Clinical and Magnetic Resonance Imaging Findings for Differentiating Nodular Fasciitis and Myxofibrosarcoma: Correlation With "Fascial Tail" Sign.

Objective: This study aimed to determine the characteristic clinical and magnetic resonance imaging (MRI) findings that can distinguish nodular fasciitis (NF) from myxofibrosarcoma (MFS) because they are sometimes difficult to differentiate due to the overlapping imaging findings, such as the "fascial tail" sign.

Methods: Thirty patients with NF and 44 with MFS were included in this study. The following MRI features were evaluated: mass size, anatomical and compartmental location, presence and type of pseudo-capsule, degree of heterogeneity, presence, and length of the "fascial tail" sign, and presence of peritumoral edema. Using diffusion-weighted images (DWI), we determined the presence of diffusion restriction and measured the apparent diffusion coefficient (ADC) values. On dynamic contrast-enhanced (DCE) images, we obtained the values of Ktrans, Kep, Ve, iAUC, and time-concentration curves using Tissue 4D.

Results: The patients with NF were significantly younger than those with MFS. The average sizes of MFS and NF were 6.27±3.74 and 3.03±1.81 cm, respectively. Linear logistic regression analysis revealed that age, recurrence, "fascial tail" length, peritumoral edema, enhancement heterogeneity, and Ve differed significantly between the NF and MFS groups. The length of "fascial tail," contrast heterogeneity, and compartmental location were statistically significant factors influencing the recurrence.

Conclusions: Older age (above 46 y), larger tumor size (>4 cm), peritumoral edema, enhancement heterogeneity, and longer "fascial tail" (>25 mm) are more frequently associated with MFS, while the functional MR imaging findings, except the Ve value (>0.417), showed no significant differences.