Nerves in a pinch: imaging of nerve compression syndromes

Nano-pulling stimulates axon regeneration in dorsal root ganglia by inducing stabilization of axonal microtubules and activation of local translation

Introduction

Axonal plasticity is strongly related to neuronal development as well as regeneration. It was recently demonstrated that active mechanical tension, intended as an extrinsic factor, is a valid contribution to the modulation of axonal plasticity.

Methods

In previous publications, our team validated a the "nano-pulling" method used to apply mechanical forces to developing axons of isolated primary neurons using magnetic nanoparticles (MNP) actuated by static magnetic fields. This method was found to promote axon growth and synaptic maturation. Here, we explore the use of nano-pulling as an extrinsic factor to promote axon regeneration in a neuronal tissue explant.

Results

Whole dorsal root ganglia (DRG) were thus dissected from a mouse spinal cord, incubated with MNPs, and then stretched. We found that particles were able to penetrate the ganglion and thus become localised both in the somas and in sprouting axons. Our results highlight that nano-pulling doubles the regeneration rate, and this is accompanied by an increase in the arborizing capacity of axons, an accumulation of cellular organelles related to mass addition (endoplasmic reticulum and mitochondria) and pre-synaptic proteins with respect to spontaneous regeneration. In line with the previous results on isolated hippocampal neurons, we observed that this process is coupled to an increase in the density of stable microtubules and activation of local translation.

Discussion

Our data demonstrate that nano-pulling enhances axon regeneration in whole spinal ganglia exposed to MNPs and external magnetic fields. These preliminary data represent an encouraging starting point for proposing nano-pulling as a biophysical tool for the design of novel therapies based on the use of force as an extrinsic factor for promoting nerve regeneration.

Transformer-Based Automated Segmentation of the Median Nerve in Ultrasound Videos of Wrist-to-Elbow Region

Segmenting the median nerve is essential for identifying nerve entrapment syndromes, guiding surgical planning and interventions, and furthering understanding of nerve anatomy. This study aims to develop an automated tool that can assist clinicians in localizing and segmenting the median nerve from the wrist, mid-forearm, and elbow in ultrasound videos. This is the first fully automated single deep learning model for accurate segmentation of the median nerve from the wrist to the elbow in ultrasound videos, along with the computation of the cross-sectional area (CSA) of the nerve. The visual transformer architecture, which was originally proposed to detect and classify 41 classes in YouTube videos, was modified to predict the median nerve in every frame of ultrasound videos. This is achieved by modifying the bounding box sequence matching block of the visual transformer. The median nerve segmentation is a binary class prediction, and the entire bipartite matching sequence is eliminated, enabling a direct comparison of the prediction with expert annotation in a frame-by-frame fashion. Model training, validation, and testing were performed on a dataset comprising ultrasound videos collected from 100 subjects, which were partitioned into 80, ten, and ten subjects, respectively. The proposed model was compared with U-Net, U-Net++, Siam U-Net, Attention U-Net, LSTM U-Net, and Trans U-Net. The proposed transformer-based model effectively leveraged the temporal and spatial information present in ultrasound video frames and efficiently segmented the median nerve with an average dice similarity coefficient (DSC) of approximately 94% at the wrist and 84% in the entire forearm region.

Nerve entrapment syndromes of the lower limb: a pictorial review

Peripheral nerves of the lower limb may become entrapped at various points during their anatomical course. While clinical assessment and nerve conduction studies are the mainstay of diagnosis, there are multiple imaging options, specifically ultrasound and magnetic resonance imaging (MRI), which offer important information about the potential cause and location of nerve entrapment that can help guide management. This article overviews the anatomical course of various lower limb nerves, including the sciatic nerve, tibial nerve, medial plantar nerve, lateral plantar nerve, digital nerves, common peroneal nerve, deep peroneal nerve, superficial peroneal nerve, sural nerve, obturator nerve, lateral femoral cutaneous nerve and femoral nerve. The common locations and causes of entrapments for each of the nerves are explained. Common ultrasound and MRI findings of nerve entrapments, direct and indirect, are described, and various examples of the more commonly observed cases of lower limb nerve entrapments are provided.Critical relevance statement This article describes the common sites of lower limb nerve entrapments and their imaging features. It equips radiologists with the knowledge needed to approach the assessment of entrapment neuropathies, which are a critically important cause of pain and functional impairment.Key points• Ultrasound and MRI are commonly used to investigate nerve entrapment syndromes.• Ultrasound findings include nerve hypo-echogenicity, calibre changes and the sonographic Tinel's sign.• MRI findings include increased nerve T2 signal, muscle atrophy and denervation oedema.• Imaging can reveal causative lesions, including scarring, masses and anatomical variants.

Magnetic Resonance Neurography of the Foot and Ankle

Peripheral neuropathies of the foot and ankle can be challenging to diagnose clinically due to concomitant traumatic and nontraumatic or degenerative orthopedic conditions. Although clinical history, physical examination, and electrodiagnostic testing comprised of nerve conduction velocities and electromyography are used primarily for the identification and classification of peripheral nerve disorders, MR neurography (MRN) can be used to visualize the peripheral nerves as well as the skeletal muscles of the foot and ankle for primary neurogenic pathology and skeletal muscle denervation effect. Proper knowledge of the anatomy and pathophysiology of peripheral nerves is important for an MRN interpretation.

Nerve Entrapments in the Pelvis and Hip

Clinical symptoms of pelvic entrapment neuropathies are widely variable and frequently nonspecific, thus rendering it difficult to localize and diagnose. Magnetic resonance imaging (MRI), and in particular MR neurography, has become increasingly important in the work-up of entrapment neuropathies involving the pelvic and hip nerves of the lumbosacral plexus. The major sensory and motor peripheral nerves of the pelvis and hip include the sciatic nerve, superior and inferior gluteal nerves, femoral nerve, lateral femoral cutaneous nerve, obturator nerve, and pudendal nerve. Familiarity with the anatomy and imaging appearance of normal and pathologic nerves in combination with clinical presentation is crucial in the diagnosis of entrapment neuropathies.

Tarsal tunnel syndrome secondary to accessory or variant muscles: a clinical and anatomical systematic review

PURPOSE

Many etiologies are known to lead to a tarsal tunnel syndrome (TTS). One rare cause is mass-occupying lesions, and particularly accessory or variant muscles (AVM). This study aimed to systematically collect published clinical cases of TTS caused by AVM.

METHODS

An electronic literature search was conducted from inception to April 2021. The diagnosis of AVM should be reported in one of the following methods: ultrasonography, magnetic resonance imaging (MRI), or per-operatively. Data extraction included types and prevalence of accessory muscles, clinical presentation and diagnosis, and treatment modalities. Twenty-five studies were identified with a total 39 patients (47 ankles).

RESULTS

The prevalence of TTS was reported in only two studies (9%). Forty-nine AVM were identified with the accessory flexor digitorum longus being the most common (52%). The most common sign/symptoms were tenderness (78.7%), pain (82.9%), dysesthesia (57.4%), Tinel sign (44.6%), and a swelling (25.5%). Decompression and excision were the most commonly performed procedures. Four accessory/variant muscles in the ankle have the potential to induce a tarsal tunnel syndrome.

CONCLUSION

This review highlights the clinical and imagery specificities of TTS secondary to accessory or variant muscles. Mass-occupying etiology should be included in the list of differential diagnoses whenever a posterior tibial nerve compression is suspected.

State of the Art and Advances in Peripheral Nerve Surgery

This review is intended to describe and actualize the basic knowledge of the three basic entities that affect the peripheral nerve system and can be treated by surgery: nerve trauma, chronic nerve compressions, and tumors.Regarding trauma, emphasis is given on the timing of surgery, given the fact that the moment in which the surgery is performed and the employed microsurgical reconstruction technique are the most important factors in the final result. Open lesions with associated nerve injury should be managed with an early exploration carried out before 7 days. Closed injuries are usually deferred, with few exceptions, from 3 to 6 months after the trauma.In turn, chronic compressions require an appropriate clinical, neurophysiological, and imaging diagnosis. Isolated sensory symptoms can be treated actively though without surgery: motor signs like atrophy should be regarded as a sign for immediate surgery, as a deferred treatment might cause an irreversible nerve and muscular damage. Endoscopic approaches are a valuable tool for treatment in selected neuropathies.Finally, nerve tumors demand a thorough preoperative evaluation, as benign tumors are treated in a very different way when compared to malignant lesions. Benign tumors can usually be safely and completely resected without sacrificing the nerve of origin. When malignancy is confirmed, extensive resection to optimize patient survival is the main objective, potentially at the expense of neurological function. This may then be followed by adjuvant radiation and/or chemotherapy, depending on the nature of the tumor and the completeness of resection attained. The role of nerve biopsy remains controversial, and several modern diagnostic techniques might be helpful.

Clinico-radiological review of peripheral entrapment neuropathies - Part 2 Lower limb

PURPOSE

This review discusses the relevant anatomy, etiopathogenesis, current notions in clinical and imaging features as well as management outline of lower limb entrapment neuropathies.

METHODS

The review is based on critical analysis of the current literature as well as our experience in dealing with entrapment neuropathies of the lower limb.

RESULTS

The complex anatomical network of nerves supplying the lower extremities are prone to entrapment by a heterogenous group of etiologies. This leads to diverse clinical manifestations making them difficult to diagnose with traditional methods such as clinical examination and electrodiagnostic studies. Moreover, some of these may mimic other common conditions such as disc pain or fibromyalgia leading to delay in diagnosis and increasing morbidity. Addition of imaging improves the diagnostic accuracy and also help in correct treatment of these entities. Magnetic resonance imaging is very useful for deeply situated nerves in pelvis and thigh while ultrasound is well validated for superficial entrapment neuropathies.

CONCLUSION

The rapidly changing concepts in these conditions accompanied by the advances in imaging has made it essential for a clinical radiologist to be well-informed with the current best practices.

Magnetic resonance imaging of the elbow

Elbow pain can cause disability, especially in athletes, and is a common clinical complaint for both the general practitioner and the orthopaedic surgeon. Magnetic resonance imaging (MRI) is an excellent tool for the evaluation of joint pathology due to its high sensitivity as a result of high contrast resolution for soft tissues. This article aims to describe the normal imaging anatomy and biomechanics of the elbow, the most commonly used MRI protocols and techniques, and common MRI findings related to tendinopathy, ligamentous and osteochondral injuries, and instability of the elbow.

Cystic degeneration of the tibial nerve: magnetic resonance neurography and sonography appearances of an intraneural ganglion cyst

Extra- and intraneural ganglion cysts have been described in the literature. The tibial nerve ganglion is uncommon and its occurrence without intra-articular extension is atypical. The pathogenesis of cystic degeneration localized to connective and perineural tissue secondary to chronic mechanical irritation or idiopathic mucoid degeneration is hypothesized. Since the above pathology is extremely rare and the magnetic resonance imaging examination detects the defining characteristics of the intrinsic alterations of the tibial nerve, the authors illustrate such a case of tibial intaneural ganglion cyst with its magnetic resonance neurography and sonography appearances.

Evaluation of median nerve T2 signal changes in patients with surgically treated carpal tunnel syndrome

OBJECTIVE

To determine the accuracy of median nerve T2 evaluation and its relation with Boston Questionnaire (BQ) and nerve conduction studies (NCSs) in pre-operative and post-operative carpal tunnel syndrome (CTS) patients in comparison with healthy volunteers.

METHODS

Twenty-three CTS patients and 24 healthy volunteers underwent NCSs, median nerve T2 evaluation and self-administered BQ. Pre-operative and 1st year post-operative median nerve T2 values and cross-sectional areas (CSAs) were compared both within pre-operative and post-operative CTS groups, and with healthy volunteers. The relationship between MRI findings and BQ and NCSs was analyzed. The ROC curve analysis was used for determining the accuracy.

RESULTS

The comparison of pre-operative and post-operative T2 values and CSAs revealed statistically significant improvements in the post-operative patient group (p<0.001 for all parameters). There were positive correlations between T2 values at all levels and BQ values, and positive and negative correlations were also found regarding T2 values and NCS findings in CTS patients. The receiver operating characteristic curve analysis for defined cut-off levels of median nerve T2 values in hands with severe CTS yielded excellent accuracy at all levels. However, this accuracy could not be demonstrated in hands with mild CTS.

CONCLUSION

This study is the first to analyze T2 values in both pre-operative and post-operative CTS patients. The presence of increased T2 values in CTS patients compared to controls and excellent accuracy in hands with severe CTS indicates T2 signal changes related to CTS pathophysiology and possible utilization of T2 signal evaluation in hands with severe CTS.

Imaging of benign complications of exostoses of the shoulder, pelvic girdles and appendicular skeleton

Exostoses are the most common benign bone tumors, accounting for 10 to 15% of all bone tumors. They develop at the bone surface by enchondral ossification and stop growing when skeletal maturity has been reached. At first, exostoses are covered by a smooth cartilage cap that progressively ossifies with skeleton maturity. Then they may regress, partly or even completely. Osteochondromas may be solitary or multiple, with the latter associated with hereditary multiple exostoses (HME). Exostoses develop during childhood and become symptomatic during the third decade of life in the case of solitary exostoses, or earlier, in case of HME. They stop growing after puberty, when the epiphyseal plates close. Most exostoses remain asymptomatic. Local complications, usually benign, may occur, such as fractures or mechanical impingements upon nearby structures. In rare cases, sarcomatous degeneration occurs. Most of these complications have been described in case reports. This article describes the imaging features of benign complications of exostoses of the shoulder, pelvic girdles and appendicular.

Elbow magnetic resonance imaging: imaging anatomy and evaluation

The elbow is a complex joint. Magnetic resonance imaging (MRI) is often the imaging modality of choice in the workup of elbow pain, especially in sports injuries and younger patients who often have either a history of a chronic repetitive strain such as the throwing athlete or a distinct traumatic injury. Traumatic injuries and alternative musculoskeletal pathologies can affect the ligaments, musculotendinous, cartilaginous, and osseous structures of the elbow as well as the 3 main nerves to the upper limb, and these structures are best assessed with MRI.Knowledge of the complex anatomy of the elbow joint as well as patterns of injury and disease is important for the radiologist to make an accurate diagnosis in the setting of elbow pain. This chapter will outline elbow anatomy, basic imaging parameters, compartmental pathology, and finally applications of some novel MRI techniques.

Ultrasound diagnosis of ulnar nerve entrapment by confirming baseline cross-sectional area measurement for normal and abnormal nerves

Background: Magnetic resonance imaging is most commonly employed, alongside electrodiagnostic studies, in the diagnosis of ulnar nerve entrapment. It is expensive, time consuming, not readily available to the general public, and limits imaging to a segment of the nerve at any given time. In contrast, high-frequency ultrasound is an inexpensive imaging modality with a flexible field of view through which the nerve can be traced. An ultrasound cross-sectional area (CSA) >0.075 cm² has previously been suggested as indicative of nerve entrapment. Objectives: To confirm the suggested CSA measurement of 0.075 cm² and discuss the difference in CSA measurement between abnormal nerves, nerves in the contra-lateral elbow of the same participant, and those of asymptomatic participants. Methods: Ultrasonography was performed on both elbows of 25 patients with confirmed unilateral ulnar nerve entrapment and on 25 healthy controls for comparison. Three CSA measurements were taken of the ulnar nerve along its course, and the mean measurement was recorded.Results: CSA measurements were significantly different between patients with ulnar nerve entrapment and healthy controls (p < 0.05). In our study, a CSA >0.070 cm² defined ulnar nerve entrapment at the elbow. Conclusion: Ultrasound CSA measurement of the ulnar nerve is accurate in the diagnosis of ulnar nerve entrapment. The range of values and varied criteria previously reported call for standardisation of the procedure and CSA measurement. We suggest that a measurement of 0.070 cm² be considered as a new baseline for the optimal diagnosis of ulnar nerve entrapment.[PDF to follow]

Ultrasonic assessment of females with carpal tunnel syndrome proved by nerve conduction study

INTRODUCTION

Carpal tunnel syndrome (CTS) is the most commonly diagnosed entrapment neuropathy of the upper extremity. The objective of this study was to diagnose CTS and to assess its severity using high resolution ultrasound (HRUS) depending on the results of nerve conduction study (NCS).

METHODS

A prospective cross-sectional study, in which HRUS was performed at 63 wrists of 35 female patients with different severity of CTS (as proved by NCS). Furthermore, 40 healthy volunteers (80 wrists) underwent the same tests as the patients and have been chosen to match the patients in gender, age, and body mass index (BMI). The cross section area (CSA) of the median nerve (MN) was obtained using HRUS at the carpal tunnel inlet by direct tracing method.

RESULTS

There was a significant difference in the CSA of the MN at the tunnel inlet in CTS patients when compared with the control group. In fact, the CSA of the control group showed a significant difference from each of patients subgroups. Furthermore, a significant difference in the CSA was seen in between these subgroups. In conclusion, the US examination of the MN seems to be a promising method in diagnosing and grading of carpal tunnel syndrome.

Peroneal nerve: Normal anatomy and pathologic findings on routine MRI of the knee

Background

Peroneal nerve lesions are not common and are often exclusively assessed clinically and electromyographically.

Methods

On a routine MR examination without dedicated MR-neurography sequences the peroneal nerve can readily be assessed. Axial T1-weighted sequences are especially helpful as they allow a good differentiation between the nerve and the surrounding fat.

Results

The purpose of this article is to review the normal anatomy and pathologic conditions of the peroneal nerve around the knee.

Conclusion

In the first part the variable anatomy of the peroneal nerve around the knee will be emphasized, followed by a discussion of the clinical findings of peroneal neuropathy and general MR signs of denervation. Six anatomical features may predispose to peroneal neuropathy: paucity of epineural tissue, biceps femoris tunnel, bifurcation level, superficial course around the fibula, fibular tunnel and finally the additional nerve branches. In the second part we discuss the different pathologic conditions: accidental and surgical trauma, and intraneural and extraneural compressive lesions.

Teaching Points

• Six anatomical features contribute to the vulnerability of the peroneal nerve around the knee.

• MR signs of muscle denervation within the anterior compartment are important secondary signs for evaluation of the peroneal nerve.

• The most common lesions of the peroneal nerve are traumatic or compressive.

• Intraneural ganglia originate from the proximal tibiofibular joint.

• Axial T1-weighted images are the best sequence to visualise the peroneal nerve on routine MRI.

Lateral epicondylitis and beyond: imaging of lateral elbow pain with clinical-radiologic correlation

The diagnosis of lateral epicondylitis is often straightforward and can be made on the basis of clinical findings. However, radiological assessment is valuable where the clinical picture is less clear or where symptoms are refractory to treatment. Demographics, aspects of clinical history, or certain physical signs may suggest an alternate diagnosis. Knowledge of the typical clinical presentation and imaging findings of lateral epicondylitis, in addition to other potential causes of lateral elbow pain, is necessary. These include entrapment of the posterior interosseous and lateral antebrachial cutaneous nerves, posterolateral rotatory instability, posterolateral plica syndrome, Panner's disease, osteochondritis dissecans of the capitellum, radiocapitellar overload syndrome, occult fractures and chondral-osseous impaction injuries, and radiocapitellar arthritis. Knowledge of these potential masquerades of lateral epicondylitis and their characteristic clinical and imaging features is essential for accurate diagnosis. The goal of this review is to provide an approach to the imaging of lateral elbow pain, discussing the relevant anatomy, various causes, and discriminating factors, which will allow for an accurate diagnosis.

3T magnetic resonance neurography of tibial nerve pathologies

Diagnosis of tibial neuropathy has been traditionally based on clinical examination and electrodiagnostic studies; however, cross-sectional imaging modalities have been used to increase the diagnostic accuracy and provide anatomic mapping of the abnormalities. In this context, magnetic resonance neurography (MRN) offers high-resolution imaging of the tibial nerve (TN), its branches and the adjacent soft tissues, and provides an objective assessment of the neuromuscular anatomy, abnormality, and the surrounding pathology. This review describes the pathologies affecting the TN and illustrates their respective 3 Tesla (T) MRN appearances with relevant case examples.

Comparison of the Diagnostic Utility of Electromyography, Ultrasonography, Computed Tomography, and Magnetic Resonance Imaging in Idiopathic Carpal Tunnel Syndrome Determined by Clinical Findings

Background:

Carpal tunnel syndrome (CTS) is the most common nerve entrapment syndrome. It is sometimes difficult to diagnose, and a late diagnosis may result in permanent nerve damage. Electromyography (EMG), ultrasonography (US), magnetic resonance imaging (MRI), and computed tomography (CT) may be performed for the diagnosis. The diagnostic accuracy of these tests is well documented, but most of these studies accept EMG as the gold standard.

Objective:

To evaluate the diagnostic accuracy of EMG, MRI, CT, and US for the diagnosis of carpal tunnel syndrome with the use of clinical findings as the gold standard.

Methods:

Patients suspected to have CTS on presentation to the outpatient clinic were evaluated. The tests were performed after a detailed physical examination. Both wrists of the 69 patients in the study were investigated.

Results:

The diagnostic accuracies of all the tests were found to be sufficient. Although EMG seemed to have the highest sensitivity and specificity, there was no statistically significant difference between the tests.

Conclusion:

EMG or US could be used as the first-step test in most cases. If they are both available, EMG should be the first choice. They may be performed together when diagnosis is challenging. CT may especially be preferred for bone-related pathological conditions, whereas MRI may be preferred for soft tissue-related pathological conditions. Even though imaging studies have been proven to be powerful diagnostic tools for CTS, no conclusive information currently exists to support replacing EMG with imaging studies.

Imaging of neuropathies about the hip

Neuropathies about the hip may be cause of chronic pain and disability. In most cases, these conditions derive from mechanical or dynamic compression of a segment of a nerve within a narrow osteofibrous tunnel, an opening in a fibrous structure, or a passageway close to a ligament or a muscle. Although the evaluation of nerve disorders primarily relies on neurological examination and electrophysiology, diagnostic imaging is currently used as a complement to help define the site and aetiology of nerve compression and exclude other disease possibly underlying the patient' symptoms. Diagnosis of entrapment neuropathies about the hip with US and MR imaging requires an in-depth knowledge of the normal imaging anatomy and awareness of the anatomic and pathologic factors that may predispose or cause a nerve injury. Accordingly, the aim of this article is to provide a comprehensive review of hip neuropathies with an emphasis on the relevant anatomy, aetiology, clinical presentation, and their imaging appearance. The lateral femoral cutaneous neuropathy (meiralgia paresthetica), femoral neuropathy, sciatic neuropathy, obturator neuropathy, superior and inferior gluteal neuropathies and pudendal neuropathy will be discussed.

What's new in the diagnosis and treatment of peripheral nerve entrapment neuropathies

Entrapment neuropathies can be common conditions with the potential to cause significant disability. Correct diagnosis is essential for proper management. This article is a review of recent developments related to diagnosis and treatment of various common and uncommon nerve entrapment disorders. When combined with classical peripheral nerve examination techniques, innovations in imaging modalities have led to more reliable diagnoses. Moreover, innovations in conservative and surgical techniques have been controversial as to their effects on patient outcome, but randomized controlled trials have provided important information regarding common operative techniques. Treatment strategies for painful peripheral neuropathies are also reviewed.

Ultrasonography in patients with ulnar neuropathy at the elbow: comparison of cross-sectional area and swelling ratio with electrophysiological severity

The aim of this study was to determine the diagnostic value of ultrasonographic measurements in ulnar neuropathy at the elbow (UNE) and to assess the relationship between the measurements and the electrophysiological severity. The largest anteroposterior diameter (LAPD) and cross-sectional area (CSA) measurements of the ulnar nerve were noted at multiple levels along the arm, and the distal-to-proximal ratios were calculated. Almost all of the measurements and swelling ratios between patients and controls showed statistically significant differences. The largest CSA, distal/largest CSA ratio, CSA at the epicondyle, and proximal LAPD had larger areas under the curve than other measurements. The sensitivity and specificity in diagnosing UNE were 95% and 71% for the largest CSA, 83% and 85% for the distal/largest CSA ratio, 83% and 81% for the CSA at the epicondyle, and 93% and 43% for the proximal LAPD, respectively. There was a statistically significant correlation between the electrophysiological severity scale score (ESSS) and the largest CSA, the CSA at the epicondyle and 2 cm proximal to the epicondyle, and the LAPD at the level of the epicondyle (P < 0.05). None of the swelling ratios showed a significant correlation with the ESSS. The largest CSA measurement is the most valuable ultrasonographic measurement both for diagnosis and determining the severity of UNE.

Reliability and size of the measurement error when determining the cross-sectional area of the tibial nerve at the tarsal tunnel with ultrasonography

An in depth analysis of the reliability of ultrasonography to measure the cross-sectional area of the tibial nerve or any other peripheral nerve is not available in the literature. This study determined the reliability and size of the measurement error of high-resolution ultrasound to measure the size of the tibial nerve at the tarsal tunnel. The cross-sectional area of the tibial nerve was measured by two experienced sonographers at 1 cm proximal to the medial malleolus. Measurements were made in 10 healthy participants without plantar heel pain. Intra and intertester reliability were determined by calculation of intraclass correlation coefficients (ICC), measurement error magnitude and smallest detectable difference (SDD). A direct (tracing) and indirect (ellipsoid formula) method were evaluated. Results demonstrated that the intra and intertester reliability were excellent (ICC, all > or =0.86). The measurement error and SDD were very small, especially when measurements from three scans were averaged (measurement error: 0.4-0.9 mm2; SDD: 1.1-2.5 mm2). The findings of this study support the view that high-resolution ultrasound is reliable to measure the cross-sectional area of a peripheral nerve. As a result of the small measurement error, a side-to-side difference as small as approximately 1.8 mm2 can be interpreted meaningfully in an individual patient. This difference is much smaller than the swelling reported in the literature for patients with tibial neuropathy.

Ultrasonography in carpal tunnel syndrome: Comparison with electrophysiological stage and motor unit number estimate

The purpose of this study was to document the ultrasonographic measurement differences in median nerve size between patients with carpal tunnel syndrome (CTS) and controls, and to correlate these findings with electrophysiological stage and motor unit number estimation (MUNE), thereby allowing us to test the validity of ultrasound as a diagnostic modality for assessing the severity of CTS. High-resolution sonography and electrophysiological studies were performed on 41 wrists of 27 patients and compared with findings on 40 wrists of 20 healthy individuals. On ultrasonographic views, cross-sectional area and flattening ratio in proximal, middle, and distal tunnel segments of the median nerve were measured both by calculating ellipsoid area by large and small cross-sectional diameters and by automated ellipsoid area calculation. We compared electrophysiological stage and MUNE with proximal, middle, and distal cross-sectional area and other ultrasonographic findings. All correlations between electrophysiological stage and cross-sectional areas in these different segments of the median nerve were significant with both measurement methods. Negative correlations were seen between MUNE and cross-sectional area in the proximal and middle segments, whereas no significant correlation was detected in the distal segment. Our results indicate that there are close correlations between the ultrasonographic findings and electrophysiological stage. Ultrasound also reflects the reduction in the number of axons estimated by the MUNE method. Therefore, we suggest that the ultrasonographic findings reflect the severity of disease in patients with CTS.

[Diagnostic imaging of nerve compression syndrome]

Compression-induced neuropathy of peripheral nerves can cause severe pain of the foot and ankle. Early diagnosis is important to institute prompt treatment and to minimize potential injury. Although clinical examination combined with electrophysiological studies remain the cornerstone of the diagnostic work-up, in certain cases, imaging may provide key information with regard to the exact anatomic location of the lesion or aid in narrowing the differential diagnosis. In other patients with peripheral neuropathies of the foot and ankle, imaging may establish the etiology of the condition and provide information crucial for management and/or surgical planning. MR imaging and ultrasound provide direct visualization of the nerve and surrounding abnormalities. Bony abnormalities contributing to nerve compression are best assessed by radiographs and CT. Knowledge of the anatomy, the etiology, typical clinical findings, and imaging features of peripheral neuropathies affecting the peripheral nerves of the foot and ankle will allow for a more confident diagnosis.

Role of magnetic resonance imaging in entrapment and compressive neuropathy--what, where, and how to see the peripheral nerves on the musculoskeletal magnetic resonance image: part 2. Upper extremity

The diagnosis of nerve entrapment and compressive neuropathy has been traditionally based on the clinical and electrodiagnostic examinations. As a result of improvements in the magnetic resonance (MR) imaging modality, it plays not only a fundamental role in the detection of space-occupying lesions, but also a compensatory role in clinically and electrodiagnostically inconclusive cases. Although ultrasound has undergone further development in the past decades and shows high resolution capabilities, it has inherent limitations due to its operator dependency. We review the course of normal peripheral nerves, as well as various clinical demonstrations and pathological features of compressed and entrapped nerves in the upper extremities on MR imaging, according to the nerves involved. The common sites of nerve entrapment of the upper extremity are as follows: the brachial plexus of the thoracic outlet; axillary nerve of the quadrilateral space; radial nerve of the radial tunnel; ulnar nerve of the cubital tunnel and Guyon's canal; median nerve of the pronator syndrome, anterior interosseous nerve syndrome, and carpal tunnel syndrome. Although MR imaging can depict the peripheral nerves in the extremities effectively, radiologists should be familiar with nerve pathways, common sites of nerve compression, and common space-occupying lesions resulting in nerve compression in MR imaging.

Role of magnetic resonance imaging in entrapment and compressive neuropathy—what, where, and how to see the peripheral nerves on the musculoskeletal magnetic resonance image: part 1. Overview and lower extremity

The diagnosis of nerve entrapment and compressive neuropathy has been traditionally based on the clinical and electrodiagnostic examinations. As a result of improvements in the magnetic resonance (MR) imaging modality, it plays not only a fundamental role in the detection of space-occupying lesions but also a compensatory role in clinically and electrodiagnostically inconclusive cases. Although ultrasound has undergone further development in the past decades and shows high resolution capabilities, it has inherent limitations due to its operator dependency. We review the general concepts that should be known to evaluate the entrapment and compressive neuropathy in MR imaging. We also review the course of normal peripheral nerves, as well as various clinical demonstrations and pathological features of compressed and entrapped nerves in the lower extremities on MR imaging, according to the nerves involved. The common sites of nerve entrapment of the lower extremity are as follows: sciatic nerve around the piriformis muscle; tibial nerve at the popliteal fossa and tarsal tunnel, common peroneal nerve around the fibular neck, and digital nerve near the metatarsal head. Although MR imaging can depict the peripheral nerves in the extremities effectively, radiologists should be familiar with nerve pathways, common sites of nerve compression, and common space-occupying lesions resulting in nerve compression in MR imaging.