Background: The mechanism by which local anesthetics spread and produce analgesia in interfascial plane blocks remains unclear. Clinical efficacy often exceeds the visible spread of injectate on imaging. This cadaveric study quantified the distribution of bupivacaine within skeletal muscle and across fascial barriers to explore diffusion as a potential contributor to interfascial plane block dynamics. Methods: Fresh and frozen–thawed human soleus muscles were injected with a mixture of bupivacaine and methylene blue, and samples were collected along and perpendicular to fiber orientation. Fresh lower limbs were used to assess transfascial transfer across sequential crural fasciae after injection with bupivacaine, iodinated contrast, and methylene blue. The limbs were imaged with CT and samples were collected from crural compartments separated by fascial layers. Finally, simulated posteromedial quadratus lumborum block was performed in fresh cadavers, with samples harvested from the quadratus lumborum, psoas major, and diaphragm. Bupivacaine concentrations were quantified using high-performance liquid chromatography–mass spectrometry. Results: In fresh muscle, bupivacaine exhibited an anisotropic pattern, with concentration gradients decreasing more slowly along muscle fiber orientation than in transverse direction (p=0.0008). This directional difference disappeared in frozen–thawed tissue. Across fascial barriers, bupivacaine decreased exponentially with the distance from injection site, compatible with diffusion-driven transport, whereas methylene blue and iodinated contrast were not detected beyond the injected compartments. After simulated quadratus lumborum block, bupivacaine was detected in the psoas major (0.7–487.6 µg/g), quadratus lumborum (0.2–266.1 µg/g), and diaphragm (9.0–27.3 µg/g) despite no evident methylene blue spread. Conclusions: Low-volume injectate of bupivacaine spread anisotropically within fresh muscle and permeated fascial barriers in ways not demonstrated by methylene blue or iodinated contrast. The exponential decrease of concentrations provides evidence that diffusion contributes to local anesthetic distribution and may help explain, at least in part, the broad and occasionally disproportionate sensory coverage observed clinically with interfascial plane blocks.

Introduction: Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) technique that measures the anisotropy of water diffusion. Clinical magnetic resonance imaging scanners enable visualization of the structural integrity of larger axonal bundles in the central nervous system and smaller structures like peripheral nerves; however, their resolution for the depiction of nerve fascicular morphology is limited. Accordingly, high-field strength MRI and strong magnetic field gradients are needed to depict the fascicular pattern. The study aimed to quantify diffusion tensor indices with high-field strength MRI within different anatomical compartments of the median nerve and determine if they correlate with nerve structure at the fascicular level.Methods: Three-dimensional pulsed gradient spin-echo (PGSE) imaging sequence in 19 different gradient directions and b value 1,150 s/mm² was performed on a 9.4T wide-bore vertical superconducting magnet. Nine-millimeter-long segments of five median nerve samples were obtained from fresh cadavers and acquired in sixteen 0.625 mm thick slices. Each nerve sample had the fascicles, perineurium, and interfascicular epineurium segmented. The diffusion tensor was calculated from the region-average diffusion-weighted signals for all diffusion gradient directions. Subsequently, correlations between diffusion tensor indices of segmentations and nerve structure at the fascicular level (number of fascicles, fascicular ratio, and cross-sectional area of fascicles or nerve) were assessed. The acquired diffusion tensor imaging data was employed for display with trajectories and diffusion ellipsoids.Results: The nerve fascicles proved to be the most anisotropic nerve compartment with fractional anisotropy 0.44 ± 0.05. In the interfascicular epineurium, the diffusion was more prominent in orthogonal directions with fractional anisotropy 0.13 ± 0.02. Diffusion tensor indices within the fascicles and perineurium differed significantly between the subjects (p < 0.0001); however, there were no differences within the interfascicular epineurium (p ≥ 0.37). There were no correlations between diffusion tensor indices and nerve structure at the fascicular level (p ≥ 0.29).Conclusion: High-field strength MRI enabled the depiction of the anisotropic diffusion within the fascicles and perineurium. Diffusion tensor indices of the peripheral nerve did not correlate with nerve structure at the fascicular level. Future studies should investigate the relationship between diffusion tensor indices at the fascicular level and axon- and myelin-related parameters.

This study aimed to compare the fascicular anatomy of upper limb nerves visualized using in situ high-resolution ultrasound (HRUS) with ex vivo imaging modalities, namely, magnetic resonance microscopy (MRM), histological cross-sections (HCS), and optical projection tomography (OPT). The median, ulnar, and superficial branch of radial nerve (n = 41) were visualized in 14 cadaveric upper limbs using 22-MHz HRUS. Subsequently, the nerves were excised, imaged with different microscopic techniques, and their morphometric properties were compared. HRUS accurately differentiated 51–74% of fascicles, while MRM detected 87–92% of fascicles when compared to the referential HCS. Among the compared modalities, HRUS demonstrated the smallest fascicular ratios and fascicular cross-sectional areas, but the largest nerve cross-sectional areas. The probability of a fascicle depicted on HRUS representing a cluster of multiple fascicles on the referential HCS increased with the fascicular size, with some differences observed between the larger median and ulnar nerves and the smaller radial nerves. Accordingly, HRUS fascicle differentiation necessitates cautious interpretation, as larger fascicles are more likely to represent clusters. Although HCS is considered the reference modality, alterations in nerve cross-sectional areas or roundness during sample processing should be acknowledged.

Background: Ultrasound (US) has been proven to be reliable in the assessment of early haemophilic arthropathy in the adult haemophilic population, however few studies so far focused on the reliability of US specifically in the paediatric haemophilic population. We were interested if the changing appearance of the growing bone hinders the ultrasonographic evaluation of the pathologic processes caused by haemophilic arthropathy. The aim of the study was to assess the reliability of US for evaluation of haemophilic arthropathy in children in comparison to magnetic resonance imaging (MRI). Patients and methods: The study included all children aged 6 years or more with severe haemophilia in the country (n = 10). We assessed their elbows, knees, and ankles bilaterally by US and compared the results to the MRI as the reference standard. Pearson correlation coefficient (r) was used to analyse correlation. Results: The correlation with MRI for the US for the total score was excellent for all joints (r = 0.849 for the elbows, r = 1 for knees, r = 0.842 for ankles). The correlation of scores for specific joint components showed fair, moderate, or excellent correlation for all joint components in all joints. The correlation was the lowest for the evaluation of cartilage and bone in the ankles (r = 0.546 and r = 0.478) and bone in the elbows (r = 0.499). Conclusions: Our study proved that US using the HEAD-US method performed by paediatric radiologists is a reliable tool for detection and quantification of haemophilic arthropathy in children in comparison to MRI.

Background and Purpose: The primary objective was to compare diffusion tensor imaging (DTI) scalar parameters of peripheral nerves between subjects with type 2 diabetes mellitus (T2DM) and those without diabetes. Secondarily, we aimed to correlate DTI scalar parameters with nerve morphometric properties. Methods: Median, tibial, and sural nerves were harvested from 34 male cadavers (17 T2DM, 17 nondiabetic). Each nerve was divided into three segments. The initial segment was scanned using 9.4 Tesla MRI system (three‐dimensional pulsed‐gradient spin‐echo sequence). DTI scalars were calculated from region‐average diffusion‐weighted signals. Second segment was optically cleared, acquired with optical projection tomography (OPT), and analyzed for morphometrical properties. Toluidine‐stained sections were prepared from last segment, and axon‐ and myelin‐related properties were evaluated. Results: DTI scalar parameters of median and tibial nerves were comparable between the groups, while sural nerves of T2DM exhibited on average 41% higher mean diffusivity (MD) ( p = 0.03), 38% higher radial diffusivity (RD) ( p = 0.03), and 27% lower fractional anisotropy (FA) ( p = 0.005). Significant differences in toluidine‐evaluated parameters of sural nerves were observed between the groups, with a positive correlation between FA with fiber density ( p = 0.0001) and with myelin proportion ( p < 0.0001) and an inverse correlation between RD and myelin proportion ( p = 0.003). OPT‐measured morphometric properties did not correlate with DTI scalar parameters. Conclusions: High‐field DTI shows promise as an imaging technique for detecting axonal and myelin‐related changes in small sural nerves ex vivo. The reduced fiber density and decreased myelin content, which can be observed in T2DM, likely contribute to observed FA reduction and increased MD/RD.