Anatomy of soft tissues of the spinal canal.

BACKGROUND AND OBJECTIVES: Important issues regarding the spread of solutions in the epidural space and the anatomy of the site of action of spinal and epidural injections are unresolved. However, the detailed anatomy of the spinal canal has been incompletely determined. We therefore examined the microscopic anatomy of the spinal canal soft tissues, including relationships to the canal walls. METHODS: Whole mounts were prepared of decalcified vertebral columns with undisturbed contents from three adult humans. Similar material was prepared from a macaque and baboon immediately on death to control for artifact of tissue change after death. Other tissues examined included nerve root and proximal spinal nerve complex and dorsal epidural fat obtained during surgery. Slides were examined by light microscopy at magnifications of 10-40x. RESULTS: There is no fibrous tissue in the epidural space. The epidural fat is composed of uniform cells enclosed in a fine membrane. The dorsal fat is only attached to the canal wall in the dorsal midline and is often tenuously attached to the dura. The dura is joined to the canal wall only ventrally at the discs. Veins are evident predominantly in the ventral epidural space. Nerve roots are composed of multiple fascicles which disperse as they approach the dorsal root ganglion. An envelope of arachnoid encloses the roots near the site of exit from the dura. CONCLUSIONS: These features of the fat explain its semifluid consistency. Lack of substantial attachments to the dura facilitate movement of the dura relative to the canal wall and allow distribution of injected solution. Fibrous barriers are an unlikely explanation for asymmetric epidural anesthesia, but the midline fat could impede solution spread. Details of nerve-root structure and their envelope of pia-arachnoid membrane may be relevant to anesthetic action.     

Use of polyester urethane (Neuro-Patch) as a dural substitute. Prospective study of 70 cases

Between October 1995 and March 1998, 70 patients were treated with a microporous polyester urethane dura substitute (Neuro-Patch), after brain or spinal surgery. These patients were assessed clinically and radiologicaly 10 days, 6 weeks and 1 year after surgery. Radiological evaluation used CT scan or MRI. All dura substitutes were fixed by continuous suture to the surrounding dura-mater. We studied the handling properties, the incidence of infection and of CSF leakage. Eleven patients underwent craniotomy again. This gave us the opportunity to examine the adhesion to the brain tissue and the integration of the dura substitute. Six sheets underwent histological examination. Our results show good handling properties of the material; 3 infections; 6 out of 9 radiological CSF leakage occurred from infratentorial surgery. During reoperation, no adhesion to the brain tissue or injury to the brain while detaching the dura substitute was noticed. An excellent histological integration was observed: pores of the Neuro-Patch were colonized by fibroblasts synthesizing collagen, and there was no immune or inflammatory reaction, with an actual 4 to 6 years follow-up. A Neuro-Patch can therefore be recommended as a dura substitute to repair spinal or cranial dural defects.     

Cervical peridural calcification as a new complication of dialysis therapy

A 66-year-old man on long-term hemodialysis for chronic renal failure presented with progressing disabilities due to cervical myelopathy. On computerized tomography (CT), bright, dotted curvi-linear bands outlined the cervical spinal dura. At operation, these bands on CT were identified as calcified plaque impregnated in fibrous membrane, constricting the dura and the spinal cord in almost the whole cervical spine. Spinal cord decompression was incomplete by merely enlarging the bony spinal canal but was accomplished by removing the calcification from the dura. A cross-sectional study on CT in a single dialysis unit disclosed that the prevalence of this pathological CT finding was 26%. Plain CT of the cervical spine, focusing on the upper cervical vertebrae in particular, was the most helpful in detecting the lesion. Based on the findings at operation, cervical peridural calcification seemed an adequate term for the lesion. This pathology should be recognized as an important complication of dialysis therapy because it is not unusual and potentially causes cervical myelopathy.     

保存硬脊膜预防椎管内术后粘连的实验研究

28只大白兔随机分为实验和对照2组,均切除L5椎板,造成12mm×5mm的硬膜囊裸露区后,实验组用酒精保存的同种异体硬脊膜覆盖,对照组不用任何间置物覆盖、术后2、4、8、12周时进行肉眼及光镜观察,8周时还进行硬膜外粘连等级评定及病理切片的计算机图像分析。结果显示,对照组硬膜外腔消失,逐渐形成致密粘连,实验组硬膜外间隙存在,粘连明显少于对照组,揭示保存硬脊膜可以有效的预防椎管内术后粘连。     

Effectiveness and handling characteristics of a three-layer polymer dura substitute: a prospective multicenter clinical study

OBJECT: The goal of this study was to assess the effectiveness and handling characteristics of a dura substitute composed of two outer layers of expanded polytetrafluoroethylene (PTFE) and a middle layer consisting of an elastomeric fluoropolymer. METHODS: In a prospective multicenter study, the dura substitute was implanted using a standard technique in 119 patients undergoing cranial or spinal surgery requiring duraplasty. Intraoperative assessments of the dura patch consisted of testing for cerebrospinal fluid (CSF) leakage employing the Valsalva maneuver and a surgeon's standard evaluation of the handling characteristics of the device. Postoperative assessments conducted during a mean follow-up time of 15.7 months (range 0.3-45.6 months) consisted of physical examinations, routine computed tomography (CT) or magnetic resonance (MR) imaging studies, and histological studies of any removed dura patches. The mean age of the 119 patients was 40 years (range < 1-81 years). The dura substitute was implanted cranially in 102 patients and spinally in 17. Intraoperative assessment including the Valsalva maneuver led to application of additional sutures in 17 patients. Handling features were rated very good to excellent. Postoperative clinical evaluation resulted in 79 excellent and 18 good results. Imaging studies (MR imaging studies in 69 patients and CT studies in 34 patients) showed no adhesions in 87 patients and minimal adhesions in seven patients (the dura was not visualized in nine patients). Postoperative complications occurred in 12 patients. There were six cases of CSF leakage, three cases of extradural hematoma, one case of arachnoid fibrosis after decompression of a Chiari malformation Type I, and two cases of infection. Eight (7%) of these complications were potentially related to the dura patch. CONCLUSIONS: In a large, multicenter clinical study of the use of an expanded-PTFE-containing dura substitute, the device was found to be easy to handle and implant. No serious dura patch-related intraoperative adverse events were observed. Postoperatively, there were no major sealing problems or long-term complications. In two cases the patch had to be removed due to fibrosis and infection. The three-layer polymer dura substitute appears to be safe and effective in minimizing CSF leakage and adhesion formation, and its use avoids any risk of prion disease transmission.     

Dural substitute with polyglycolic acid mesh and fibrin glue for dural repair: technical note and preliminary results

Background An ideal dural substitute that enables watertight closure, has sufficient strength, and can be absorbed without remnant materials that induce inflammation, adhesion, and infection is not available. The purpose of this study was to evaluate the efficacy of a bioabsorbable polyglycolic acid (PGA) mesh and fibrin glue as a substitute for dural repair. Methods Altogether, 10 patients with noted dural tears during extradural spinal surgery and 20 patients who underwent durotomy for intradural spinal surgery were included in this study. In a series of 20 consecutive cases, dural closure was performed by suture and fibrin glue. In the subsequent 10 consecutive patients, dural closure was performed by suture and fibrin glue with the use of absorbable PGA mesh. The medical records and magnetic resonance imaging (MRI) of the surgical site were retrospectively reviewed to evaluate the presence of a cerebrospinal fluid (CSF) fistula or leakage after the surgery. Results A CSF fistula occurred in five patients who underwent dural repair with fibrin glue alone, and postoperative MRI showed CSF leakage in two patients with incidental dural tears after laminectomy for ossification of ligamentum flavum. No CSF fistula was present in patients who underwent dural repair using PGA mesh and fibrin glue, and no adverse effects or complications were encountered postoperatively. Follow-up MRI revealed no evidence of CSF leakage around the reconstructed dura mater. Conclusions The use of PGA mesh and fibrin glue for the repair of dura mater is a useful method of preventing CSF leakage in spinal surgery.     

山羊硬脊膜的微观形貌及三维结构特征

目的 获取山羊硬脊膜形貌及三维微观结构特征,为构建与之空间结构近似的人工硬脊膜提供相关资料。方法山羊硬脊膜取材后,进行标本处理及大体观察,光镜、扫描电镜及透射电镜观察微观结构、组织学成分、内外表面形貌、胶原纤维直径、分布以及分布模型。结果 大体观察可见硬脊膜为一乳白色、质韧、弹性半透明膜;光镜下观察硬脊膜的组成主要由“取向性”结构的胶原纤维及少量散在分布的成纤维细胞组成;扫描电镜观察显示,其内外表面如连绵山峰状隆起;透射电镜见胶原纤维有序分布,胶原纤维的平均直径为(627±60)nm,且呈现双峰分布。结论 山羊硬脊膜是主要由纳米级的“取向性”胶原纤维及散在分布的成纤维细胞组成的半透明薄膜。     

钛网椎管成形在脊柱融合术中的应用

目的　介绍一种治疗椎体爆裂性骨折椎板减压后脊柱融合的方法。方法　椎体爆裂性骨折病人 3 4例 ,均有不同程度的脊柱不稳及硬膜囊或神经根压迫。在进行后路椎板减压、经椎弓根内固定后 ,采用钛网椎管成形脊柱后路融合重建脊柱的稳定性。结果　全部病例经 1 2～ 1 8个月随访 ,内固定物无断裂 ,钛网在位 ,椎管成形良好 ,硬膜囊及神经根无压迫。 3 1例神经功能有不同程度的恢复。结论　钛网椎管成形脊柱融合术治疗椎体爆裂性骨折效果良好。此方法操作简单 ,安全 ,能够在恢复椎管形状、免除硬膜囊及神经根压迫的同时 ,进行植骨融合 ,增加脊柱的稳定性 ,易于推广应用。     

The morphology and clinical significance of the dorsal meningovertebra ligaments in the cervical epidural space

Background contextThe dural sac is anchored within the vertebral canal by connective tissue called meningovertebral ligaments in the epidural space. During flavectomy and laminectomy, inadvertent disruption of the dorsal meningovertebral ligaments may lead to dura laceration and cerebrospinal fluid (CSF) leaks. All the described dorsal meningovertebral ligaments were located in the lumbar region. A rare study is available about dorsal meningovertebral ligaments of the cervical spinal dura to the adjacent vertebrae.PurposeTo identify and describe the dorsal meningovertebral ligaments at each cervical level and discuss their clinical significance.Study designA dissection-based study of 22 embalmed cadavers.MethodsThe anatomy was studied in 22 whole cervical cadavers (11 females, 11males), prepared with formaldehyde, whose ages at the time of death ranged from 55 to 78 years. The vertebral canal was divided to expose the dural sac and the spinal nerve roots. At all levels of the cervical vertebra, the morphology, quantity, origin, insertion, and spatial orientation of the dorsal meningovertebral ligaments were determined and the length, width or diameter, and thickness of the ligaments were measured with vernier calipers.ResultsThe dorsal meningovertebral ligaments in the cervical region anchored the posterior dural sac to the ligamentum flavum or laminae. The number of attachment points on the ligamentum flavum was relatively larger than that on the lamina, and the occurrence rate of dorsal meningovertebral ligaments was 100% at C1–C2 and C4––C5. The thickest ligaments were observed at the C1 and C2 vertebrae. The length of the ligaments varied from 1.50 to 35.22 mm, and the orientation of the ligaments mostly was craniocaudal. The morphology of the dorsal meningovertebral ligaments was divided into four types: strip type, cord type, grid type, and thin slice type.ConclusionsIn the cervical spine, the dorsal meningovertebral ligaments exist between the posterior dural sac and the ligamentum flavum or lamina. The dorsal meningovertebral ligaments may be of clinical importance to surgeons. Dissecting the dorsal meningovertebral ligaments before the cervical flavectomy and laminectomy may be an important step in reducing postoperative dura laceration and CSF leaks, which may result in significant benefits for patients and health-care organizations.     

Ultrasound-guided epidural block

Epidural block is performed with surface landmark guidance and loss of resistance technique. Ultrasound visualization of the spinal column and surrounding structures gives additional anatomical information, which could make the block easier and safer. Previous studies revealed that there is strong correlation between the depth of the epidural space measured using ultrasound and the depth of the needle inserted. In order to obtain an image of the spinal canal, the ultrasound probe is positioned at the interspace of spinous processes in transverse and longitudinal planes. The dura mater is identified as an echogenic structure inside the spinal canal. Prepuncture ultrasound examination offers useful information for epidural block such as puncture point and depth as well as angle to the epidural space.     

The spinal cord and its membranes

The spinal cord is 45 cm long in the adult. In the early fetus, it extends the length of the vertebral canal; differential growth results in its termination at L3 in the newborn. In the adult it terminates, as the conus medullaris, at the disc between L1 and L2, although there is a range from T12 to L3. Inferiorly, the nerve roots form the cauda equina, while the lower end of the cord is attached by the filum terminale, of pia mater, to the coccyx. The dural sac terminates usually at the second segment of the sacrum. The cord receives its arterial supply from the anterior and posterior spinal arteries, which descend from the foramen magnum. They are reinforced serially via the intervertebral foramina from segmental vessels, especially the arteria magna. The three layers of the meninges are the dura mater, arachnoid mater and pia mater. The cerebrospinal fluid is contained within the subarachnoid space. The epidural space contains fat, blood vessels, lymphatics and the nerve roots.     

The morphology and clinical significance of the dorsal meningovertebra ligaments in the lumbosacral epidural space

STUDY DESIGN.: A dissection-based study of 30 embalmed cadavers. OBJECTIVE.: To determine the morphology and morphometry of the dorsal meningovertebral ligaments in the lumbosacral segments and to discuss their clinical significance. SUMMARY OF BACKGROUND DATA.: Postoperative cerebrospinal fluid leakage is associated with longer hospital stays and significant implications for the patient, the surgeons, and society as a whole. To protect the dural sac during lumbar surgery, knowledge of the surgical anatomy of the dorsal meningovertebral ligaments is crucial. METHODS.: A total of 30 adult embalmed cadavers (52-70 yr of age; mean age of 64 yr) were used. The vertebral canal was divided to expose the dural sac and the spinal nerve roots, and the spinal cord was removed. The morphology, quantity, and attachment of the dorsal meningovertebral ligaments in the lumbosacral region were observed, and the length, width, or diameter and thickness of the ligaments were measured with vernier calipers. RESULTS.: The dorsal meningovertebral ligaments in the lumbosacral region connect the dura to the ligamenta flava or the lamina. The number of the attachment points on the ligamenta flava was relatively larger than that on the lamina, and the occurrence rate of dorsal meningovertebral ligaments was 97% at L5-S1. The thickest ligaments were observed at the L5 and S1 vertebrae. The length of the ligaments varied from 5.16 to 40.24 mm, and the ligaments extended caudally from their origin on the dura to their attachment to the lamina or the ligamentum flavum. The morphology of the dorsal meningovertebral ligaments was divided into 5 types: strip type, cord type, "Y"-shaped type, grid type, and thin slice type. CONCLUSION.: The dorsal meningovertebral ligaments may contribute to dura laceration and epidural hemorrhage during flavectomy and laminectomy, and an appreciation of this relationship might help reduce the risk of such complications.     

Identification of the lumbar intervertebral level using ultrasound imaging in a post-laminectomy patient

A spinal block was performed in a post-laminectomy patient, using both ultrasound imaging and X-ray imaging. Ultrasound imaging clearly identified the L3/4 intervertebral level, the spinal canal, the corpus vertebrae, and the dura mater. Using ultrasound imaging, we measured the distance from the skin surface to the dura mater (39 mm). A 25-G needle for the spinal block was accurately advanced into the spinal canal with the use of X-ray imaging (43 mm from the skin to the subarachnoid space). We report here that ultrasound imaging was useful for performing a spinal block in a post-laminectomy patient in whom there was anatomical change around the spine.     

Reconstruction of the sellar dura in transsphenoidal surgery using an expanded polytetrafluoroethylene dural substitute

BACKGROUND: The transsphenoidal approach for resecting pituitary tumors has classically included reconstruction of the anterior wall of the sella turcica. A variety of materials have been used in this process for the purpose of both recreating the original anatomy and preventing postoperative cerebrospinal fluid (CSF) leaks. We studied the use of an ePTFE dural substitute (GORE Preclude MVP, W.L. Gore & Associates, Flagstaff, Arizona, USA), as a method for obtaining reliable reconstruction of the sellar dura. METHODS: A prospective alternate case trial was designed to assess this new dural substitute wherein 60 patients who underwent transsphenoidal surgical resection of intrasellar lesions larger than 1 cm were included. Thirty patients had the sellar dura closed with ePTFE dural substitute, whereas 30 patients underwent anterior wall reconstruction as ordinarily performed in our institution. RESULTS: Each patient was reassessed at closure, and the operative site and sphenoid sinus were evaluated with 3-months-postoperative magnetic resonance imaging. Three patients experienced postoperative CSF leaks: 1 with ePTFE dural substitute and 2 without. All 3 patients underwent a second operation to repair the CSF leak, without further complications. No other postoperative complications were noted in the series. CONCLUSION: Expanded polytetrafluoroethylene dural substitute provides a safe and effective adjunctive method for reconstruction of the sellar dura.     

Postoperative cerebrospinal-fluid fistula associated with erosion of the dura. Findings after anterior resection of ossification of the posterior longitudinal ligament in the cervical spine.

Of twenty-two patients who had had anterior decompression of the spinal canal for ossification of the posterior longitudinal ligament and cervical myelopathy, seven had absence of the dura adjacent to the ossified part of the ligament. The spinal cord and nerve-roots were visible through this defect. Although the arachnoid membrane appeared to be intact and watertight in most patients, a cerebrospinal-fluid fistula developed postoperatively in five, and three had a second operation to repair the defect in the dura. On the basis of this experience, we recommend use of autogenous muscle or fascial dural patches, immediate lumbar subarachnoid shunting, and modification of the usual postoperative regimen, such as limitation of mechanical pulmonary ventilation to the shortest time that is safely possible and use of anti-emetic and antitussive medications to protect the remaining coverings of the spinal cord when the dura is found to be absent adjacent to an ossified portion of the posterior longitudinal ligament in the cervical spine.     

Laminar hook instrumentation in the cervical spine. An experimental study on the relation of hooks to the spinal cord

Several anterior and posterior methods are today available for stabilization of the cervical spine. Factors such as level and degree of instability, method of decompression, bone quality, length of fixation and safety factors influence the choice of method for a particular patient. The use of laminar hooks in the cervical spine has been restricted by fear of cord compression with the potential of tetraplegia. The aim of the present study was to assess the safety and determine the anatomical relation between hooks inserted in the cervical spinal canal and the dura and spinal cord. Thirteen cadavers from seven women and six men with no evidence of cervical spine disorder were included. The mean age was 81.3 years (range 65-101 years). The cervical spine was instrumented with cervical Compact Cotrel Dubousset hooks and rods. The effect of the hook on the dura was studied by myelography in nine cadavers. The deformation of the dural sac was quantified by measurement of the maximal width of the indentation of the contrast column at each level. A CT myelography scan was obtained in three cadavers. The ratio between the distance of maximal hook intrusion into the spinal canal and the canal diameter in the direction of the hook was calculated. The relation between inserted hooks and the spinal cord and dura was documented in a fresh cadaver studied with CT myelography. A hemilaminectomy was performed at all levels in three cadavers with direct visual inspection and photography of the hook sites before and after excision of the dura. A dural deformation of 2 mm or less, as observed by myelography, was found at four out of 77 (5%) hook sites. The deformation was caused by a supralaminar hook at C3, C6 and C7 and by an infralaminar hook at C6. The mean hook intrusion in the spinal canal, as observed on CT, was 27% (range 8-43) of the canal diameter. On visual inspection, 14 out of 18 hooks were in contact with the dura. After removal of the dura, two out of the 18 hooks in the same cadaver were in contact with the spinal cord. However, no deformation of the cord was observed. To our knowledge this is the first study systematically documenting the relation between hooks and the spinal cord in cadavers. In 95% of the hooks no deformation of the dural sac was observed and there was no evidence of spinal cord deformation. From an anatomical point of view, laminar hook instrumentation can be considered a safe procedure. The study shows, however, that hooks inserted in the cervical spine have a close anatomical relationship with the neuraxis, and at stenotic levels the use of other techniques is therefore recommended.     

Anterior approach for dumbbell type cervical neurinoma

A one-stage anterior approach was performed in four patients for total removal of dumbbell type neurinoma at the cervical level. In each case, the neurinoma compressed the spinal cord in the cervical canal, developed anteriorly through the intervertebral foramen, and compressed the vertebral artery. A conventional cervical anterior approach at the tumor site was performed, followed by confirmation of the tumor located outside the spinal canal. After identification of the vertebral artery, corpectomy was carried out and the extradural component of the tumor was resected. In cases with a portion of the tumor located also within the dura mater, the dura mater was opened for removal of the intradural tumor. We found the anterior approach to be effective for the total removal of some kinds of cervical dumbbell type neurinomas.     

The anatomy of the thoracic spinal canal investigated with magnetic resonance imaging (MRI)

BACKGROUND AND OBJECTIVES: Anesthesiologists are reluctant to consider higher levels for spinal anesthesia, largely due to direct threats to the spinal cord. The goal of this study is to investigate, with magnetic resonance imaging (MRI), the distances between the relevant structures of the spinal canal (spinal cord, thecal tissue, etc.) to determine modal anatomical positions for neuraxial anesthesia. METHOD: A group of 19 patients were imaged with an MRI scanner in supine position. Medial sagittal slices of the thoracic and lumbar spine were measured for the relative distances between anatomical structures, including epidural space, dura, and spinal cord. RESULTS: The posterior dura - spinal cord distance is significantly greater in the middle thoracic region than at upper and lower thoracic levels (e.g. T6 9.5 +/- 1.8 mm, T12 3.7 +/- 1.2 mm, p < 0.001, T1 4.7 +/- 1.7 mm, p < 0.001). There is variation in modal distances between the structures important for neuraxial anesthesia, at different levels of the spinal canal. CONCLUSIONS: The spinal cord tends to follow the straightest line through the imposed geometry of the spine. Considering the necessary angle of entry of the needle at mid-thoracic levels, there is relatively (more than at upper thoracic and lumbar levels) substantial separation of cord and surrounding thecal tissue. Anesthesiologists perform spinal blockades up to the L2-L3 interspace, but avoid higher levels for fear of neurological damage. The information that there is substantially more space in the dorsal subarachnoid space at thoracic level, might lead to potential applications in regional anesthesia. In contrast, the cauda equina sits more dorsally in the lumbar region.     

An unusual complication of silastic dural substitute: case report

A case is presented in which a patient developed an unusual complication after the use of Silastic dural substitute. In 1983, the patient underwent removal of a meningioma with the involved dura. Five years later, he developed around the graft material a very thick connective tissue capsule, which simulated a recurrent meningioma clinically and radiologically.