The overall goal of this procedure is to evaluate morphologic changes of cranial nerves in vivo using MRI, something that can be found for example in inflammatory changes. This method can help answer key questions in the medical field such as do we see changes of neural structures in other conditions in vivo? The main advantage of this technique is that it can be used in vivo with possible implications for diagnosis and therapy of diseases.
In our study, we have looked at the vestibular cochlea nerves in patients with Meniere's disease. We have looked at the diameter of the nerve to see how thick it is and whether there's any thinning of the nerve. You can easily use this technique also for other cranial nerves to look into other disease processes so it can be easily translated to other disease areas.
Begin by escorting the patient into the MRI room and having them lie on the scanner table. Be sure to position their heads straight at the isocenter of the scanner and then secure the head coil. Next perform the MRI scan according to the study protocol including 3D flare and 3D real IR sequences for detection of endolymphatic hydrops in the patient group as well as strong T2-weighted 3D cysts for morphologic analysis of cranial nerves in the patient group and healthy controls.
After the scan is complete, check the MRI image quality with regard to artifacts like fold over artifacts, pulsation artifacts, metal artifacts, and take special account of the target of evaluation. In this case, the cranial nerves VII and VIII throughout their course. Finally, evaluate the endolymphatic hydrops in the MRI scans of patient group.
Check for degree of cochlear and labyrinthine endolymphatic hydrops made visible by examining the acquired 3D flare and 3D real IR sequences. Begin by running the DICOM viewer by double clicking the icon of the application to display the database window. Import the patient image data by left mouse clicking on file in the upper dropdown menu.
Then select import and then import file. In the file selector, select the patient image data in order to see the patient name and data in the database window. Next in the database window, expand the patient image folder by left clicking onto the triangle symbol on the left side of the patient name.
Select the sequence of choice from this folder and double left click on it to open the corresponding image data. Next prepare for reconstructing transverse sections of the cranial nerves to avoid measurement errors derived from oblique slices through the course of the nerve by selecting 3D MPR in the 3D viewer dropdown menu at the top of the screen. Then adjust zoom levels to accommodate reconstruction by selecting the zoom tool from the change mouse button function area in the toolbar in the upper left part of the MPR window.
Move the mouse cursor to each of the three planes in the MPR window and adjust zoom levels by left clicking and dragging. Reconstruct the central XIII nerve and set the reconstruction plane orthogonal to the nerve's course in the middle of the Cerebellopontine Angle or CPA. Check and adapt the orientation of the reconstructed plane in all three planes'windows.
Check for out of plane traversing of the nerve and correct the plane orientation respectively. Adjust the orientation of the three axes to the nerve's course using the rotate function available by moving the mouse to the lateral aspects of each axis. Then hold the leftmost button pressed and drag the mouse to adjust the plane orientation in all three windows of the MPR window.
In order to reconstruct a plane traverse of the XIII nerve's course at the end of the middle of the CPA, go to the left lower window of the MPR window and move the mouse to the middle of the axis crosshair so the mouse cursor will transform again into a hand symbol. Then left click and drag the plane to the desired location. Left click onto the upper right window of the MPR window to select this plane.
Select file, then export, then export to DICOM files. In the DICOM export window, select current image only. Rename the series VIII CPA then click the OK button on the right lower aspect of the DICOM export window.
Next reconstruct the orthogonal views of the branches of XIII nerve, Cochlear Nerve, CN, Superior Vestibular Nerve, SVN, and Inferior Vestibular Nerve, IVN, at the level of the meatus of the IAC where representative visualization is usually well feasible. Then grab the axis crosshair in each of the three planes with the grab tool indicated by a hand icon and move the axis toward the CN, SVN, and IVN respectively at the level of the meatus of the Internal Auditory Canal or IAC. Adjust their orientation to the nerve's course using the rotate function available at the lateral aspects of each axis depicted by the curved icon.
Export and rename the reconstructed planes. Begin by selecting the previously reconstructed image of cranial XIII at the level of CPA by left clicking the corresponding image file in the database window of the DICOM viewer and opening it. Zoom into the image structures and select length next to the change the mouse button function in the toolbar on top of the screen.
Left click and hold the left mouse button to draw a line of measurement for the Longest Diameter of the cranial nerve XIII called LD.Then perform a measurement perpendicular to LD for the SD measurement. Evaluate CSA using the closed polygon region of interest to account for possible inhomogeneities in the contour of the cranial nerve's cross-section. Finally, outline the contour of the cranial nerve XIII by left clicking multiple times on the border of the nerve.
To close the polygon, double left click at the desired point to display the complete contour. A significant difference between the mean values of the patient group and healthy control group can be found for measurements of the CSA of the facial nerve, CN, SVN, and IVN. CSA measurements in the patient group showed significantly larger values compared to healthy controls.
Short Diameter, SD of the SVN, was significantly larger in the patient group compared to the healthy control group whereas the Long Diameter, LD, was found to be not significantly different. Further, measurements of the cross-sectional area of the cochlear nerve is shown here, followed by the measurement of the LD and perpendicular SD.Once mastered, this technique can be performed in a few minutes if done properly. While attempting this procedure, it's important to remember to consistently evaluate diameters and cross-sectional areas with regard to partial volume effects.
Following this procedure, other methods like morphometric evaluation of different intracranial structures can be performed in order to answer additional questions like how do we find morphometric changes of cranial nerves for example in multiple sclerosis? How are possible changes evolving through time and different therapies? And can we appreciate a therapeutic response by evaluating morphologic changes?
It has been observed that there is a swelling of the cranial nerves and this swelling helps to corroborate the diagnosis of Meniere's disease. It is also very interesting for basic knowledge on Meniere's disease because this might be associated with inflammatory reaction of the cranial nerves and this is a potential pathogenesis of Meniere's disease. After its development, this technique paved the way for researchers in the field of healthcare to explore possible morphometric changes in several pathologic conditions.
After watching the video, you should have a good understanding of how to evaluate possible morphologic changes of cranial nerves and other brain structures while at the same time being aware of possible biases and account for possible errors. Don't forget that working with MR scanners can be extremely hazardous if using metal objects like certain implants and precautions such as careful patient exploration should always be taken while performing this procedure.
