Visualization of peripheral nerve regeneration

Ultrasound Landmarks in the Approach to the Common Peroneal Nerve in a Sheep Model-Application in Peripheral Nerve Regeneration

Peripheral nerve injury (PNI) remains a medical challenge with no easy resolution. Over the last few decades, significant advances have been achieved in promoting peripheral nerve regeneration, and new assessment tools have been developed, both functional and imaging, to quantify the proportion and quality of nerve recovery. The exploration of new animal models, larger, more complex, and with more similarities to humans, has made it possible to reduce the gap between the results obtained in classic animal models, such as rodents, and the application of new therapies in humans and animals of clinical interest. Ultrasonography is an imaging technique recurrently used in clinical practice to assess the peripheral nerves, allowing for its anatomical and topographic characterization, aiding in the administration of anesthesia, and in the performance of nerve blocks. The use of this technique in animal models is scarce, but it could be a useful tool in monitoring the progression of nerve regeneration after the induction of controlled experimental lesions. In this work, sheep, a promising animal model in the area of peripheral nerve regeneration, were subjected to an ultrasonographic study of three peripheral nerves of the hind limb, the common peroneal, and tibial and sciatic nerves. The main aim was to establish values of dimensions and ultrasound appearance in healthy nerves and landmarks for their identification, as well as to perform an ultrasound evaluation of the cranial tibial muscle, an effector muscle of the common peroneal nerve, and to establish normal values for its ultrasound appearance and dimensions. The results obtained will allow the use of these data as control values in future work exploring new therapeutic options for nerve regeneration after induction of common peroneal nerve injuries in sheep.

Imaging in the repair of peripheral nerve injury

Surgical intervention followed by physical therapy remains the major way to repair damaged nerves and restore function. Imaging constitutes promising, yet underutilized, approaches to improve surgical and postoperative techniques. Dedicated methods for imaging nerve regeneration will potentially provide surgical guidance, enable recovery monitoring and postrepair intervention, elucidate failure mechanisms and optimize preclinical procedures. Herein, we present an outline of promising innovations in imaging-based tracking of in vivo peripheral nerve regeneration. We emphasize optical imaging because of its cost, versatility, relatively low toxicity and sensitivity. We discuss the use of targeted probes and contrast agents (small molecules and nanoparticles) to facilitate nerve regeneration imaging and the engineering of grafts that could be used to track nerve repair. We also discuss how new imaging methods might overcome the most significant challenges in nerve injury treatment.

Combining micro-computed tomography with histology to analyze biomedical implants for peripheral nerve repair

BACKGROUND

Biomedical implants used in tissue engineering repairs, such as scaffolds to repair peripheral nerves, can be too large to examine completely with histological analyses. Micro-computed tomography (micro-CT) with contrast agents allows ex vivo visualization of entire biomaterial implants and their interactions with tissues, but contrast agents can interfere with histological analyses of the tissues or cause shrinkage or loss of antigenicity.

NEW METHOD

Soft tissue, ex vivo micro-CT imaging using Lugol's iodine was compatible with histology after using a rapid (48 h) method of removing iodine.

RESULTS

Adult normal and repaired rat sciatic nerves were infiltrated ex vivo with iodine, imaged with micro-CT and then the iodine was removed by incubating tissues in sodium thiosulfate. Subsequent paraffin sections of normal nerve tissues showed no differences in staining with hematoxylin and eosin or immunostaining with multiple antibodies. Iodine treatment and removal did not alter axonal diameter, nuclear size or relative area covered by immunostained axons (p>0.05). Combining imaging modalities allowed comparisons of macroscopic and microscopic features of nerve tissues regenerating through simple nerve conduits or nerve conduits containing a titanium wire for guidance.

COMPARISON WITH EXISTING METHODS

Quantification showed that treatment with iodine and sodium thiosulfate did not result in tissue shrinkage or loss of antigenicity.

CONCLUSIONS

Because this combination of treatments is rapid and does not alter tissue morphology, this expands the ex vivo methods available to examine the success of biomaterial implants used for tissue engineering repairs.