Characteristic contrast-enhanced MRI findings of nodular fasciitis and their chronological change

Purpose This study aimed to identify characteristic contrast-enhanced MRI features of nodular fasciitis that aid in differentiating it from malignant tumors and to evaluate their chronological changes. Materials and methods We analyzed 62 histologically confirmed nodular fasciitis lesions from 61 patients. All patients underwent T2-weighted and post-contrast MRI. Non-enhancing patterns were categorized as follows: type 1 (homogeneous enhancement), type 2 (central non-enhancement), type 3 (heterogeneous non-enhancement), and type 4 (predominantly non-enhancing). Type 4 was subdivided into type 4a (predominantly non-enhancing with minimal peripheral enhancement) and type 4b (completely non-enhancing with perilesional enhancement). MRI findings from 50 malignant tumors served as controls. Results The initial MRI patterns included type 1 ( n = 24, 39%), type 2 ( n = 17, 27%), type 3 ( n = 9, 15%), and type 4 ( n = 12, 19%). Among the 12 type 4 lesions, 8 exhibited type 4b. Three additional lesions evolved into type 4b, totaling 11 (17%) of the 62. A follow-up MRI was performed in 5 type 4b lesions; 4 demonstrated changes to other types, although without a consistent transformation pattern. Type 4b lesions were absent in the malignant control group. Conclusion In this cohort, type 4b was observed in nodular fasciitis and not in the malignant controls evaluated; specificity beyond this control spectrum remains unknown and requires external validation. The temporal evolution from type 4b to other patterns was variable, potentially explaining the previously reported heterogeneity in MRI findings. Follow-up imaging may help explain the variability in reported MRI appearances.