。然后我们在屈伸状态下测量了：（1）颈髓角（CMA）；（2）脑干腹侧表面的移位（即脑桥前池和延髓前池的深度）；（3）鞍上池和脑干腹侧池联合的矢状面总面积；（4）基底动脉尖至灰结节的距离。
相对于头部中立位，所有15例患者平均伸展角度为-15.8度，6例患者平均屈曲角度为+9.9度。平均CMA在屈曲时为146度，伸展时为158度。从伸展位屈曲时，脑桥前池和延髓前池深度平均分别减少0.7mm和0.5mm。鞍上池和脑干腹侧池联合面积从屈曲时的402mm² 轻微减少至伸展时的399mm²。基底动脉尖从屈曲到伸展时位置无明显移动，距灰结节分别为5.3mm和5.2mm。
运动MRI显示，即使在头部轻度生理屈伸变化范围内，脑干至斜坡的移位也极小。重要的是，这些移位很小，在适度屈伸时基底动脉尖位置无明显改变。这些结果对于神经内镜手术（如第三脑室造瘘术和扩大经鼻蝶入路至斜坡后间隙）术前最佳患者体位的规划应具有重要意义。
