Advanced Imaging of the Peripheral Nerves, From the AJR "How We Do It" Special Series.

Advanced imaging of peripheral nerves is occupying an increasingly important role in the diagnostic workup of peripheral nerve disorders. Advances in MR neurography (MRN) and high-resolution ultrasound have addressed historical challenges in peripheral nerve imaging related to nerves' small size and non-linear course, and difficult differentiation from surrounding tissues. Modern MRN depicts neuromuscular anatomy with exquisite contrast resolution, and MRN has become the workhorse imaging modality for peripheral nerve evaluation. MRN protocols vary across institutions and are adjusted in individual patients, although commonly include nerve-selective sequences and diffusion tensor imaging tractography. Ultrasound offers a dynamic, real-time high-resolution assessment of peripheral nerves, and is widely accessible and less costly than MRN. Ultrasound has greater ability to interrogate peripheral nerves at the fascicular level and provides complementary information to MRN. However, ultrasound of peripheral nerves requires substantial skill and experience and is operator-dependent. The two modalities have distinct advantages and disadvantages, and the selection between these depends on the clinical context. This article provides an overview of advanced imaging techniques used for evaluation of peripheral nerves, with attention to MRN and high-resolution ultrasound. We draw on our institutional experience in performing both modalities to highlight technical considerations for optimizing examinations.

Unusual neuroimaging findings in spontaneous intracranial hypotension.

PURPOSE: The most common neuroimaging manifestations of patients suffering from spontaneous intracranial hypotension (SIH) include subdural fluid collections, enhancement of the pachymeninges, engorgement of venous structures, pituitary hyperemia, sagging of the brainstem, and cerebellar hemosiderosis. However, infrequently patients may present with separate neuroradiological findings which could be easily mistaken for other pathology. METHODS: We describe patients who presented with unique neuroimaging findings who were eventually found to have a spinal CSF leak or venous fistula. Relevant clinical history and neuroradiology findings are presented, and a relevant review of the literature is provided. RESULTS: We present six patients with a proven CSF leak or fistula who presented with dural venous sinus thrombosis, compressive ischemic injury, spinal hemosiderosis, subarachnoid hemorrhage, pial vascular engorgement, calvarial hyperostosis, and spinal dural calcifications. CONCLUSION: Radiologists should be familiar with atypical neuroimaging manifestations of SIH in order to avoid misdiagnosis and guide the clinical trajectory of the patient towards accurate diagnosis and eventual cure.

Brain herniation (encephalocele) into arachnoid granulations: prevalence and association with pulsatile tinnitus and idiopathic intracranial hypertension.

PURPOSE: Brain herniation into arachnoid granulations (BHAG) of the dural venous sinuses is a recently described finding of uncertain etiology. The purpose of this study was to investigate the prevalence of BHAG in a cohort of patients with pulsatile tinnitus (PT) and to clarify the physiologic and clinical implications of these lesions. METHODS: The imaging and charts of consecutive PT patients were retrospectively reviewed. All patients were examined with MRI including pre- and post-contrast T1- and T2-weighted sequences. Images were reviewed separately by three blinded neuroradiologists to identify the presence of BHAG. Their location, signal intensity, size, presence of arachnoid granulation, and associated dural venous sinus stenosis were documented. Clinical records were further reviewed for idiopathic intracranial hypertension, history of prior lumbar puncture, and opening pressure. RESULTS: Two hundred sixty-two consecutive PT patients over a 4-year period met inclusion criteria. PT patients with BHAG were significantly more likely to have idiopathic intracranial hypertension than PT patients without BHAG (OR 4.2, CI 1.5-12, p = 0.006). Sixteen out of 262 (6%) patients were found to have 18 BHAG. Eleven out of 16 (69%) patients had unilateral temporal or occipital lobe herniations located in the transverse sinus or the transverse-sigmoid junction. Three out of 16 (19%) patients had unilateral cerebellar herniations and 2/16 (13%) patients had bilateral BHAG. CONCLUSION: In patients with PT, BHAG is a prevalent MRI finding that is strongly associated with the clinical diagnosis of IIH. The pathogenesis of BHAG remains uncertain, but recognition should prompt comprehensive evaluation for IIH.

Neurological manifestations of polyarteritis nodosa: a tour of the neuroaxis by case series.

BACKGROUND: Heterogenous central nervous system (CNS) neurologic manifestations of polyarteritis nodosa (PAN) are underrecognized. We review three cases of patients with PAN that illustrate a range of nervous system pathology, including the classical mononeuritis multiplex as well as uncommon brain and spinal cord vascular manifestations. CASE PRESENTATION: Case 1 presented with mononeuritis multiplex and characteristic skin findings. Case 2 presented with thunderclap headache and myelopathy due to spinal artery aneurysm rupture. Both patients experienced disease remission upon treatment. Case 3 presented with headache and bulbar symptoms due to partially thrombosed intracranial aneurysms, followed by systemic manifestations related to visceral aneurysms. She demonstrated clinical improvement with treatment, was lost to follow-up, then clinically deteriorated and entered hospice care. CONCLUSIONS: Although the peripheral manifestations of PAN are well-known, PAN association with CNS neurovascular disease is relatively underappreciated. Clinician awareness of the spectrum of neurologic disease is required to reduce diagnostic delay and promote prompt diagnosis and treatment with immunosuppressants.

The Use of Contrast Agents in Interventional Pain Procedures: A Multispecialty and Multisociety Practice Advisory on Nephrogenic Systemic Fibrosis, Gadolinium Deposition in the Brain, Encephalopathy After Unintentional Intrathecal Gadolinium Injection, and Hypersensitivity Reactions.

This Practice Advisory presents a comprehensive and evidence-based set of position statements and recommendations for the use of contrast media in interventional pain procedures. The advisory was established by an international panel of experts under the auspices of 11 multinational and multispecialty organizations based on a comprehensive review of the literature up to December 31, 2019. The advisory discusses the risks of using gadolinium-based contrast agents. These include nephrogenic systemic fibrosis, gadolinium brain deposition/retention, and encephalopathy and death after an unintentional intrathecal gadolinium injection. The advisory provides recommendations on the selection of a specific gadolinium-based contrast agent in patients with renal insufficiency, those who had multiple gadolinium-enhanced magnetic resonance imaging examinations, and in cases of paraspinal injections. Additionally, recommendations are made for patients who have a history of mild, moderate, or severe hypersensitivity reactions to contrast medium.

Cerebrospinal fluid-lymphatic fistula causing spontaneous intracranial hypotension in a child with kaposiform lymphangiomatosis.

Spontaneous intracranial hypotension is an uncommon etiology of secondary headaches in children. We report a unique case of a girl with kaposiform lymphangiomatosis who developed postural headaches and imaging features of spontaneous intracranial hypotension without a spinal extradural collection. The girl underwent dynamic computed tomography myelography which revealed a cerebrospinal fluid (CSF)-lymphatic fistula related to a lymphatic malformation associated with the right T10 nerve. She underwent surgical ligation of the CSF-lymphatic fistula, resulting in resolution of the headaches. Spinal CSF-lymphatic fistulas are rare and have previously been reported in two patients with Gorham-Stout disease. The current report suggests that patients with systemic lymphatic anomalies who develop postural headaches should undergo evaluation for spontaneous intracranial hypotension and a CSF-lymphatic fistula. If discovered, surgical ligation is a potential treatment.

The Reliability of a Grading System for Digital Subtraction Imaging Quality During Cervical Transforaminal Epidural Steroid Injection.

OBJECTIVE: Digital subtraction imaging (DSI) decreases the risk of intravascular injection during cervical transforaminal epidural steroid injection (CTFESI); however, sequence acquisition and interpretation are operator-dependent skills. This study tests the reliability of a grading system to determine adequate DSI during CTFESI. SETTING: Academic tertiary medical center. METHODS: A grading scheme for adequate DSI quality during CTFESI was created by the study authors based on patient positioning, mask image, and volume of contrast injected. The inter-rater and intrarater reliability values of this grading scheme were tested using 50 DSI images evaluated by three raters during two distinct sessions separated by four weeks. Based on a power analysis, a sample of 50 scans was sufficient to detect significant correlations. Inter-rater reliability was determined by percent agreement between graders for dichotomized categories of "quality of DSI is adequate for safe C-TFESI" vs "quality of DSI is inadequate for safe C-TFESI." The percentage of agreement was reported, along with Gwet's agreement coefficient (AC). The intrarater (pre/post) correlation was assessed using Yule's Q statistics. RESULTS: Correlation coefficients were interpreted as follows: 0.00-0.19 "very weak," 0.20-0.39 "weak," 0.40-0.59 "moderate," 0.60-0.79 "strong," and 0.80-1.00 "very strong." Inter-rater reliability analyses demonstrated that the patient position category had "very strong" agreement, contrast volume had "strong" agreement, and mask image had "moderate" agreement. The overall inter-rater reliability was "moderate." All of the raters demonstrated "very strong" intrarater reliability. CONCLUSIONS: The proposed grading system for adequate-quality DSI during CTFESI showed overall "moderate" and "very strong" inter- and intrarater reliability, respectively. This scheme provides an objective measure of DSI quality for CTFESI. Refinement is needed to improve the reliability of this scheme.

Cervical spinal canal narrowing in idiopathic syringomyelia.

INTRODUCTION: The cervical spine in Chiari I patient with syringomyelia has significantly different anteroposterior diameters than it does in Chiari I patients without syringomyelia. We tested the hypothesis that patients with idiopathic syringomyelia (IS) also have abnormal cervical spinal canal diameters. The finding in both groups may relate to the pathogenesis of syringomyelia. METHODS: Local institutional review boards approved this retrospective study. Patients with IS were compared to age-matched controls with normal sagittal spine MR. All subjects had T1-weighted spin-echo (500/20) and T2-weighted fast spin-echo (2000/90) sagittal cervical spine images at 1.5 T. Readers blinded to demographic data and study hypothesis measured anteroposterior diameters at each cervical level. The spinal canal diameters were compared with a Mann-Whitney U test. The overall difference was assessed with a Friedman test. Seventeen subjects were read by two reviewers to assess inter-rater reliability. RESULTS: Fifty IS patients with 50 age-matched controls were studied. IS subjects had one or more syrinxes varying from 1 to 19 spinal segments. Spinal canal diameters narrowed from C1 to C3 and then enlarged from C5 to C7 in both groups. Diameters from C2 to C4 were narrower in the IS group (p < 0.005) than in controls. The ratio of the C3 to the C7 diameters was also smaller (p = 0.004) in IS than controls. Collectively, the spinal canal diameters in the IS were significantly different from controls (Friedman test p < 0.0001). CONCLUSION: Patients with IS have abnormally narrow upper and mid cervical spinal canal diameters and greater positive tapering between C3 and C7.

Diffusion Imaging of the Spinal Cord: Clinical Applications.

Spinal cord pathologic condition often presents as a neurologic emergency where timely and accurate diagnosis is critical to expedite appropriate treatment and minimize severe morbidity and even mortality. MR imaging is the gold standard imaging technique for diagnosing patients with suspected spinal cord pathologic condition. This review will focus on the basic principles of diffusion imaging and how spinal anatomy presents technical challenges to its application. Both the promises and shortcomings of spinal diffusion imaging will then be explored in the context of several clinical spinal cord pathologies for which diffusion has been evaluated.

Academic Neuroradiology: 2023 Update on Turn-Around Time, Financial Recruitment and Retention Strategies.

The ASNR Neuroradiology Division Chief Working Group's 2023 survey, with responses from 62 division chiefs, provides insights into turn-around times, faculty recruitment, moonlighting opportunities, and academic funds.In emergency cases, 61% aim for a turn-around time of less than 45-60 minutes, with two-thirds meeting this expectation more than 75% of the time. For inpatient CT and MRI scans, 54% achieve a turn-around time of 4-8 hours, with three quarters meeting this expectation at least 50% of the time. Outpatient scans have an expected turn-around time of 24-48 hours, which is met in 50% of cases.Faculty recruitment strategies included 35% offering sign-on bonuses, with a median of $30,000. Additionally, 23% provided bonuses to fellows during fellowship to retain them in the practice upon completion of their fellowship. Internal moonlighting opportunities for faculty were offered by 70% of divisions, with a median pay of $250 per hour.The median annual academic fund for a full-time neuroradiology faculty member was $6,000, typically excluding license fees but including ACR and ABR membership, leaving $4,000 for professional expenses.This survey calls for further dialogue on adapting and innovating academic institutions to meet evolving needs in neuroradiology.

Temporal Characteristics of CSF-Venous Fistulas on Dynamic Decubitus CT Myelography: A Retrospective Multi-Institution Cohort Study.

BACKGROUND AND PURPOSE: CSF-venous fistula can be diagnosed with dynamic decubitus CT myelography. This study aimed to analyze the temporal characteristics of CSF-venous fistula visualization on multiphase decubitus CT myelography. MATERIALS AND METHODS: A retrospective, multisite study was conducted on patients diagnosed with CSF-venous fistula at 2 institutions between June 2017 and February 2023. Both institutions perform decubitus CT myelography with imaging immediately following injection and usually with at least 1 delayed scan. The conspicuity of CSF-venous fistula was assessed on each phase of imaging. RESULTS: Forty-eight patients with CSF-venous fistula were analyzed. CSF-venous fistulas were better visualized on the early pass in 25/48 cases (52.1%), the delayed pass in 6/48 cases (12.5%) and were seen equally on both passes in 15/48 cases (31.3%). Of 25 cases in which the CSF-venous fistula was better visualized on the early pass, 21/25 (84%) fistulas were still at least partially visible on a delayed pass. Of 6 cases in which the CSF-venous fistula was better visualized on a delayed pass, 4/6 (67%) were partially visible on the earlier pass. Six of 48 (12.5%) CSF-venous fistulas were visible only on a single pass. Of these, 4/6 (66.7%) were seen only on the first pass, and 2/6 (33.3%) were seen only on a delayed pass. One fistula was found with one pass only, and one fistula was discovered upon contralateral decubitus imaging without a dedicated second injection. CONCLUSIONS: A dynamic decubitus CT myelography imaging protocol that includes an early and delayed phase, likely increases the sensitivity for CSF-venous fistula detection. Further studies are needed to ascertain the optimal timing and technique for CSF-venous fistula visualization on dynamic decubitus CT myelography and its impact on patient outcomes.

Duration of neurological deficit and outcomes in the surgical treatment of spinal coccidioidomycosis.

OBJECTIVE: Vertebral osteomyelitis is a rare complication of coccidioidomycosis infection. Surgical intervention is indicated when there is failure of medical management or presence of neurological deficit, epidural abscess, or spinal instability. The relationship between timing of surgical intervention and recovery of neurological function has not been previously described. The purpose of this study was to investigate if the duration of neurological deficits at presentation affects neurological recovery after surgical intervention. METHODS: This was a retrospective study of all patients diagnosed with coccidioidomycosis involving the spine at a single tertiary care center between 2012 and 2021. Data collected included patient demographics, clinical presentation, radiographic information, and surgical intervention. The primary outcome was change in neurological examination after surgical intervention, quantified according to the American Spinal Injury Association Impairment Scale. The secondary outcome was the complication rate. Logistic regression was used to test if the duration of neurological deficits was associated with improvement in the neurological examination after surgery. RESULTS: Twenty-seven patients presented with spinal coccidioidomycosis between 2012 and 2021; 20 of these patients had vertebral involvement on spinal imaging with a median follow-up of 8.7 months (IQR 1.7-71.2 months). Of the 20 patients with vertebral involvement, 12 (60.0%) presented with a neurological deficit with a median duration of 20 days (range 1-61 days). Most patients presenting with neurological deficit (11/12, 91.7%) underwent surgical intervention. Nine (81.2%) of these 11 patients had an improved neurological examination after surgery and the other 2 had stable deficits. Seven patients had improved recovery sufficient to improve by 1 grade according to the AIS. The duration of neurological deficits on presentation was not significantly associated with neurological improvement after surgery (p = 0.49, Fisher's exact test). CONCLUSIONS: The duration of neurological deficits on presentation should not deter surgeons from operative intervention in cases of spinal coccidioidomycosis.

MRI and MR angiography evaluation of pulsatile tinnitus: A focused, physiology-based protocol.

BACKGROUND AND PURPOSE: Pulsatile tinnitus (PT) is the subjective sensation of a pulse-synchronous sound, most often due to a cerebrovascular etiology. PT can severely impact quality of life and may indicate a life-threatening process, yet a timely and accurate diagnosis can often lead to effective treatment. Clinical assessment with a history and physical examination can often suggest a diagnosis for PT, but is rarely definitive. Therefore, PT should be evaluated with a comprehensive and targeted radiographic imaging protocol. MR imaging provides a safe and effective means to evaluate PT. Specific MR sequences may be used to highlight different elements of cerebrovascular anatomy and physiology. However, routine MR evaluation of PT must comply with economic and practical constraints, while effectively capturing both common and rarer, life-threatening etiologies of PT. METHODS: In this state-of-the-art review, we describe our institutional MR protocol for evaluating PT. RESULTS: This protocol includes the following dedicated sequences: time-of-flight magnetic resonance angiography; arterial spin labeling; spoiled gradient recalled acquisition in the steady state; time-resolved imaging of contrast kinetics; diffusion weighted imaging, and 3-dimensional fluid-attenuated inversion recovery. CONCLUSIONS: We describe the physiologic and clinical rationale for including each MR sequence in a comprehensive PT imaging protocol, and detail the role of MR within the broader evaluation of PT, from clinical presentation to treatment.

Diagnostic Approach to Pulsatile Tinnitus: A Narrative Review.

Importance: Pulsatile tinnitus is a debilitating symptom affecting millions of Americans and can be a harbinger of hemorrhagic or ischemic stroke. Careful diagnostic evaluation of pulsatile tinnitus is critical in providing optimal care and guiding the appropriate treatment strategy. Observations: An underlying cause of pulsatile tinnitus can be identified in more than 70% of patients with a thorough evaluation. We advocate categorizing the myriad causes of pulsatile tinnitus into structural, metabolic, and vascular groups. Structural causes of pulsatile tinnitus include neoplasms and temporal bone pathologic abnormalities. Metabolic causes of pulsatile tinnitus include ototoxic medications and systemic causes of high cardiac output. Vascular causes of pulsatile tinnitus include idiopathic intracranial hypertension and dural arteriovenous fistulas. This categorization facilitates a practical evaluation, referral, and treatment pattern. Conclusions and Relevance: Categorizing the underlying cause of pulsatile tinnitus ensures that dangerous causes of pulsatile tinnitus are not missed, and that patients receive the appropriate care from the proper specialist when needed.

Cerebrospinal Fluid-Venous Fistulas: A Systematic Review and Examination of Individual Patient Data.

BACKGROUND: Spontaneous intracranial hypotension (SIH) is usually caused by a spinal cerebrospinal fluid (CSF) leak. CSF-venous fistula is an underdiagnosed cause of spinal CSF leak, as it is challenging to identify on myelography. OBJECTIVE: To review existing literature to summarize common presentations, diagnostic imaging modalities, and current treatment strategies for CSF-venous fistulas. METHODS: We conducted a systematic review using PubMed, Embase, Scopus, and Web of Science databases to identify studies discussing CSF-venous fistulas. Titles and abstracts were screened. Studies meeting prespecified inclusion criteria were reviewed in full. RESULTS: Of 180 articles identified, 16 articles met inclusion criteria. Individual patient data was acquired from 7 studies reporting on 18 patients. CSF-venous fistula most frequently presented as positional headache. Digital subtraction myelography provided greatest detection of CSF-venous fistula in the lateral decubitus position and detected CSF-venous fistula in all individual patient cases. Dynamic computed tomography (CT) myelogram enabled detection and differentiation of CSF-venous fistulas from low-flow epidural leaks. The majority of fistulas were in the thoracic spine and slightly more common on the right. Epidural blood patch (EBP) provided temporary or no relief in all individual patients. Resolution or improvement of clinical symptoms and radiologic normalization were observed in all surgically treated patients. CONCLUSION: Although rare, CSF-venous fistula is an important cause of spinal CSF leak contributing to SIH. Dynamic CT myelogram and digital subtraction myelography, particularly in the lateral decubitus position, are the most accurate and effective diagnostic imaging modalities. EBPs often provide only transient relief, while surgical management is preferred.

Vertebral augmentation.

Vertebral augmentation, including vertebroplasty and kyphoplasty, is a minimally invasive, image-guided procedure in which cement (typically polymethylmethacrylate (PMMA)) is injected into a vertebral body to treat painful fractures. The majority of vertebroplasty and kyphoplasty procedures are performed to treat symptomatic osteoporotic compression fractures refractory to conservative medical therapy; however, there is also evidence to suggest the benefits of augmentation in patients with refractory pain in the acute compression setting. The primary goal of augmentation is decreasing pain and improving a patient's functional status. The secondary goal of augmentation is vertebral body stabilization. This chapter outlines the indications, contraindications, techniques, and literature behind vertebral augmentation.