Diffusion-weighted imaging and diffusion tensor imaging as adjuncts to conventional MRI for the diagnosis and management of peripheral nerve sheath tumors: current perspectives and future directions.

Peripheral nerve sheath tumors (PNSTs) account for ~ 5% of soft tissue neoplasms and are responsible for a wide spectrum of morbidities ranging from localized neuropathy to fulminant metastatic spread and death. MR imaging represents the gold standard for identification of these neoplasms, however, current anatomic MR imaging markers do not reliably detect or differentiate benign and malignant lesions, and therefore, biopsy or excision is required for definitive diagnosis. Diffusion-weighted MR imaging (DWI) serves as a useful tool in the evaluation and management of PNSTs by providing functional information regarding the degree of diffusion, while diffusion tensor imaging (DTI) aids in determining the directional information of predominant diffusion and has been shown to be particularly useful for pre-operative planning of these tumors by delineating healthy and pathologic fascicles. The article focuses on these important neurogenic lesions, highlighting the current utility of diffusion MR imaging and future directions including computerized radiomic analysis. KEY POINTS: • Anatomic MRI is moderately accurate in differentiating benign from malignant PNST. • Diffusion tensor imaging facilitates pre-operative planning of PNSTs by depicting neuropathy and tractography. • Radiomics will likely augment current observer-based diagnostic criteria for PNSTs.

Effects of extracellular calcium and surgical techniques on restoration of axonal continuity by polyethylene glycol fusion following complete cut or crush severance of rat sciatic nerves.

Complete crush or cut severance of sciatic nerve axons in rats and other mammals produces immediate loss of axonal continuity. Loss of locomotor functions subserved by those axons is restored only after months, if ever, by outgrowths regenerating at ∼1 mm/day from the proximal stumps of severed axonal segments. The distal stump of a severed axon typically begins to degenerate in 1-3 days. We recently developed a polyethylene glycol (PEG) fusion technology, consisting of sequential exposure of severed axonal ends to hypotonic Ca(2+) -free saline, methylene blue, PEG in distilled water, and finally Ca(2+) -containing isotonic saline. This study examines factors that affect the PEG fusion restoration of axonal continuity within minutes, as measured by conduction of action potentials and diffusion of an intracellular fluorescent dye across the lesion site of rat sciatic nerves completely cut or crush severed in the midthigh. Also examined are factors that affect the longer-term PEG fusion restoration of lost behavioral functions within days to weeks, as measured by the sciatic functional index. We report that exposure of cut-severed axonal ends to Ca(2+) -containing saline prior to PEG fusion and stretch/tension of proximal or distal axonal segments of cut-severed axons decrease PEG fusion success. Conversely, trimming cut-severed ends in Ca(2+) -free saline just prior to PEG fusion increases PEG fusion success. PEG fusion prevents or retards the Wallerian degeneration of cut-severed axons, as assessed by measures of axon diameter and G ratio. PEG fusion may produce a paradigm shift in the treatment of peripheral nerve injuries. © 2016 Wiley Periodicals, Inc.

NeuroMix with MR Angiography: A Fast MR Protocol to Reduce Head and Neck CT Angiography for Patients with Acute Neurological Presentations.

BACKGROUND AND PURPOSE: Overuse of computed tomography (CT)-based cerebrovascular imaging in the emergency department (ED) and inpatient settings, notably CT angiography of the head and neck (CTAHN) for minor and non-focal neurological presentations, stresses imaging services and exposes patients to radiation and contrast. Furthermore, such CT-based imaging is often insufficient for definitive diagnosis, necessitating additional MR imaging. Recent advances in fast MRI may allow for timely assessment and reduced need for CTAHN in select populations. MATERIALS AND METHODS: We identified inpatients or ED patients who underwent CTAHN (including non-contrast and post-contrast CTH, with or without CT perfusion [CTP] imaging) followed within 24 hours by a 3T MRI study that included NeuroMix (an unenhanced 2.5 min multi-contrast sequence) and intracranial time-of-flight MR angiography (MRA; a 5 min sequence) during a 9-month period (April to December 2022). Cases were classified by 4 radiologists in consensus as to whether NeuroMix and NeuroMix+MRA detected equivalent findings, detected unique findings, or missed findings relative to CTAHN. RESULTS: 174 cases (mean age 67±16 yrs; 56% female) met the inclusion criteria. NeuroMix alone and NeuroMix+MRA protocols were determined to be equivalent or better compared to CTAHN in 71% and 95% of patients, respectively. NeuroMix always provided equivalent or better assessment of the brain parenchyma, with unique findings on NeuroMix and NeuroMix+MRA in 35% and 36% of cases, respectively, most commonly acute infarction or multiple microhemorrhages. In 8/174 cases (5%), CTAHN identified vascular abnormalities not seen on the NeuroMix+MRA protocol due to CTAHN's wider coverage of the cervical arteries. CONCLUSIONS: A fast MR imaging protocol consisting of NeuroMix+MRA provided equivalent or better information compared to CTAHN in 95% of cases in our population of patients with an acute neurological presentation. The findings provide a deeper understanding of the benefits and challenges of a fast unenhanced MR-first approach with NeuroMix+MRA, which could be used to design prospective trials in select patient groups, with the potential to reduce radiation dose, mitigate adverse contrast-related patient and environmental effects, and lessen the burden on radiologists and healthcare systems. ABBREVIATIONS: CTAHN = CTA Head and Neck including non-contrast and delayed post-contrast CT Head with or without CT perfusion, NeuroMix = unenhanced multi-contrast MR brain sequence.

Soft tissue mycetoma: "Dot-in-circle" sign on magnetic resonance imaging.

A 36-year-old Mexican female with a slowly growing foot mass was referred to orthopedic surgery clinic for further evaluation. Foot magnetic resonance imaging revealed an infiltrative soft tissue mass along the dorsal aspect of the fourth metatarsal. T2-weighted images revealed multiple central low-signal "dots" surrounded by areas of bright signal intensity, known as the "dot-in-circle" sign, which is highly specific for mycetoma. Surgical biopsy confirmed the diagnosis of bacterial mycetoma in this patient. Mycetoma can lead to progressive deformity and loss of function, as well as possible limb amputation in the case of delayed diagnosis or misdiagnosis. The "dot-in-circle" sign on magnetic resonance imaging can assist in rendering a final diagnosis and distinguish mycetoma from other etiologies of a soft tissue mass, such as a sarcoma or benign soft tissue lesions.

MR neurography of the brachial plexus in adult and pediatric age groups: evolution, recent advances, and future directions.

Introduction: MR neurography (MRN) of the brachial plexus has emerged in recent years as a safe and accurate modality for the identification of brachial plexopathies in pediatric and adult populations. While clinical differentiation of brachial plexopathy from cervical spine-related radiculopathy or nerve injury has long relied upon nonspecific physical exam and electrodiagnostic testing modalities, MRN now permits detailed interrogation of peripheral nerve anatomy and pathology, as well as assessment of surrounding soft tissues and musculature, thereby facilitating accurate diagnosis. The reader will learn about the current state of brachial plexus MRN, including recent advances and future directions, and gain knowledge about the adult and pediatric brachial plexopathies that can be characterized using these techniques.Areas Covered: The review details recent developments in brachial plexus MRN, including increasing availability of 3.0-T MR scanners at both private and academic diagnostic imaging centers, as well as the advent of multiple new vascular and fat signal suppression techniques. A literature search of PubMed and SCOPUS was used as the principal source of information gathered for this review.Expert Opinion: Refinement of fat-suppression, 3D techniques and diffusion MR imaging modalities has improved the accuracy of MRN, rendering it as a useful adjunct to clinical findings during the evaluation of suspected brachial plexus lesions.