|Year : 2020 | Volume
| Issue : 1 | Page : 31-36
Morphometric evaluation of trigeminal nerve and meckel cave with 3.0 magnetic resonance imaging
Selva Sen1, Sabriye Sennur Bilgin2, Alper Atasever1
1 Department of Anatomy, School of Medicine, Istanbul Medipol Universty, Istanbul, Turkey
2 Department of Radiology, Istanbul Medipol Universty Hospital, Istanbul, Turkey
|Date of Submission||12-Apr-2019|
|Date of Acceptance||05-Feb-2020|
|Date of Web Publication||11-Apr-2020|
Ms. Selva Sen
Department of Anatomy, School of Medicine, İstanbul Medipol University, Kavacık Kavşağı, Atatürk Caddesi No. 19 34000, Kavacık, Beykoz İstanbul
Source of Support: None, Conflict of Interest: None
Introduction: This study aimed to investigate morphometric features of the trigeminal nerve in healthy people on magnetic resonance images. The alterations in the size of the trigeminal nerve in the cisternal region along with aging and asymmetry between the right and left trigeminal nerves were also assessed. The knowledge of normal morphometric properties of the trigeminal nerve may be useful in evaluating patients having trigeminal neuralgia. Material and Methods: This retrospective study included 120 (62 males, 58 female) healthy individuals over 20 years old who had no previous or current cranial pathology. According to age ranges, individuals were evaluated in four groups as 20–29 years, 30–39 years, 40–49 years, and 50 years and older. Besides the long- and short-axis lengths of the trigeminal nerve, long- and short-axis lengths of Meckel cave, as well as the trigeminal-pons angle, were measured using three-dimensional balance fast-field echo sequence with 3T magnetic resonance imaging on the right and left sides.Results: It was observed that the lengths of trigeminal nerve were shorter on the right side in comparison to the left side (mean long axis 0,79 ± 0,20 cm on the right, 0,86 ± 0,28 cm on the left, P <0,05; and mean short-axis: 0,36 ± 0,10 cm on the right and 0,41 ± 0,17 cm on the left, P <0,05). Moreover, in males, the long-axis length of the Meckel cave was higher on both the right and left sides compared to females (P < 0.05). Discussion and Conclusion: This study shows that, both the width and length of the right trigeminal nerve are shorter compared to left in healthily population. In addition, long axis of Meckel Cave, that is posterolateral to anteromedial extend, was longer on both the right and left sides in males compared to females.Results: It was observed that the long axis (mean: 0.79 ± 0.20 cm on the right, 0.86 ± 0.28 cm on the left, P < 0.05) and short axis (mean: 0.36 ± 0.10 cm on the right and 0.41 ± 0.17 cm, P < 0.05). Moreover, in males, the long-axis length of the Meckel cave was higher on both the right and left sides compared to females (P < 0.05). Conclusion: This study shows that, both the width and length of the right trigeminal nerve are shorter compared to left in healthily population. In addition, long axis of Meckel Cave, that is posterolateral to anteromedial extend, was longer on both the right and left sides in males compared to females.
Keywords: Aging, morphometry, trigeminal ganglion, trigeminal nerve, trigeminal neuralgia
|How to cite this article:|
Sen S, Bilgin SS, Atasever A. Morphometric evaluation of trigeminal nerve and meckel cave with 3.0 magnetic resonance imaging. J Anat Soc India 2020;69:31-6
|How to cite this URL:|
Sen S, Bilgin SS, Atasever A. Morphometric evaluation of trigeminal nerve and meckel cave with 3.0 magnetic resonance imaging. J Anat Soc India [serial online] 2020 [cited 2023 Feb 4];69:31-6. Available from: https://www.jasi.org.in/text.asp?2020/69/1/31/282301
| Introduction|| |
The trigeminal nerve is the thickest cranial nerve which provides sensitive innervation of the head and face region, as well as the motor innervation of the masticatory muscles besides some other small muscles.
The trigeminal nerve emerges from the anterolateral surface of the pons with two roots: the smaller being one is the motor and the bigger one is the sensory root. These two roots penetrate the pontocerebellar cistern (prepontine cistern), a large cavity containing cerebrospinal fluid, and extend to the apex of the petrous part of the temporal bone. At the apex of the petrous part, it enters the Meckel cave which is a sac formed by dura mater. In this sac, there is the trigeminal ganglion, where the cell bodies of the sensory axons in the trigeminal nerve are located. Distal to the ganglion, the three main branches of the trigeminal nerve arise: ophthalmic nerve, maxillary nerve, and mandibular nerve. Spreading to the head and face, these branches carry pain-temperature, pressure-touch, and vibration senses to the central nervous system. Motor root also enters the Meckel cave and joins the mandibular branch as it passes through the oval foramen.,
Magnetic resonance imaging (MRI) is a noninvasive method to image the intracranial portion of the trigeminal nerve., Daniels et al. demonstrated that the magnetic resonance (MR) images of the intracranial portion of the trigeminal nerve matched the photos obtained from the anatomical sections of the same cadaver and concluded that the MRI images could be used to evaluate the cisternal part of the trigeminal nerve.
Lesions involving the cisternal segment of the trigeminal nerve typically present with trigeminal neuralgia (TN). TN is more common in females and on the right side. Incidence increases with age and usually observed after the fifth decade., Although theories exist, the exact mechanism (s) underlying the idiopathic (primary) TN is not yet understood. Previous studies have described atrophy and size differences of the affected trigeminal nerve relative to the unaffected side or control group.,,, The nerve may also be impinged upon by various lesions involving this area. The knowledge of the normal morphometric properties of the trigeminal nerve may be useful for better evaluation of such pathological conditions.
There are only a few studies evaluated the length of trigeminal nerves and branches on cadavers; however, the information obtained from the cadaver may differ from that of a living human due to the applied fixation and manipulation methods.,, To our knowledge, there is no previous study reporting the morphometric characteristics of the cisternal portion of the trigeminal nerve in healthy individuals using MRI, as well as comparison of trigeminal nerve morphometry in terms of lateralization, age, and gender.
This study aimed to investigate morphometric features of the trigeminal nerve in healthy people on MR images. We have also assessed alterations in the size of the trigeminal nerve in the cisternal region along with aging and evaluate the asymmetry between the right and left trigeminal nerves.
| Material and Methods|| |
This study was conducted in the Istanbul Medipol Universty Hospital Radiology Department with the approval of the Ethics Committee of Medipol University. In this retrospective study, we included MR images of 120 (62 male, 58 female) individuals who were admitted with various complaints but proven to have no intracranial pathology and no history of TN. Cases were divided into four age groups: 20–29 years, 30–39 years, 40–49 years, and 50 years and older.
All MR examinations were performed on a whole-body 3T unit (Intera Achieva; Philips, Best, the Netherlands) using an 8-channel sensitivity-encoding head coil. Three-dimensional balance fast-feld echo sequences were performed in addition to the routine Magnetic Rezonans sequences. All images were transferred to Philips IntelliSpace workstation, sagittal and coronal reconstruction was utilized on the workstation, For standardization, the measurements were carried out by a single person with the supervision of an experienced neuroradiologist by three repetitions, which were then averaged.
The following anatomical parameters of the trigeminal nerve were measured on both sides:
- The length of the long axis of the trigeminal nerve in the cisternal region (trigeminal long axis): In axial images, the length of the trigeminal nerve between its origins from the pons to the entrance of the Meckel cavity was measured in the prepontine cistern [Figure 1]A
- The length of the short axis of the trigeminal nerve in the cisternal region (trigeminal short axis): The thickness of the mid-point of the trigeminal long-axis length was measured [Figure 1]B
- The length of the long axis of the Meckel cave (Meckel long axis): The longest distance of the Meckel cave in axial images was measured [Figure 2]A
- The length of the short axis of the Meckel cave (Meckel short axis): The thickness at the mid-point of the Meckel long axis was measured [Figure 2]B
- Trigeminal-pons angle (pons angle): The angle between the medial margin of the trigeminal nerve and the anterior surface of the pons at the root entry zone was measured on axial images [Figure 3].
Statistical analyses were performed using the SPSS 15.0 for Windows statistical software (SPSS Inc., Chicago, IL, USA). The normal distribution suitability of the variables was tested with one-sample Kolmogorov–Smirnov test. Variables with normal distribution were shown by mean and standard error averages (mean ± standard deviation [SD]). Chi-square, Student's t independent, one-way analysis of variance (ANOVA), and correlation analysis (Pearson and Spearman) tests were used for statistical analysis. The homogeneity of the variances was tested with the Levene test. Two-tailed post hoc comparisons were performed using Tukey's honestly significant difference test for groups with significant ANOVA outcome. For statistical significance, P < 0.05 was accepted.
| Results|| |
The long and short axes of the trigeminal nerve, trigeminal diameter, long and short axes at the Meckel cave, and pons angle were measured on both sides. Measurements of the right and left sides, as well as gender and age group differences, were compared.
The mean values and SDs of the measurements are shown in [Table 1] according to gender and laterality. Among genders, none of the measurements showed any statistically significant difference except the Meckel long axis. The long axis of the Meckel cave was higher in males on both the right and left sides. When the right- and left-side measurements are compared in all cases, trigeminal long and the short axes were longer on the left side. Trigeminal diameter, as well as the Meckel long and short-axis measurements of the right and left sides, showed no significant difference.
|Table 1: The mean values and standard deviations of measurements by gender and laterality|
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Comparisons of measurements among age groups did not show any significant difference [Table 2].
| Discussion|| |
The trigeminal nerve is the thickest cranial nerve that receives general sensation from the head region. It also innerves muscles of mastication and some small muscles in the head region. Changes in the structure of the trigeminal nerve may cause clinical problems such as neuralgia and sensory and motor loss. Knowing the morphometric characteristics of the trigeminal nerve and its ganglion in MR images is important in the evaluation of patients with problems involving the trigeminal nerve and its ganglion.
Histologic studies on the anatomy of the trigeminal nerve mostly deal with the axon count and lengths of its branches. Songur et al. studied tissue samples of the intracranial portion of trigeminal nerves obtained from forty cadavers. The mean length of the trigeminal nerve was calculated as 25.32 ± 2.90 mm and trigeminal ganglion width as 13.5 ± 1.2 mm. Ajayi et al. have investigated the anatomy of the nerve. They calculated the mean length and width of trigeminal ganglion as 18.3 mm and 7.9 mm, respectively. Ziyal et al. studied six trigeminal nerves obtained from cadavers and reported the length of the trigeminal nerve ranging from 28 to 31 mm. These values are considerably lower than the values obtained in our study, which we think might be due to the used chemicals in cadaver studies and the differences in the measurement method.
Yıldız et al. studied the volumes of the cisternal portions of trigeminal nerves on both sides in 100 healthy individuals with MRI and compared the differences between genders and the differences between the right and left sides. They reported no significant difference between the left and right trigeminal nerve volumes and also no difference among genders. However, volume differences between the left and right sides in the healthy individuals were low (4.6% ±3.6%) compared to reported differences in TN patients. They stated that the difference in trigeminal nerve volume between normal and symptomatic sides might be an important finding in suspected cases of TN, though it is not clear whether trigeminal nerve atrophy is a cause or consequence of TN.
Taarnhøj and Olivecrona suggest that the elongation of the brainstem with atrophy in the elderly leads to stretching of the trigeminal nerve., Kakizawa et al. evaluated 110 healthy individuals and found that the long axis of the trigeminal nerve in the cisternal segment at the sagittal oblique plane MRI was significantly longer in healthy elderly individuals and suggested that this was due to brain stem atrophy.
Rasche et al. suggested that cisternal volume should be higher due to brainstem atrophy in the elderly, and therefore, the position of the superior cerebellar artery is changed as the cerebellar tentorium is displaced caudally. This displacement may increase trigeminal nerve compression by blood vessels. With the above reasoning, they suggested that the length of the trigeminal nerve in the cisternal segment and the angle of emergence from the pons might be important in TN etiology. In our study, there was no significant statistical difference in the variance analysis of long- and short-axis length of the trigeminal nerve, Meckel cave, and trigeminal-pons angle among the age groups. We could not find any other studies dealing with the in-depth analysis of the morphological characteristics of the trigeminal nerve with aging.
In our study, the average length of the long axis of the trigeminal nerve was 0.79 ± 0.20 cm on the right and 0.86 ± 0.28 cm on the left side, and the average length of the short axis was 0.36 ± 0.10 cm on the right and 0.41 ± 0.17 cm on the left side. The trigeminal long-axis length values were little higher than the findings of Parise et al. (6.33 ± 2.19 mm) and similar with those of Cheng et al. (8.3 ± 2.2 mm) with the measurements obtained from TN patients., Ha et al. measured the short-axis length of 3.46 mm in 30 healthy individuals. Ha et al. reported that there was no significant difference in the length of the short and long axes of the trigeminal nerve between the right and left sides in healthy individuals and only in TN patients between the affected and unaffected sides. Other than this study, we could not found any studies assessing the trigeminal short-axis length in the literature. Interestingly, in our study, both short- and long-axis lengths were significantly shorter on the right side, where TN was frequently seen.
Park et al. analyzed the relationship between the morphometric characteristics of the trigeminal nerve and pontine cisternal volume on TN patients. On the affected side, they observed the smaller the pontine cisternal volume is, the shorter is the trigeminal nerve becomes. Smaller pontine cistern and shorter trigeminal nerve might be more prone to be compressed by vessels.
Cheng et al. measured the length of the cisternal segment of the trigeminal nerve in 60 TN patients and 30 healthy individuals. They observed that there were no significant difference between the right and left sides in healthy people and no difference also between the affected and unaffected sides in TN patients.
Parise et al. suggested that anatomic factors such as the volume of the posterior cranial fossa may affect the proximity between the vascular structures and the trigeminal nerve. They measured the volume of the cisternal region and the length of the trigeminal nerve in 18 healthy individuals and 26 TN patients. They reported that in the TN group, the cisternal length of the trigeminal nerve was shorter on the affected side. Furthermore, the cisternal length of the trigeminal nerve in all TN patients was shorter than healthy individuals, though the difference was not statistically significant. Shorter cisternal region and the length of the nerve may predispose to compression in terms of closer proximity with the surrounding structures. However, if the brainstem atrophy and caudal sagging occur with age, these findings are inconsistent, as one would expect that the length of the trigeminal nerve should be greater on the affected side.
Bjerrum and Thornval, et al. suggested that mechanical factors altering the shape of the skull could cause neuralgia by stretching the trigeminal nerve. Gardner stated that asymmetrically petrous apex is higher on one side, causing trigeminal nerve stretching and resulting TN. He observed that elevation of the petrous apex is more common on the right side even in healthy people. Smith and Mumford suggested that the angle of the petrous part of the temporal bone was considerably variable and it might have a role in the etiology of TN. Bjerrum and Thornval reported that petrous apex was higher on the affected side in TN cases. Our findings are inconsistent as one would expect that the length of the trigeminal nerve should be greater on the right side due to the elevation of the petrous apex, where TN was frequently seen. Rothman and Wepsic determined that a high position of the petrous apex was a poor risk factor for TN and did not correlate with the greater presence of neuralgia on the right side. Brinzeu et al. measured the angle of the petrous ridge and angle of the nerve on passing over the ridge in 42 TN patients. They found that the bony angle of the petrous ridge was more acute on the affected side in TN patients and also significantly more acute compared to the controls. Hence, the trigeminal nerve may be stretched by the petrous bone in TN.
Ha et al. suggested that the decrease of pons angle on the affected side in patients with TN may increase microvascular compression at the medial margin of the trigeminal nerve. In their study, evaluating 30 TN patients, they found the mean pons angle as 40.17° on the affected side, 51.39° on the unaffected side, and 52.02° in healthy individuals. There was no difference in the right and left sides in healthy individuals.
Cheng et al. measured the mean pons angle as 42.4° on the affected side, 47.6° on the nonaffected side, and 46.0° in the control group. Cheng et al. and Ha et al. found that the pons angle on the affected side is smaller than the nonaffected side in patients with TN. Therefore, they suggested that a small angle may increase the possibility of neurovascular compression.,
In our study, the mean trigeminal-pons angle was measured as 39.13 °±13.93° on the right side and 34.92° ±11.86° o n the left side. The mean trigeminal-pons angle values were found to be higher on the right side, but this difference was not statistically significant. Furthermore, there was no statistically significant difference between gender and age groups. The pons angle values in our study were found to be less than those mentioned above, which might be due to racial differences.
Rasche et al. suggested that prepontine cistern and Meckel cave should be smaller in patients with TN as a consequence of the more caudal displacement of the cerebellar tentorium.
Ha et al. measured Meckel cave volume on axial MRI and found no significant difference between healthy individuals and TN patients.
In our study, the long axis of the Meckel cave was found to be longer on both sides in males than females. This might be due to the bigger skull size in males. The short axis of the Meckel cave did not show any difference among all compared groups.
| Conclusion|| |
We have not found any change in the morphometric properties of the trigeminal nerve and the Meckel cave with aging. Short- and long-axis lengths of the trigeminal nerve were shorter on the right side, and the right pons angle was larger than the left side. It needs further studies to evaluate whether the shorter length and larger pons angle of the trigeminal nerve play a role in the etiology of TN and more frequent occurrence on the right side.
In this study, only healthy individuals were evaluated. For more accurate investigations of the etiology of TN, our findings should be compared with MR images obtained from TN patients.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]