Quantitative STIR of muscle for monitoring nerve regeneration

Detection of Traumatic and Postoperative Nerve Lesions following Upper Extremity Fractures in a Pediatric Cohort Using MR Neurography

INTRODUCTION

 Fractures of the upper extremity are common traumatic injuries in children. Nerve lesions are a rare but typical complication of these fractures. Additional to physical, electrophysiological, and sonographic examinations, magnetic resonance neurography (MRN) can be used to assess the degree and exact localization of nerve damage. This retrospective study was conducted to evaluate the potential role of this examination technique for children and to test a proposed MRN classification of traumatic nerve injury according to Chhabra in a pediatric cohort.

MATERIALS AND METHODS

 Pediatric patients undergoing MRN for traumatic nerve injury from January 2016 to December 2020 were retrospectively identified. A total of 12 consecutive patients with sufficient clinical data, an MRN, and if available follow-up examination were enrolled and analyzed.

RESULTS

 In 10 of 12 cases one or more nerve lesions could be identified by MRN using the classification proposed by Chhabra et al. MRN was used to assess nerve injuries, imaging results were compared with clinical course. Clinical follow-up examinations of 10 patients showed an overall good clinical recovery, even in one case with severe trauma and nerve surgery.

CONCLUSION

 MRN as a noninvasive procedure can help in the evaluation of nerve injury, especially for the identification of lower grade nerve damage and to objectify suspected nerve damage in case of uncertain clinical examination results; thus, can help in decision making whether surgical revision or conservative treatment is preferable.

Quantitative T2 -mapping magnetic resonance imaging for assessment of muscle motor unit recruitment patterns

INTRODUCTION

In this study, we aimed to determine whether muscle transverse relaxation time (T₂ ) magnetic resonance (MR) mapping results correlate with motor unit loss, as defined by motor unit recruitment patterns on electromyography (EMG).

METHODS

EMG and 3-Tesla MRI exams were acquired no more than 31 days apart in subjects referred for peripheral nerve MRI. Two musculoskeletal radiologists qualitatively graded T₂ -weighted, fat-suppressed sequences for severity of muscle edema-like patterns and manually placed regions of interest within muscles to obtain T₂ values from T₂ -mapping sequences. Concordance was calculated between qualitative and quantitative MR grades and EMG recruitment categories (none, discrete, decreased) as well as interobserver agreement for both MR grades.

RESULTS

Thirty-four muscles (21 abnormal, 13 control) were assessed in 13 subjects (5 females and 8 males; mean age, 46 years) with 14 EMG-MRI pairs. T₂ -relaxation times were significantly (P < .001) increased in all EMG recruitment categories compared with control muscles. T₂ differences were not significant between EMG grades of motor unit recruitment (P = .151-.702). T₂ and EMG score concordance was acceptable (Harrell's concordance index [c index]: rater A, 0.71; 95% confidence interval [CI], 0.51-0.87; rater B, 0.77; 95% CI, 0.57-0.91). Qualitative MRI and EMG score concordance was poor to acceptable (c index: rater A, 0.60; 95% CI, 0.50-0.79; rater B, 0.72; 95% CI, 0.55-0.89). T₂ values had moderate-to-substantial ability to distinguish between absent vs incomplete (ie, decreased or discrete) motor unit recruitment (c index: rater A, 0.78; 95% CI, 0.50-1.00; rater B, 0.86; 95% CI, 0.57-1.00).

DISCUSSION

Quantitative T₂ MR muscle mapping is a promising tool for noninvasive evaluation of the degree of motor unit recruitment loss.

A quantitative method to assess muscle edema using short TI inversion recovery MRI

Muscle inflammation is an important component of disease pathophysiology in several muscular dystrophies. Hyperintensities on MRI sequences with short TI inversion recovery (STIR) reflect edema, or inflammation (STIR+). Conventionally, STIR evaluation has been done by visual inspection. In this study, we developed a quantitative STIR method, and tested its ability to identify STIR+ lesions in healthy controls and patients with Facioscapulohumeral muscular dystrophy and compared the results with visual STIR evaluation and quantitative T2 relaxation time mapping. The method was based on pixel-by-pixel histograms of the distribution of signal intensities from muscles. Signal intensities from healthy control muscles were averaged and used to define an upper reference limit. Muscles with >2.5% pixels above the limit were defined as being STIR+. The new method showed agreement with T2 relaxation time mapping in 95% of muscles. The visual STIR method only showed agreement with the quantitative STIR method and T2 relaxation time mapping in 88 and 84%, respectively. STIR sequences are available on most MR scanners and the post-processing used in the new quantitative method can be performed using free software. We therefore believe that the new method can play an important role in identifying STIR+ lesions in patients with neuromuscular diseases.

Strategies for Peripheral Nerve Repair

PURPOSE OF REVIEW

This review focuses on biomechanical and cellular considerations required for development of biomaterials and engineered tissues suitable for implantation following PNI, as well as translational requirements relating to outcome measurements for testing success in patients.

RECENT FINDINGS

Therapies that incorporate multiple aspects of the regenerative environment are likely to be key to improving therapies for nerve regeneration. This represents a complex challenge when considering the diversity of biological, chemical and mechanical factors involved. In addition, clinical outcome measures following peripheral nerve repair which are sensitive and responsive to changes in the tissue microenvironment following neural injury and regeneration are required.

SUMMARY

Effective new therapies for the treatment of PNI are likely to include engineered tissues and biomaterials able to evoke a tissue microenvironment that incorporates both biochemical and mechanical features supportive to regeneration. Translational development of these technologies towards clinical use in humans drives a concomitant need for improved clinical measures to quantify nerve regeneration.

Magnetic resonance neurography: current perspectives and literature review

Magnetic resonance neurography (also called MRN or MR neurography) refers to MR imaging dedicated to the peripheral nerves. It is a technique that enhances selective multiplanar visualisation of the peripheral nerve and pathology by encompassing a combination of two-dimensional, three-dimensional and diffusion imaging pulse sequences. Referring physicians who seek imaging techniques that can depict and diagnose peripheral nerve pathologies superior to conventional MR imaging are driving the demand for MRN. This article reviews the pathophysiology of peripheral nerves in common practice scenarios, technical considerations of MRN, current indications of MRN, normal and abnormal neuromuscular appearances, and imaging pitfalls. Finally, the emerging utility of diffusion-weighted and diffusion tensor imaging is discussed and future directions are highlighted.

KEY POINTS

• Lesion relationship to neural architecture is more conspicuous on MRN than MRI. • 3D multiplanar imaging technique is essential for pre-surgical planning. • Nerve injuries can be classified on MRN using Sunderland's classification. • DTI provides quantitative information and insight into intraneural integrity and pathophysiology.