Changes of blood flow, oxygen tension, action potential and vascular permeability induced by arterial ischemia or venous congestion on the spinal cord in canine model.

It is generally considered that the genesis of myelopathy associated with the degenerative conditions of the spine may result from both mechanical compression and circulatory disturbance. Many references about spinal cord tissue ischemic damage can be found in the literature, but not detailed studies about spinal cord microvasculature damage related to congestion or blood permeability. This study investigates the effect of ischemia and congestion on the spinal cord using an in vivo model. The aorta was clamped as an ischemia model of the spinal cord and the inferior vena cava was clamped as a congestion model at the 6th costal level for 30 min using forceps transpleurally. Measurements of blood flow, partial oxygen pressure, and conduction velocity in the spinal cord were repeated over a period of 1 h after release of clamping. Finally, we examined the status of blood-spinal cord barrier under fluorescence and transmission electron microscope. Immediately after clamping of the inferior vena cava, the central venous pressure increased by about four times. Blood flow, oxygen tension and action potential were more severely affected by the aorta clamping; but this ischemic model did not show any changes of blood permeability in the spinal cord. The intramedullar edema was more easily produced by venous congestion than by arterial ischemia. In conclusions, venous congestion may be a preceding and essential factor of circulatory disturbance in the compressed spinal cord inducing myelopathy.

Experimental syringohydromyelia induced by adhesive arachnoiditis in the rabbit: changes in the blood-spinal cord barrier, neuroinflammatory foci, and syrinx formation.

There are many histological examinations of syringohydromyelia in the literature. However, there has been very little experimental work on blood permeability in the spinal cord vessels and ultrastructural changes. We prepared an animal model of spinal adhesive arachnoiditis by injecting kaolin into the subarachnoid space at the eighth thoracic vertebra of rabbits. The animals were evaluated 4 months later. Of the 30 rabbits given kaolin injection into the cerebrospinal fluid, 23 showed complete circumferential obstruction. In the 7 animals with partial obstruction of the subarachnoid space, intramedullary changes were not observed. However, among the 23 animals showing complete obstruction of the subarachnoid space, dilatation of the central canal (hydromyelia) occurred in 21, and intramedullary syrinx (syringomyelia) was observed in 11. In animals with complete obstruction, fluorescence microscopy revealed intramedullary edema around the central canal, extending to the posterior columns. Electron microscopy of hydromyelia revealed a marked reduction of villi on the ependymal cells, separation of the ependymal cells, and cavitation of the subependymal layer. The dilated perivascular spaces indicate alterations of fluid exchange between the subarachnoid and extracellular spaces. Syringomyelia revealed that nerve fibers and nerve cells were exposed on the surface of the syrinx, and necrotic tissue was removed by macrophages to leave a syrinx. Both pathologies differ in their mechanism of development: hydromyelia is attributed to disturbed reflux of cerebrospinal fluid, while tissue necrosis due to disturbed intramedullary blood flow is considered to be involved in formation of the syrinx in syringomyelia.

Vasomotion of intraradicular microvessels in rat.

STUDY DESIGN: This study is to investigate the changes of vasomotion of intraradicular microvessels in vivo. OBJECTIVE: We have observed microvascular corrosion casts of the lumbar nerve root by scanning electron microscopy and used an immunohistochemical technique to investigate the presence and distribution of autonomic and sensory nerve in blood vessels of the nerve root. SUMMARY OF BACKGROUND DATA: It is generally considered that the genesis of radiculopathy associated with the degenerative conditions of the spine may result from both mechanical compression and circulatory disturbance. However, the neurogenic control of intraradicular blood flow has received little attention in the past. METHODS: For three-dimensional observation of intraradicular vessels, we used scanning electron microscopic examination of microvascular corrosion casts in ten Wister rats. To investigate the mechanism of vasomotion of the nerve root, we used immunohistochemical methods. The sections were incubated overnight with antisera to tyrosine hydroxylase, choline acetyl transferase, substance P, calcitonin-gene-related peptide, vasoactive intestinal peptide, somatostatin, neuropeptide Y, leucine-enkephalin, cholecystokinin octapeptide, brain-nitric oxide synthase, and endothelium-nitric oxide synthase. Abidin-biotin complex method was used as the immunohistochemical procedure and the sections were observed under the light microscope. RESULTS: The general view of whole vascular casts of the lumbar spinal cord and nerve roots showed a high density of vessels. Bifurcation or anastomoses of capillaries approximately took place at right angles in a T-shaped pattern and capillaries showed a lot of ring-like compressions. This ring-like compression on the cast may represent a vascular sphincter in the microvessels. This study also reveals the existence of perivascular adrenergic, cholinergic, peptidergic, and nitroxydergic innervation with a possible role in neurogenic regulation of nerve root circulation. CONCLUSION: Perivascular nerve plexuses around intraradicular microvessels suggest that the autonomic nerves play an important role in intraradicular circulation.

Fine structure of cartilage canal and vascular buds in the rabbit vertebral endplate. Laboratory investigation.

OBJECT: The vascular terminations (vascular buds) in the bone-disc junction area are structurally very similar to cartilage. In all previous studies to date, however, the roles of cartilage canals and vascular buds were mainly discussed using histological and transparent sections but not electron microscopic sections. The purpose of this study was to clarify the ultrastructure of the vascular bud seen in the bone-disc junction in comparison to the cartilage canal. METHODS: Japanese white rabbits from 2 days to 6 months of age were used in this study. The bone-disc junctions were examined by microangiogram and light and electron microscopy, and morphological changes and their association with the age of the animals were noted. RESULTS: The fine structure of the vascular bud was similar to that of the cartilage canal that nourished the growing cartilage. They were composed of arteries, veins, capillaries, cells resembling fibroblasts, and macrophages. The capillaries in the cartilage canal were all the fenestrated type. Vascular buds were seen over the entire bone-cartilage interface, with maximum density in the area related to the nucleus pulposus. They projected into the bone-disc junction area from the vertebral body contacting the cartilaginous endplate directly. CONCLUSIONS: The results of this study clarify the formation process and ultrastructure of the vascular bud seen in the bone-disc junction. The authors found a strong structural resemblance between the vascular bud and the cartilage canal and hypothesize that the immature cells seen surrounding the cartilage canal and vascular bud represent a common precursor for the 3 main types of connective tissue cells seen during early vertebral development.

Atlantoaxial subluxation-induced myelopathy in cleidocranial dysplasia. Case report.

The authors describe the clinical course and treatment of a patient with cleidocranial dysplasia in whom spastic myelopathy developed due to atlantoaxial subluxation. This 27-year-old woman with cleidocranial dysplasia and a history of atlantoaxial subluxation presented with spastic myelopathy. Surgery was performed twice for cervical myelopathy and atlantoaxial subluxation, including laminectomy at the atlas and cervicooccipital fusion in which the Luque rod system was used, as well as C1-2 fusion via the transpharyngeal route. Solid bone fusion was achieved by 7 months postsurgery. Postoperative magnetic resonance imaging studies demonstrated that spinal cord compression was relieved, but atrophy persisted. At 2 years postsurgery there was no neurological disease progression, but spasticity persisted. The patient could walk with a cane. Cleidocranial dysplasia is an extremely rare cause of myelopathy in patients with atlantoaxial subluxation; the authors know of only two reports of this condition. When managing cleidocranial dysplasia, the practitioner should always be aware that atlantoaxial subluxation may be the cause of cervical myelopathy.

Effect of mechanical compression on the lumbar nerve root: localization and changes of intraradicular inflammatory cytokines, nitric oxide, and cyclooxygenase.

STUDY DESIGN: Investigation of intraradicular inflammation induced by mechanical compression. OBJECTIVE: To investigate the mechanism of nerve root pain, this study used a lumbar nerve root compression model. SUMMARY OF BACKGROUND DATA: The manifestation of pain at sites of inflammation has a close relationship with the release of mediators from macrophages. However, the mediators involved in inflammation of nerve roots as a result of mechanical compression remain almost unknown. METHODS: In this study, the seventh lumbar nerve root of dogs was compressed with a clip for 3 weeks to observe the changes caused by compression. Immunohistochemistry was performed using the avidin-biotin-peroxidase complex method to observe the changes of T cells (CD45) and macrophages (Mac-1) after compression. Antibodies against as interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), inducible nitric oxide synthase (i-NOS), and cyclooxygenase (COX)-1 and 2 were used to examine the localization and changes of these mediators caused by nerve root compression. RESULTS: In control animals, resident T cells were detected, but there were no macrophages. IL-1beta and COX-2 were positive in the Schwann cells and vascular endothelial cells, while COX-1 was detected in the vascular endothelial cells. However, no cells showed TNF-alpha or i-NOS positively. After nerve root compression, numerous T cells and macrophages appeared among the demyelinized nerve fibers. The macrophages were positive for IL-1beta, TNF-alpha, i-NOS, and COX-2. CONCLUSION: Inflammatory cytokines, NO, and COX-2 may be deeply involved in radiculitis caused by mechanical compression, and these mediators seem to be important in the manifestation of root pain.

Localization and changes of intraneural inflammatory cytokines and inducible-nitric oxide induced by mechanical compression.

STUDY DESIGN: Investigation of intraneural inflammation induced by mechanical compression. OBJECTIVES: In order to investigate the mechanism of neuropathy, this study used a median nerve compression model in dogs. Immunohistochemistry was used to examine the localization and changes of inflammatory cytokines and nitric oxide (NO). SUMMARY OF BACKGROUND DATA: The manifestation of pain at sites of inflammation has a close relationship with the release of mediators from macrophages such as interleulin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha), as well as with NO. However, the mediators involved in inflammation of nerve due to mechanical compression remain almost unknown. METHODS: In this study, the median nerve of dogs was compressed with a clip for three weeks to observe the changes caused by compression. Immunohistochemistry was done by the avidin-biotin-peroxidase complex method to observe the changes of T cells (CD45) and macrophages (Mac-1) after compression. Antibodies against IL-1beta, TNF-alpha, and inducible nitric oxide synthesis (i-NOS) were used to examine the localization and changes of these mediators caused by nerve compression. RESULTS: In control animals, resident T cells were detected, but there were no macrophages. IL-1beta was positive in the Schwann cells and vascular endothelial cells. However, no cells showed TNF-alpha or i-NOS positively. After nerve compression, numerous T cells and macrophages appeared among the demyelinized nerve fibers. The macrophages were positive for IL-1beta, TNF-alpha and i-NOS. CONCLUSION: Inflammatory cytokines and NO may be involved in intraneural inflammatory changes arising from mechanical compression. Such mediators may be of importance in the manifestation of neuropathy.

Commentary on the prevention of paralysis after traumatic spinal cord injury in humans: the neglected factor--urgent restoration of spinal cord circulation.

Although advances in the management of spinal injuries during the past 60 years have led to greatly increased life expectancy for paralysed patients, most remain disabled. Around the world, spinal injury centres have become specialized rehabilitation units, where staff accepts the inevitability of persisting paralysis. In part, this pessimism has been based on incorrect information about the anatomy and function of the circulation of the spinal cord. Since the publication of accurate descriptions of the segmental nature of spinal vasculature, research and clinical data suggest that reversal or prevention of paralysis after spinal injury may be possible in many patients. These improved outcomes will depend on the recognition that urgent correction of cord blood supply in patients with traumatic spinal injury is critical to the long-term results of treatment. The creation of specialist spinal units within trauma centres for the urgent treatment of patients following spinal injury will require considerable logistical change, but has the potential to lead to a revolution in spinal care, driven by the knowledge that spinal cord function can often be saved.

Changes of calcitonin gene-related peptide in primary sensory neurons and their central branch after nerve root compression of the dog.

OBJECTIVE: To investigate changes in axonal flow after nerve root compression by using immunohistochemical techniques to detect calcitonin gene-related peptide (CGRP), which is thought to be involved in pain sensation. DESIGN: Experimental, controlled study. SETTING: University medical school in Japan. ANIMALS: Forty adult mongrel dogs (weight, 7-15kg). INTERVENTIONS: In dogs, the lumbar nerve roots were compressed using 4 types of clips with different pressures. Changes of CGRP levels in the spinal dorsal horn, dorsal root, and dorsal root ganglia (DRG) were examined immunohistochemically after compression for 24 hours or for 1 week. MAIN OUTCOME MEASURES: CGRP-positive neurons and CGRP-positive fibers. RESULTS: After compression, axonal flow in the dorsal root was impaired, accumulation of CGRP was observed distal to the site of compression, and the number of DRG cells showing positively for CGRP decreased. Compression for 1 week resulted in a decrease in the number of CGRP-positive fibers in the spinal dorsal horn. CONCLUSIONS: These findings indicate that CGRP dynamics are modified by nerve compression.

Effect of lumbar nerve root compression on primary sensory neurons and their central branches: changes in the nociceptive neuropeptides substance P and somatostatin.

STUDY DESIGN: This study examined the effect of lumbar nerve root compression on nociceptive neuropeptides in the axonal flow using an in vivo model. OBJECTIVES: The aim was to investigate changes in axonal flow after nerve root compression by using immunohistochemical techniques to detect substance P (SP) and somatostatin (SOM), which is thought to be involved in temperature and pain sensation. SUMMARY OF BACKGROUND DATA: Disturbance of intraradicular blood flow and nerve fiber deformation caused by mechanical compression are thought to be involved in the pathophysiology of diseases characterized by radicular symptoms, such as lumbar disc herniation and lumbar canal stenosis. However, little research has been conducted into the changes of axonal flow associated with nerve root compression. METHODS: In dogs, the lumbar nerve roots were compressed using four types of clips with different pressures. Changes of SP and SOM levels in the spinal dorsal horn, dorsal root, and dorsal root ganglions were examined immunohistochemically after compression for 24 hours or 1 week. RESULTS: After compression for 24 hours, axonal flow in the dorsal root was impaired, accumulation of SP and SOM was observed distal to the site of compression, and there was a decrease in the number of dorsal root ganglion cells showing positively for these neurotransmitters. Compression for 1 week resulted in a decrease in the number of SP- and SOM-positive fibers in the spinal dorsal horn. CONCLUSION: Change of axonal flow resulting from direct nerve compression could affect the metabolism of neurotransmitters that flow inside the axons and may be a primary cause of the decline in nerve function.

Pathology of lumbar nerve root compression. Part 1: Intraradicular inflammatory changes induced by mechanical compression.

STUDY DESIGN: This study is to investigate the intraradicular inflammation induced by mechanical compression using in vivo model. OBJECTIVES: The relationship between the intraradicular edema and nerve fiber degeneration induced by mechanical compression was determined in the nerve root. SUMMARY OF BACKGROUND DATA: Recently some studies reported that mechanical compression increased microvascular permeability of the endoneurial capillaries and resulted in an intraradicular inflammation. These changes may be an important factor of the pathogenesis of radiculopathy. However, the natural courses of the intraradicular inflammation after mechanical compression are still poorly understood. METHODS: In dogs, laminectomy was performed at L7 and the seventh nerve root was exposed to compression at 7.5 gram force (gf) clipping power. The animals were evaluated at 1 and 3 weeks after clipping. After the appropriate period of nerve root compression, Evans blue albumin (EBA) was injected intravenously. The nerve root sections were divided into two groups. The sections were used to investigate the status of the blood-nerve barrier function under the fluorescence microscope. The other sections were used for light and transmission electron microscopic study. RESULTS: After 1 and 3 weeks, intraradicular edema was observed not only at the site of compression but also in the peripheral zone of a compressed anterior root and in the central zone of a compressed posterior root. The evidence of active Wallerian degeneration was also seen in the area of intraradicular edema. In addition, the nerve roots showing Wallerian degeneration were infiltrated by inflammatory cells, such as macrophages and mast cells. CONCLUSIONS: Inflammatory reaction, such as Wallerian degeneration, breakdown of blood-nerve barrier and appearance of macrophage, may be deeply involved in radiculitis arising from mechanical compression, and these factors seem to be important in the manifestation of radiculopathy.

Pathology of lumbar nerve root compression. Part 2: morphological and immunohistochemical changes of dorsal root ganglion.

STUDY DESIGN: This study is to investigate the changes of dorsal root ganglion (DRG) induced by mechanical compression using in vivo model. OBJECTIVES: The effect of axonal flow disturbance induced by nerve root compression was determined in DRG. SUMMARY OF BACKGROUND DATA: The dorsal root ganglion should not be overlooked when considering the mechanism of low back pain and sciatica, so it is important to understand the morphologic and functional changes that occur in primary sensory neurons of the dorsal root ganglion as a result of nerve root compression. However, few studies have looked at changes of neurons within the dorsal root ganglion caused by disturbance of axonal flow and the axon reaction as a result of mechanical compression of the dorsal root through which the central branches of the primary sensory nerves pass. METHODS: In mongrel dogs, the seventh lumbar nerve root was compressed for 24 h, one week, or three weeks using a clip with a pressure of 7.5 gf. Morphologic changes of the primary sensory neurons in the dorsal root ganglion secondary to the axon reaction were examined by light and electron microscopy. Changes of immunostaining for substance P (SP), calcitonin gene-related peptide (CGRP), and somatostatin (SOM) in the primary sensory neurons affected by central chromatolysis after nerve root compression were also examined. RESULTS: Light microscopy showed central chromatolysis of neurons in the dorsal root ganglion from one week after the start of compression. Electron microscopy of the affected neurons revealed movement of the nucleus to the cell periphery and the loss of rough endo-plasmic reticulum and mitochondria from the central region. Immunohistochemical studies showed a marked decrease of SP, CGRP, and SOM staining in small ganglion cells with central chromatolysis when compared with cells from control ganglia. CONCLUSION: It is important to be aware that in patients with nerve root compression due to lumbar disc herniation or lumbar canal stenosis, dysfunction is not confined to degeneration at the site of compression, but also extends to the primary sensory neurons within the dorsal root ganglion as a result of the axon reaction. Patients with sensory disturbance should therefore be fully informed of the fact that these symptoms will not resolve immediately after surgery.

Changes in nerve root motion and intraradicular blood flow during intraoperative femoral nerve stretch test. Report of four cases.

OBJECT: It is not known whether changes in intraradicular blood flow (IRBF) occur during the femoral nerve stretch test (FNST) in patients with lumbar disc herniation. An FNST was conducted in patients with lumbar disc herniation to observe the changes in IRBF, and results were then compared with clinical features. METHODS: The study was composed of four patients with L3-4 disc herniation who underwent microdiscectomy. Patients were placed prone immediately before surgery, so that their knee flexed on the operating table with the hip joint kept in hyperextension, and the FNST was performed to confirm at which region pain developed in the anterolateral thigh. During the operation, the hernia-affected nerve roots were visualized under a microscope. The needle sensor of a laser Doppler flowmeter was then inserted into each nerve root immediately above the hernia, and the change in IRBF was measured during the intraoperative FNST. After removal of the herniated disc, a similar procedure was repeated and IRBF was measured again. The intraoperative FNST showed that the hernia compressed the nerve roots and there was marked disturbance of gliding, which was reduced to only a few millimeters. During the test, IRBF decreased by 92.8 to 100% (mean 96.9 +/- 3.7% [+/- standard error of the mean]) relative to the blood flow before the test. This study demonstrated that the blood flow in the nerve root is reduced when the nerve root is compressed in vivo. CONCLUSIONS: The intraoperative FNST showed that the hernia compressd the nerve roots and there was marked disturbance of gliding, which was reduced to only a few millimeters. During the test, IRBF decreased by 92.8 to 100% (96.9 +/- 3.7% [mean +/- standard error of the mean]).

Changes in nerve root motion and intraradicular blood flow during an intraoperative straight-leg-raising test.

STUDY DESIGN: An intraoperative straight-leg-raising (SLR) test was conducted to investigate patients with lumbar disc herniation to observe the changes in intraradicular blood flow, which then were compared with the clinical features. OBJECTIVE: The legs of each patient were hung down from the operating table as a reverse SLR test during surgery, and intraradicular blood flow was measured. SUMMARY OF BACKGROUND DATA: It is not known whether intraradicular blood flow changes during the SLR test in patients with lumbar disc herniation. METHODS: The subjects were 12 patients with lumbar disc herniation who underwent microdiscectomy. The patients were asked to adopt the prone position immediately before surgery, so that their legs hung down from the operating table. A reverse SLR test was performed to confirm the angle at which sciatica developed. During the operation, the nerve roots affected by the hernia were observed under a microscope. Then the needle sensor of a laser Doppler flow meter was inserted into each nerve root immediately above the hernia. The patient's legs were allowed to hang down to the angle at which sciatica had occurred, and the change in intraradicular blood flow was measured. After removal of the hernia, a similar procedure was repeated, and intraradicular blood flow was measured again. RESULTS: Intraoperative microscopy showed that the hernia was adherent to the dura mater of the nerve roots in all patients. The intraoperative reverse SLR test showed that the hernia compressed the nerve roots, and that there was marked disturbance of gliding, which was reduced to only a few millimeters. During the test, intraradicular blood flow showed a sharp decrease at the angle that produced sciatica, which lasted for 1 minute. Intraradicular flow decreased by 40% to 98% (average, 70.6% +/- 20.5%) in the L5 nerve root, and by 41% to 96% (average, 72.0% +/- 22.9%) in the S1 nerve roots relative to the blood flow before the test. At 1 minute after completion of the test, intraradicular blood flow returned to the value obtained at baseline. After removal of the hernia, all thepatients showed smooth gliding of the nerve roots during the second intraoperative test, and there was no marked decrease in intraradicular blood flow. CONCLUSIONS: This study demonstrated that the blood flow in the nerve root is reduced when the nerve root is compressed in vivo.

Effect of mechanical compression on the vascular permeability of the dorsal root ganglion.

The dorsal root ganglion contains primary sensory neurons and is closely related to low back pain and sciatia. The present study investigated whether endoneurial edema, which is involved in the onset of pain and nerve dysfunction, was increased in the dorsal root ganglion by compression. The influence of mechanical compression on the vascular permeability of the lumbar dorsal root ganglion was determined. The dorsal root ganglion is reported to have a higher vascular permeability compared with other nerve tissues as well as lacking a blood-nerve barrier. However, only a few studies have assessed the influence of mechanical compression on the dorsal root ganglion. especially its vascular permeability. In dogs, laminectomy was performed at L7 and the dorsal root ganglion of the seventh lumbar spinal nerve was compressed for 1 h using four kinds of clips with various strengths. After clip removal, Evans blue albumin (EBA) or horseradish peroxidase (HRP) was administered intravenously as a tracer. After sacrifice, the EBA-injected specimens were observed by fluorescence microscopy and the HRP-injected specimens were observed by light and transmission electron microscopy. After compression of the dorsal root ganglion at 15 gf or more, leakage of tracer into the endoneurial space was markedly increased compared with the sham-operated group and severe edema was noted. Extravascular leakage of tracer was obvious around venules and capillaries. Electron microscopy showed an increase of extravascular HRP in the gap junctions and fenestrae between endothelial cells due to increased vascular permeability. However, the dorsal root ganglion was covered with a thick perineurium and HRP that leaked from the blood vessels did not enter the epineurium even after compression at 60 gf. It was proven that the increased vascular permeability occurred as well as in leakage of dye within the dorsal root ganglion after a single hour of compression of the dorsal root ganglion.