SUSTAINED SPINAL CORD COMPRESSION

Transcutaneous contrast-enhanced ultrasound imaging of the posttraumatic spinal cord

STUDY DESIGN

Experimental animal study.

OBJECTIVE

The current study aims to test whether the blood flow within the contused spinal cord can be assessed in a rodent model via the acoustic window of the laminectomy utilizing transcutaneous ultrasound.

SETTING

Department of Neurological Surgery, University of Washington, Seattle WA.

METHODS

Long-Evans rats (n = 12) were subjected to a traumatic thoracic spinal cord injury (SCI). Three days and 10 weeks after injury, animals underwent imaging of the contused spinal cord using ultrafast contrast-enhanced ultrasound with a Vantage ultrasound research system in combination with a 15 MHz transducer. Lesion size and signal-to-noise ratios were estimated via transcutaneous, subcutaneous, or epidural ultrasound acquisition through the acoustic window created by the original laminectomy.

RESULTS

Following laminectomy, transcutaneous and subcutaneous contrast-enhanced ultrasound imaging allowed for assessment of perfusion and vascular flow in the contused rodent spinal cord. An average loss of 7.2 dB from transcutaneous to subcutaneous and the loss of 5.1 dB from subcutaneous to epidural imaging in signal-to-noise ratio (SNR) was observed. The hypoperfused injury center was measured transcutaneously, subcutaneously and epidurally (5.78 ± 0.86, 5.91 ± 0.53, 5.65 ± 1.07 mm²) at 3 days post injury. The same animals were reimaged again at 10 weeks following SCI, and the area of hypoperfusion had decreased significantly compared with the 3-day measurements detected via transcutaneous, subcutaneous, and epidural imaging respectively (0.69 ± 0.05, 1.09 ± 0.11, 0.95 ± 0.11 mm², p < 0.001).

CONCLUSIONS

Transcutaneous ultrasound allows for measurements and longitudinal monitoring of local hemodynamic changes in a rodent SCI model.

Contrast-enhanced ultrasound to visualize hemodynamic changes after rodent spinal cord injury

OBJECTIVE

Traumatic spinal cord injury (tSCI) causes an almost complete loss of blood flow at the site of injury (primary injury) as well as significant hypoperfusion in the penumbra of the injury. Hypoperfusion in the penumbra progresses after injury to the spinal cord and is likely to be a major contributor to progressive cell death of spinal cord tissue that was initially viable (secondary injury). Neuroprotective treatment strategies seek to limit secondary injury. Clinical monitoring of the temporal and spatial patterns of blood flow within the contused spinal cord is currently not feasible. The purpose of the current study was to determine whether ultrafast contrast-enhanced ultrasound (CEUS) Doppler allows for detection of local hemodynamic changes within an injured rodent spinal cord in real time.

METHODS

A novel ultrafast CEUS Doppler technique was developed utilizing a research ultrasound platform combined with a 15-MHz linear array transducer. Ultrafast plane-wave acquisitions enabled the separation of higher-velocity blood flow in macrocirculation from low-velocity flow within the microcirculation (tissue perfusion). An FDA-approved contrast agent (microbubbles) was used for visualization of local blood flow in real time. CEUS Doppler acquisition protocols were developed to characterize tissue perfusion both during contrast inflow and during the steady-state plateau. A compression injury of the thoracic spinal cord of adult rats was induced using iris forceps.

RESULTS

High-frequency ultrasound enabled visualization of spinal cord vessels such as anterior spinal arteries as well as central arteries (mean diameter [± SEM] 145.8 ± 10.0 µm; 76.2 ± 4.5 µm, respectively). In the intact spinal cord, ultrafast CEUS Doppler confirmed higher perfusion of the gray matter compared to white matter. Immediately after compression injury of the thoracic rodent spinal cord, spinal cord vessels were disrupted in an area of 1.93 ± 1.14 mm2. Ultrafast CEUS Doppler revealed a topographical map of local tissue hypoperfusion with remarkable spatial resolution. Critical loss of perfusion, defined as less than 40% perfusion compared to the surrounding spared tissue, was seen within an area of 2.21 ± 0.6 mm2.

CONCLUSIONS

In our current report, we introduce ultrafast CEUS Doppler for monitoring of spinal vascular structure and function in real time. Development and clinical implementation of this type of imaging could have a significant impact on the care of patients with tSCI.

Design and testing of a controlled electromagnetic spinal cord impactor for use in large animal models of acute traumatic spinal cord injury

BACKGROUND

Spinal cord injury (SCI) causes debilitating neurological dysfunction and has been observed in warfighters injured in IED blasts. Clinical benefit of SCI treatment remains elusive and better large animal models are needed to assess treatment options. Here, we describe a controlled electromagnetic spinal cord impactor for use in large animal models of SCI.

METHODS

A custom spinal cord impactor and platform were fabricated for large animals (e.g., pig, sheep, dog, etc.). Impacts were generated by a voice coil actuator; force and displacement were measured with a load cell and potentiometer respectively. Labview (National Instruments, Austin, TX) software was used to control the impact cycle and import force and displacement data. Software finite impulse response (FIR) filtering was employed for all input data. Silicon tubing was used a surrogate for spinal cord in order to test the device; repeated impacts were performed at 15, 25, and 40 Newtons.

RESULTS

Repeated impacts demonstrated predictable results at each target force. The average duration of impact was 71.2 ±6.1ms. At a target force of 40N, the output force was 41.5 ±0.7N. With a target of 25N, the output force was 23.5 ±0.6N; a target of 15Newtons revealed an output force of 15.2 ±1.4N. The calculated acceleration range was 12.5-21.2m/s².

CONCLUSIONS

This custom spinal cord impactor reliably delivers precise impacts to the spinal cord and will be utilized in future research to study acute traumatic SCI in a large animal.

In vivo two-photon imaging of axonal dieback, blood flow, and calcium influx with methylprednisolone therapy after spinal cord injury

Severe spinal cord injury (SCI) can cause neurological dysfunction and paralysis. However, the early dynamic changes of neurons and their surrounding environment after SCI are poorly understood. Although methylprednisolone (MP) is currently the standard therapeutic agent for treating SCI, its efficacy remains controversial. The purpose of this project was to investigate the early dynamic changes and MP's efficacy on axonal damage, blood flow, and calcium influx into axons in a mouse SCI model. YFP H-line and Thy1-GCaMP transgenic mice were used in this study. Two-photon microscopy was used for imaging of axonal dieback, blood flow, and calcium influx post-injury. We found that MP treatment attenuated progressive damage of axons, increased blood flow, and reduced calcium influx post-injury. Furthermore, microglia/macrophages accumulated in the lesion site after SCI and expressed the proinflammatory mediators iNOS, MCP-1 and IL-1β. MP treatment markedly inhibited the accumulation of microglia/macrophages and reduced the expression of the proinflammatory mediators. MP treatment also improved the recovery of behavioral function post-injury. These findings suggest that MP exerts a neuroprotective effect on SCI treatment by attenuating progressive damage of axons, increasing blood flow, reducing calcium influx, and inhibiting the accumulation of microglia/macrophages after SCI.

Real-time and spatial quantification using contrast-enhanced ultrasonography of spinal cord perfusion during experimental spinal cord injury

STUDY DESIGN

Experimental study in male Wistar rats.

OBJECTIVE

To quantify temporal and spatial changes simultaneously in spinal cord blood flow and hemorrhage during the first hour after spinal cord injury (SCI), using contrast-enhanced ultrasonography (CEU).

SUMMARY OF BACKGROUND DATA

Post-traumatic ischemia and hemorrhage worsen the primary lesions induced by SCI. Previous studies did not simultaneously assess temporal and spatial changes in spinal cord blood flow.

METHODS

SCI was induced at Th10 in 12 animals, which were compared with 11 sham-operated controls. Spinal cord blood flow was measured in 7 adjacent regions of interest and in the sum of these 7 regions. Blood flow was quantified using CEU with intravenous microbubble injection. Spinal cord hemorrhage was measured on conventional B-mode sonogram slices.

RESULTS

CEU allowed us to measure the temporal and spatial changes in spinal cord blood flow in both groups. In the SCI group, spinal cord blood flow was significantly decreased in the global region of interest (P = 0.0016), at the impact site (epicenter), and in the 4 regions surrounding the epicenter, compared with the sham group. The blood flow decrease was maximum at the epicenter. No statistically significant differences between the sham groups were found for the most rostral and caudal regions of interest. Hemorrhage size increased significantly with time (P < 0.0001), from 30.3 mm(2) (±2) after 5 minutes to 39.6 mm(2) (±2.3) after 60 minutes.

CONCLUSION

CEU seems reliable for quantifying temporal and spatial changes in spinal cord blood flow. After SCI, bleeding occurs in the spinal cord parenchyma and increases significantly throughout the first hour.

Anatomy and biomechanics of the spinal column and cord

The field of biomechanics combines the disciplines of biology and engineering, attempting to quantitatively describe the complicated properties of biological materials. These properties depend not only upon the inherent attributes of its constituents but also upon how the constituents are arranged relative to each other. Its importance in understanding spinal column and spinal cord pathology cannot be overemphasized. This chapter is a primer on the application of biomechanical principles to the normal and pathological spine. The basic concepts of biomechanics will first be reviewed followed by a review of the structural anatomy of the osteoligamentous spinal column and the biomechanics of injury. Relevant spinal cord anatomy will then be addressed as well as current biomechanical theories of spinal cord injury.

Blood supply and vascular reactivity of the spinal cord under normal and pathological conditions

The authors present a review of spinal cord blood supply, discussing the anatomy of the vascular system and physiological aspects of blood flow regulation in normal and injured spinal cords. Unique anatomical functional properties of vessels and blood supply determine the susceptibility of the spinal cord to damage, especially ischemia. Spinal cord injury (SCI), for example, complicating thoracoabdominal aortic aneurysm repair is associated with ischemic trauma. The rate of this devastating complication has been decreased significantly by instituting physiological methods of protection. Traumatic SCI causes complex changes in spinal cord blood flow, which are closely related to the severity of injury. Manipulating physiological parameters such as mean arterial blood pressure and intrathecal pressure may be beneficial for patients with an SCI. Studying the physiopathological processes of the spinal cord under vascular compromise remains challenging because of its central role in almost all of the body's hemodynamic and neurofunctional processes.

Methylprednisolone worsening neuropathic pain in non-traumatic thoracic myelopathy

Methylprednisolone (MP) is the only neuroprotective medication currently in widespread use for the treatment of spinal cord injury. Increasingly, published studies challenge its clinical effects in view of its serious side-effects including wound infection, pneumonia, sepsis and steroid myopathy. Most cases with spontaneous spinal epidural haematoma (SSEH) need emergency evacuation, and typically show good neurologic recovery. Some patients with SSEH given preoperative or postoperative MP within hours of the onset of symptoms, and have had good motor recovery, although no mention was made of sensory function. Severe, intractable neuropathic pain has not been reported in patients with SSEH. We present a case of SSEH treated with a high-dose MP 16 h after onset of symptoms. Surgical decompression was performed 1 h after MP treatment. Motor recovery was good; however, intractable neuropathic pain developed 5 weeks postoperatively. We discuss the factors contributing to intractable pain. We speculate that the severe, intractable pain might be due to misuse of large-dose steroids in this case of non-traumatic spinal myelopathy, and not because of the injury per se.

Influência do estreitamento do canal vertebral e do tempo para a descompressão na recuperação locomotora de ratos

OBJETIVO: o objetivo deste trabalho foi estudar as consequências da lesão por contusão da medula espinhal, associada ao estreitamento do canal vertebral, no comportamento motor de ratos, avaliando-se o efeito do tempo para descompressão na recuperação neurológica dos animais. MÉTODOS: foram utilizados ratos Wistar machos (n=6 por grupo), subdivididos nos seguintes grupos experimentais: laminectomia (T9-T10, Grupo Controle), contusão por queda de peso (10 g de peso, 15 cm de altura), estreitamento do canal vertebral em 35% (hastes de policarbonato; espessura de 0,78 mm) e contusão associada ao estreitamento do canal vertebral. O grupo de lesão associada foi ainda subdividido em sem ou com descompressão 24 ou 72 horas após a cirurgia. Os animais foram sacrificados sete dias após os procedimentos cirúrgicos. A função locomotora dos animais foi avaliada por meio do teste do campo aberto, do teste do plano inclinado e pela aplicação da escala BBB, antes da cirurgia, 24 e 72 horas depois da cirurgia e após 7 dias do procedimento cirúrgico. RESULTADOS: a lesão por queda de peso e compressão da medula espinhal, bem como a lesão mista, prejudicaram o comportamento motor dos animais, sendo que a descompressão cirúrgica após 24 e 72 horas da cirurgia não melhorou a recuperação motora dos animais, como mostram os resultados da avaliação de campo aberto, no plano inclinado e pela escala BBB. Por outro lado, os animais que sofreram lesão medular por queda de peso apresentaram melhores escores na escala BBB e ângulos maiores no plano inclinado do que aqueles que sofreram lesão por estreitamento do canal vertebral ou lesão mista. CONCLUSÕES: a lesão por queda de peso ou estreitamento do canal vertebral provocou alterações no comportamento motor dos animais, sendo que a descompressão não trouxe melhora funcional significativa.

End organ effects of high-dose human equivalent methylprednisolone in a spinal cord injury rat model

STUDY DESIGN

Interventional study.

OBJECTIVE

To analyze the histologic effects of high-dose human equivalent methylprednisolone on the pulmonary, cardiac, intestinal, renal, hepatic, and splenic tissues in a spinal cord injury rat model.

SUMMARY OF BACKGROUND DATA

There are numerous investigations of various medical interventions for the treatment of acute spinal cord trauma. Currently, the only generally accepted medical intervention in an acute spinal cord trauma is the intravenous administration of high doses of methylprednisolone. Although it has been nearly 2 decades since the first National Acute Spinal Cord Injury Study investigated the role high-dose steroids might play in the treatment of acute spinal cord trauma, controversy still exists regarding the efficacy of this treatment. To our knowledge, no study has examined the role of high-dose methylprednisolone in organ systems other than the spinal cord in an acute spinal cord injury model at the histologic level. This study attempts to characterize end organ histologic response to human dose equivalent (HDE) intravenous methylprednisolone administration in a rodent model of acute spinal cord injury.

METHODS

A total of 48 Sprague-Dawley rats were divided equally into control and experimental groups. Each group was subdivided into 6 sets of 4 animals each, according to intervals after injury. Groups 1-6 consisted of animals euthanized at 0, 4, 8, 16, 24, and 48 hours after spinal cord injury. Paraplegia after lower thoracic laminectomy was achieved using a standardized Allen weight drop technique. Within 1 hour of injury, experimental animals were treated with HDE methylprednisolone, infused for 23 hours continuously. Liver, kidney, lung, intestine, spleen, and heart were harvested at variable intervals after injury and prepared for histologic examination. These slides were analyzed with microscopic staining techniques and compared in a blinded manner by a qualified pathologist.

RESULTS

Of all the end organs analyzed, the spleens were most affected. Lymphocytic depletion was seen in as little as 4 hours after methylprednisolone infusion and continued until 48 hours. Pulmonary tissues variably showed interstitial congestion and eosinophilic alveolar collections. Intestinal mucosal tissues showed edema and autolyzed mucosa from 16 hours onwards. Cardiac, kidney, and hepatic tissue did not differ significantly from controls.

CONCLUSIONS

Histologically, HDE methylprednisolone caused significant splenic lymphocytic depletion changes in as little as 4 hours. This trend of end organ lymphocytopenia continued to progress until 48 hours. Pulmonary eosinophilic infiltrates were seen from 8 until 24 hours. Intestinal mucosal edema and necrosis were seen in samples at 16 hours throughout 48 hours. This study was designed to evaluate end organ changes seen in an animal model of an acute spinal cord injury treated with HDE methylprednisolone. Study animals were infused with HDE methylprednisolone given according to the National Acute Spinal Cord Injury Study II protocol. The kidney, lung, cardiac, intestinal, splenic, and hepatic tissues from the aforementioned animals were then sectioned and analyzed using histologic staining techniques by a qualified pathologist.

FK 506 reduces tissue damage and prevents functional deficit after spinal cord injury in the rat

We examined the efficacy of FK 506 in reducing tissue damage after spinal cord injury in comparison to methylprednisolone (MP) treatment. Rats were subjected to a photochemical injury (T8) and were given a bolus of MP (30 mg/kg), FK 506 (2 mg/kg), or saline. An additional group received an initial bolus of FK 506 (2 mg/kg) followed by daily injections (0.2 mg/kg intraperitoneally). Functional recovery was evaluated using open-field walking, inclined plane tests, motor evoked potentials (MEPs), and the H-reflex response during 14 days postoperation (dpo). Tissue sparing and glial fibrillary acidic protein (GFAP), biotinylated tomato lectin LEC, cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and interleukin 1 beta (IL-1 beta) immunoreactivity were quantified in the injured spinal cord. FK 506-treated animals demonstrated significantly better neurologic outcome, higher MEP amplitudes, and lower H-wave amplitude compared to that of saline-treated rats. In contrast, administration of MP did not result in significant differences with respect to the saline-treated group. Histologic examination revealed that tissue sparing was largest in FK 506-treated compared to saline and MP-treated animals. GFAP and COX-2 reactivity was decreased in animals treated with FK 506 compared to that in animals given MP or saline, whereas IL-1 beta expression was similarly reduced in both FK 506- and MP-treated groups. Microglia/macrophage response was reduced in FK 506 and MP-injected animals at 3 dpo, but only in MP-treated animals at 7 dpo with respect to saline-injected rats. Repeated administrations of FK 506 improved functional and histologic results to a greater degree than did a single bolus of FK 506. The results indicate that FK 506 administration protects the damaged spinal cord and should be considered as potential therapy for treating spinal cord injuries.

Spinal blood flow in 24-hour megadose glucocorticoid treatment in awake pigs

OBJECT

Because of the controversy regarding the benefits of 24-hour administration of methylprednisolone in patients with spinal cord injury (SCI), it is important to investigate its mechanism of action and side effects. This study was conducted to determine if high-dose methylprednisolone modulates neural and vertebral blood flow in an awake large-sized animal model without SCI.

METHODS

From a group of 18 immature female domestic pigs born to nine different litters, nine animals were randomly allocated to receive methylprednisolone treatment, whereas their nine female siblings served as controls. Drug or placebo was applied in a blinded fashion by a third person not involved in the study. The following treatment for SCI, as suggested by the North American Spinal Cord Injury Study, was administered to the awake pig: methylprednisolone (30 mg/kg of body weight) was infused into the jugular vein during a 15-minute period, followed by a 45-minute pause, and the infusion was maintained over a 23-hour period at a dose of 5.4 mg/kg body weight/hour. By means of the radioactive tracer microsphere technique, spinal cord blood flow (SCBF) was measured in the awake standing pig in the cerebrum, and in spinal gray and white matter, nerve roots, endplates, cancellous bone, cortical shell, and T12-L2 discs. Blood flow was measured before, 1 hour after initiation of infusion, and 24 hours postinfusion. Examination of blood flow in the neural and vertebral tissue samples, as well as of central hemodynamics, revealed no significant difference between the experimental and control groups, and this parity was maintained throughout the experimental phases.

CONCLUSIONS

In the awake pig model, 24-hour methylprednisolone treatment does not modulate cerebral or SCBF, nor does it increase the risk for vertebral osteonecrosis by producing vertebral ischemia.