Anatomic Study And Clinical Significance Of Dorsal Meningovertebral Ligaments Of The Thoracic Dura Mater

Normal ligamentous structures are present between the spinal dura mater and the surrounding wall of the spinal canal and were called meningovertebral ligaments in the 40th edition of Gray’s Anatomy. These ligaments connect the dura to the posterior longitudinal ligament or the dorsal spinal surface in the front and to the ligamentum flavum or the lamina in the rear. Some scholars also referred to these structures as Hofmann ligaments. These ligaments have been reported and described but have ye to become well known amongst general populations. In recent years, the clinical significance of meningovertebral ligaments, especially for spine surgery, has gained increased recognition. Based on surgical experience, Solaroglu et al reported that at the L5/S1 level, there is ligament connection between the dura mater and the ligamentum flavum in the posterior, which is referred to as the "ATA" ligament. The authors considered that these ligaments were very important and represented potential risk factors contributing to intraoperative dural laceration. Hence, they proposed that before laminectomy decompression, severing this ligament was a key step to minimizing postoperative cerebrospinal fluid leakage. Likewise, after systematic anatomic study on the dorsal meningovertebral ligaments of the lumbar and cervical dura mater, Shi et al also argued that the meningovertebral ligaments were associated with the dural laceration and epidural hemorrhage occurring during surgeries of the meningovertebral ligaments and the spine. The authors made a similar proposal about preoperative examination and severing of the ligaments to reduce the occurrence of surgical complications. Unfortunately, little effort has been dedicated to studying the dorsal meningovertebral ligaments of the thoracic dura mater. Posterior laminectomy decompression is a common approach for thoracic surgery. However, this surgical approach requires removal of the ligamentum flavum or the lamina; therefore, it may damage the dura mater and cause cerebrospinal fluid leakage, vascular damage and subsequent hemorrhage and even epidural hematoma and may eventually result in severe complications.The incidence of dural injury during spine surgery ranges from 0.6%-17.4%, whereas that of postoperative cerebrospinal fluid leakage ranges from 2.31%-9.37%.The dural injury in addition to the primary damage, the first of all is iatrogenic, especially in the process of operation, give priority to with clamp injury or laceration. Thoracic posterior vertebral canal decompression is common thoracic surgery, because the operation to remove vertebral plate and yellow ligament, cerebrospinal fluid leakage, damage that might damage the epidural vascular hemorrhage caused by epidural hematoma, etc., and even cause serious complications. The dural injury if handled incorrectly,this complication is associated with the risks of poor wound healing, meningitis, andpseudomeningocele. How to prevent dural tear and its complications is one of the spine surgeon must face the problem. Dural injury located in the dorsal lateral accounted for 74.6 percent according to some literatures.Performer rough or the anatomical structure of operation such as unclear all can lead to iatrogenic injury of the catheter, cerebrospinal fluid leakage. Therefore, in order to prevent the occurrence of damage to cerebrospinal fluid leakage of stiff backbone film, in the recognition of anatomical structure and fine operation is particularly important.According to a review by Newell, Meckel (1817) and Humphry (1858) first reported the fiber bundles between the dura mater and the spinal canal wall, before these fiber strips were described in detail by Trolard (1888) and Hofmann(1889). In 1986, Blomberg employed a modified endoscope, which he termed epiduroscopy, to study the lumbar epidural space of some autopsy subjects and revealed that a dorsal connective tissue band in the midline of the epidural space connected the dura mater and the flaval ligaments. Geers et al studied the lumbar spines of aborted fetuses and noted the presence of meningovertebral ligaments. Histological examination revealed that the meningovertebral ligaments were mainly composed of dense connective tissue mixed with elastic fibers and that the ligaments were surrounded by fat lobules. Special immunohistochemical methods demonstrated that the ligaments were principally composed of type I collagen fibers. Similarly, our histological study also showed that the meningovertebral ligaments mainly consisted of collagen fibers with low elastic fiber contents. By observing the meningovertebral ligaments of the spinal epidural space of fetuses, it was revealed that these ligaments shared similar histological features with the corresponding ligaments in adults. As such, these ligaments are congenially formed, not postnatally acquired.We believe that the current for dorsal meningovertebral ligaments of the thoracic dura mater research still exist the following problems:(1) Dura mater ventral and lateral connection structure in the lumbosacral epidural space were identified well at home and abroad, but there is rare reports for them in dorsal meningovertebral ligaments of the thoracic dura mater.(2) The dorsal meningovertebral ligaments in the cervical and lumbosacral epidural space of anatomic study more, but up to now, there was little effort has been dedicated to anatomic studying the dorsal meningovertebral ligaments of the thoracic dura mater.(3) The clinical significance of the ligaments of the dura mater around the spinal canal wall,, especially in the back of the thoracic epidural connection structure is unclear and related damage caused by these ligments are not yet clear.To solve the above problem, we performed depth and detailed study to fully reveal these ligaments’ traits and clarify their clinical significance in the thoracic spine surgery. Expect this structure to add new knowledge to these structures, provide clinicians with more detailed anatomical information in order to reduce relate.This study includes the two parts as follws:Chapter 1 The observation of the dorsal meningovertebral ligaments in the thoracic dura mater performed by naked eye and surgical microscopeObjective:Fully reveal the department behind the epidural membrane vertebral ligaments of the character and the role of epidural injury in the context of the thoracic surgery, provide a more detailed anatomic data for clinical doctor, at the same time provide the basis for further research.Methods:Eighteen thoracic specimens of normal adult autopsy subjects (10 males,8 females,37-75 years old, average 55 years old) that were intact and treated with antiseptic were collected. Regional vascular injections were performed in the cadavers using colored latex. Those specimens displaying thoracic deformities or lesions or having undergone thoracic surgeries were excluded. Routine anatomic preparation was performed to remove the paravertebral muscle. The back side of the thoracic vertebra was divided into 23 segments:T1 lamina, T1-T2 ligamentum flavum (the ligamentum flavum between levels 1 and 2), T2 lamina, T2-T3 ligamentum flavum, T3 lamina, T3-T4 ligamentum flavum, T4 lamina, T4-T5 ligamentum flavum, T5 lamina, T5-T6 ligamentum flavum, T6 lamina, T6-T7 ligamentum flavum, T7 lamina, T7-T8 ligamentum flavum, T8 lamina, T8-T9 ligamentum flavum, T9 lamina, T9-T10 ligamentum flavum, T10 lamina, T10-T11 ligamentum flavum, T11 lamina, and T11-T12 ligamentum flavum. Each vertebral body was removed after a power saw was used to break it at the two bilateral pedicles. Care was taken to avoid damaging the connecting structure between the dura mater and the spinal posterior wall. The rear dural space was fully exposed before epidural fat and other tissues were microscopically removed between the dura mater and the spinal posterior wall. Subsequently, locations, numbers, morphologies, orientations and attachment sites of the meningovertebral ligaments between the dura mater and spinal posterior wall were monitored, and images (including microscopic images) were captured. Under a surgical microscope, the dimensions (length, diameter/width, and thickness) of the ligaments were measured using a vernier caliper (precision of approximately 0.01 mm). Statistical analysis on the measurements was performed using IBM SPSS Statistics 20.0 (SPSS Inc., Chicago, IL, USA). The measurement data were expressed in the form of "±(min～max)", and the enumeration data were tested using the chi-square test.Results:①MMeningovertebral ligaments were noted on the dorsal dural sides of all 18 specimens of thoracic vertebra. Overall, the dorsal meningovertebral ligaments of the thoracic dura mater were more likely to emerge on the ligamentum flavum than on the lamina, as evidenced by the appearance rates of 53.6% on the former surface and 46.4% on the latter (5.697, P=0.017). The meningovertebral ligaments displayed relatively even distribution along the thoracic vertebrae, especially along its upper levels (T1-T7). Along the lower thoracic vertebrae (T7-T12), the appearance rate of the meningovertebral ligaments exhibited an upward trend of enhancement. ②The attachment sites of the meningovertebral ligaments to the lamina and the ligamentum flavum were in the median or paramedian positions on the posterior dural sac, with the paramedian positions composed of left and right sides. The median, left paramedian, and right paramedian meningovertebral ligaments accounted for 20.3%, 37.5%, and 42.2%of the total, respectively. A segment accommodating a single ligament bundle was more likely to be present in the upper thoracic levels, whereas one bearing 2 bundles or more was more likely to be found in the lower levels. ③ The ligament morphology could be divided into four types:stripe type (22.3%), cord type (73.1%), Y-shaped type (1.6%), and slice type (3%). There were considerable variations in the dimensions of the ligaments, with lengths ranging from 5.45 mm to 31.11 mm, a maximum width of 2.70 mm, and a maximum thickness of 0.49 mm. ④Typically, a dorsal meningovertebral ligaments of the thoracic dura mater attached to the dura at one end and to the ligamentum flavum or the lamina at the other.As a consequence, most observed ligaments (65.1%) displayed an orientation of "low in the front and high in the rear". However, some ligaments exhibited the opposite pattern of "high in the front and low in the rear", which accounted for 28.3% of observed ligaments. Moreover,6.6% of the ligaments displayed horizontal orientation. The meningovertebral ligaments were tightly associated with the dura. Retrograde dissection revealed that ligament fiber bundles extended to enter the dural posterior wall and became integral parts of the structure. Stretching the bundles with force might cause avulsion to the meningovertebral ligaments along with parts of enthuses, which caused thinning and even laceration of the dural posterior wall. Some meningovertebral ligaments were accompanied by or adjacent to arteries and/or veins. In addition, some ligaments originated from the wall of small arteries and veins in the corresponding entheses of the lamina and ligamentum flavum and became a part of the vascular wall.Conclusion:The ligaments connecting the dura and yellow ligament as well as lamina exist in dorsal of the thoracic. According to the distribution of dorsal meningovertebral ligaments of the thoracic dura mater and anatomical features of the form, it may be for thoracic posterior surgery in the epidural pseudocyst, dural tear and anatomical factors of complications such as epidural blood out advice intraoperative shall be cut off, leading to distinguish and to reduce the related surgical complications.Chapter 2 Histologic study and clinical significance of dorsal meningovertebral ligaments of the thoracic dura materObjective:Understanding meningovertebral histological characteristics and its significance.Methods:Eighteen thoracic specimens of normal adult autopsy subjects (10 males,8 females,37-75 years old, average 55 years old) that were intact and treated with antiseptic were collected. Regional vascular injections were performed in the cadavers using colored latex. Those specimens displaying thoracic deformities or lesions or having undergone thoracic surgeries were excluded. Routine anatomic preparation was performed to remove the paravertebral muscle. The back side of the thoracic vertebra was divided into 23 segments:Tl lamina, T1-T2 ligamentum flavum (the ligamentum flavum between levels 1 and 2), T2 lamina, T2-T3 ligamentum flavum, T3 lamina, T3-T4 ligamentum flavum, T4 lamina, T4-T5 ligamentum flavum, T5 lamina, T5-T6 ligamentum flavum, T6 lamina, T6-T7 ligamentum flavum, T7 lamina, T7-T8 ligamentum flavum, T8 lamina, T8-T9 ligamentum flavum, T9 lamina, T9-T10 ligamentum flavum, T10 lamina, T10-T11 ligamentum flavum, T11 lamina, and T11-T12 ligamentum flavum. Each vertebral body was removed after a power saw was used to break it at the two bilateral pedicles. Care was taken to avoid damaging the connecting structure between the dura mater and the spinal posterior wall. The rear dural space was fully exposed before epidural fat and other tissues were microscopically removed between the dura mater and the spinal posterior wall. Subsequently, locations, numbers, morphologies, orientations and attachment sites of the meningovertebral ligaments between the dura mater and spinal posterior wall were monitored, and images (including microscopic images) were captured. The ligament morphology could be divided into four types:stripe type, cord type, Y-shaped type, and slice type. Specimens were prepared from four types of thoracic meningovertebral ligaments specimen male, female each one, which were subject to regular paraffin embedding, sectioning, hematoxylin and eosin (HE) staining, and Masson trichrome staining before the histological properties were examined under a microscope. Understanding how men and women thoracic meningovertebral structure with indifference, and four types of thoracic meningovertebral structure with indifference, and then take pictures record.Results:①Under a light microscope, HE staining revealed that the meningovertebral ligaments were composed of fibrous connective tissue. Masson trichrome staining, which labels collagen fibers with blue and elastic fibers with red, revealed that the meningovertebral ligaments consisted mostly of collagen fibers and a few elastic fibers.②Men and women meningovertebral ligaments structure of the thoracic has no obvious difference. And four types of the thoracic meningovertebral structure has no significant difference.Conclusion:The meningovertebral ligaments were mainly composed of dense connective tissue mixed with elastic fibers and that the ligaments were surrounded by fat lobules. Special immunohistochemical methods demonstrated that the ligaments were principally composed of type Ⅰ collagen fibers. Similarly, our histological study also showed that the meningovertebral ligaments mainly consisted of collagen fibers with low elastic fiber contents. By observing the meningovertebral ligaments of the spinal epidural space of fetuses, it was revealed that these ligaments shared similar histological features with the corresponding ligaments in adults. As such, these ligaments are congenitally formed, not postnatally acquired.