Wait, scan and then? Exploring the long-term natural course of 119 low-grade central cartilaginous lesions of the long bones with MRI follow-up.

objectivesThis study aims to identify MRI characteristics to better understand the natural course of low-grade central cartilage lesions (LG-CCLs) to promote active MRI-based surveillance as an alternative to invasive surgery. MATERIALS AND

methodsIn this single-center retrospective cohort study, baseline and > 48-month follow-up MRIs of 119 patients with a solitary LG-CCL of the long bones were retrospectively analyzed. None of the included cases had aggressive MRI characteristics, nor had biopsy. Two observers assessed MRI characteristics, length, cortical scalloping, intralesional fat entrapment and fat replacement. LG-CCLs were classified as in regression, stable or progressive. Statistical analysis was assessed using the Kruskal-Wallis rank sum test and Fisher's exact test. Interobserver agreement was calculated using Cohen's Kappa coefficient and Intraclass Correlation Coefficient.

resultsThe majority of LG-CCLs were labeled as in regression (78/119; 66%) or stable (27/119; 23%). 108/119 patients (91%) showed initial fat entrapment; 56/119 (47%) developed increased fat entrapment and 80/119 (67%) developed fat replacement. Out of 14 patients (median age 30) with tumor growth (14/119; 12%), nine had initial fat entrapment (5/9 also developed fat replacement), and two developed fat entrapment. One LG-CCL with developing fat entrapment and fat replacement showed new scalloping, and two LG-CCLs showed growth and new scalloping without any fat. None developed aggressive MRI characteristics. Interobserver agreement varied from substantial to near perfect agreement, except for moderate agreement on scalloping at baseline.

conclusionThis study on the natural course of LG-CCLs of the long bones shows that increasing fat entrapment and/or fat replacement over time on MRI may help prognosticate benign biological behaviour and might be supportive for watchful waiting over surgical treatment. KEY POINTS: Question Can specific MRI features help identify benign behavior in low-grade central cartilage lesions of long bones to support MRI-based surveillance? Findings Most low-grade lesions were stable or regressed (89%); increasing fat entrapment and/or fat replacement were associated with a benign natural course on MRI. Clinical relevance MRI features like fat entrapment and fat replacement support safe non-operative surveillance of LG-CCLs, avoiding unnecessary surgery.