Contrast-enhanced MRI findings of the knee in healthy children; establishing normal values

Best practice in rheumatology new developments in ultrasound and MRI imaging of pediatric rheumatic diseases

The evidence base for ultrasound and MRI imaging in pediatric rheumatic diseases continues to grow, enabling the routine clinical use of the two techniques that complement each other. Ultrasound imaging has a superior spatial resolution, the ability to assess several joints at the same time without sedation and provides very detailed assessments of important structures like the entheses. MRI has advantages in the assessment of osteochondral damage and certain anatomic regions like the temporomandibular joint (TMJ) and the axial skeleton. Significant progress in the standardization of image acquisition and quantification of findings allows the utilisation of both techniques as an outcome measure. This will improve the standard of care in pediatric rheumatic diseases where objective measurements of disease activity are urgently needed. Finally, the integration of artificial intelligence (AI) represents a groundbreaking development in the field and potential applications will be discussed.

Knee-ultrasound: reference values for the amount of joint fluid and synovial appearances in healthy children and adolescents

BACKGROUND

With increasing ultrasound use, data for the normal amount of joint fluid and synovial appearances are needed.

OBJECTIVE

To establish reference values for knee-ultrasound in healthy volunteers by age. To examine the association of joint fluid and synovial appearances with age, sex, and time spent in sports activities.

MATERIALS AND METHODS

Prospective, cross-sectional, including 3-17-year-old volunteers. Examinations were performed by one of two experienced radiologists after meticulous standardisation of the technique. Knees were examined in 30° flexion, in extension and during provocation.

RESULTS

One hundred twenty-seven volunteers (67 females), median age 10.9 years (percentile 2.5th-97.5th: 3.4-17.2), were included. With 30° knee flexion, the median amount of suprapatellar recess joint fluid (sagittal view) was 0.5 mm for females and 0.9 mm for males (P = 0.014), increasing to 1.9 mm and 2.4 mm (P = 0.031), respectively, during provocation. The amount of fluid during provocation increased with age for both sexes (P = 0.007 females; P = 0.012 males) and by time spent in sport-activities (P = 0.003). Further, there was a positive association between the presence of joint fluid speckles and sport-activities (P = 0.039). Median double-layered synovium was 1.5 mm in 3-6-year-olds, increasing to 2.1 mm in 7-9-year-olds and 2.0 mm in 10-17-year-olds (P = 0.024). No synovial Doppler signal was seen. Observers' agreement was excellent, with ICC values ≥ 0.9.

CONCLUSION

The majority of healthy children have measurable knee joint fluid, more so when examined with a flexed knee and under provocation. Speckles within the joint fluid are seen in one-fourth, especially in males, and the presence of speckles and joint fluid amount are associated with sports-activity.

MRI features distinguishing pediatric Lyme arthritis from septic arthritis

OBJECTIVE

This study aims to identify distinguishing MRI features of Lyme arthritis (LA), an increasingly prevalent cause of pediatric infectious arthritis in the USA, to enable rapid discrimination from septic arthritis (SA) and facilitate appropriate management.

MATERIALS AND METHODS

A single-center, retrospective analysis was conducted on a convenience sample of pediatric patients with LA in an endemic area using EPIC electronic health record data between January 2010 and December 2020. Patients with positive serologic testing and concurrent MRI were selected. MRI scans were reviewed by a subspecialty-trained pediatric radiologist. Key MRI features analyzed include joint effusion, synovitis, myositis, soft tissue edema, and osseous edema and erosions. MRI features, demographics, and clinical data were compared using univariable and multivariable analyses.

RESULTS

Fifty cases of knee LA and 13 cases of knee SA were included. Larger joint effusion (p = 0.0055, z =  - 2.779) and abnormally thickened synovium (p = 0.0011, χ2 = 10.622) were more associated with LA. In contrast, increased myositis, subcutaneous edema, and osseous changes were more prevalent in SA. Abnormal bone marrow signal (p < 0.0001, χ2 = 36.893) and bone erosion (p < 0.0001, χ2 = 25.506) were observed in 84.6% (11/13) and 46.2% (6/13) of SA cases, respectively, while no bone erosion was found in LA.

CONCLUSION

MRI can be a valuable tool in differentiating LA from SA. Abnormal synovium and increasing joint effusion favor LA, while increasing soft tissue edema and osseous changes favor SA. Notably, the presence of bone erosion effectively excluded LA from consideration.

Juvenile Idiopathic Arthritis and Spondylarthritis

Juvenile idiopathic arthritis (JIA) is a heterogeneous disorder affecting children < 16 years of age. The clinical heterogeneity translates to imaging, where no specific joint is affected. This article highlights a general imaging approach to JIA, using specific examples of the knee, hand, and wrist as the typical joints affected. We then focus on unique joints that are commonly affected by JIA: the temporomandibular joint, the joints of the upper cervical spine, and the sacroiliac joint. For these latter anatomical sites, regional anatomy and development, location-specific imaging considerations, and arthritis, treatment decision making, and potential differential considerations are reviewed. We highlight, where applicable, a multimodal approach to imaging using developed or developing standardized scoring systems.

Imaging of Juvenile Idiopathic Arthritis

MRI, ultrasound, and conventional radiography each play distinct roles in the evaluation of juvenile idiopathic arthritis (JIA), with MRI being the preferred imaging modality of choice for assessing both inflammatory and destructive changes. These various imaging modalities provide valuable insights into JIA in pediatric patients. However, challenges persist in terms of achieving precision, ensuring validity, and distinguishing between pathologic findings and normal anatomic variations. Establishing normal reference values and implementing scoring systems can aid in the precise evaluation of disease activity and provide information to assist treatment decisions for children with JIA. Ongoing advancements in imaging techniques and standardization initiatives aim to bolster the accuracy of JIA diagnosis and assessment, ultimately leading to enhanced patient care and treatment outcomes.

Measuring synovial thickness on knee MRI in pediatric patients with arthritis: is contrast necessary?

BACKGROUND

The use of contrast-enhanced imaging has long been standard for magnetic resonance imaging (MRI) assessments of synovitis in juvenile idiopathic arthritis (JIA). However, advancements in MRI technology have allowed for reliable identification of synovium without contrast.

OBJECTIVE

To assess the equivalence of unenhanced MRI with contrast-enhanced MRI in evaluating synovial thickness.

MATERIALS AND METHODS

This is an institutional review board approved, retrospective study performed in a tertiary children's hospital. Pediatric JIA patients under 21 years old were included who underwent knee MRI scans (1.5 T or 3 T) without and with contrast between January 2012 and January 2022. Two radiologists independently measured synovial thickness at 6 knee sites on contrast-enhanced and unenhanced sequences. Numerical measurements and ordinal scores based on juvenile idiopathic arthritis magnetic resonance imaging scoring (JAMRIS) system were recorded, and tests of equivalence were conducted, as well as between-reader and within-reader reliability by concordance correlation coefficient (CCC). All tests were considered significant at the 5% level.

RESULTS

A total of 38 studies from 35 patients (25 females, median age 14 years; interquartile range 7 to 15.7) were included. Equivalence was demonstrated at each of the 6 sites for both continuous measurements (P-values < 0.05) and ordinal scores (P-values < 0.05) based on the average over readers. Within-reader reliability was moderate to high (CCC 0.50-0.89), except for the cruciate ligaments site. Averaged over the 6 sites, reliability between readers was low for unenhanced (CCC 0.47, with 95% CI: [0.41, 0.53]) and moderate for contrast-enhanced (CCC 0.64, with 95% CI: [0.59, 0.69]) sequences.

CONCLUSION

Unenhanced knee MRI is equivalent to contrast-enhanced MRI in assessment of synovial thickness using conventional MRI sequences. Contrast material helped improve inter-reader reliability.

Fluid-attenuated inversion-recovery sequence with fat suppression as an alternative to contrast-enhanced MRI in pediatric synovitis

BACKGROUND

Non-contrast magnetic resonance imaging (MRI) fluid-attenuated inversion-recovery sequence (FLAIR) with fat suppression (FS) has not been validated in children.

OBJECTIVE

Compare FLAIR to T1-weighted post contrast (T1CE) in the detection of knee synovitis.

METHODS AND MATERIALS

Institutional review board (IRB) waived consent. Children who underwent T1CE and FLAIR sequences of the knee on a 3-T magnet from April 2021 to December 2021 were included. Two pediatric radiologists assessed axial FLAIR and T1CE images for synovitis and synovial thickness. Reliability and agreement were assessed. Sensitivities, specificities, and accuracy were calculated for FLAIR using T1CE as reference standard.

RESULTS

In total, 42 knees (39 patients) were assessed (median age 12.9 years (2.3-17.8 years); 62% male, 38% female). Readers judged 20/42 (48%) knees to have synovitis. Sensitivity of FLAIR for reader 1 was 79% (19/24; 95% CI 0.58, 0.93) and 84% (16/19; 95% CI 0.60, 0.97) for reader 2. Specificity of FLAIR for reader 1 was 94% (17/18; 95% CI 0.73, 1) and 83% (19/23; 95% CI 0.61, 0.95) for reader 2. Accuracy for readers 1 and 2 was 86% (36/42; 95% CI 0.71, 0.95) and 83% (35/42; 95% CI 0.69, 0.93), respectively. Inter-reader reliability was good (0.75-0.90) for synovial measurements for FLAIR (ICC = 0.80; 95% CI 0.71, 0.86) and moderate for T1 CE (ICC = 0.62 (95% CI 0.48, 0.73)).

CONCLUSION

FLAIR FS depicts synovium in the pediatric knee with similar reliability to T1 CE and may be an acceptable alternative to contrast in the initial diagnosis of synovitis.

Preliminary MRI-based investigation of characteristics and prognosis of knee bone marrow edema in children with juvenile idiopathic arthritis

Introduction

Bone marrow edema (BME) is one of the main imaging characteristics of juvenile idiopathic arthritis (JIA) in children and rheumatoid arthritis (RA) in adult. Previous studies have shown that BME occurred in approximately 64% of adults with RA and was a key predictor of poor prognosis. But BME with JIA has not been of great concern. Therefore, we evaluated the prevalence, characteristics, and prognosis of knee joint BME in children with JIA.

Methods

In this retrospective study, we included children with JIA and knee joint involvement from January 2017 to December 2019. BME was evaluated according to the Juvenile Arthritis MRI Scoring system. Clinical characteristics were compared between the BME group and the non-BME group. The characteristics and prognosis of the BME were observed.

Results

A total of 128 children with 136 knee joint MRI data were identified, with 37 knee joints (27.2%) having BME. BME has positive correlation with synovial hypertrophy (Rs = 0.562, p = 0.019). There were significant differences in age (p = 0.010) and disease duration (p = 0.013) between the BME and non-BME groups. BME was found to be more common in older children and the patients with long duration of disease. Locations with BME were the lateral tibial plateau (17/37, 45.9%), the lateral weight-bearing femur (16/37, 43.2%), the medial tibial plateau and the medial femoral condyle (both with 15/37, 40.5%), and the medial weight-bearing femur (12/37, 32.4%). The lateral femoral condyle and both the lateral and medial sides of the patella were rarely involved. Of the 15 BME joints with the MRI follow-up data (interval 6.5 ± 3.0 months), the lesions disappeared or improved within 12 months after the treatments in 13 (86.7%) joints.

Conclusions

The prevalence of knee BME in JIA was 27.2%. There was positive correlation between BME and synovial hypertrophy. Older children and children with long disease duration had a higher risk for BME, which was commonly a late presentation and more likely involved the weight-bearing surfaces of the joint. The overall prognosis was satisfactory after the standard treatments.

Key Points • To the best of our knowledge, this paper is the first one to investigate the MRI manifestation in JIA focus on knee BME sign.

Development of PBPK model for intra-articular injection in human: methotrexate solution and rheumatoid arthritis case study

A physiologically based model describing the dissolution, diffusion, and transfer of drug from the intra-articular (IA) space to the plasma, was developed for GastroPlus® v9.8. The model is subdivided into compartments representing the synovial fluid, synovium, and cartilage. The synovium is broken up into two sublayers. The intimal layer acts as a diffusion barrier between the synovial fluid and the subintimal layer. The subintimal layer of the synovium has fenestrated capillaries that allow the free drug to be transported into systemic circulation. The articular cartilage is broken up into 10 diffusion sublayers as it is much thicker than the synovium. The cartilage acts as a depot tissue for the drug to diffuse into from synovial fluid. At later times, the drug will diffuse from the cartilage back into synovial fluid once a portion of the dose enters systemic circulation. In this study, a listing of all relevant details and equations for the model is presented. Methotrexate was chosen as a case study to show the application and utility of the model, based on the availability of intravenous (IV), oral (PO) and IA administration data in patients presenting rheumatoid arthritis (RA) symptoms. Systemic disposition of methotrexate in RA patients was described by compartmental pharmacokinetic (PK) model with PK parameters extracted using the PKPlus™ module in GastroPlus®. The systemic PK parameters were validated by simulating PO administration of methotrexate before being used for simulation of IA administration. For methotrexate, the concentrations of drug in the synovial fluid and plasma were well described after adjustments of physiological parameters to account for RA disease state, and with certain assumptions about binding and diffusion. The results indicate that the model can correctly describe PK profiles resulting from administration in the IA space, however, additional cases studies will be required to evaluate ability of the model to scale between species and/or doses.

Magnetic resonance imaging of the knee joint in juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is an umbrella term for a group of diseases in children younger than 16 years old lasting six weeks or longer. Synovitis may lead to destructive and irreversible joint changes with subsequent functional impairment. Prompt diagnosis is essential to prevent permanent joint damage and preserve joint functionality. In the course of JIA both the axial and peripheral skeleton may be involved in the inflammatory process, but the knee joint is most frequently affected. New drugs and treatment protocols have forced the need for diagnosis at the earliest possible stage. Magnetic resonance imaging (MRI) allows early detection of lesions and constitutes a superior diagnostic imaging method. Synovitis, tenosynovitis, enthesitis, bursitis, osteitis, cartilage loss, bone cysts, and erosions are lesions diagnosed in JIA, and they can be precisely imaged in MRI. This article aims to present MRI inflammatory features of the knee in children with JIA based on the literature.

Formulation of Topical Dosage Forms Containing Synthetic and Natural Anti-Inflammatory Agents for the Treatment of Rheumatoid Arthritis

Topical anti-inflammatory and analgesic effect for the treatment of rheumatoid arthritis is of major interest because of their fewer side effects compared to oral therapy. The purpose of this study was to prepare different types of topical formulations (ointments and gels) containing synthetic and natural anti-inflammatory agents with different excipients (e.g.,: surfactants, gel-forming) for the treatment of rheumatoid arthritis. The combination of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), diclofenac sodium, a topical analgesic agent methyl salicylate, and a lyophilized extract of Calendula officinalis with antioxidant effect were used in our formulations. The aim was to select the appropriate excipients and dosage form for the formulation in order to enhance the diffusion of active substances and to certify the antioxidant, analgesic, and anti-inflammatory effects of these formulations. To characterize the physicochemical properties of the formulations, rheological studies, and texture profile analysis were carried out. Membrane diffusion and permeability studies were performed with Franz-diffusion method. The therapeutic properties of the formulations have been proven by an antioxidant assay and a randomized prospective study that was carried out on 115 patients with rheumatoid arthritis. The results showed that the treatment with the gel containing diclofenac sodium, methyl salicylate, and lyophilized Calendula officinalis as active ingredients, 2-propenoic acid homopolymer (Synthalen K) as gel-forming excipient, distilled water, triethanolamine, and glycerol had a beneficial analgesic and local anti-inflammatory effect.

Imaging assessment of children presenting with suspected or known juvenile idiopathic arthritis: ESSR-ESPR points to consider

Juvenile idiopathic arthritis (JIA) is the most common paediatric rheumatic disease. It represents a group of heterogenous inflammatory disorders with unknown origin and is a diagnosis of exclusion in which imaging plays an important role. JIA is defined as arthritis of one or more joints that begins before the age of 16 years, persists for more than 6 weeks and is of unknown aetiology and pathophysiology. The clinical goal is early suppression of inflammation to prevent irreversible joint damage which has shifted the emphasis from detecting established joint damage to proactively detecting inflammatory change. This drives the need for imaging techniques that are more sensitive than conventional radiography in the evaluation of inflammatory processes as well as early osteochondral change. Physical examination has limited reliability, even if performed by an experienced clinician, emphasising the importance of imaging to aid in clinical decision-making. On behalf of the European Society of Musculoskeletal Radiology (ESSR) arthritis subcommittee and the European Society of Paediatric Radiology (ESPR) musculoskeletal imaging taskforce, based on literature review and/or expert opinion, we discuss paediatric-specific imaging characteristics of the most commonly involved, in literature best documented and clinically important joints in JIA, namely the temporomandibular joints (TMJs), spine, sacroiliac (SI) joints, wrists, hips and knees, followed by a clinically applicable point to consider for each joint. We will also touch upon controversies in the current literature that remain to be resolved with ongoing research. KEY POINTS: • Juvenile idiopathic arthritis (JIA) is the most common chronic paediatric rheumatic disease and, in JIA imaging, is increasingly important to aid in clinical decision-making. • Conventional radiographs have a lower sensitivity and specificity for detection of disease activity and early destructive change, as compared to MRI or ultrasound. Nonetheless, radiography remains important, particularly in narrowing the differential diagnosis and evaluating growth disturbances. • Mainly in peripheral joints, ultrasound can be helpful for assessment of inflammation and guiding joint injections. In JIA, MRI is the most validated technique. MRI should be considered as the modality of choice to assess the axial skeleton or where the clinical presentation overlaps with JIA.

Evaluation of Periarticular Soft Tissues in Patients With Juvenile Idiopathic Arthritis by Superb Microvascular Imaging and Shear Wave Elastography

OBJECTIVES

This study aims to compare the vascularity and elasticity of periarticular soft tissues by superb microvascular imaging (SMI) and power Doppler (PD) ultrasound along with shear wave elastography (SWE) between children with juvenile idiopathic arthritis (JIA) and healthy children.

PATIENTS AND METHODS

This prospective single center study, conducted between March 2018 and May 2018, included 22 children with JIA (14 males, 8 females; mean age 11.27±5 years; range, 5 to 17 years) and 24 healthy pediatric volunteers (12 males, 12 females; mean age 13±5.5 years; range, 7 to 17 years). Quadriceps tendon (QT), patellar tendon (PT), infraarticular and supraarticular soft tissue elasticities were calculated via SWE. Supraarticular and infraarticular soft tissue vascularity index (VI) were evaluated via SMI and PD.

RESULTS

No significant difference was found among the mean ages of the participants in study and control groups. Mean VI of both supraarticular (8.15%) and infraarticular soft tissues (7.9%) by SMI were significantly higher in study group compared to control group (2.88% vs. 2.57%, respectively). Mean VI of both supraarticular (9.1%) and infraarticular soft tissues (8.12%) by PD were significantly higher in study group compared to control group (3.4% vs. 3.1%, respectively). Highly significant good positive correlation was found between VI values obtained with PD and SMI (r=0.9, p=0.001). There was a significant moderate positive correlation between the mean elasticity of the QT with VI of the supraarticular soft tissues by SMI (r=0.4, p=0.003). There was a significant moderate positive correlation of VI of infraarticular soft tissues by SMI with mean elasiticity of PT (r=0.42, p=0.002).

CONCLUSION

Vascularity index by SMI and PD could differentiate patients with JIA from healthy subjects. The SWE examination of tendons and soft tissues did not show any significant difference among patients with JIA and healthy subjects.

Exploring contrast-enhanced MRI findings of the clinically non-inflamed symptomatic pediatric wrist

BACKGROUND

Knowledge of the synovial and tenosynovial appearance of the clinically non-arthritic symptomatic juvenile wrist using contrast-enhanced magnetic resonance imaging (MRI) is sparse.

OBJECTIVES

To analyze contrast-enhanced MRI findings of the clinically non-inflamed symptomatic pediatric wrist, focusing on the enhancing synovial and tenosynovial membrane. To evaluate the coexistent presence of (teno)synovial enhancement, joint fluid, bony depressions and medullary changes suggestive of bone marrow edema.

MATERIALS AND METHODS

We included 20 children (15 girls; age range: 7.5-17.6 years) who underwent contrast-enhanced MRI of the wrist, based on initial clinical indication, and eventually turned out to be unaffected by arthritic or orthopedic disorders. Various imaging characteristics of the synovium, tenosynovium, joint fluid, bone tissue and bone marrow were evaluated using existing MRI scoring systems.

RESULTS

In 3/20 (15%) children, mild or moderate-severe synovial enhancement was observed and 2/20 (10%) children showed mild tenosynovial enhancement/thickening. Joint fluid (11/20 children; 55%), bony depressions (20/20 children; 100%) and medullary changes suggestive of bone marrow edema (6/20; 30%) were found in a substantial percentage of children. The most frequently observed combination of coexisting imaging characteristics was bony depressions with ≥2 mm joint fluid, which was found in 7/20 (35%) children. Simultaneous presence of synovial and tenosynovial enhancement/thickening, bony depressions and medullary changes suggestive of bone marrow edema was observed in one child.

CONCLUSION

Several juvenile idiopathic arthritis-relevant MRI characteristics can be observed in the clinically non-inflamed symptomatic pediatric wrist.

Can quantitative MRI be used in the clinical setting to quantify the impact of intra-articular glucocorticoid injection on synovial disease activity in juvenile idiopathic arthritis?

BACKGROUND

Juvenile idiopathic arthritis (JIA), the most common chronic rheumatic disease of childhood, is characterised by synovitis. Clinical assessments of synovitis are imperfect, relying on composite and indirect measures of disease activity including clinician-reported measures, patient-reported measures and blood markers. Contrast-enhanced MRI is a more sensitive synovitis assessment technique but clinical utility is currently limited by availability and inter-observer variation. Improved quantitative MRI techniques may enable future development of more stringent MRI-defined remission criteria. The objective of this study was to determine the utility and feasibility of quantitative MRI measurement of synovial volume and vascularity in JIA before and twelve weeks after intra-articular glucocorticoid injection (IAGI) of the knee and to assess the acceptability of MRI to participating families.

METHODS

Children and young people with JIA and a new episode of knee synovitis requiring IAGI were recruited from the Great North Children's Hospital in Newcastle upon Tyne. Quantitative contrast-enhanced MRI was performed prior to and twelve weeks after IAGI, in addition to standard clinical assessment tools, including the three-variable clinical juvenile arthritis disease activity score (cJADAS) and active joint count.

RESULTS

Eleven young people (5 male, median age 13 years, range 7-16) with JIA knee flare were recruited and 10 completed follow-up assessment. Following IAGI, the median (interquartile range) cJADAS improved from 8.5 (2.7) to 1.6 (3.9), whilst the median synovial volume improved from 38.5cm³ (82.1cm³) to 0.0cm³ (0.2cm³). Six patients presented with frank synovitis outside normal limits on routine MRI reporting. A further three had baseline MRI reports within normal limits but the quantitative measurements identified measurable synovial uptake. Post-IAGI quantitative measurements highlighted significant improvements in 9 patients.

CONCLUSIONS

IAGI led to a marked reduction in synovial volume, with quantitative MRI identifying more patients with an improved synovial volume than routine qualitative clinical reporting. Improvements in cJADAS scores were more variable with the patient/parent global assessment component contributing most to the scores. Further work is indicated, exploring the utility of quantitative MRI in the assessment of less accessible joints and comparing the impact of different treatment modalities.

Prolonged time between intravenous contrast administration and image acquisition results in increased synovial thickness at magnetic resonance imaging in patients with juvenile idiopathic arthritis

BACKGROUND

Post-contrast synovial thickness measurement is necessary for scoring disease activity in juvenile idiopathic arthritis (JIA). However, the timing of post-contrast sequences varies widely among institutions. This variation in timing could influence thickness measurements.

OBJECTIVE

To measure thickness of the synovial membrane on early and late post-contrast knee magnetic resonance (MR) images of patients with JIA.

MATERIALS AND METHODS

Dynamic contrast-enhanced T1-weighted knee MR images of 53 children with JIA with current or past knee arthritis were used to study synovial thickness at time point 1 (about 1 min) and time point 2 (about 5 min after contrast administration). Two experienced readers, who were blinded for the time point, independently measured synovial thickness at a predefined, marked location in the patellofemoral compartment on randomized images. Synovial thickness at the two time points was compared using the Wilcoxon signed rank test. Repeatibility of the synovial thickness measurements was studied using intraclass correlation coefficients and Bland-Altman plots.

RESULTS

Median synovial thickness of the 53 patients (median age: 13.5 years, 59% female) increased with prolonged post-contrast interval with a synovial thickness of 1.4 mm at time point 1 and a synovial thickness of 1.5 mm at time point 2 (P<0.001). Repeated synovial thickness measurements showed an intraclass correlation coefficient (ICC) of 0.75, P<0.05 for time point 1 and an ICC of 0.91, P<0.05 for time point 2.

CONCLUSION

Post-contrast synovial membrane thickness measurements are time-dependent. Therefore, standardization of post-contrast image acquisition timing is important to achieve consistent grading of synovial inflammation.

MRI of synovitis and joint fluid

Synovitis and joint effusion are common manifestations of rheumatic disease and play an important role in the disease pathophysiology. Earlier detection and accurate assessment of synovial pathology, therefore, can facilitate appropriate clinical management and hence improve prognosis. Magnetic resonance imaging (MRI) allows unparalleled assessment of all joint structures and associated pathology. It has emerged as a powerful tool, which enables not only detection of synovitis and effusion, but also allows quantification, detailed characterization, and noninvasive monitoring of synovial processes. The purpose of this article is to summarize the pathophysiology of synovitis and to review the role of qualitative, semiquantitative, and quantitative MRI in the assessment of synovitis and joint fluid. We also discuss the utility of MRI as an outcome measure to assess treatment response, particularly with respect to osteoarthritis and rheumatoid arthritis. Emerging applications such as hybrid positron emission tomography / MRI and molecular imaging are also briefly discussed. Level of Evidence: 5 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019.

Juvenile idiopathic arthritis: magnetic resonance imaging of the clinically unaffected knee

BACKGROUND

Synovial thickening detected on magnetic resonance imaging (MRI) is present in a significant number of children with clinically inactive juvenile idiopathic arthritis (JIA).

OBJECTIVE

To evaluate patient characteristics and disease activity parameters in a cohort of children with clinically inactive JIA, both with and without synovial thickening, in order to clarify the observed discrepancy between clinical and MRI assessments.

MATERIALS AND METHODS

We prospectively enrolled 52 clinically inactive JIA patients (median age 13.3 years, 63.5% girls) who underwent MRI of the knee as major target joint in JIA. Children were divided into two groups based on MRI outcome: group 1, with synovial thickening on MRI; and group 2, with no synovial thickening on MRI. We used the Juvenile Arthritis MRI Scoring system to evaluate synovial thickness. We compared patient characteristics and disease activity parameters between the groups.

RESULTS

Synovial thickening on MRI was present in 18 clinically inactive patients (group 1, 34.6%). The age was significantly lower for the patients in group 1 (median 10.7 versus 14.4, P=0.008). No significant differences were observed in any of the other patient characteristics nor the disease activity parameters tested.

CONCLUSION

Synovial thickening on MRI was present in nearly 35% of the children with clinically inactive JIA. Children with synovial thickening on MRI were significantly younger than those without. This might indicate that younger patients are at risk of subclinical disease activity and under-treatment, although the exact clinical relevance of synovial thickening on MRI has not been determined.

Imaging of the knee in juvenile idiopathic arthritis

In juvenile idiopathic arthritis (JIA), imaging is increasingly used in clinical practice. In this paper we discuss imaging of the knee, the clinically most commonly affected joint in JIA. In the last decade, a number of important steps have been made in the development of imaging outcome measures in children with JIA knee involvement. Ultrasound is undergoing a fast validation process, which should be accomplished within the next few years. The validation processes of MRI as an imaging biomarker for clinical trials in the JIA knee are at an advanced stage, with important data available on the feasibility, reliability and validity of the Juvenile Arthritis MRI Scoring system. Moreover, both US and MRI data are emerging on the normal appearance of the growing knee joint.