Human pegivirus identified in severe myelitis and optic neuritis in immunocompromised patients: A pathogenic role for a forgotten virus?

The role of Human pegivirus (HPgV) in patients with encephalitis has been recently questioned. We present cases of 4 patients with similar clinical, biological, and radiological characteristics, including a past history of transplantation with long-term immunosuppression and a progressive course of severe and predominantly myelitis, associated in 3 cases with optic neuropathy causing blindness. Extensive workup was negative but analysis of the CSF by use of pan-microorganism DNA- and RNA-based shotgun metagenomics was positive for HPgV. This case series further supports the hypothesis of HPgV CNS infection and highlights the utility of metagenomic next-generation sequencing of CSF in immunocompromised patients.

MRI characteristics of MOG-Ab associated disease in adults: An update.

Our knowledge of the radiological spectrum of myelin oligodendrocyte glycoprotein antibody associated disease (MOGAD) is growing rapidly. An update on the radiological features of the disease, and its evolution is thus necessary. Magnetic resonance imaging (MRI) has an increasingly important role in the differential diagnosis of MOGAD particularly from aquaporin-4 antibody-positive neuromyelitis optica spectrum disorder (AQP4-NMOSD), and multiple sclerosis (MS). Differentiating these conditions is of prime importance because the management is different between the three inflammatory diseases, and thus could prevent further attack-related disability. Therefore, identifying the MRI features suggestive of MOGAD has diagnostic and prognostic implications. We herein review optic nerve, spinal cord and the brain MRI findings from MOGAD adult patients, and compare them to AQP4-NMOSD and MS.

Advanced multiparametric magnetic resonance imaging of multinodular and vacuolating neuronal tumor.

BACKGROUND AND PURPOSE: Multinodular and vacuolating neuronal tumor (MVNT) of the cerebrum is a rare brain lesion with suggestive imaging features. The aim of our study was to report the largest series of MVNTs so far and to evaluate the utility of advanced multiparametric magnetic resonance (MR) techniques. METHODS: This multicenter retrospective study was approved by our institutional research ethics board. From July 2014 to May 2019, two radiologists read in consensus the MR examinations of patients presenting with a lesion suggestive of an MVNT. They analyzed the lesions' MR characteristics on structural images and advanced multiparametric MR imaging. RESULTS: A total of 64 patients (29 women and 35 men, mean age 44.2 ± 15.1 years) from 25 centers were included. Lesions were all hyperintense on fluid-attenuated inversion recovery and T2-weighted imaging without post-contrast enhancement. The median relative apparent diffusion coefficient on diffusion-weighted imaging was 1.13 [interquartile range (IQR), 0.2]. Perfusion-weighted imaging showed no increase in perfusion, with a relative cerebral blood volume of 1.02 (IQR, 0.05) and a relative cerebral blood flow of 1.01 (IQR, 0.08). MR spectroscopy showed no abnormal peaks. Median follow-up was 2 (IQR, 1.2) years, without any changes in size. CONCLUSIONS: A comprehensive characterization protocol including advanced multiparametric magnetic resonance imaging sequences showed no imaging patterns suggestive of malignancy in MVNTs. It might be useful to better characterize MVNTs.

Clinical, imaging and follow-up study of optic neuritis associated with myelin oligodendrocyte glycoprotein antibody: a multicentre study of 62 adult patients.

BACKGROUND AND PURPOSE: There are few clinico-radiological data on optic neuritis (ON) with myelin oligodendrocyte glycoprotein antibody (MOG-IgG). The objective was to characterize the clinico-radiological phenotype and outcome of patients with MOG-IgG-related ON. METHODS: The records of all adult patients admitted in three medical centres with MOG-IgG-associated ON who underwent orbital and brain magnetic resonance imaging (MRI) at the acute phase were reviewed. Spinal cord MRI within 1 month from the ON and all of the follow-up MRI were reviewed. RESULTS: Of 62 patients, 41.9% had bilateral ON and 66.2% optic disc swelling. On initial MRI, lesions were anterior (92%), extensive (63%) and associated with optic perineuritis (46.6%). Silent brain lesions were found in 51.8% of patients but were mainly non-specific (81%). Of 39 individuals with spinal MRI at onset, nine had abnormal findings (four were asymptomatic). Two symptomatic patients had longitudinally extensive myelitis with concurrent H-sign. At last follow-up, 5% of patients had visual acuity ≤0.1. Brain MRI remained unchanged in 41 patients (87%). CONCLUSIONS: Our study supports a mostly benign ophthalmological course of MOG-IgG-associated ON, despite initially longitudinally extensive lesions and development of optic nerve atrophy on orbital MRI. Spinal MRI could be of interest in detecting silent suggestive lesions.

3D PSIR MRI at 3 Tesla improves detection of spinal cord lesions in multiple sclerosis.

BACKGROUND: Spinal imaging in multiple sclerosis remains challenging because of its small size and numerous artifacts. OBJECTIVE: To compare 3D Phase-Sensitive Inversion Recovery (PSIR) to a conventional dataset of 3D Short Tau Inversion Recovery (STIR) and T2-weighted imaging at 3 Tesla to detect multiple sclerosis spinal cord lesions. METHODS: This prospective single-center study was approved by a national research ethics board and included 54 patients (median age 44) enrolled from December 2016 to August 2018. Two neuroradiologists individually analyzed the two datasets separately and in random order. Discrepancies were resolved by consensus with a third neuroradiologist. The primary judgment criterion was the number of spinal cord lesions. Secondary judgment criteria included location of the lesions, reader-reported confidence and conspicuity assessed with the lesion-to-cord contrast ratio (LCCR). RESULTS: 3D PSIR detected significantly more lesions than the conventional dataset (371 versus 173, respectively, p < 0.05). Seven patients had no detected lesion with the conventional dataset, whereas 3D PSIR detected at least one lesion. LCCR mean reader-reported confidence (p < 0.001) and inter-observer agreement were higher using 3D PSIR. CONCLUSIONS: 3D PSIR significantly improved overall spinal cord lesion detection in MS patients, with higher reader-reported confidence, higher lesion contrast, and higher inter-reader agreement.

[Optic neuropathy in positive anti-MOG antibody syndrome]. / Neuropathie optique dans le syndrome des anticorps anti MOG positif.

INTRODUCTION: The diagnosis of optic neuritis (ON), or inflammation of the optic nerve, is based on clinical findings: first marked by rapidly progressive visual decline associated with eye pain accentuated by eye movements; abnormalities of color perception and/or contrast sensitivity may also be reported. In this case, inflammatory neuropathies are associated with anti-MOG antibodies. MOGs, oligodendrocytic glycoproteins involved in the production of myelin, were identified nearly three decades ago in association with demyelinating ON. The first series were reported in children following demyelinating neurological manifestations, particularly in ADEM (acute demyelinating encephalomyelitis) or multiple sclerosis (MS) [1]. Anti-MOGs are associated with neuropathies in the phenotypic setting of the neuromyelitis optica (NO) spectrum, and anti-Aquaporin 4 antibodies (AQP4) are negative by definition. Thus, anti-MOG could explain up to 30 % of cases of seronegative optic neuritis; their presence thus represents a significant diagnostic aid for the clinician, especially during a first neurological episode [1]. The first short published series in AQP4-/MOG+populations revealed primarily ophthalmological involvement with a good prognosis for recovery [1]. Knowledge of these antigens is important; it may permit not only an understanding of the physiopathology but also the stratification of patients in terms of prognosis and response to treatment [2]. Thus, the early diagnosis of anti-MOG positive ON must prompt aggressive initial treatment and a more or less maintenance therapy to prevent recurrence. The role of the ophthalmologist remains paramount, since most cases present with purely ocular involvement. MATERIALS AND METHODS: We report herein the clinical, ophthalmological, laboratory and radiological data for 25 patients (45 eyes) managed between February 2011 and January 2017. All of our patients had optic neuritis associated with anti-MOG antibodies. All patients underwent the following testing: - Visual acuity; - Humphrey and/or Goldmann visual field; - Non-mydriatic fundus photography; - Optic disc OCT; - 3 Tesla orbital-cerebral MRI with and without contrast; - Standard and immunological laboratory testing for anti-MOG and anti AQP4 antibodies by Western Blot and ELISA. RESULTS: The male: female ratio of the population was 0.92 (13 women and 12 men). The average age at onset was 35.68 years (15 to 60 years); 40 % of the subjects were between 31 and 40 years old. The initial symptoms leading to consultation were mostly visual acuity (80 %) and pain (88 %). Involvement was bilateral in 80 % of cases (5 unilateral). Initial visual acuity was poor; 52 % of eyes were less than or equal to count fingers. The course was favorable however, with visual acuity returning to 10-12/10 after 6 months of follow-up (84 % of eyes). Orbital/cerebral MRI with attention to the visual pathways revealed involvement of the anterior visual pathways with gadolinium uptake in 92 % of cases. Of the 35 eyes initially considered affected, the main initial diagnoses were: - 36 % retro-bulbar optic neuritis (RBON); - 40 % anterior optic neuritis (AON); - 24 % other; of which 16 % were initially diagnosed as acute anterior ischemic optic neuropathy (AAION). 96 % of patients received corticosteroid treatment in the acute phase. 16 % required plasma exchange sessions. Maintenance therapy was proposed for only 36 % of the population. CONCLUSION: Optic neuritis is a pathology frequently encountered in ophthalmology; a good knowledge of symptoms and clinical signs is essential for early diagnosis and optimal management. The identification of autoantibodies, including anti-MOG antibodies, is important for patient management and is part of the required testing for all cases of optic neuritis, in order to adapt the treatment of the acute episode and to provide maintenance therapy to avoid recurrence.

Multinodular and Vacuolating Posterior Fossa Lesions of Unknown Significance.

Multinodular and vacuolating neuronal tumor of the cerebrum is a rare supratentorial brain tumor described for the first time in 2013. Here, we report 11 cases of infratentorial lesions showing similar striking imaging features consisting of a cluster of low T1-weighted imaging and high T2-FLAIR signal intensity nodules, which we referred to as multinodular and vacuolating posterior fossa lesions of unknown significance. No relationship was found between the location of the lesion and clinical symptoms. A T2-FLAIR hypointense central dot sign was present in images of 9/11 (82%) patients. Cortical involvement was present in 2/11 (18%) of patients. Only 1 nodule of 1 multinodular and vacuolating posterior fossa lesion of unknown significance showed enhancement on postcontrast T1WI. DWI, SWI, MRS, and PWI showed no malignant pattern. Lesions did not change in size or signal during a median follow-up of 3 years, suggesting that multinodular and vacuolating posterior fossa lesions of unknown significance are benign malformative lesions that do not require surgical intervention or removal.

Optimizing 3D FLAIR to detect MS lesions: pushing past factory settings for precise results.

BACKGROUND: To assess the diagnostic value of three 3D FLAIR sequences with differing repetition-times (TR) at 3-Tesla when detecting multiple sclerosis (MS) lesions. METHODS: In this prospective study, approved by the institutional review board, 27 patients with confirmed MS were prospectively included. One radiologist performed manual segmentations of all high-signal intensity lesions using three 3D FLAIR data sets with different TR of 4800 ms ("FLAIR4800"), 8000 ms ("FLAIR8000") and 10,000 ms ("FLAIR10,000") and two radiologists double-checked it. The main judgment criterion was the overall number of lesions; secondary objectives were the assessment of lesion location, as well as measuring contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR). A non-parametric Wilcoxon's test was used to compare the differing FLAIR. RESULTS: The FLAIR8000 and FLAIR10,000 detected significantly more overall lesions per patient as compared with the FLAIR4800 [116.1 (± 61.7) (p = 0.02) and 115.8 (± 56.3) (p = 0.03) versus 99.2 (± 66.9), respectively]. The FLAIR8000 and FLAIR10,000 detected four and eight times more cortical or juxta-cortical lesions per patient as compared with FLAIR4800 [1.6 (± 2.2) (p = 0.001) and 4.1 (± 5.9) (p = 6 × 10-5) versus 0.4 (± 1.1), respectively]. CNR was significantly correlated to the TR value. It was significantly higher with FLAIR10,000 than it was with FLAIR8000 and FLAIR4800 [16.3 (± 3.5) versus 15 (± 2.4) (p = 0.01) and 12 (± 2.2) (p = 2 × 10-6), respectively] CONCLUSION: An optimized 3D FLAIR with a long TR significantly improved both overall lesion detection and CNR in MS patients as compared to a 3D FLAIR with factory settings.

Diagnosis and Prediction of Relapses in Susac Syndrome: A New Use for MR Postcontrast FLAIR Leptomeningeal Enhancement.

BACKGROUND AND PURPOSE: Leptomeningeal enhancement can be found in a variety of neurologic diseases such as Susac Syndrome. Our aim was to assess its prevalence and significance of leptomeningeal enhancement in Susac syndrome using 3T postcontrast fluid-attenuated inversion recovery MR imaging. MATERIALS AND METHODS: From January 2011 to December 2017, nine consecutive patients with Susac syndrome and a control group of 73 patients with multiple sclerosis or clinically isolated syndrome were included. Two neuroradiologists blinded to the clinical and ophthalmologic data independently reviewed MRIs and assessed leptomeningeal enhancement and parenchymal abnormalities. Follow-up MRIs (5.9 MRIs is the mean number per patient over a median period of 46 months) of patients with Susac syndrome were reviewed and compared with clinical and retinal fluorescein angiographic data evaluated by an independent ophthalmologist. Fisher tests were used to compare the 2 groups, and mixed-effects logistic models were used for analysis of clinical and imaging follow-up of patients with Susac syndrome. RESULTS: Patients with Susac syndrome were significantly more likely to present with leptomeningeal enhancement: 5/9 (56%) versus 6/73 (8%) in the control group (P = .002). They had a significantly higher leptomeningeal enhancement burden with ≥3 lesions in 5/9 patients versus 0/73 (P < .001). Regions of leptomeningeal enhancement were significantly more likely to be located in the posterior fossa: 5/9 versus 0/73 (P < .001). Interobserver agreement for leptomeningeal enhancement was good (κ = 0.79). There was a significant association between clinical relapses and increase of both leptomeningeal enhancement and parenchymal lesion load: OR = 6.15 (P = .01) and OR = 5 (P = .02), respectively. CONCLUSIONS: Leptomeningeal enhancement occurs frequently in Susac syndrome and could be helpful for diagnosis and in predicting clinical relapse.

A 3T Phase-Sensitive Inversion Recovery MRI Sequence Improves Detection of Cervical Spinal Cord Lesions and Shows Active Lesions in Patients with Multiple Sclerosis.

BACKGROUND AND PURPOSE: Magnetic Resonance Imaging is the modality of choice to detect spinal cord lesions in patients with Multiple Sclerosis (MS). However, this imaging is challenging. New sequences such as phase-sensitive inversion recovery have been developed to improve detection. Our aim was to compare a 3D phase-sensitive inversion recovery and a conventional imaging dataset including postcontrast T2WI and T1WI to detect MS spinal cord lesions. MATERIALS AND METHODS: This retrospective single-center study included 100 consecutive patients with MS (mean age, 41 years) from January 2015 to June 2016. One senior neuroradiologist and 1 junior radiologist blinded to clinical data checked for new spinal cord lesions, individually analyzing conventional and 3D phase-sensitive inversion recovery datasets separately, placing a 3-week delay between the 2 readings. A consensus reading was done with a third senior neuroradiologist. A Wilcoxon test was used to compare the 2 imaging datasets. Intra- and interobserver agreement was assessed by the κ coefficient. RESULTS: 3D phase-sensitive inversion recovery detected significantly more lesions than conventional imaging (480 versus 168, P < .001). Eleven patients had no detected lesions on T2WI, whereas 3D phase-sensitive inversion recovery detected at least 1 lesion. All postcontrast T1WI enhancing lesions were also visible on 3D phase-sensitive inversion recovery. The signal-to-noise ratio was significantly higher using 3D phase-sensitive inversion recovery (0.63 versus 0.46, P = .03). Mean reading confidence was significantly higher using 3D phase-sensitive inversion recovery. Inter- and intraobserver agreement was good for both datasets. CONCLUSIONS: Our study showed that 3D phase-sensitive inversion recovery significantly improved detection of cervical spinal cord lesions, including both enhancing and nonenhancing lesions in patients with MS.

Acute idiopathic optic neuritis: not always benign.

BACKGROUND AND PURPOSE: Few recent data are available concerning idiopathic optic neuritis (ON). We aimed to describe a large cohort of patients with idiopathic ON. We compared this cohort with patients with ON related to myelin oligodendrocyte glycoprotein (MOG) or ON related to aquaporin-4 (AQP4) antibodies. METHODS: This was a monocentric retrospective observational study. Inclusion criteria for idiopathic ON were as follows: age ≥ 16 years, follow-up of at least 2 years, negative for antibodies against MOG and AQP4 immunoglobulin G, and no magnetic resonance imaging (MRI) lesions suggestive of demyelination (two brain MRI scans, one at baseline and one during follow-up, and one spinal cord MRI scan). RESULTS: Among 23 patients with idiopathic ON (female, 82.6%; median age, 36 years; median follow-up time, 41.4 months), 56.5% had recurrent ON (median time to a second ON episode, 6 months). The final visual acuity in this group (median, 0; mean, 0.43; range, 0-3) was similar to that in the AQP4 group (n = 18; P-value after Bonferroni correction = 0.936) but worse than that in the MOG group (n = 25; P-value after Bonferroni correction = 0.019). At the last evaluation, visual acuity levels were ≤0.5 and <0.2, respectively, in 36.8% and 21% of the idiopathic ON group, 58.3% and 26.7% of the AQP4 group, and 0% and 0% of the MOG group. CONCLUSION: The recovery of visual acuity among patients with idiopathic ON was poor, similar to that observed in the AQP4 group.

Inaugural tumor-like multiple sclerosis: clinical presentation and medium-term outcome in 87 patients.

BACKGROUND: Tumefactive demyelinating lesions of the central nervous system can be the initial presentation in various pathological entities [multiple sclerosis (the most common), Balo's concentric sclerosis, Schilder's disease and acute disseminated encephalomyelitis] with overlapping clinical presentation. The aim of our study was to better characterize these patients. METHODS: Eighty-seven patients (62 women and 25 men) from different MS centers in France were studied retrospectively. Inclusion criteria were (1) a first clinical event (2) MRI showing one or more large demyelinating lesions (20 mm or more in diameter) with mass-like features. Patients with a previous demyelinating event (i.e. confirmed multiple sclerosis) were excluded. RESULTS: Mean age at onset was 26 years. The most common initial symptoms (67% of the patients) were hemiparesis or hemiplegia. Aphasia, headache and cognitive disturbances (i.e. atypical symptoms for demyelinating diseases) were observed in 15, 18 and 15% of patients, respectively. The mean largest diameter of the tumefactive lesions was 26.9 mm, with gadolinium enhancement in 66 patients (81%). Twenty-one patients (24%) had a single tumefactive lesion. During follow-up (median time 5.7 years) 4 patients died, 70 patients improved or remained stable and 12 worsened. 86% of patients received initial corticosteroid treatment, and 73% received disease-modifying therapy subsequently. EDSS at the end of the follow-up was 2.4 ± 2.6 (mean ± SD). CONCLUSION: This study provides further evidence that the clinical course of MS presenting with large focal tumor-like lesions does not differ from that of classical relapsing-remitting MS, once the noisy first relapsing occurred.

Improved Detection of New MS Lesions during Follow-Up Using an Automated MR Coregistration-Fusion Method.

BACKGROUND AND PURPOSE: MR imaging is the key examination in the follow-up of patients with MS, by identification of new high-signal T2 brain lesions. However, identifying new lesions when scrolling through 2 follow-up MR images can be difficult and time-consuming. Our aim was to compare an automated coregistration-fusion reading approach with the standard approach by identifying new high-signal T2 brain lesions in patients with multiple sclerosis during follow-up MR imaging. MATERIALS AND METHODS: This prospective monocenter study included 94 patients (mean age, 38.9 years) treated for MS with dimethyl fumarate from January 2014 to August 2016. One senior neuroradiologist and 1 junior radiologist checked for new high-signal T2 brain lesions, independently analyzing blinded image datasets with automated coregistration-fusion or the standard scroll-through approach with a 3-week delay between the 2 readings. A consensus reading with a second senior neuroradiologist served as a criterion standard for analyses. A Poisson regression and logistic and γ regressions were used to compare the 2 methods. Intra- and interobserver agreement was assessed by the κ coefficient. RESULTS: There were significantly more new high-signal T2 lesions per patient detected with the coregistration-fusion method (7 versus 4, P < .001). The coregistration-fusion method detected significantly more patients with at least 1 new high-signal T2 lesion (59% versus 46%, P = .02) and was associated with significantly faster overall reading time (86 seconds faster, P < .001) and higher reader confidence (91% versus 40%, P < 1 × 10-4). Inter- and intraobserver agreement was excellent for counting new high-signal T2 lesions. CONCLUSIONS: Our study showed that an automated coregistration-fusion method was more sensitive for detecting new high-signal T2 lesions in patients with MS and reducing reading time. This method could help to improve follow-up care.

Etiologies of acute demyelinating optic neuritis: an observational study of 110 patients.

BACKGROUND AND PURPOSE: New criteria for the diagnosis of multiple sclerosis (MS) and discovery of myelin oligodendrocyte glycoprotein (MOG) or aquaporin-4 (AQP4) antibodies (Abs) have changed the management of optic neuritis (ON). Our aim was to specify, in view of these recent advances, the etiologies of acute demyelinating ON for consecutive patients. METHODS: Retrospective database analysis was undertaken of consecutive adult patients with acute ON admitted from 1 December 2014 to 31 January 2016. Diagnosis of MS was made according to the 2010 McDonald criteria. Patients with Abs to AQP4 or MOG were classified as ON-AQP4 and ON-MOG, respectively. Patients who did not fulfill the diagnostic criteria and were negative for AQP4 and MOG Ab tests were classified as having idiopathic ON. RESULTS: Of 110 patients assessed, 78 had ON related to MS (70.9%). All patients without MS were tested for AQP4 and MOG Abs: 11 had MOG Ab (10%), 5 had AQP4 Ab (4.5%) and 16 were considered as having idiopathic ON (14.5%). Presence of intrathecal IgG oligoclonal bands was strongly associated with MS (mean, 88.4% vs. 34.4% in patients without MS; after Bonferroni correction, P < 0.0001). CONCLUSIONS: Optic neuritis related to MOG Ab was the second cause identified of demyelinating ON in our center. Idiopathic ON was as frequent as both ON-AQP4 and ON-MOG combined.

Combined brain and anterior visual pathways' MRIs assist in early identification of neuromyelitis optica spectrum disorder at onset of optic neuritis.

Acute optic neuritis (ON) is the initial presentation in half of neuromyelitis optica spectrum disorder (NMO-SD) cases. Our objective was to evaluate accuracy of combined MRIs of the anterior visual pathways and of the brain to correctly identify NMO-SD among patients with acute ON. We performed a retrospective study on patients with acute ON in NMO-SD (16 episodes) and first-event non-NMO-SD (32 episodes). All MRIs included exams of the brain and anterior visual pathways using T2-weighted and post-gadolinium T1-weighted coronal thin slices. Images were reviewed by a neuroradiologist who was blinded to the final diagnosis. There were no multiple sclerosis (MS)-like lesions with dissemination in space (DIS) with NMO-SD (0 vs. 53%, p < 0.01). Non-NMO-SD ON usually spared the chiasma (3 vs. 44%, p < 0.01) and the optic tracts (0 vs. 19%, p < 0.01). Optic nerve lesions were longer [median (range) 26 mm (14-64) vs. 13 mm [8-36], p < 0.01] and the number of segments involved higher (3 [1-8] vs. 1 [1-4], p < 0.01) in NMO-SD. Bilateral optic nerve involvement, or involvement of ≥3 segments, or involvement of the chiasma, or optic tracts in the absence of MS-like lesions with DIS were suggestive of NMO-SD with a sensitivity of 69% (CI 95% 41-89) and a specificity of 97% (CI 95% 84-99) (p < 0.01). Combining brain and anterior visual pathways' MRIs seems efficient for detecting acute ON patients who are at high risk for NMO-SD.

Infraorbital nerve involvement on magnetic resonance imaging in European patients with IgG4-related ophthalmic disease: a specific sign.

OBJECTIVES: To measure the frequency of infraorbital nerve enlargement (IONE) on magnetic resonance imaging (MRI) in European patients suffering from an IgG4-related ophthalmic disease (IgG4-ROD) as compared to patients suffering from non-IgG4-related ophthalmic disease (non-IgG4-ROD). METHODS: From January 2006 through April 2015, 132 patients were admitted for non-lymphoma, non-thyroid-related orbital inflammation. Thirty-eight had both pre-therapeutic orbital MRI and histopathological IgG4 immunostaining. Fifteen patients were classified as cases of IgG4-ROD and 23 patients as cases of non-IgG4-ROD. Two readers performed blinded analyses of MRI images. The main criterion was the presence of an IONE, defined as the infraorbital nerve diameter being greater than the optic nerve diameter in the coronal section. RESULTS: IONE was present in 53% (8/15) of IgG4-ROD cases whereas it was never present (0/23) in cases of non-IgG4-ROD (P < 0.0001). IONE was only present in cases where, on MRI, the inflammation of the inferior quadrant was present and in direct contact with the ION canal. CONCLUSIONS: In European patients suffering from orbital inflammation, the presence of IONE on an MRI is a specific sign of IgG4-ROD. Recognition of this pattern may facilitate the accurate diagnosis for clinicians and allow for the adequate management and appropriate care of their patients. KEY POINTS: • IONE on an MRI is a specific sign of IgG4-ROD. • IONE recognition allows for a quicker diagnosis and appropriate management. • IONE appears when inflammation is in direct contact with the ION canal.