Myositis and Its Mimics: Guideline Updates, MRI Characteristics, and New Horizons.

Myositis is defined as inflammation within skeletal muscle and is a subcategory of myopathy, which is more broadly defined as any disorder affecting skeletal muscle. Myositis may be encountered as a component of autoimmune and connective tissue disease, where it is described as idiopathic inflammatory myopathy. Myositis can also be caused by infections, as well as toxins and drugs, including newer classes of medications. MRI plays an important role in the diagnosis and evaluation of patients with suspected myositis, but many entities may have imaging features similar to myositis and can be considered myositis mimics. These include muscular dystrophies, denervation, deep venous thrombosis, diabetic myonecrosis, muscle injury, heterotopic ossification, and even neoplasms. In patients with suspected myositis, definitive diagnosis may require integrated analysis of imaging findings with clinical, laboratory, and pathology data. The objectives of this article are to review the fundamental features of myositis, including recent updates in terminology and consensus guidelines for idiopathic inflammatory myopathies, the most important MRI differential diagnostic considerations for myositis (i.e., myositis mimics), and new horizons, including the potential importance of artificial intelligence and multimodal integrated diagnostics in the evaluation of patients with muscle disorders.

Does the presence of macroscopic intralesional fat exclude malignancy? An analysis of 613 histologically proven malignant bone lesions.

OBJECTIVE: To determine if macroscopic intralesional fat detected in bone lesions on CT by Hounsfield unit (HU) measurement and on MRI by macroscopic assessment excludes malignancy. MATERIALS AND METHODS: All consecutive CT-guided core needle biopsies (CNB) of non-spinal bone lesions performed at a tertiary center between December 2005 and September 2021 were reviewed. Demographic and histopathology data were recorded. All cases with malignant histopathology were selected, and imaging studies were reviewed. Two independent readers performed CT HU measurements on all bone lesions using a circular region of interest (ROI) to quantitate intralesional fat density (mean HU < -30). MRI images were reviewed to qualitatively assess for macroscopic intralesional fat signal in a subset of patients. Inter-reader agreement was assessed with Cronbach's alpha and intraclass correlation coefficient. RESULTS: In 613 patients (mean age 62.9 years (range 19-95 years), 47.6% female), CT scans from the CNB of 613 malignant bone lesions were reviewed, and 212 cases had additional MRI images. Only 3 cases (0.5%) demonstrated macroscopic intralesional fat on either CT or MRI. One case demonstrated macroscopic intralesional fat density on CT in a case of metastatic prostate cancer. Two cases demonstrated macroscopic intralesional fat signal on MRI in cases of chondrosarcoma and osteosarcoma. Inter-reader agreement was excellent (Cronbach's alpha, 0.95-0.98; intraclass correlation coefficient, 0.90-0.97). CONCLUSION: Malignant lesions rarely contain macroscopic intralesional fat on CT or MRI. While CT is effective in detecting macroscopic intralesional fat in primarily lytic lesions, MRI may be better for the assessment of heterogenous and infiltrative lesions with mixed lytic and sclerotic components. CLINICAL RELEVANCE STATEMENT: Macroscopic intralesional fat is rarely seen in malignant bone tumors and its presence can help to guide the diagnostic workup of bone lesions. KEY POINTS: • Presence of macroscopic intralesional fat in bone lesions has been widely theorized as a sign of benignity, but there is limited supporting evidence in the literature. • CT and MRI are effective in evaluating for macroscopic intralesional fat in malignant bone lesions with excellent inter-reader agreement. • Macroscopic intralesional fat is rarely seen in malignant bone lesions.

MRI of patellar stabilizers: Anatomic visibility, inter-reader reliability, and intra-reader reproducibility of primary and secondary ligament anatomy.

OBJECTIVE: To compare MRI features of medial and lateral patellar stabilizers in patients with and without patellar instability. METHODS: Retrospective study of 196 patients (mean age, 33.1 ± 18.5 years; 119 women) after diagnosis of patellar instability (cohort-1, acute patellar dislocation; cohort-2, chronic patellar maltracking) or no patellar instability (cohort-3, acute ACL rupture; cohort-4, chronic medial meniscus tear). On MRI, four medial and four lateral stabilizers were evaluated for visibility and injury by three readers independently. Inter- and intra-reader agreement was determined. RESULTS: Medial and lateral patellofemoral ligaments (MPFL and LPFL) were mostly or fully visualized in all cases (100%). Of the secondary patellar stabilizers, the medial patellotibial ligament was mostly or fully visualized in 166 cases (84.7%). Other secondary stabilizers were mostly or fully visualized in only a minority of cases (range, 0.5-32.1%). Injury scores for all four medial stabilizers were higher in patients with acute patellar dislocation than the other 3 cohorts (p < .05). Visibility inter- and intra-reader agreement was good for medial stabilizers (κ 0.61-0.78) and moderate-to-good for lateral stabilizers (κ 0.40-0.72). Injury inter- and intra-reader agreement was moderate-to-excellent for medial stabilizers (κ 0.43-0.90) and poor-to-moderate for lateral stabilizers (κ 0-0.50). CONCLUSION: The MPFL and LPFL were well visualized on MRI while the secondary stabilizers were less frequently visualized. The secondary stabilizers were more frequently visualized medially than laterally, and patellotibial ligaments were more frequently visualized compared to the other secondary stabilizers. Injury to the medial stabilizers was more common with acute patellar dislocation than with chronic patellar maltracking or other knee injuries.

Distant migration of gluteal augmentation fat presenting as a soft tissue knee mass.

Gluteal augmentation with autologous fat grafting is an increasingly popular procedure. While complication rates are low, the clinical and imaging evaluation of the various complications can be challenging. We report a case of distal migration of a failed gluteal fat graft in a young female patient presenting as a soft tissue mass in the knee, mimicking a soft tissue sarcoma. Surgical resection of the migrated fat graft confirmed the diagnosis. The diagnosis was challenging as the patient was initially reluctant to disclose her surgical history due to perceived negative social stigmas related to cosmetic contouring procedures. This case highlights the imaging findings of a rare complication following autologous fat grafting for gluteal augmentation and the importance of obtaining a thorough medical history.

Undersized Rigid Nonplanar Annuloplasty: The Key to Effective and Durable Repair of Functional Tricuspid Regurgitation.

BACKGROUND: Previous clinical experiences have demonstrated high early and late recurrence rates after repair of functional tricuspid regurgitation (TR). We investigated the results of functional TR repair with undersized rigid nonplanar annuloplasty rings. METHODS: From January 2007 to December 2013, 216 consecutive patients with moderate or greater functional TR were treated with undersized (size 26 mm or 28 mm) rigid nonplanar annuloplasty rings. RESULTS: The mean age was 69 ± 13 years. There was a previous history of cardiac operation in 25% (54 of 216 patients). Tricuspid regurgitation was graded as severe in 47% (102 of 216) and moderate in 53% (114 of 216). Concomitant operations included mitral valve procedures in 92% (198 of 216), coronary artery bypass grafting in 21% (45 of 216), aortic valve procedures in 9% (20 of 216), and cryomaze procedures in 35% (76 of 216). Size 26 mm rings were used in 38% of patients (81 of 216), and size 28 mm in 62% (135 of 216). The perioperative mortality rate was 6% (14 of 216). On predischarge echocardiography, TR grade was none or mild in 94% (176 of 187 patients), moderate in 4% (7 of 187), and severe in 2% (4 of 187). At a mean follow-up of 33.0 ± 24.0 months, TR grade was none or mild in 81% of patients (130 of 160), moderate in 16% (26 of 160), and severe in 2% (4 of 160). There were no reoperations for recurrent TR, and no patients have had tricuspid stenosis or annuloplasty ring dehiscence. CONCLUSIONS: Treatment of functional TR with undersized (26 mm or 28 mm) nonplanar rigid annuloplasty rings is safe and highly effective, with a near absence of recurrent severe TR at midterm follow-up.