Sciatic nerve fascicle differentiation on high-resolution ultrasound with histological verification: An ex vivo study.

INTRODUCTION/AIMS: The development of high-resolution ultrasound (HRUS) has enabled the depiction of peripheral nerve microanatomy in vivo. This study compared HRUS fascicle differentiation to the structural depiction in histological cross-sections (HCS). METHODS: A human cadaveric sciatic nerve was marked with 10 surgical sutures, and HRUS image acquisition was performed with a 22-MHz probe. The nerve was excised and cut into five segments for HCS preparation. Selected HCS were cross-referenced to HRUS, with sutures to improve orientation. Sciatic nerve and fascicle contouring were performed to assess nerve and fascicular cross-sectional area (CSA), fascicle count, and interfascicular distances. Three groups were defined based on HRUS fascicle differentiation in comparison to HCS, namely single fascicle (SF), fascicular cluster (FC), and no depiction (ND) group. RESULTS: On cross-referenced HRUS to HCS images, 58% of fascicles were differentiated. On HRUS, significantly larger fascicle CSA and smaller fascicle count were observed compared with HCS. Group analysis showed that 41% of fascicles were defined as SF, 47% as FC, and 12% as ND. The mean fascicle CSA in the ND group was 0.05 mm2. Compared with the SF, the FC had significantly larger fascicle CSA (1.2 ± 0.7 vs. 0.6 ± 0.4 mm2; p < .001) and shorter interfascicular distances (0.1 ± 0.04 vs. 0.5 ± 0.3 µm; p < .001). DISCUSSION: While HRUS can depict fascicular anatomy, only half of the fascicles visualized on HRUS directly correspond to single fascicles observed on HCS. The amount of interfascicular epineurium appears to influence the ability of HRUS to differentiate individual fascicles.

Ultrasound-guided thread versus ultrasound-guided needle release of the A1 pulley: a cadaveric study.

PURPOSE: To assess and compare two ultrasound-guided, minimally invasive procedures to release the A1-pulley (needle release and thread release) regarding efficacy and safety in an anatomical specimen model. MATERIALS AND METHODS: Twenty-one ultrasound-guided needle releases and 20 ultrasound-guided thread releases were performed on digits of Thiel-embalmed anatomical specimens. A scoring system was developed to assess ultrasound visibility, intervention outcome (incomplete, almost complete, or full transection of the A1 pulley), and injury to adjacent structures (neurovascular structures, tendons, A2 pulley). Statistical analysis was performed to compare the score of the two groups (group 1: needle release,group 2: thread release). A P-value of ≤ 0.05 was considered significant. RESULTS: Needle release was completely successful in 15 cases (71.5%), almost complete release was achieved in four cases (19%), and incomplete transection occurred in two cases (9.5%). Thread release was completely successful in 17 cases (85%), and almost complete transection was observed in the remaining three cases (15%). In both procedures no neurovascular structures were harmed. Slight injury of flexor tendons occurred in two cases (9.5%) in needle release and in five cases (25%) in thread release. There were no significant statistical differences between the groups regarding ultrasound visibility, intervention safety and outcome, (P > 0.05). CONCLUSION: Ultrasound-guided needle release and ultrasound-guided thread release have similar success of release, both being effective and safe techniques for the release of the A1 pulley.

High-resolution ultrasound demonstrates in vivo effects of wrist movement on the median nerve along the forearm.

INTRODUCTION/AIMS: High-resolution ultrasound (HRUS) is the imaging method of choice to visualize peripheral nerve size, structure, and biomechanical performance. The purpose of this study was to show and quantify the effects of active and passive wrist alignment on median nerve (MN) cross-sectional area (CSA) along the forearm in a healthy population. METHODS: Sixteen healthy volunteers underwent HRUS of their dominant forearm (n = 16, 10 males, 6 females, 18-55 y of age). Median nerve's CSA was assessed at four defined areas on the forearm in relation to active and passive wrist alignment. RESULTS: Changes in wrist alignment were significantly associated with MN CSA (P < .001), regardless if the wrist was moved actively or passively. MN CSA was lowest during passive extension of the wrist joint and highest during passive flexion of the wrist joint (range: 4.5-23.2 mm2 ). DISCUSSION: The elasticity of nerve tissue, the loose connective tissue between the fascicles, and the paraneurium allow peripheral nerves to adapt to longitudinal strain. HRUS enables the demonstration of significant median nerve CSA changes along the forearm during active and passive wrist movement in healthy volunteers.

Cutaneous nerve fields of the anteromedial lower limb-Determination with selective ultrasound-guided nerve blockade.

BACKGROUND: This study aimed to determine the peripheral cutaneous nerve fields (CNF), their variability, and potential overlap by selectively blocking the intermediate (IFCN) and medial (MFCN) femoral cutaneous nerves and the infrapatellar branch of the saphenous nerve (IPBSN) in healthy volunteers. METHODS: In this prospective study, ultrasound-guided nerve blockades of the IFCN, MFCN, and IPBSN in 14 healthy volunteers were administered. High-frequency probes (15-22 MHz) and 1 ml of 1% lidocaine per nerve were used. The area of sensory loss was determined using a pinprick, and all fields were drawn on volunteers' skin. A three-dimensional (3D) scan of all lower limbs was obtained and the three CNF and their potential overlap were measured. RESULTS: The mean size of innervation areas showed a high variability of peripheral CNF, with 258.58 ± 148.26 mm2 (95% CI, 169-348.18 mm2 ) for the IFCN, 193.26 ± 72.08 mm2 (95% CI, 124.45-262.08 mm2 ) for the MFCN, and 166.78 ± 121.30 mm2 (95% CI, 94.1-239.46 mm2 ) for the IPBSN. In 11 volunteers, we could evaluate an overlap between the IFCN and MFCN (range, 4.11-139.68 ± 42.70 mm2 ), and, in 10 volunteers, between the MFCN and IPBSN (range, 11.12-224.95 ± 79.61 mm2 ). In only three volunteers was an overlap area found between the IFCN and IPBSN (range, 7.46-224.95 ± 88.88 mm2 ). The 3D-scans confirmed the high variability of the peripheral CNF. CONCLUSIONS: Our study successfully determined CNF, their variability, and the overlap of the MFCN, IFCN, and IPBSN in healthy volunteers. Therefore, we encourage physicians to use selective nerve blockades to correctly determine peripheral CNF at the anteromedial lower limb.

Ultrasound Anatomic Demonstration of the Infrapatellar Nerve Branches.

PURPOSE: To (1) confirm the correct identification of the infrapatellar branches of the saphenous nerve (IPBSNs) by high-resolution ultrasound (HRUS) with ink marking and consecutive dissection in anatomic specimens; (2) evaluate the origin, course, and end-branch distribution in healthy volunteers; and (3) visualize the variable anatomic course of the IPBSN by HRUS. METHODS: HRUS with high-frequency probes (15-22 MHz) was used to locate the IPBSN in 14 fresh anatomic specimens at 4 different locations. The correct identification of the IPBSN was verified by ink marking and consecutive dissection. Moreover, the IPBSNs were located in both knees of 20 healthy volunteers (n = 40). Their courses were marked on the volunteers' skin in a flexed-knee position. Distances were measured from the IPBSN branch closest to the median of the patella base (D1), center (D2), and apex (D3) and in a 45° (D4) and 0° (D5) relation to the median patella apex. Standardized photographs of all knees were mapped on 1 typically shaped knee. RESULTS: Dissection confirmed the correct identification of the IPBSN in 86% to 100% of branches, depending on their location. Intraindividual differences for distance measurements were observed for D1 (P < .001) and D2 (P = .002). The coefficient of variation was highest for D5 (0.86) and lowest for D1 (0.14). Mapping of the nerve branches on a typical knee showed a highly variable course for the IPBSN. CONCLUSIONS: This study confirmed the reliable ability to visualize the IPBSN and its variations with HRUS in anatomic specimens and in healthy volunteers; such visualization may therefore enhance the diagnostic and therapeutic management of patients with anteromedial knee pain. CLINICAL RELEVANCE: Ultrasound successfully pinpoints the variable course of the IPBSN from the origin to the most distal point and, therefore, may enable the correct identification of (iatrogenic) nerve damage in every location.

High-resolution ultrasound visualization of the deep branch of the ulnar nerve.

INTRODUCTION: The value of imaging the deep branch of the ulnar nerve (DBUN) over its entire course has not been clarified. Therefore, this study evaluates the feasibility of visualizing the DBUN from its origin to the most distal point. METHODS: We performed high-resolution ultrasound (HRUS) with high-frequency probes (18-22 MHZ), HRUS-guided ink marking, and consecutive dissection in 8 fresh cadaver hands. In both hands of 10 healthy volunteers (n = 20), the cross-sectional area (CSA) was measured at 2 different locations (R1 and R2). RESULTS: The DBUN was clearly visible in all anatomical specimens and in healthy volunteers. Dissection confirmed HRUS findings in all anatomical specimens. The mean CSA was 1.8 ± 0.5 mm2 at R1 and 1.6 ± 0.4 mm2 at R2. DISCUSSION: This study confirms that the DBUN can be reliably visualized over its entire course with HRUS in anatomical specimens and in healthy volunteers. Muscle Nerve 56: 1101-1107, 2017.

High-resolution ultrasound visualization of the recurrent motor branch of the median nerve: normal and first pathological findings.

PURPOSE: To evaluate in a prospective study the possibility of visualization and diagnostic assessment of the recurrent motor branch (RMB) of the median nerve with high-resolution ultrasound (HRUS). MATERIALS AND METHODS: HRUS with high-frequency probes (18-22 MhZ) was used to locate the RMB in eight fresh cadaveric hands. To verify correct identification, ink-marking and consecutive dissection were performed. Measurement of the RMB maximum transverse-diameter, an evaluation of the origin from the median nerve and its course in relation to the transverse carpal ligament, was performed in both hands of ten healthy volunteers (n = 20). Cases referred for HRUS examinations for suspected RMB lesions were also assessed. RESULTS: The RMB was clearly visible in all anatomical specimens and all volunteers. Dissection confirmed HRUS findings in all anatomical specimens. Mean RMB diameter in volunteers was 0.7 mm ± 0.1 (range, 0.6-1). The RMB originated from the radial aspect in 11 (55%), central aspect in eight (40%) and ulnar aspect in one (5%) hand. Nineteen (95%) extraligamentous courses and one (5%) subligamentous course were detected. Three patients with visible RMB abnormalities on HRUS were identified. CONCLUSION: HRUS is able to reliably visualize the RMB, its variations and pathologies. KEY POINTS: • Ultrasound allows visualization of the recurrent motor branch of the median nerve. • Ultrasound may help clinicians to assess patients with recurrent motor branch pathologies. • Patient management may become more appropriate and targeted therapy could be improved.

Neuroimaging of classic neuralgic amyotrophy.

INTRODUCTION: Neuralgic amyotrophy (NA) often imposes diagnostic problems. Recently, MRI and high-resolution ultrasound (HRUS) have proven useful in diagnosing peripheral nerve disorders. METHODS: We performed a chart and imaging review of patients who were examined using neuroimaging and who were referred because of clinically diagnosed NA between March 1, 2014 and May 1, 2015. RESULTS: Six patients were included. All underwent HRUS, and 5 underwent MRI. Time from onset to evaluation ranged from 2 weeks to 6 months. HRUS showed segmental swelling of all clinically affected nerves/trunks. Atrophy of muscles was detected in those assessed >1 month after onset. MRI showed T2-weighted hyperintensity in all clinically affected nerves, except for the long thoracic nerve, and denervation edema of muscles. CONCLUSIONS: HRUS and MRI are valuable diagnostic tools in NA. This could change the diagnostic approach from one now focused on excluding other disorders to confirming NA through imaging markers. Muscle Nerve 54: 1079-1085, 2016.

Acute radial nerve entrapment at the spiral groove: detection by DTI-based neurography.

OBJECTIVES: This study evaluated the potential of three-tesla diffusion tensor imaging (DTI) and tractography to detect changes of the radial (RN) and median (MN) nerves during transient upper arm compression by a silicon ring tourniquet. METHODS: Axial T2-weighted and DTI sequences (b = 700 s/mm(2), 16 gradient encoding directions) of 13 healthy volunteers were obtained. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of the MN and RN were measured at the spiral groove and further visualized in 3D by deterministic tractography (thresholds: FA = .15, angle change = 27°). RESULTS: Local/lesional RN FA values increased (p = 0.001) and ADC values decreased (p = 0.02) during a 20-min upper arm compression, whereas no significant FA (p = 0.49) or ADC (p = 0.73) changes of the MN were detected. There were no T2-w nerve signal changes or alterations of nerve trajectories in 3D. CONCLUSIONS: Acute nerve compression of the RN leads to changes of its three-tesla DTI metrics. Peripheral nerve DTI provides non-invasive insights into the "selective" vulnerability of the RN at the spiral groove. KEY POINTS: • DTI-based neurography detects nerve changes during acute nerve compression. • Compression leads to a transient increase in local radial nerve FA values. • DTI provides insights into radial nerve vulnerability at the spiral groove.

Ultrasound-guided minimally invasive thread release of Guyon's canal: initial experience in cadaveric specimens.

OBJECTIVE: Guyon's canal syndrome is caused by compression of the ulnar nerve at the wrist, occasionally requiring decompression surgery. In recent times, minimally invasive approaches have gained popularity. The aim of this study was to assess the efficacy and safety of ultrasound-guided thread release for transecting the palmar ligament in Guyon's canal without harming surrounding structures, in a cadaveric specimen model. METHODS: After ethical approval, thirteen ultrasound-guided thread releases of Guyon's canal were performed on the wrists of softly embalmed anatomic specimens. Cadavers showing injuries or prior operations at the hand were excluded. Subsequently, the specimens were dissected, and the outcome of the interventions and potential damage to adjacent anatomical structures as well as ultrasound visibility were evaluated with a score from one to three. RESULTS: Out of 13 interventions, a complete transection was achieved in ten cases (76.9%), and a partial transection was documented in three cases (23.1%). Irrelevant lesions on the flexor tendons were observed in two cases (15.4%), and an arterial branch was damaged in one (7.7%). Ultrasound visibility varied among specimens, but essential structures were delineated in all cases. CONCLUSION: Ultrasound-guided thread release of Guyon's canal has shown promising first results in anatomic specimens. However, further studies are required to ensure the safety of the procedure. RELEVANCE STATEMENT: Our study showed that minimally invasive ultrasound-guided thread release of Guyon's canal is a feasible approach in the anatomical model. The results may provide a basis for further research and refinement of this technique. KEY POINTS: • In Guyon's canal syndrome, the ulnar nerve is compressed at the wrist, often requiring surgical release. • We adapted and tested a minimally invasive ultrasound-guided thread release technique in anatomic specimens. • The technique was effective; however, in one specimen, a small anatomic branch was damaged.

Ultrasound-guided minimally invasive cubital tunnel thread release: An experimental study.

INTRODUCTION: Cubital Tunnel Syndrome is characterized by the compression of the ulnar nerve in the cubital tunnel and can cause restrictions to the activities of daily living. Traditional treatment includes conservative methods and, in more severe cases, different types of surgery. In these cases, common side effects of surgery may limit the clinical success. A new alternative could be a minimally invasive Ultrasound-guided (US-guided) thread release of cubital tunnel retinaculum also known as the Osborne's ligament. The aim of this study was to assess the efficacy and safety of ultrasound-guided thread cubital tunnel release (TCuTR) in an anatomical specimen model. METHODS: In this single-center prospective experimental study, US-guided thread cubital tunnel release (TCuTR) was performed on 11 softly embalmed anatomic specimens. Subsequently, the elbows were dissected to assess the transection of Osborne's ligament and potential damage to adjacent structures. RESULTS: Due to calcification, one specimen was ineligible for the intervention. In all remaining ten interventions, Osborne's ligament (OL) was completely transected, without any damage to the surrounding nerves, blood vessels, tendons, or muscles. CONCLUSION: US-guided decompression has demonstrated a high success rate in transecting Osborne's ligament while averting damage to neighboring structures. This emerging technique appears to present an efficient and secure alternative to existing procedures.

3D fascicular reconstruction of median and ulnar nerve: initial experience and comparison between high-resolution ultrasound and MR microscopy.

BACKGROUND: The complex anatomy of peripheral nerves has been traditionally investigated through histological microsections, with inherent limitations. We aimed to compare three-dimensional (3D) reconstructions of median and ulnar nerves acquired with tomographic high-resolution ultrasound (HRUS) and magnetic resonance microscopy (MRM) and assess their capacity to depict intraneural anatomy. METHODS: Three fresh-frozen human upper extremity specimens were prepared for HRUS imaging by submersion in a water medium. The median and ulnar nerves were pierced with sutures to improve orientation during imaging. Peripheral nerve 3D HRUS scanning was performed on the mid-upper arm using a broadband linear probe (10-22 MHz) equipped with a tomographic 3D HRUS system. Following excision, nerves were cut into 16-mm segments and loaded into the MRM probe of a 9.4-T system (scanning time 27 h). Fascicle and nerve counting was performed to estimate the nerve volume, fascicle volume, fascicle count, and number of interfascicular connections. HRUS reconstructions employed artificial intelligence-based algorithms, while MRM reconstructions were generated using an open-source imaging software 3D slicer. RESULTS: Compared to MRM, 3D HRUS underestimated nerve volume by up to 22% and volume of all fascicles by up to 11%. Additionally, 3D HRUS depicted 6-60% fewer fascicles compared to MRM and visualized approximately half as many interfascicular connections. CONCLUSION: MRM demonstrated a more detailed fascicular depiction compared to 3D HRUS, with a greater capacity for visualizing smaller fascicles. While 3D HRUS reconstructions can offer supplementary data in peripheral nerve assessment, their limitations in depicting interfascicular connections and small fascicles within clusters necessitate cautious interpretation. CLINICAL RELEVANCE STATEMENT: Although 3D HRUS reconstructions can offer supplementary data in peripheral nerve assessment, even in intraoperative settings, their limitations in depicting interfascicular branches and small fascicles within clusters require cautious interpretation. KEY POINTS: 3D HRUS was limited in visualizing nerve interfascicular connections. MRM demonstrated better nerve fascicle depiction than 3D HRUS. MRM depicted more nerve interfascicular connections than 3D HRUS.

Median nerve versus flexor tendons: visualization of median nerve level changes in the proximal carpal tunnel during wrist movement with dynamic high-resolution ultrasound.

Aim: The purpose of this prospective ultrasound study was to document dorso-palmar (vertical) displacement of the median nerve in relation to the superficial flexor tendons at the level of the carpal tunnel. Furthermore, the gliding patterns of the median nerve were characterized. The presence of vertical gliding was intended to serve as an additional bio-kinematic parameter of median nerve movement, and will be referred to as a 'level change'. Material and methods: In this study, a total of 32 healthy young individuals underwent dynamic high-resolution ultrasound examinations of both wrists. The neutral position, and maximum flexion and extension of the wrist had to be reached in active and passive movement. The gliding patterns were determined in relation to the superficial flexor tendons. When no vertical nerve gliding was observed, it was characterized as 'no level change'. Results: The presence of a level change prevailed in the healthy young cohort and was observed in 84% (27/32) of individuals during wrist flexion. The following gliding pattern was distinctively the most common: gliding of the entire nerve in between the flexor tendons in active but not in passive movement of the right and left wrists (13/27; 48%). The extent of vertical displacement was found to be associated with the gliding pattern (Kruskal-Wallis test). Conclusions: Movement in the carpal tunnel allows the median nerve to adapt to biomechanical stress. Dynamic ultrasound can demonstrate median nerve level changes in response to wrist movements. Furthermore, a typical gliding pattern was characterized. The presence of level change and gliding patterns were proposed as additional movement parameters during wrist flexion in healthy individuals.

High-Resolution Ultrasound and Magnetic Resonance Imaging of Abnormal Ligaments in Thoracic Outlet Syndrome in a Series of 16 Cases.

INTRODUCTION: Neurogenic thoracic outlet syndrome (NTOS) is a complex entity that comprises various clinical presentations, which are all believed to result from mechanical stress to the brachial plexus. Causes for the stress can include fibrous bands, spanning from the transverse processes, stump, or cervical ribs to the pleural cupula. The aim of this case series is to document how the combined potential of high-resolution neurography, including high-resolution ultrasound (HRUS), and magnetic resonance imaging (MRI) can be used to identify, anatomical compression sites, such as stump ribs and their NTOS associated ligamentous bands. MATERIALS AND METHODS: Retrospective chart and image reviews identified patients, who underwent HRUS between 2011 and 2021 and the diagnosis of NTOS caused by accessory ligaments was subsequently confirmed by radiological imaging (MRI) and/or surgical exploration. RESULTS: Sixteen patients were included in this study. In all cases, a ligament extending from the tip of a stump rib to the pleural cupula could be depicted. In all cases, these structures led to compression of the lower trunk of the brachial plexus. All surgically explored cases confirmed the radiological findings. CONCLUSION: This case-series demonstrates that HRUS and MRI can directly and reliably visualize accessory costocupular ligaments and a stump rib in patients with symptoms of NTOS. HRUS may be used as the first imaging modality to diagnose suspected NTOS.

Validity of SyMRI for Assessment of the Neonatal Brain.

PURPOSE: The purpose of this study was to assess the diagnostic accuracy of T1-weighted and T2-weighted contrasts generated by the MR data postprocessing software SyMRI (Synthetic MR AB, Linköping, Sweden) for neonatal brain imaging. METHODS: In this study 36 cases of neonatal MRI were retrospectively collected, which included T1-weighted and T2-weighted sequences as well as multi-dynamic multi-echo (MDME) sequences. Of the 36 neonates 32 were included in this study and 4 neuroradiologists independently assessed neonatal brain examinations on the basis of conventional and SyMRI-generated T1-weighted and T2-weighted contrasts, in order to determine the presence or absence of lesions. The sensitivity and specificity of both methods were calculated and compared. RESULTS: Compared to conventionally acquired T1 and T2-weighted images, SyMRI-generated contrasts showed a lower sensitivity but a higher specificity (SyMRI sensitivity 0.88, confidence interval (CI): 0.72-0.95; specificity 1, CI: 0.89-1/conventional MRI: sensitivity: 0.94, CI: 0.80-0.98; specificity: 0.94, CI: 0.80-0.98). CONCLUSION: The T1-weighted and T2-weighted images generated by SyMRI showed a diagnostic accuracy comparable to that of conventionally acquired contrasts. In addition to semiquantitative imaging data, SyMRI provides diagnostic images and leads to a more efficient use of available imaging time in neonatal brain MRI.

High-Resolution Ultrasound Visualization of Pacinian Corpuscles.

The aim of this study was to evaluate the possibility of visualizing Pacinian corpuscles in the palm of the hand with high-resolution ultrasound (HRUS). In this prospective study, HRUS with a high-frequency probe (22 MHz) was used. The palms of two fresh cadaveric hands were screened for potential Pacinian corpuscles. Still ultrasound images and dynamic video sequences were obtained. In five regions with large amounts of suspected Pacinian corpuscles, tissue blocks were excised and histologically processed, and corresponding slices were compared with ultrasound images. Further, the transverse diameters of five Pacinian corpuscles, at the level of the metacarpal heads in the palm, were assessed on both sides (in total 100) in healthy volunteers. On ultrasound, Pacinian corpuscles presented as echolucent dots in the subcutis, adjacent to digital nerves and vessels and located 2-3 mm beneath the surface. On histologic sections, these echolucent dots corresponded to Pacinian corpuscles with respect to their position and topographic relationships. The mean transverse diameter for all volunteers was 1.40 ± 0.23 mm (range: 0.8-2.2 mm). This study confirms the ability to reliably visualize Pacinian corpuscles with HRUS, which contributes to our basic understanding of ultrasonographically visible subcutaneous structures and may enhance the diagnosis of pathologies related to Pacinian corpuscles.