Identification of spread after deliberated intraneural injection in five mammalian species: not all animal models and needle types are valid for studying the effect of intraneural injections in humans.

INTRODUCTION: This research endeavors to investigate the phenomenon of intraneural spread across distinct locations: subcircumneurium, extrafascicular intraneural, intrafascicular intraneural, and intraperineurium after deliberate intraneural injections across five mammalian species. The study also aims to propose determinants influencing this spread. Furthermore, the investigation strives to ascertain the optimal animal species and needle configuration for extrapolating intraneural injection outcomes to human contexts. METHODS: This study examined 60 sciatic nerves from 30 fresh and untreated cadavers of rats, rabbits, dogs, pigs, and sheep. The specimens were organized into five groups, each comprising an equal number of nerves. Histological assessments were performed on 30 nerves, involving fascicle metrics. The remaining 30 nerves underwent intentional intraneural injections, facilitated by 19G and 23G needles under ultrasound and direct visualization guidance.Heparinized erythrocytes combined with a methylene blue solution were used as a marker to analyze the extent and patterns of intraneural spread. Needle orifice measurements were obtained, and these data were overlaid onto images of both nerves and needles. This enabled a comparative evaluation of sizes and an assessment of marker diffusion. RESULTS: The findings indicated that sciatic nerves in rats, rabbits, and dogs were oligofascicular, characterized by larger fascicles, whereas pigs and sheep exhibited polyfascicular nerves comprised of numerous smaller fascicles. Fascicular diameters were variable across species, with dogs presenting the largest measurements. While intraneural spread was observed and documented, intrafascicular marker spreading was rare, occurring only in one rabbit specimen. Needle orifice attributes were scrutinized and visually depicted. CONCLUSIONS: Despite the formidable challenges associated with the practical realization of intrafascicular injection, the utilization of animal models possessing monofascicular or oligofascicular nerves, such as rats, rabbits, and dogs, in conjunction with needles featuring aperture dimensions surpassing those of the fascicles, likely contributes to the compromised reliability of investigations into intraneural injection outcomes.

Comparison of Subacute Vascular Damage Caused by ADAPT versus Stent Retriever Devices after Thrombectomy in Acute Ischemic Stroke: Histological and Ultrastructural Study in an Animal Model.

OBJECTIVES: To assess the delayed (15 days) histological and ultrastructural changes occurring following endovascular treatment with a direct aspiration first pass technique (ADAPT) or stent retrievers (SRs) and to compare the findings in order to determine which is the least harmful technique and what changes occur. MATERIALS AND METHODS: Damage to the wall of swine extracranial arteries was evaluated after ADAPT with the Penumbra system or thrombectomy with various SRs. The procedures were performed using two pigs as animal models; extracranial cervical arteries were selected based on their diameters in order to reproduce the procedures as in human intracranial arteries, and endovascular thrombectomies were done after the injection of autologous thrombi. Two weeks later, the animals were euthanized, and 60 arterial samples were obtained for analysis by optical and electron microscopy. RESULTS: Optical and electron microscopy revealed that both techniques cause, in different way, alterations to the structure of the vessel wall. CONCLUSIONS: Both techniques caused damage to the vessel wall. The main damages were localized at the level of the tunica media and adventitia, instead of the tunica intima as in the acute phase. Further investigation is required to better understand whether these alterations could have chronic consequences.

Microanatomical Nerve Architecture of 6 Mammalian Species: Is Trans-Species Translational Anatomic Extrapolation Valid?

BACKGROUND AND OBJECTIVES: Various animal models have historically been used to study iatrogenic nerve injury during performance of conduction nerve blocks. Our aims were to compare the microstructures of nerves in commonly used species to those of humans and to explore the validity of the extrapolating these findings to humans. METHODS: High-resolution, light-microscopic images were obtained from cross sections of sciatic nerves at their bifurcation from fresh rat, rabbit, pig, sheep, dog, and human cadavers. Various microanatomical characteristics were measured and compared between the species. P < 0.0033 indicated significant differences. RESULTS: Forty-four samples were studied. There were some interspecies similarities, but the majority of the microanatomical measurements of all 5 species differed significantly from those of humans. Exceptions were rat fascicle cross-sectional area (P = 0.367) and fascicle circumference (P = 0.396); ratio of dog, pig, and sheep fascicle area to total nerve area (dog: P = 0.350; pig: P = 0.958; sheep: P = 0.052); and number of fascicles (pig: P = 0.454; sheep P = 0.077). CONCLUSIONS: Although some of the metrics could reasonably be expected to differ because of the size of the species-for example, nerve cross-sectional area-there was little microanatomical similarity between the sciatic nerves of humans and those of the nonprimate mammalian species studied. This may question the validity of some conclusions reached over the years by direct translation from these species to humans. Further studies on nerve function, intraneural injection, and microanatomy of nonhuman primate species are warranted.