CT/MRI配准对圆孔、卵圆孔、棘孔、舌下神经管及舌下神经的显示

Visualization of foramen rotundum,ovale,spinosum,hypoglossal canal and nerve in registration of CT and MRI

背景与目的：不同学者对MRI与CT在鼻咽癌颅底区域的影像显示的看法存在分歧。为明确MRI对鼻咽癌颅底区域靶区显示的情况，分析无颅神经侵犯鼻咽癌患者的CT、MRI，比较圆孔、卵圆孔、棘孔、舌下神经管及舌下神经CT、MRI的显示情况和影像表现，探讨圆孔、卵圆孔及棘孔、舌下神经管及舌下神经在鼻咽癌放射治疗靶区勾画的意义。方法：研究我院2005年3-4月未经治疗的无颅神经侵犯20例鼻咽癌患者CT、MRI。在Pinnacle3 7．0工作站上采用互信息法配准后分析圆孔、卵圆孔、棘孔及舌下神经管在CT／MRI图像上显示特点。记录CT、MRI横断面显示情况；测量舌下神经管两侧纵径、内径及两侧纵径分别与矢状面的角度，并进行数据统计学分析。结果：在CT骨窗上圆孔显示为低密度的管状结构，卵圆孔及棘孔显示为低密度的孔状结构。7例（35％）圆孔在CT上为双侧显示，5例（25％）为单侧显示，8例（40％）未见显示。全部患者卵圆孔、棘孔在CT上均为双侧显示，卵圆孔两侧对称者13例（65％），不对称者7例（35％）。卵圆孔呈圆形8例（20％），呈椭圆形32例（80％）。棘孔两侧对称3例（15％），两侧不对称者17例（85％）。全部病例圆孔在MRI各个序列上均未见显示，卵圆孔及棘孔在T1WI、T2WI上均未见显示，在增强T1WI上表现为高信号血管影。全部患者卵圆孔及棘孔在增强T1WI上为双侧显示，卵圆孔两侧对称13例（65％），两侧不对称7例（35％）；呈圆形8例（20％），呈椭圆形32例（80％）。增强CT未见圆孔、卵圆孔及棘孔内血管显示。全部舌下神经管在CT上显示，各项指标如下：左管径3．9～8．5mm，平均（6．17±1．3）mm、左管长5．8—10．1mm，平均（6．5±2．0）mm、左管倾角44．2°±0．6°（42°-58°）、右管径4．2—9．7mm，平均（5．78±1．2）mm、右管长5．6～10．6mm，平均（6．8±1．9）mm、右管倾角44．5°±1．7°（41°-66°）。两侧管径比较t=1．202 P〉0．05，两侧管长比较t=-1．216P〉0．05，两侧管倾角比较t=0．252P〉0．05。在MRI上均为全管双侧显示各项指标显示如下：双侧100％；左管径4．2—8．7mm，平均（6．3±1．3）mm、左管长5．6-10．2mm，平均（6．6±1．8）mm、左管倾角平均44．1°±0．7°（41°～59°）、右管径4．8—9．7mm，平均（5．9±0．9）mm、右管长5．7—10．5mm，平均（6．9±1．7）mm、右管倾角平均44．3°±1．7°（41°-68°）。两侧管径比较t=1．11，P〉0．05，两侧管长比较t=-0．984，P〉0．05，两侧管倾角比较t=0．532，P〉0．05。舌下神经CT未能显示，舌下神经池内段、管内段在MRI上亦可显示，但是管外段未见显示。结论：在MRI上对圆孔的识别还有很大困难，但是MRI可以显示正常卵圆孔及棘孔，为今后直接在MRI勾画鼻咽癌靶区（卵圆孔）制定放疗计划提供了影像解剖及靶区确定的依据。在舌下神经管和舌下神经显示及影像诊断上MRI较CT有明显优势。MRI较CT具有同时显示舌下神经管及舌下神经的优势，特别是对舌下神经麻痹的患者，可以很好判断病灶，有助于制定治疗计划。在临床上对于鼻咽癌我们推荐MRI检查以便更确切地评价病灶。

Background and purpose： The imaging of the skull base is challenging in nasopharyngeal carcinoma, through studying visualization and the appearance of foramen ovale, foramen rotundum, foramen spinosum, hypoglossal canal and nerve which can be identified on registration of CT and MRI for nasopharyngeal carcinoma, in order to define the target volume of nasopharyngeal carcinoma in radiotherapy planning. Methods： 20 nasopharyngeal carcinoma cases without cranial nerve involvement were scanned by CT and MRI during March to April 2004. The foramen ,rotundum ovale ,spinosum, hypoglossal canal and hypoglossal nerve on CT and MR images were analyzed, with normalized mutual information registration in Pinnacle3 7.0 workstation. Results： The foramen rotundum could be identified on CT as lower density canal, bilateral rotundum canal were found in 7 cases （35%）, unilateral rotundum canal were found in 5 cases （25%） and canal were not seen in 8 cases （40%） ; Bilateral foramen ovale and spinosum were seen on CT in 20 cases, among them symmetric foramen ovale in 13 cases（65%） and asymmetric foramen ovale in 7 cases（ 35%）; rotundum in 8 sides（20%）, ovale in 32 sides （80%）. For the foramen spinosum, bilateral symmetry in 3 cases（15%） and asymmetry in 17cases（85%）. Rotundum canal were not seen on MRI sequence for 20 cases. The foramen ovale, and spinosum were not seen in T1 WI andT2 WI, but could be detected as high signal in contrash WI due to bilateral blood vessels. For the foramen ovale in MRI, bilateral symmetry 13 cases（65% ） and asymmetry 7 cases（ 35% ） ; rotundum 8 sides（20% ）, ovale 32 sides（ 80% ）. No blood vessel in the foramen rotundum, ovale and spinosum were seen in contrast CT. All hypoglossal canals could be identified on CT with the values as following： Mean width of left canal was 6.17 mm ± 1.3 mm（ 3.9-8.5 mm）, mean length of left canal was 6.5 mm±2.0 mm （5.8-10. 1 mm）, mean angle of axis of left canal was 44.2° ±0.6°（42°-58°）, mean width of right canal was 5.78 mm ± 1.2 mm（4.2-9.7 mm）, mean length of right canal was 6.8 mm ± 1.9 mm（5.6-10.6 mm）, mean angle of axis of right canal was 44.5° ± 1.7°（41 °-66°）. No statistical difference was found among all the above parameters. All complete hypoglossal canal could be depicted on MRI with the values as following： Mean width of left canal was 6.3 mm ± 1.3 mm（4.2-8.7 mm）, mean length of left canal was 6.6 mm ± 1.8 mm（ 5.6-10.2 mm）, mean angle of axis of left canal was 44.1° ＋0.7°（41°-59°）, mean width of right canal was 5.9 mm±0.9 mm（4.8-9.7 mm）, mean length of right canal was 6.9 mm ± 1.7 mm （ 5.7-10.5 mm）, mean angle of axis of right canal was 44.3° ± 1.7°（ 41 °-68°）. No statistical difference was found among all the above parameters on MRI. Conclusions： Our data showed that the foramen rotundum were not found in MRI, and the foramen ovale and spinosum could be identified on MRI, which could provide the image anatomy basis for delineating targets in the treatment planning radiotherapy for the patients with nasopharyngeal carcinoma. The identification of hypoglossal canal could be improved on MRI in comparison with CT. Especially, MRI was recommended to clarify whether hypoglossal nerve is invaded, so that the lesion, target volume could be accurately delineated.