Are we overcalling sacroiliitis on MRI? Differential diagnosis that every rheumatologist should know - Part I.

Diagnosing early spondyloarthritis remains a challenge in routine practice, especially in its axial (SpA) form. Magnetic resonance imaging (MRI) is capable of detecting early bone marrow edema (BME) in the sacroiliac joints (SIJs), a key criterion for the diagnosis of active SpA according to the "imaging arm" of the Assessment of Spondyloarthritis International Society (ASAS) classification. However, despite MRI having superior reliability compared to radiographs and being recognized as a crucial imaging biomarker of SpA, it has several limitations, including its limited specificity and sensitivity. Based on the established literature, there is currently an "overcall" of sacroiliitis on MRIs. In this setting, differential diagnoses and their imaging features come into play. In this two-part article, we will review both the imaging features that constitute a "positive" MRI in SpA and the most common differential diagnoses. In order to understand the pathophysiology of sacroiliitis and the spectrum of developing lesions, one needs to be familiar with the complex SIJs anatomy, both on radiographs and on cross-sectional imaging studies (particularly MRI). As such, in the first part of this article, we provide a brief background on anatomy and different imaging modalities used in this clinical setting and we review the imaging criteria for a "positive" MRI study of sacroiliitis in adults (imaging arm of the ASAS classification).

Are We Overcalling Sacroillitis on MRI? Differential diagnosis that every rheumatologist should know - Part II.

In the second part of this review article we will describe the imaging features of non- spondyloarthritis (SpA) pathologies that may mimic sacroiliitis on Magnetic Resonance Imaging (MRI), and that readers should be aware (part 2). Based on the established literature, there is currently an "overcall" of sacroiliitis on MRIs. In this setting, differential diagnoses and their imaging features come into play. In fact, non-SpA related sacroiliac joints (SIJs) pathologies are more commonly found than true sacroiliitis on MRI of the SIJs, even in patients with inflammatory type back pain. An imaging literature review, highlighting "easy-to-use" learning points regarding MRI interpretations in patients with suspected sacroiliitis and/or nonspecific lumbar back pain is presented. This two-part article aims to be a snapshot of the most common inflammatory versus non-inflammatory entities found on SIJs imaging studies in routine practice, while trying to keep this review article simple, educational and above all, practical.

Following unenhanced MRI assessment for local recurrence after surgical resection of mesenchymal soft tissue tumors, do additional gadolinium-enhanced images change reader confidence or diagnosis?

PURPOSE: Evaluate if gadolinium enhanced MR imaging (GeMRI) improves confidence, changes the final diagnosis, or improves accuracy in the assessment of musculoskeletal (MSK) tumor residual or recurrence following surgical resection. We also assess if different experience levels change the above results. METHODS AND MATERIALS: Initially, pre-contrast images were independently reviewed by two radiologists, one with 25 years of experience (R1) and one undergoing MSK specialty training (R2). Two questions were answered: (1) Mass present? and (2) Likelihood of malignancy? Subsequently, both pre-contrast and post-contrast images were independently reviewed. The same questions were again answered plus four others including if GeMRI changed mass characterization, better defined cystic versus solid, better defined tumor extent, or improved conspicuity. Lastly, the readers answered whether GeMRI changed confidence, and changed their final diagnosis. Histologic diagnoses were available in 43 cases, with the remaining 44 cases based upon clinical and/or imaging follow-up. RESULTS: GeMRI definitely improved confidence in 8/7 cases, and slightly improved confidence in 20/29 cases and changed the final diagnosis in 11/8 cases for R1 and R2 respectively. Positive and negative predictive values statistically improved for R2 (positive predictive value 36.4% versus 50%, p=0.02; negative predictive value 75.4% versus 79.1%, p=0.04) but not for R1. Reader concordance for malignancy improved with GeMRI (κ=0.44 pre-contrast and κ=0.71 post-contrast). CONCLUSION: GeMRI improved reader confidence, improved reader concordance and modestly improved accuracy for the less experienced reader. Where possible, GeMRI should be used in the assessment of MSK tumor residual or recurrence.