Role of 3D T2 weighted imaging at 3T in evaluation of cranial nerve pathologies - An overview

Transcription

1 Role of 3D T2 weighted imaging at 3T in evaluation of cranial nerve pathologies - An overview Poster No.: C-1153 Congress: ECR 2013 Type: Educational Exhibit Authors: V. Kasi Arunachalam 1, R. Renganathan 2, R. Arkar 2, K. A. Arjunasamy 2, S. Lakshmanan 2, P. Mehta 3, M. P. Cherian 1 ; 1 Coimbatore, Tamilnadu/IN, 2 Coimbatore/IN, 3 Coimbatore, Ta/IN Keywords: DOI: Education and training, Education, MR, Neuroradiology brain /ecr2013/C-1153 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 13

2 Learning objectives To study about the imaging findings in cranial nerve pathologies. To know about 2D T2 and 3D T2 imaging techniques at 3T and their differences. To evaluate the role of 3D T2 imaging at 3T in identifying the cranial nerve pathologies. Images for this section: Fig. 1: Bilateral optic nerves Page 2 of 13

3 Background History : Pneumoencephalography and high resolution tomodensitometry have been performed in the past for cranial nerve imaging using air and ionized contrast agents. Now a days, MRI is preferred because its is non-invasive, does not use radiation, has multiplanar imaging capability and can show structures less than 1.0mm size. Also with advent of microsurgery methods, relation between tumor and cranial nerves as well as small vessels and cranial nerves becomes more important. Introduction: MRI is a multi-planar imaging. Small caliber structures like cranial nerves may not be seen well on images acquired with distance interval gap between them. Also it is difficult to trace the cranial nerves on distance interval gap images. 3D T2 imaging is a new volumetric imaging technique without distance interval gap to better demonstrate cranial nerve anatomy and pathology. Normal cranial nerves: There are twelve pairs of cranial nerves. Except olfactory and optic nerves, all of them arise from brain-stem. Midbrain: occulomotor, trochlear. Pons: Trigeminal, abducens, facial, vestobulo-cochlear. Medulla: glossopharyngeal, vagus, spinal accessory, hypoglossal. These cranial nerve appear hypointense to CSF. Cranial nerves are identified on MRI depending on their course. Cranial nerve pathologies: Cranial nerves are affected by various pathological conditions. Classification of cranial nerve pathologies: 1. Congenital: Absence of fourth cranial nerve in congenital Brown syndrome. 2. Inflammatory: neuritis. 3. Infective: secondary to meningitis. Page 3 of 13

4 4. Neoplastic: Schwannoma, glioma, nerve sheath meningioma. 5. Traumatic: transection of nerve, contusion, compression within bony canal. 6. vascular: vascular loops causing neuro-vascular conflicts. 7. Others: compression by tumor arising from adjacent structures. MR technique: Equipment: 3 tesla SIEMENS. The 3 tesla provides high signal to noise ratio (SNR) inherent in high field strength. All indicated patients were subjected to 3D-T2 SPACE sequence with additional routine sequences as needed; hence reducing total study time. SPACE = sampling perfection with application-optimized contrasts by using different flip angle evolutions. TR: 1000, TE:133, Acquisition plane: axial. After acquiring the 3D T2 images, the axial and the post processed images are carefully examined about the following characteristics of the affected cranial nerve: a. course. b. caliber. c. signal intensity. d. adjacent structures. Gradient based v/s spin echo based 3D: Gradient based 3D: susceptibility artifacts. More SAR( specific absorption ratio). Spin echo based 3D: blurring artifacts due to longer echo trains. :Less SAR as compared to Gradient based 3D. 3D T2 SPACE& its advantages: SPACE: Fast spine echo with variable flip angles reduces image blurring. High tissue contrast. Volumetric data can be viewed in any view, any plane or any slice from single acquisition with same high resolution as the native plane. This avoids retakes needed to image missing or misaligned slices or planes; hence reducing study time. More consistently detects lesions as small as 2.0mm. 2D v/s 3D T2W: Page 4 of 13

5 characteristics 2D T2W 3D T2W Distance interval gap Yes No Multi-planar reformation Not possible Possible Contrast resolution Good Better Course of the nerve Difficult to demonstrate Well demonstrated TR TE Flip angles Acquisition time 1.55 minutes 4.18 minutes Thickness 3mm -- Interval 1.2mm -- Imaging findings OR Procedure details We acquired 3D T2 SPACE in axial plane in all patients suspected of having cranialnerve pathology as first sequence and additional sequences were aquires as needed; hence minimising study time. Case 1: Left hemifacial spasm(figure 2). Vascular loop of left Anterior inferior cerebellar artery is seen indenting the cisternal segment of left facial nerve. Case 2: Right trigeminal neuralgia(figure 3). Vascular loop of right superior cerebellar artrey is compressing the root entry zone and cisternal segment of right trigeminal nerve with change in caliber as well as course of right trigeminal nerve. Case 3: Right labyrinthine ossificans (Figure 4 & Figure 5). Case 4: Page 5 of 13

6 Complete transection of right optic nerve(figure 6). History of trauma. Altered signal intensity and breach in the continuity of right optic nerve is seen. Case 5: Left optic nerve ischaemia with occlusion of left internal carotid artery(figure 7). T2 SPACE image shows hyperintense signal abnormality involving left optic nerve. MR angiography images shows complete absent flow signal in intracranial segment of left internal carotid artery. Case 6: Neuromyelitis optica with left optic nerve atrophy(figure 8). T2 SPACE image shows hyperintense signal abnormlaity in left optic tract and adjacent left half of left optic chiasma. The left optic nerve is small in caliber as compared to right side represents left optic nerve atrophy. Images for this section: Page 6 of 13

7 Fig. 2: Left hemifacial spasm Page 7 of 13

8 Fig. 3: Right trigeminal neuralgia Page 8 of 13

9 Fig. 4: Right Labyrinthine ossificans Page 9 of 13

10 Fig. 5: Right Labyrinthine ossificans Page 10 of 13

11 Fig. 6: Complete trans-section of right optic nerve Page 11 of 13

12 Fig. 7: Left optic nerve ischemia with occlusion of left internal carotid artery. Fig. 8: Hyperintensity in left optic tract. Left optic nerve atrophy. Page 12 of 13

13 Conclusion Conclusion 3D T2 weighted imaging is an excellent tool for the evaluation of cranial nerve pathologies. This information plays an important role in deciding mode of management of these conditions. Significant reduction of time is also achieved by 3D-T2 imaging in cranial nerve evaluation. References Katherine T,. Scott, Stuart H. Schmeets, Siemens MEdical Solutions,; SPACE: An Innovative Solution to Rapid, LOw SAR, T2-W Contrast in 3D Spin Echo Imaging. Portia S. Silk, John I. Lane, Colin L. Driscoll: Surgical Approaches to Vestibular Schwannomas: What the Radiologist Needs to Know.;Radiographics 2009; 29; Personal Information Page 13 of 13