Published online before print June 11, 2003, 10.1148/radiol.2282020439
(Radiology 2003;228:539-545.)
© RSNA, 2003
Trigeminal Neuralgia: Evaluation of Neuralgic Manifestation and Site of Neurovascular Compression with 3D CISS MR Imaging and MR Angiography1
Norio Yoshino, DDS,
Hideaki Akimoto, MD,
Ichiro Yamada, MD,
Tsukasa Nagaoka, MD,
Akemi Tetsumura, DDS,
Tohru Kurabayashi, DDS,
Eiichi Honda, DDS,
Shin Nakamura, DDS and
Takehito Sasaki, DDS
1 From the Departments of Oral and Maxillofacial Radiology (N.Y., A.T., T.K., E.H., S.N., T.S.), Neurosurgery (H.A., T.N.), and Diagnostic Radiology and Oncology (I.Y.), Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan. Received April 15, 2002; revision requested June 17; final revision received November 12; accepted December 19. Address correspondence to N.Y. (e-mail: norio.orad@tmd.ac.jp).
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ABSTRACT
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PURPOSE: To evaluate three-dimensional (3D) constructive interference in steady-state (CISS) magnetic resonance (MR) imaging and MR angiography with multiplanar reconstruction (MPR) for detection of neurovascular compression (NVC) in patients with trigeminal neuralgia and to evaluate the relationship between clinical symptoms related to trigeminal branches and those related to the site of trigeminal nerve compression.
MATERIALS AND METHODS: Fifty-four consecutive patients with trigeminal neuralgia were examined at 3D CISS imaging and MR angiography with a 1.5-T MR system. Original transverse and four reformatted images were used for image interpretation. Vascular contact with the trigeminal nerve at the root entry zone (REZ) was determined, and the nature of the involved vessels was identified. The position of the blood vessel compressing the nerve was classified into cranial, caudal, medial, or lateral sites. Statistical analysis was performed with the 
2 test or the Fisher exact test between two groups and with the 2 test among more than two groups.
RESULTS: In 12 of 15 patients who underwent surgery, the artery that was considered a responsible vessel at 3D CISS imaging and MR angiography was confirmed as such. In the other three patients, the vein was the responsible vessel, which was detected only at 3D CISS imaging. Sixteen (89%) of 18 patients with symptoms related to the maxillary division had NVC at the medial site of the REZ, while 16 (76%) of 21 patients with symptoms related to the mandibular division had NVC at the lateral site (P < .001, 2 test).
CONCLUSION: 3D CISS MR imaging with MPR is useful in the detection of NVC in patients with trigeminal neuralgia, compared with MR angiography. A close relationship was found between the region of neuralgic manifestation and the site of trigeminal nerve compression.
© RSNA, 2003
Index terms: Magnetic resonance (MR), comparative studies, 154.121411, 154.121412, 154.12142, 154.12143 • Magnetic resonance (MR), vascular studies, 175.121411, 175.121412, 175.12142, 175.12143 • Nerves, trigeminal, 154.1363, 154.91, 154.92 • Neuralgia, 154.899
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INTRODUCTION
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It has been established that microvascular decompression is a useful method for the treatment of trigeminal neuralgia, because the main cause of trigeminal neuralgia is neurovascular compression (NVC) in the root entry zone (REZ) of the trigeminal nerve in the cerebellopontine angle cistern (1–3). Magnetic resonance (MR) angiography has been reported to be effective in the detection of NVC in trigeminal neuralgia (4–7). To our knowledge, there is no radiologic report dealing with preoperative evaluation of the relationship between clinical symptoms related to the trigeminal branches and those related to the site of compression at the REZ of the nerve. The preoperative evaluation of the relation between clinical symptoms and the direction of compression of the nerve is important for both a more accurate microvascular decompression procedure and the selective rhizotomy of the trigeminal nerve in patients with trigeminal neuralgia (3,8,9).
A high-spatial-resolution three-dimensional (3D) MR imaging with constructive interference in steady-state (CISS) sequence has been used in the evaluation of the cerebellopontine angle and the inner ear (10–12). The use of 3D CISS MR imaging, which has a high spatial resolution and excellent contrast between structures, may allow a much more detailed study of the trigeminal nerve and the adjacent structures than does MR angiography. To our knowledge, no report has dealt with the comparison of 3D CISS imaging and MR angiography in trigeminal neuralgia. The purpose of this study was to evaluate 3D CISS MR imaging and MR angiography with multiplanar reconstruction (MPR) in the detection of NVC in patients with trigeminal neuralgia and to evaluate the relationship between clinical symptoms related to the trigeminal branches and those related to the site of trigeminal nerve compression.
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MATERIALS AND METHODS
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Patients
The subjects were 54 consecutive patients with trigeminal neuralgia (36 women and 18 men; age range, 22–81 years; mean age, 58 years) who visited our dental hospital from August 1996 to November 1998. Table 1 shows the classification of patients with trigeminal neuralgia according to the neuralgic manifestation of the branch areas of the trigeminal nerve. Conventional MR imaging was used to confirm that patients had neither multiple sclerosis nor a brain tumor.
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TABLE 1. Patients with Trigeminal Neuralgia Classified according to the Clinical Manifestation of Branch Areas of the Trigeminal Nerve
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The study protocol was approved by the institutional review board, and informed consent was obtained from all patients.
Imaging Examinations
A 1.5-T superconducting system (Magnetom Vision; Siemens, Erlangen, Germany) with a 25 mT/m maximum gradient capability and a circularly polarized head coil was used to obtain all MR images. Conventional single-section sagittal, coronal, and transverse scout images of the head were initially obtained.
High-spatial-resolution 3D MR imaging was performed by using a 3D CISS sequence with the following parameters: 12.25/5.9 (repetition time msec/echo time msec), 70° flip angle, and one signal acquired. The acquisition matrix was 512 x 512 for a field of view of 230 x 230 mm. The other imaging parameters included a 34-mm slab thickness, 34 sections, and a bandwidth of 195 Hz per pixel, which gave a section thickness of 1 mm and a voxel size of 0.2 mm3. The acquisition slab was oriented in the transverse direction on the sagittal and coronal scout images so that the trigeminal nerve on both sides could be included in the image. The acquisition time was 7 minutes 8 seconds. After data acquisition was completed and each of the 46 sections were obtained, coronal and sagittal reformatted images were obtained by using an MPR algorithm. The other two reformatted images, angled parallel and perpendicular to the trigeminal nerve at the REZ, were also obtained by using an MPR algorithm. For the interpretation of MR images, both the original transverse and the four reformatted images were reviewed.
MR angiography was performed by using a 3D fast imaging with steady-state precession sequence with the following parameters: 39/6.5, 20° flip angle, and one signal acquired. The field of view was 230 x 230 mm, with a matrix of 256 x 512. The other imaging parameters included a slab thickness of 60 mm and 60 sections, which gave a section thickness of 1 mm and a voxel size of 0.4 mm3. The presaturation pulse was added to the cranial side parallel to the slab, and a magnetization transfer pulse was not used. The acquisition slab was oriented transversely to cover the posterior fossa. The acquisition time was 10 minutes 1 second. Coronal and sagittal reformatted images and the other two reformatted images parallel and perpendicular to the trigeminal nerve were obtained by using an MPR algorithm. For the interpretation of MR images, both the original transverse and the four reformatted images were reviewed.
In all patients, transverse T1-weighted spin-echo images (560/14) were obtained with two signals acquired. The T1-weighted images were acquired with a field of view of 230 x 230 mm, a matrix of 256 x 256, and a section thickness of 3 mm with a 1-mm intersection gap. Transverse T2-weighted turbo spin-echo images (5,000/96; echo train length, seven) were obtained with two signals acquired. The T2-weighted images were acquired with a field of view of 230 x 230 mm, a matrix of 256 x 512, and a section thickness of 3 mm with a 1-mm intersection gap. Transverse T1- and T2-weighted images were obtained of the posterior fossa. The spatial resolution of the 3D CISS images was much higher than that of the MR angiographic images.
Image Analysis
All 3D CISS and MR angiographic images were independently analyzed by two radiologists (N.Y., I.Y.) who were blinded to the clinical findings. The presence of vascular contact with the trigeminal nerve at the REZ was determined, and the nature of the involved vessels was identified. Compression was diagnosed when contact of the blood vessel and the nerve at the REZ was clearly detected in two or more sections of the transverse images. The identification of the responsible blood vessel for the compression was performed with complete observation of all the images. For the image analysis, the transverse original images, the coronal and sagittal reformatted images, and the other reformatted images obtained parallel and perpendicular to the trigeminal nerve at the REZ were used. After the blinded study, discrepancies were resolved with consensus. Furthermore, interobserver and intraobserver agreement was assessed by using 
statistics.
By using MPR, the position of the blood vessel compressing the nerve was classified into one of the following four sites: cranial, caudal, medial, or lateral (Fig 1). When compression was detected in two or more sites, it was defined as a compression of two or more sites.
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Figure 1. Schematic demonstrates the classification of the position of a blood vessel that compresses the trigeminal nerve on its cross section. When the blood vessel has compressed the trigeminal nerve at the position shown in this schematic, it is classified as a medial site.
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Surgical Findings
Surgical findings were available for comparison with the MR imaging findings in 15 patients who underwent microvascular decompression surgery after MR imaging.
Statistical Analysis
To compare neuralgic manifestation with the site of NVC, statistical analysis was performed with the 2 test or the Fisher exact test between two groups. The 2 test was used when all expected frequencies were greater than five, and the Fisher exact test was used when some of the expected frequencies were equal to or less than five. Furthermore, the differences among more than two groups were analyzed with the 2 test. P values less than .05 were considered to indicate a statistically significant difference.
The values were calculated for interobserver and intraobserver agreement. A value of less than 0.40 was considered to indicate poor agreement; that of 0.40–0.59, fair agreement; that of 0.60–0.74, good agreement; and that of 0.75–1.00, excellent agreement. Differences in values between 3D CISS imaging and MR angiography were compared by using a paired t test or a 95% CI.
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RESULTS
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Comparison of 3D CISS Imaging and MR Angiography
Figure 2 shows typical transverse images obtained with 3D CISS imaging and MR angiography (3D fast imaging with steady-state precession) for the cerebellopontine angle cistern. On MR angiographic images, the artery was shown as a structure with a high signal intensity, the nerve as that with an intermediate signal intensity, and the cerebrospinal fluid as that with a low signal intensity. On 3D CISS images, the blood vessel and the nerve were shown as structures with a low signal intensity, and the cerebrospinal fluid was shown as a structure with a high signal intensity, thus providing high contrast resolution between the structures.
Detection of NVC with 3D CISS Imaging and MR Angiography
On 3D CISS images, the superior cerebellar artery was determined to be responsible for NVC in 25 (46%) patients; the anterior inferior cerebellar artery, in nine (17%) patients; both the superior cerebellar artery and anterior inferior cerebellar artery, in five (9%) patients; basilar artery, in two patients (4%); the posterior cerebellar artery, in one patient (2%); and the vein, in three (6%) patients (the vein alone in two patients and the vein and anterior inferior cerebellar artery in one patient) (Table 2). However, MR angiography could not depict the responsible vein in three patients, although it depicted the responsible artery in the other patients.
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TABLE 2. Responsible Blood Vessels in Detection of NVC at 3D CISS MR Imaging and MR Angiography in 54 Patients with Trigeminal Neuralgia
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Of the 45 patients with positive findings for NVC at 3D CISS imaging, 15 patients underwent microvascular decompression surgery, and the responsible blood vessels were surgically confirmed in all 15 patients. At surgery, the artery was confirmed as the responsible blood vessel in 12 patients, which corresponded to the findings of 3D CISS imaging and MR angiography (Fig 3). In two of the patients in whom the vein was determined to be the responsible blood vessel at surgery, only the vein was identified on the 3D CISS images as a low-signal-intensity structure. However, the vein could not be identified on the MR angiographic images. In another patient, both the vein and the anterior inferior cerebellar artery were found to be the responsible blood vessels at surgery. In this instance, the 3D CISS MR images depicted both the vein and the artery along with the nerve as low-signal-intensity structures, but the MR angiographic image could not depict the vein, and thus insufficient information was provided for surgical intervention in this patient (Fig 4).
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Figure 3a. Images in a 63-year-old man with trigeminal neuralgia, with NVC caused by the superior cerebellar artery. (a, b) Two adjacent transverse 3D CISS MR images (12.25/5.9, 70° flip angle) show that the superior cerebellar artery (short arrow) has compressed the REZ of the right trigeminal nerve (long arrow) at the medial site. (c, d) Reformatted (c) coronal and (d) sagittal 3D CISS MR images (12.25/5.9, 70° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (e, f) Two adjacent transverse MR angiographic images (39/6.5, 20° flip angle) show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (g, h) Reformatted (g) coronal and (h) sagittal MR angiographic images (39/6.5, 20° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site.
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Figure 3b. Images in a 63-year-old man with trigeminal neuralgia, with NVC caused by the superior cerebellar artery. (a, b) Two adjacent transverse 3D CISS MR images (12.25/5.9, 70° flip angle) show that the superior cerebellar artery (short arrow) has compressed the REZ of the right trigeminal nerve (long arrow) at the medial site. (c, d) Reformatted (c) coronal and (d) sagittal 3D CISS MR images (12.25/5.9, 70° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (e, f) Two adjacent transverse MR angiographic images (39/6.5, 20° flip angle) show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (g, h) Reformatted (g) coronal and (h) sagittal MR angiographic images (39/6.5, 20° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site.
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Figure 3c. Images in a 63-year-old man with trigeminal neuralgia, with NVC caused by the superior cerebellar artery. (a, b) Two adjacent transverse 3D CISS MR images (12.25/5.9, 70° flip angle) show that the superior cerebellar artery (short arrow) has compressed the REZ of the right trigeminal nerve (long arrow) at the medial site. (c, d) Reformatted (c) coronal and (d) sagittal 3D CISS MR images (12.25/5.9, 70° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (e, f) Two adjacent transverse MR angiographic images (39/6.5, 20° flip angle) show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (g, h) Reformatted (g) coronal and (h) sagittal MR angiographic images (39/6.5, 20° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site.
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Figure 3d. Images in a 63-year-old man with trigeminal neuralgia, with NVC caused by the superior cerebellar artery. (a, b) Two adjacent transverse 3D CISS MR images (12.25/5.9, 70° flip angle) show that the superior cerebellar artery (short arrow) has compressed the REZ of the right trigeminal nerve (long arrow) at the medial site. (c, d) Reformatted (c) coronal and (d) sagittal 3D CISS MR images (12.25/5.9, 70° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (e, f) Two adjacent transverse MR angiographic images (39/6.5, 20° flip angle) show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (g, h) Reformatted (g) coronal and (h) sagittal MR angiographic images (39/6.5, 20° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site.
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Figure 3e. Images in a 63-year-old man with trigeminal neuralgia, with NVC caused by the superior cerebellar artery. (a, b) Two adjacent transverse 3D CISS MR images (12.25/5.9, 70° flip angle) show that the superior cerebellar artery (short arrow) has compressed the REZ of the right trigeminal nerve (long arrow) at the medial site. (c, d) Reformatted (c) coronal and (d) sagittal 3D CISS MR images (12.25/5.9, 70° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (e, f) Two adjacent transverse MR angiographic images (39/6.5, 20° flip angle) show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (g, h) Reformatted (g) coronal and (h) sagittal MR angiographic images (39/6.5, 20° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site.
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Figure 3f. Images in a 63-year-old man with trigeminal neuralgia, with NVC caused by the superior cerebellar artery. (a, b) Two adjacent transverse 3D CISS MR images (12.25/5.9, 70° flip angle) show that the superior cerebellar artery (short arrow) has compressed the REZ of the right trigeminal nerve (long arrow) at the medial site. (c, d) Reformatted (c) coronal and (d) sagittal 3D CISS MR images (12.25/5.9, 70° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (e, f) Two adjacent transverse MR angiographic images (39/6.5, 20° flip angle) show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (g, h) Reformatted (g) coronal and (h) sagittal MR angiographic images (39/6.5, 20° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site.
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Figure 3g. Images in a 63-year-old man with trigeminal neuralgia, with NVC caused by the superior cerebellar artery. (a, b) Two adjacent transverse 3D CISS MR images (12.25/5.9, 70° flip angle) show that the superior cerebellar artery (short arrow) has compressed the REZ of the right trigeminal nerve (long arrow) at the medial site. (c, d) Reformatted (c) coronal and (d) sagittal 3D CISS MR images (12.25/5.9, 70° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (e, f) Two adjacent transverse MR angiographic images (39/6.5, 20° flip angle) show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (g, h) Reformatted (g) coronal and (h) sagittal MR angiographic images (39/6.5, 20° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site.
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Figure 3h. Images in a 63-year-old man with trigeminal neuralgia, with NVC caused by the superior cerebellar artery. (a, b) Two adjacent transverse 3D CISS MR images (12.25/5.9, 70° flip angle) show that the superior cerebellar artery (short arrow) has compressed the REZ of the right trigeminal nerve (long arrow) at the medial site. (c, d) Reformatted (c) coronal and (d) sagittal 3D CISS MR images (12.25/5.9, 70° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (e, f) Two adjacent transverse MR angiographic images (39/6.5, 20° flip angle) show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site. (g, h) Reformatted (g) coronal and (h) sagittal MR angiographic images (39/6.5, 20° flip angle) also show that the superior cerebellar artery (short arrow) has compressed the right trigeminal nerve (long arrow) at the medial site.
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Figure 4a. Images in a 55-year-old woman with trigeminal neuralgia, with NVC caused by both the vein and anterior inferior cerebellar artery. (a) Transverse 3D CISS MR image (12.25/5.9, 70° flip angle) shows that both the vein (curved arrow) and the anterior inferior cerebellar artery (short straight arrow) have compressed the left trigeminal nerve (long straight arrow) at the REZ. This finding was confirmed at surgery. (b) Transverse MR angiographic image (39/6.5, 20° flip angle) does not depict the vein, although it shows the anterior inferior cerebellar artery (short arrow) that has compressed the REZ of the left trigeminal nerve (long arrow). This was insufficient information at surgery.
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Figure 4b. Images in a 55-year-old woman with trigeminal neuralgia, with NVC caused by both the vein and anterior inferior cerebellar artery. (a) Transverse 3D CISS MR image (12.25/5.9, 70° flip angle) shows that both the vein (curved arrow) and the anterior inferior cerebellar artery (short straight arrow) have compressed the left trigeminal nerve (long straight arrow) at the REZ. This finding was confirmed at surgery. (b) Transverse MR angiographic image (39/6.5, 20° flip angle) does not depict the vein, although it shows the anterior inferior cerebellar artery (short arrow) that has compressed the REZ of the left trigeminal nerve (long arrow). This was insufficient information at surgery.
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Therefore, it was confirmed that 3D CISS images provided more sufficient information for surgical intervention in patients with trigeminal neuralgia than did MR angiography, and the findings of the 3D CISS images were identical to the surgical findings in patients who underwent microvascular decompression surgery.
Interobserver agreement for detection of vascular contact was excellent or good for both techniques. The value for 3D CISS imaging (0.827) was larger than that for MR angiography (0.744), although this difference was not statistically significant (P = .161, paired t test). Intraobserver agreement was also excellent or good for both techniques. The respective values for observer 1 were 0.823 and 0.713 at 3D CISS imaging and MR angiography (P > .05, 95% CI), and the respective values for observer 2 were 0.824 and 0.725 (P > .05, 95% CI).
Comparison of Neuralgic Manifestation with NVC Site
All MPR images demonstrated the neurovascular relationship. Figure 3 shows MPRs in a typical case, including coronal and sagittal reformatted images. This case was in a patient who had symptoms in the region of the second branch of the trigeminal nerve, and it was subsequently determined that the superior cerebellar artery had compressed the medial site of the nerve at the REZ. Table 3 shows the compressed site of the NVC on the MR images and the clinically manifested region of the branches of the trigeminal nerve. On the basis of the results in Table 3, the position of the blood vessel that compressed the nerve was reclassified into medial and lateral sites (Table 4). Patients in whom the vessels compressed the nerve only at either the cranial or the caudal site were excluded in Table 4. A statistically significant difference was observed between the NVC site and the clinically manifested symptoms in the branches of the trigeminal nerve (P < .001, 2 test). Sixteen (89%) of 18 patients with symptoms related to the maxillary division (V2) had their NVC at the medial site of the REZ. Sixteen (76%) of 21 patients with symptoms related to the mandibular division (V3) had their NVC at the lateral site of the REZ.
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TABLE 3. Compressed Sites of the NVC at MR Imaging and Clinically Manifested Regions of Branches of the Trigeminal Nerve
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TABLE 4. Clinically Manifested Regions of Branches of the Trigeminal Nerve and the Reclassified Compressed Sites at MR Imaging
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These data demonstrated a close relationship between the region of neuralgic manifestation and the site of trigeminal nerve compression at the REZ.
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DISCUSSION
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Our data demonstrate that 3D CISS imaging with MPR is considerably useful in the detection and evaluation of NVC in patients with trigeminal neuralgia, compared with MR angiography. The trigeminal nerve and the arteries were identified on both 3D CISS and MR angiographic images for both the pathologic and normal sides, but the veins were only identifiable on the 3D CISS images. It has been reported that NVC caused by the arteries could be evaluated by using the source images of MR angiography, including 3D fast imaging with steady-state precession or 3D spoiled gradient-recalled acquisition in the steady state (4–7). Since an artery with a fast blood flow is shown as a structure of high signal intensity and a nerve is shown as a structure of intermediate signal intensity, the responsible artery could be identified by using MR angiography. At MR angiography, however, the contrast resolution between the cerebrospinal fluid and the nerve is somewhat unclear (13). Furthermore, the depiction of the vein is impossible with MR angiography because of the slow blood flow in the vein.
In this regard, our results demonstrate that 3D CISS images provide high spatial resolution and excellent contrast resolution between the cerebrospinal fluid and the nerve, compared with MR angiography. Because vascular compression can be demonstrated only when the vascular structures and nerves are well visualized simultaneously, both the spatial and contrast resolution need to be of the best quality. Furthermore, 3D CISS images did clearly demonstrate the veins that were responsible for the NVC in trigeminal neuralgia, although MR angiography could not depict these veins. Demonstration of venous contact is markedly important for treatment of patients with trigeminal neuralgia, because venous compression is an important predictor of eventual recurrence of trigeminal neuralgia after microvascular decompression surgery (2).
It is true that contrast between the artery and the nerve was greater in MR angiography than in 3D CISS imaging, but 3D CISS imaging could clearly depict the veins that MR angiography could not depict. On 3D CISS images, the arteries were identified by tracing the vessels to the origin in the basilar artery and the veins were identified by tracing the vessels to a larger vein. The trigeminal nerve was identified on the basis of its course from the pons to the trigeminal cavity (Meckel cavity). Thus, the nerve and vessels (including the artery and vein) were distinguishable on 3D CISS images.
Therefore, it may be good to use MR angiography for the identification of the responsible artery because it depicts the artery that has a fast blood flow. However, we believe that it is necessary in patients with trigeminal neuralgia to add 3D CISS imaging with MPR for a complete evaluation of the neurovascular relationships, including both the artery and the vein.
Furthermore, our data demonstrate a close relationship between the region of neuralgic manifestation, where a corresponding division of the trigeminal nerve is distributed, and the site of vascular compression in the trigeminal nerve. It has been reported that the first branch fibers of the trigeminal nerve at the REZ are distributed in one-third of the cranial area; the second branch fibers, in one-third of the middle area; and the third branch fibers, in one-third of the caudal area (14). As shown in Figure 5, the nerve fibers of the second branch are widely distributed medially and those of the third branch are widely distributed laterally (15). To our knowledge, there is no report of MR imaging in which the relationship between clinical symptoms related to the trigeminal branches and the site of compression of the nerve at the REZ was evaluated. In the present study, patients with symptoms related to the maxillary division tended to have their NVC at the medial site of the REZ, and patients with symptoms related to the mandibular division tended to have their NVC at the lateral site of the REZ. Our results appear to reflect an anatomic feature of the trigeminal nerve fiber array at the REZ. In the previous report in which the compression position of the nerve fibers was electrophysiologically evaluated in four patients with trigeminal neuralgia, all of the nerve fiber areas that are related to the clinical symptoms were confirmed to be compressed at surgery in all patients (9). Therefore, our data demonstrate that high-spatial-resolution 3D CISS imaging coupled with MPR noninvasively reveals a detailed topographic anatomic relationship of the nerve and the blood vessel in patients with trigeminal neuralgia and provides useful information for neurosurgeons to perform surgical intervention.
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Figure 5. Schematic of the trigeminal nerve fiber array at the REZ. The nerve fibers of the second branch (V2) are widely distributed medially, those of the third branch (V3) are widely distributed laterally, and those of the first branch (V1) are distributed cranially.
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The possible limitation of our study may be that we did not use gadopentetate dimeglumine in MR angiography. Other investigators have shown that MR angiography can help separate the arteries from veins, provided MR angiography is performed before and after intravenous contrast enhancement (16). However, we believe that the high spatial resolution and excellent contrast resolution, which 3D CISS imaging provides, are important for a complete evaluation of the neurovascular relationships in patients with trigeminal neuralgia. Another limitation was that we did not use isotropic resolution. This was owing to limitations of our MR system, although this degrades MPR images significantly. 3D CISS imaging and MR angiography had inherently different spatial resolutions, and this was the reason why 3D CISS imaging had higher spatial resolution than did MR angiography.
In conclusion, 3D CISS MR imaging with MPR is useful in the detection of NVC in patients with trigeminal neuralgia, compared with MR angiography. 3D CISS imaging offers high spatial resolution and excellent contrast resolution and depicts both the artery and the vein responsible for the NVC. Furthermore, a close relationship was found between the region of neuralgic manifestation, where corresponding trigeminal branch fibers are distributed, and the site of the vascular compression in the trigeminal nerve.
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FOOTNOTES
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Abbreviations: CISS = constructive interference in steady state,
MPR = multiplanar reconstruction,
NVC = neurovascular compression,
REZ = root entry zone,
3D = three-dimensional
Author contributions: Guarantors of integrity of entire study, N.Y., T.S.; study concepts, N.Y., H.A., I.Y., T.N.; study design, N.Y., I.Y.; literature research, N.Y., I.Y.; clinical studies, N.Y., A.T., T.K., E.H., S.N.; data acquisition, N.Y., I.Y.; data analysis/interpretation, N.Y., I.Y., T.S.; statistical analysis, N.Y.; manuscript preparation and editing, N.Y.; manuscript definition of intellectual content, N.Y., S.T.; manuscript revision/review, I.Y., S.T.; manuscript final version approval, all authors.
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TOP
ABSTRACT
INTRODUCTION
) as a high-signal-intensity structure, thus providing high contrast resolution between the structures. (b) Transverse MR angiographic image (39/6.5, 20° flip angle) depicts the artery (short arrow) as a high-signal-intensity structure, the nerve (long arrows) as an intermediate-signal-intensity structure, and the cerebrospinal fluid (
) as a low-signal-intensity structure.