Peripheral nerve regeneration: the effects of postoperative irradiation

Mesenchymal stem cells and local tacrolimus delivery synergistically enhance neurite extension

BACKGROUND

The aim of this study was to investigate the combined effect of mesenchymal stem cells (MSC) and local delivery of tacrolimus (FK506) on nerve regeneration when applied to nerve autografts and decellularized allografts.

METHODS

A three-dimensional in vitro compartmented cell culture system consisting of a neonatal dorsal root ganglion adjacent to a nerve graft was used to evaluate the regenerating neurites into the peripheral nerve scaffold. Nerve autografts and allografts were treated with (i) undifferentiated MSCs, (ii) FK506 (100 ng/mL) or (iii) both (N = 9/group). After 48 hours, neurite extension was measured to quantify nerve regeneration and stem cell viability was evaluated.

RESULTS

Stem cell viability was confirmed in all MSC-treated grafts. Neurite extension was superior in autografts treated with FK506, and MSCs and FK506 combined (p < 0.001 and p = 0.0001, respectively), and autografts treated with MSCs (p = 0.12) were comparable to untreated autografts. In allografts, FK506 treatment and combined treatment were superior to controls (p < 0.001 and p = 0.0001, respectively), and treatment with MSCs (p = 0.09) was comparable to controls. All autograft groups were superior compared to their respective allograft treatment group (p < 0.05) in neurite extension.

CONCLUSIONS

Alone, either MSC or FK506 treatment improved neurite outgrowth, and combined they further enhanced neurite extension in both autografts and allografts.

Functional Restoration Following Resection of Malignant Peripheral Nerve Sheath Tumour of the Median Nerve: A Case Report

Management of malignant peripheral nerve sheath tumours (MPNSTs) is primarily surgical, involving surgical resection with wide margins, and frequently radiation therapy. When a MPNST involves a major peripheral nerve, wide resection leads to significant distal neurologic deficits. A patient who underwent resection of a MPNST involving the median nerve above the elbow is presented. Staged tendon and nerve transfers were performed to restore sensation to the thumb and index finger, thumb opposition and flexion, finger flexion and forearm pronation. These included: 1. radial sensory nerve branches to digital nerves of thumb and index finger, 2. ulnar nerve branch of flexor carpi ulnaris to pronator teres, 3. brachioradialis to flexor pollicis longus, 4. side-to-side transfer of flexor digitorum profundus tendon of index finger to middle, ring and little fingers, 5. extensor indicis proprius to abductor pollicis brevis. The rationale, approach, and favourable results of functional reconstruction in this patient are detailed.

Restoration of Neurological Function Following Peripheral Nerve Trauma

Following peripheral nerve trauma that damages a length of the nerve, recovery of function is generally limited. This is because no material tested for bridging nerve gaps promotes good axon regeneration across the gap under conditions associated with common nerve traumas. While many materials have been tested, sensory nerve grafts remain the clinical “gold standard” technique. This is despite the significant limitations in the conditions under which they restore function. Thus, they induce reliable and good recovery only for patients < 25 years old, when gaps are <2 cm in length, and when repairs are performed <2–3 months post trauma. Repairs performed when these values are larger result in a precipitous decrease in neurological recovery. Further, when patients have more than one parameter larger than these values, there is normally no functional recovery. Clinically, there has been little progress in developing new techniques that increase the level of functional recovery following peripheral nerve injury. This paper examines the efficacies and limitations of sensory nerve grafts and various other techniques used to induce functional neurological recovery, and how these might be improved to induce more extensive functional recovery. It also discusses preliminary data from the clinical application of a novel technique that restores neurological function across long nerve gaps, when repairs are performed at long times post-trauma, and in older patients, even under all three of these conditions. Thus, it appears that function can be restored under conditions where sensory nerve grafts are not effective.

A systematic review of functional outcomes after nerve reconstruction in extremity soft tissue sarcomas: A need for general implementation in the armamentarium

Resection of nerves in extremity soft tissue sarcomas (STS) can lead to large functional deficits. Nerve reconstructions are rarely performed and little is known on their outcomes and indications for their use, even though they are essential in restoring sensation in limb salvage procedures. This study investigated current knowledge on functional outcomes and considerations to be taken before performing such reconstructions after sarcoma resection. A systematic search was performed in July 2018 in PubMed and Embase databases according to PRISMA guidelines. Search terms related to "soft tissue sarcoma" and "nerve reconstruction" were used. Studies evaluating functional outcomes after nerve grafting or nerve transfers in extremity STS were included. Qualitative synthesis was performed on all studies. Nineteen studies were included after full-text screening, describing 26 patients. The majority of patients had a nerve reconstruction in the upper extremity (65%). Perioperative radiotherapy was administered in 67% and perioperative chemotherapy in 29% of patients. Nerve grafting was most commonly performed (n = 23) and nerve transfers were performed in six patients. A wide variety of outcome measures were used. Most patients recovered at least some motor function and sensation, but success rates were higher after upper than lower extremity defects. Multimodal treatment did not preclude successful reconstructions. Nerve reconstructions in extremity STS allow the restoration of sensation in limb salvation, even motor nerve function can be restored with satisfactory function. The use of multimodal therapy does not seem to interfere with success. Nerve reconstructions should therefore be considered in STS patients.

Effects of Postoperative Radiotherapy on Vascularized Nerve Graft for Facial Nerve Repair in a Rabbit Model

PURPOSE

High fractional dose radiotherapy (RT) produces better radiobiological results. However, a concern always exists regarding radiation-induced damage to normal tissues, in particular, the peripheral nerves. In the present study, we assessed the effects of postoperative RT on vascularized facial nerve grafts in a rabbit model.

MATERIALS AND METHODS

Surgical defects were created bilaterally on the upper buccal branches of the facial nerve in rabbits. One side received a vascularized nerve graft (VNG), and the other side received a free nerve graft (FNG). RT was planned in 1 group at 1 month postoperatively. The dose was equivalent to 60 Gy for each side. Evaluation of the facial performance, electrophysiologic monitoring, histologic studies, toluidine blue staining, and scanning electron microcopy were performed at 3 months after RT.

RESULTS

In the RT group, the pathological changes included surrounding tissue fibrosis, nerve cell shrinkage, Schwann cell injury, and demyelination. Compared with the control group, postoperative RT had no obvious effect on the regeneration and functional recovery of the facial nerves. The functional recovery rate of the VNG was faster than that of the FNG in the RT group. In addition, the difference in the nerve conduction velocity and amplitude was statistically significant between the 2 groups.

CONCLUSIONS

Postoperative RT influenced the functional recovery of facial nerves to a certain degree. The use of VNGs could alleviate the adverse effects of RT on facial nerve regeneration.

Direct effect of radiation on the peripheral nerve in a rat model

Radiation neuropathy is one of the severe complications of radiotherapy. Entrapment neuropathy, caused by surrounding soft tissue fibrosis induced by radiation, plays a key role in the onset of this neuropathy. Meanwhile, the pathophysiology of the direct effect of radiation on the peripheral nerve is not yet fully understood. The aim of this study is to investigate the direct effects of radiation on rat sciatic nerves that are isolated from surrounding soft tissue. In the radiation group (R group), only the exposed sciatic nerve was irradiated with 90 Gy X-radiation. In the sham group (S group), the surgical procedures were completed without radiation. The sciatic functional index (SFI) result demonstrated no statistical differences between the R group and S group. However, even though the surrounding soft tissue was not irradiated, the macroscopic and histological findings of the R group at 24 weeks after radiation showed scar formation around the radiated nerve. These findings on radiation neuropathy indicate that neurohumoral factors derived from the radiated nerve itself may cause fibrosis. The electromyographic and histological examination showed axonal degeneration in the R group. Furthermore, the axon diameter and axon packing density in the R group demonstrated the axonal degeneration, even though it was 0.5 cm more proximal to the radiated portion than the axon packing density in the S group. This appearance was assumed to be "dying-back" neuropathy. It is believed that this study is a first step toward identifying an accurate pathophysiology for intractable radiation-induced peripheral neuropathy.

Recovery of sensation in immediate breast reconstruction with latissimus dorsi myocutaneous flaps after breast-conservative surgery and skin-sparing mastectomy

In breast reconstruction, sensation in the reconstructed breasts affects the patients' quality of life along with its aesthetic outcome. Fortunately, less invasive procedures such as breast-conservative surgery (BCS) and skin-sparing mastectomy (SSM) have greatly contributed to the improved aesthetic outcome in immediate breast reconstruction. However, there are few reports on the recovery of breast sensation after BCS and SSM. We retrospectively reviewed 104 consecutive patients who underwent immediate breast reconstruction with the latissimus dorsi myocutaneous flap between 2001 and 2006 at our institution. The sensations of pain, temperature, touch, and vibration were examined at the nipple and skin envelope during the follow-up period (range: 12-61 months, mean: 31 months), and a stratified analysis was performed to determine the critical factors affecting the sensation recovery after BCS and SSM. We found that large breast size significantly impaired the recovery of sensation in the nipple and skin envelope after BCS as well as SSM. Older age and high body mass index value were the factors which negatively affected the sensation in the skin envelope after SSM. While all our BCS patients underwent postoperative radiation therapy, it did not negatively affect the recovery of sensation in SSM patients. On the basis of these findings, we could further improve the sensation of the reconstructed breasts after BCS and SSM. Especially after SSM, the use of innervated flaps is recommended in the patients with large breast, increased age, or obesity when the nipple-areola complex is resected.

End-to-side neurorrhaphy for median nerve repair after elbow tumor resection: case report

We report a case of a median to ulnar end-to-side neurorrhaphy with epineurectomy but without fascicular donor nerve section. Surgery was performed for the curative treatment of an elbow synovial sarcoma at the level of the elbow that necessitated resection of 10 cm of the median nerve. The patient was followed up for 24 months. After 4 months, a recovery of protective sensation in the territory of the median nerve was noticed and had stabilized by 1 year.

Preliminary Report of the Effect of High-Dose Adjuvant Intensity Modulated Radiation Therapy on the Sural Nerve Graft for Cavernosal Nerve Sacrifice After Radical Prostatectomy

PURPOSE

A sural nerve graft may replace a killed cavernosal nerve. The effect of intensity-modulated radiation therapy (IMRT) on function of the graft has not been reported.

MATERIALS AND METHODS

Between 1998 and 2001, 8 patients (9 nerve grafts) were treated with postoperative IMRT (mean dose, 70 Gy). Two patients had neoadjuvant Lupron 30 mg 2 months prior to radiation. Potency was defined as ability to achieve spontaneous erection sufficient for vaginal penetration. Median follow-up was 31.6 months.

RESULTS

Five patients (62.5%) who had erectile function after prostatectomy preserved spontaneous erectile function after radiation. Of these, 3 patients had both nerves resected (two receiving unilateral grafts and one receiving bilateral grafts) and 2 others had one graft and one nerve preserved. The impotent patients were impotent after surgery.

CONCLUSION

High-dose postprostatectomy IMRT does not place sural nerve grafts at greater risk for failure. Larger numbers of patients are needed to confirm these encouraging, preliminary findings.

Effects of External Beam Radiation in the Rat Tibial Nerve after Crush, Transection and Repair, or Nerve Isograft Paradigms

INTRODUCTION

In head and neck surgery, radiation therapy is often administered to an injured nerve. Previous studies have examined the effects of either preoperative or postoperative radiation on nerve regeneration in rodents. In these studies, histomorphometric analysis was performed up to 8 month postoperatively. Given the exceptional neuroregenerative capacity of rodents, significant differences in nerve regeneration may go undetected if nerves are evaluated at such distant postoperative time points. This study is designed with a more appropriate model and investigates the effects of radiation after three common nerve injury paradigms.

METHODS

Sixty-four Lewis rates were randomized to 8 groups corresponding to uninjured, tibial nerve crush, transection and repair, or reconstruction with isografts. Half of the animals in each of these paradigms (n = 8 per group) were treated with 10 Gy of external beam radiation to the site of nerve injury at 7 days postoperatively. On postoperative day 28, functional recovery and histomorphometric assessment was performed.

RESULTS

For a given paradigm of nerve injury, no significant differences in nerve fiber number, neural density, neural debris, or fiber width were noted between the control and radiated groups, and radiation did not affect functional recovery.

CONCLUSION

Radiation had no discernible effect on nerve regeneration or functional recovery in the rodent nerve injury models studied. All assessments were made at time points suitable for detecting differences in nerve regeneration between groups. These findings suggest that administration of radiation to fields containing injured peripheral nerve is unlikely to adversely affect functional outcomes.

The Effect of Low-dose External Beam Radiation on Extraneural Scarring after Peripheral Nerve Surgery in Rats

OBJECTIVE

Scar tissue is an inevitable result of peripheral nerve surgery. A variety of substances have been used to prevent epineurial scarring. In this study, the effect of low-dose radiation therapy on epineurial scarring was investigated.

METHODS

Seventy-eight male Sprague-Dawley rats were studied. A total of 60 rats were subjected to one of three types of surgical procedure on the sciatic nerve, as follows: Procedure 1, external neurolysis (n = 20); Procedure 2, abrasive injury (n = 20); and Procedure 3, anastomosis (n = 20). On the left sciatic nerves, 700 cGy external beam radiation was administered 24 hours after surgery, and the right sciatic nerves served as a control group (surgery only). Eighteen animals without surgical intervention were used to establish the fibrotic effect of radiotherapy on normal nerves. A neurological examination was performed weekly. Six weeks after surgery, the extent of extraneural scarring was examined by gross microdissection by means of a numerical grading scheme and histological analysis. Cellular density and surface measurements of scar tissue were also evaluated.

RESULTS

The dissection around the nerve was easier in rats treated with low-dose radiation compared with the control group. Furthermore, grading scores in both nerve adherence and nerve separability were significantly lower in treated nerves than in the control group (P < or = 0.05). Low-dose radiotherapy decreased the scores of cellular density and surface measurement of scar tissue (P < or = 0.05). In normal nerves, radiotherapy did not produce any fibrotic effects and the density of fibroblasts/fibrocytes was also very low.

CONCLUSION

In the case of surgery or local trauma to peripheral nerve, the use of low-dose radiation therapy may be a safe method of limiting postoperative epineurial scar formation.