Bridging the neural gap

Benign peripheral nerve tumors: treatment algorithm and reconstructive options

Peripheral nerve tumors are mostly benign; however, their excision can result in profound deficits. Nerve reconstruction strategies offer techniques to minimize morbidity. In this prospective study, 20 consecutive patients with benign peripheral nerve tumors were treated using a single-stage surgical paradigm between 2003 and 2007. Nerve fascicles were microdissected off of the tumor; any fascicle that gave origin to the tumor (was inseparable from tumor) was reconstructed using nerve conduits. Patients were followed from 6 to 24 months. All patients had neuropathic pain before tumor excision; only 1 patient had pain persist postoperatively. Seventeen patients had complete functional recovery after nerve reconstruction. No perioperative complications occurred. Benign peripheral nerve tumors require highly specialized surgical care. Tumor excision with immediate nerve reconstruction, for fascicles inseparable from the tumor, optimizes outcomes. Nerve reconstruction with available conduits or allografts should be attempted to restore anatomic integrity to any killed fascicles, thereby minimizing possible deficits.

Transplantation of autologous Schwann cells for the repair of segmental peripheral nerve defects

Peripheral nerve injuries are a source of chronic disability. Incomplete recovery from such injuries results in motor and sensory dysfunction and the potential for the development of chronic pain. The repair of human peripheral nerve injuries with traditional surgical techniques has limited success, particularly when a damaged nerve segment needs to be replaced. An injury to a long segment of peripheral nerve is often repaired using autologous grafting of "noncritical" sensory nerve. Although extensive axonal regeneration can be observed extending into these grafts, recovery of function may be absent or incomplete if the axons fail to reach their intended target. The goal of this review was to summarize the progress that has occurred in developing an artificial neural prosthesis consisting of autologous Schwann cells (SCs), and to detail future directions required in translating this promising therapy to the clinic. In the authors' laboratory, methods are being explored to combine autologous SCs isolated using cell culture techniques with axon guidance channel (AGC) technology to develop the potential to repair critical gap length lesions within the peripheral nervous system. To test the clinical efficacy of such constructs, it is critically important to characterize the fate of the transplanted SCs with regard to cell survival, migration, differentiation, and myelin production. The authors sought to determine whether the use of SC-filled channels is superior or equivalent to strategies that are currently used clinically (for example, autologous nerve grafts). Finally, although many nerve repair paradigms demonstrate evidence of regeneration within the AGC, the authors further sought to determine if the regeneration observed was physiologically relevant by including electrophysiological, behavioral, and pain assessments. If successful, the development of this reparative approach will bring together techniques that are readily available for clinical use and should rapidly accelerate the process of bringing an effective nerve repair strategy to patients with peripheral nerve injury prior to the development of pain and chronic disability.

Improving nerve regeneration of acellular nerve allografts seeded with SCs bridging the sciatic nerve defects of rat

The objective of the paper is to evaluate the effect of acellular nerve allografts (ANA) seeded with Schwann cells to promote nerve regeneration after bridging the sciatic nerve defects of rats and to discuss its acting mechanisms. Schwann cells were isolated from neonatal Wistar rats. In vitro Schwann cells were microinjected into acellular nerve allografts and co-cultured. Twenty-four Wistar rats weighing 180-220 g were randomly divided into three groups with eight rats in each group: ANA seeded with Schwann cells (ANA + SCs), ANA group and autografts group. All the grafts were, respectively, served for bridging a 10-mm long surgically created sciatic nerve gap. Examinations of regeneration nerve were performed after 12 weeks by transmission electron microscope (TEM), scanning electron microscope (SEM), and electrophysiological methods, and then analyzed statistically. The results obtained indicated that in vitro Schwann cells displayed the feature of bipolar morphology with oval nuclei. Compared with ANA group, the conduction velocity of ANA + SCs group and autograft group was faster after 12 weeks, latent period was shorter, and wave amplitude was higher (P < 0.05). The difference between ANA + SCs group and autograft group is not significant (P > 0.05). Regeneration nerve myelinated fiber number, myelin sheath thickness, and myelinated fibers/total nerves (%) in both ANA + SCs group and autograft group are higher than that in ANA group; the difference is significant (P < 0.05). The difference between the former two is not significant (P > 0.05). In conclusion, ANA seeded with SCs could improve nerve regeneration and functional recovery after bridging the sciatic nerve gap of rats, which offers a novel approach for the repair peripheral nerve defect.

EVALUATION OF THE PROPRIOCEPTIVE INFLUENCE OF THE CUTANEOUS AFFERENTS TO THE ANKLE IN PATIENTS AFTER SURAL NERVE HARVESTING

OBJECTIVE

Cutaneous afferent nerves contribute to joint proprioception. The aim of this study was to retrospectively analyze the proprioceptive influence of the cutaneous afferents to the ankle in patients after sural nerve harvesting in comparison to controls.

METHODS

The proprioception of the ankle in 24 patients after sural nerve harvesting was investigated. The sural nerve was harvested bilaterally in Group 1 (n = 10), in the right leg in Group 2 (n = 6), and in the left leg in Group 3 (n = 8). The proprioception of the ankle was also tested in controls (Group 4, n = 24). The peroneal reaction time (PRT) was measured on a tilting platform. The position sense test was performed. Balance control was investigated with the Biodex Stability System (Biodex Medical Systems, Shirley, NY) at the stable Level 8 and unstable Level 2.

RESULTS

No significant differences among the groups were seen in the position sense test, the PRT, and all scores of the Biodex Stability System. The PRT showed significant differences in comparison to the contralateral leg for the peroneus brevis muscle in Group 1 (P = 0.005) and Group 4 (P = 0.001) as well as for the peroneus longus muscle in Group 3 (P = 0.036) and Group 4 (P = 0.001).

CONCLUSION

The proprioception of the ankle in patients after sural nerve harvesting is not reduced in comparison to controls. Significant differences of the PRT between the left and right legs are attributable to leg dominance in most cases and not to a loss of innervation. Harvesting of the sural nerve does not result in ankle instability.

Evaluation and management of peripheral nerve injury

Common etiologies of acute traumatic peripheral nerve injury (TPNI) include penetrating injury, crush, stretch, and ischemia. Management of TPNI requires familiarity with the relevant anatomy, pathology, pathophysiology, and the surgical principles, approaches and concerns. Surgical repair of TPNI is done at varying time intervals after the injury, and there are a number of considerations in deciding whether and when to operate. In neurapraxia, the compound muscle and nerve action potentials on stimulating distal to the lesion are maintained indefinitely; stimulation above the lesion reveals partial or complete conduction block. The picture in axonotmesis and neurotmesis depends on the time since injury. The optimal timing for an electrodiagnostic study depends upon the clinical question being asked. Although conventional teaching usually holds that an electrodiagnostic study should not be done until about 3 weeks after the injury, in fact a great deal of important information can be obtained by studies done in the first week. Proximal nerve injuries are problematic because the long distance makes it difficult to reinnervate distal muscles before irreversible changes occur. Decision making regarding exploration must occur more quickly, and exploration using intraoperative nerve action potential recording to guide the choice of surgical procedure is often useful.

Fabrication of a PLGA-collagen peripheral nerve scaffold and investigation of its sustained release property in vitro

This study deals with the fabrication of a peripheral nerve scaffold prepared with poly (lactic acid-co-glycolic acid) [PLGA] and acellularized pigskin collagen micro particles and the investigation of its sustained release property in vitro. We took bovine serum albumin [BSA] as model drug to investigate the sustained-release property of the scaffold in vitro. The results showed the scaffold could release BSA steadily with a rate of 6.6 ng/d (r=0.994) or so. In a 1-month test period, the accumulative release ratio of BSA from the scaffold was up to 43%, and the shape of the scaffold was still originally well kept. In addition, the scaffold outcome non-immunogenicity, good cell adhesion and biodegradability. The results indicated a scaffold constructed by this technique would be a potential implanting support with prolonged sustained release function, such as for the use of nerve scaffold.

Experience with nerve allograft transplantation

Nerve allograft transplantation should be used for the repair of devastating peripheral nerve injuries that cannot be reconstructed through traditional means such as autologous nerve grafting or nerve transfer procedures. The risks of required systemic immunosuppression, although only temporary for nerve allograft recipients, preclude widespread use of this treatment modality. Translational research has led to several advancements in this field including the use of preoperative allograft cold preservation in University of Wisconsin organ preservation solution and inclusion of tacrolimus as part of the immunosuppressive regimen. Investigation of how to further diminish nerve allograft immunogenicity, speed neuroregeneration by use of agents such as tacrolimus, and promote preferential motor regeneration will further advance this field with the goal of restoring optimal function while minimizing patient morbidity.

Selection of the donor nerve for end-to-side neurorrhaphy

Object

The authors of other studies have reported that the selection of an agonistic donor nerve is required for recovering voluntary motor control after end-to-side nerve repair. In this experimental investigation, the authors' goal was to verify this assumption by performing end-to-side neurorrhaphy of the rat median nerve on its antagonistic radial nerve.

Methods

The left median nerve in 10 adult female rats was repaired by end-to-side neurorrhaphy after epineuriotomy on the radial nerve at the middle of the brachium. The time course of median nerve functional recovery was then assessed using the grasping test until postoperative Week 30. Before removing the nerve, the surgical site was carefully explored to exclude contamination by the proximal nerve stump, and the functional anatomy of median and radial nerves was assessed by electrical stimulation. Repaired nerves were then processed for resin embedding, and semithin sections were obtained for nerve fiber histomorphometry by using the dissector method.

Results

Repaired median nerves were repopulated by nerve fibers regenerating from the radial donor nerve as previously shown. Moreover, voluntary motor control of the flexor muscles innervated by the median nerve was progressively recovered beginning in postoperative Week 10 and reaching 42% of normal by Week 30.

Conclusions

Contrary to previously reported data, recovery of voluntary motor function after end-to-side nerve repair can also be expected when an antagonistic nerve is used as a donor nerve.

Hyperbaric oxygenation in peripheral nerve repair and regeneration

Peripheral nerves are essential connections between the central nervous system and muscles, autonomic structures and sensory organs. Their injury is one of the major causes for severe and longstanding impairment in limb function. Acute peripheral nerve lesion has an important inflammatory component and is considered as ischemia-reperfusion (IR) injury. Surgical repair has been the standard of care in peripheral nerve lesion. It has reached optimal technical development but the end results still remain unpredictable and complete functional recovery is rare. Nevertheless, nerve repair is not primarily a mechanical problem and microsurgery is not the only key to success. Lately, there have been efforts to develop alternatives to nerve graft. Work has been carried out in basal lamina scaffolds, biologic and non-biologic structures in combination with neurotrophic factors and/or Schwann cells, tissues, immunosuppressive agents, growth factors, cell transplantation, principles of artificial sensory function, gene technology, gangliosides, implantation of microchips, hormones, electromagnetic fields and hyperbaric oxygenation (HBO). HBO appears to be a beneficial adjunctive treatment for surgical repair in the acute peripheral nerve lesion, when used at lower pressures and in a timely fashion (<6 hours).

A double-transgenic mouse used to track migrating Schwann cells and regenerating axons following engraftment of injured nerves

We propose that double-transgenic thy1-CFP(23)/S100-GFP mice whose Schwann cells constitutively express green fluorescent protein (GFP) and axons express cyan fluorescent protein (CFP) can be used to serially evaluate the temporal relationship between nerve regeneration and Schwann cell migration through acellular nerve grafts. Thy1-CFP(23)/S100-GFP and S100-GFP mice received non-fluorescing cold preserved nerve allografts from immunologically disparate donors. In vivo fluorescent imaging of these grafts was then performed at multiple points. The transected sciatic nerve was reconstructed with a 1-cm nerve allograft harvested from a Balb-C mouse and acellularized via 7 weeks of cold preservation prior to transplantation. The presence of regenerated axons and migrating Schwann cells was confirmed with confocal and electron microscopy on fixed tissue. Schwann cells migrated into the acellular graft (163+/-15 intensity units) from both proximal and distal stumps, and bridged the whole graft within 10 days (388+/-107 intensity units in the central 4-6 mm segment). Nerve regeneration lagged behind Schwann cell migration with 5 or 6 axons imaged traversing the proximal 4 mm of the graft under confocal microcopy within 10 days, and up to 21 labeled axons crossing the distal coaptation site by 15 days. Corroborative electron and light microscopy 5 mm into the graft demonstrated relatively narrow diameter myelinated (431+/-31) and unmyelinated (64+/-9) axons by 28 but not 10 days. Live imaging of the double-transgenic thy1-CFP(23)/S100-GFP murine line enabled serial assessment of Schwann cell-axonal relationships in traumatic nerve injuries reconstructed with acellular nerve allografts.

End-to-side (terminolateral) nerve regeneration: a challenge for neuroscientists coming from an intriguing nerve repair concept

The last 15 years have seen a growing interest regarding a technique for nerve repair named end-to-side (terminolateral) neurorrhaphy. This technique is based on the concept that nerve fiber regeneration along the distal stump of a transected nerve, the proximal stump of which was lost, can be obtained by just suturing the proximal end of its distal stump to the epinerium of a neighbor healthy and undamaged donor nerve. A large body of experimental studies have shown that end-to-side neurorrhaphy, in fact, is able to induce collateral sprouting from donor nerve's axons which is at the basis of the massive repopulation of the distal nerve stump. The regenerating nerve fibers eventually reinnervate the periphery of the severed nerve leading to a recovery of the lost function the degree of which varies depending on factors that still have to be elucidated. Surprisingly, this puzzling concept of nerve regeneration has attracted very little attention from basic neuroscientists so far and, thus, the present paper is intended to call for more biological research on it by overviewing the relevant literature and indicating the several unanswered questions that this concept asks to the neuroscience community.

Laminin and growth factor receptor activation stimulates differential growth responses in subpopulations of adult DRG neurons

Neurons in the adult rat dorsal root ganglion (DRG) can be classified into at least three separate subpopulations based on morphologic and phenotypic differences. In this study we have focused on the growth response of these specific subpopulations in vitro with respect to laminin (LN) and growth factor receptor activation. Using a cell selection approach we show that LN-induced neurite growth occurs in the absence of added trophic factors only in heavy-chain neurofilament-positive and calcitonin gene-related peptide-positive DRG neurons [nerve growth factor (NGF)-responsive population]. In contrast, LN alone is not sufficient to stimulate significant neurite growth from lectin Griffonia simplicifolia IB4-positive neurons (IB4+ve), although it is still required to elicit a growth response from these cells in the presence of glial-derived neurotrophic factor (GDNF, e.g. neurite growth occurred only when cells were plated on LN in the presence of GDNF). By using chemical inhibitors we demonstrate that only the phosphatidylinositol 3 kinase (PI 3-K)/Akt pathway is required for neurite growth from the NGF-responsive cell population. However, both the PI 3-K/Akt and MEK/mitogen-activated protein kinase signaling pathways are required for neurite growth from the IB4+ve cell population. Thus, we have identified specific signaling events and environmental requirements associated with neurite growth for different subpopulations of adult DRG neurons, pointing to potential therapeutic targets while identifying an inability for any one treatment alone to repair peripheral nerve damage.

From experimental rat hindlimb to clinical face composite tissue allotransplantation: Historical background and current status

The purpose of this article is to review the historical background and clinical status of composite tissue allotransplantation and to discuss the scientific evolution of clinical face transplantation. Composite tissue allotransplantation (CTA) rapidly progressed in the 1980s with the discovery of cyclosporine. Although the most success has been achieved with hand transplantation, others have made progress with allografts of trachea, peripheral nerve, flexor tendon apparatus, vascularized knee, larynx, abdominal wall, and most recently, partial face. The world's first partial face allotransplantation occurred in November 2005 in France. In April of 2006, there was a second performed in China. As of today, there are now multiple institutions with plans to attempt the world's first full facial/scalp transplant. Complete facial/scalp allotransplantation offers a viable alternative for unfortunate individuals suffering severe facial disfigurement and is a product of many decades of experimental research, beginning with rat hindlimb allografts.