Incidental enchondromas at knee magnetic resonance imaging: intraobserver and interobserver agreement and prevalence of imaging findings*

Objective: To evaluate intraand interobserver agreement in the identification of incidental enchondromas at knee magnetic resonance imaging, and to assess the prevalence of imaging findings. Materials and Methods: Retrospective study reviewing 326 knee magnetic resonance images acquired in the period between November 2009 and September 2010. The images were independently and blindly analyzed by two specialists in musculoskeletal radiology, with the objective of identifying incidental enchondromas, presence of foci with signal similar to bone marrow and foci of signal absence suggestive of calcifications within the enchondromas. Interand intraobserver agreements were analyzed. Results: Eleven lesions compatible with enchondromas (3.3%) were identified. The interobserver agreement for the presence of enchondroma was high. Prevalence of foci of bone marrow signal inside the enchondromas was of 54.55%, and foci suggestive of calcification corresponded to 36.36%. The intraobserver agreement for foci of bone marrow signal in enchondromas was perfect, and interobserver agreement was high. Conclusion: The prevalence of incidental enchondromas in the current study was compatible with data in the literature. Excellent agreement was observed in the identification of enchondromas and in the assessment of imaging findings. A higher prevalence of fat signal foci was observed as compared with signal absence suggestive of calcifications.