Imaging findings of radiologically misdiagnosed nodular fasciitis.

Background Nodular fasciitis rarely occurs in young adults and children; it usually resembles other tumors, even malignancy. Purpose To review the imaging findings of six cases of nodular fasciitis misdiagnosed radiologically. Material and Methods The clinical and radiologic features of six cases of histologically proven but radiologically misdiagnosed nodular fasciitis were reviewed retrospectively. Two cases underwent both plain and enhanced computed tomography (CT) scans and the other four had both regular and enhanced magnetic resonance (MR) scans. Results All six patients were young (five children and one young adult). A rapid growing mass, pain or painless, was the most frequent presentation. Most masses were oval, well-defined, and homogeneous, with an average diameter of 2.2 cm. Five were found in superficial fascia with a broad base. Two cyst-like masses showed hypodensity relative to muscle on plain CT and without enhancement. Compared to muscle, these masses showed isointensity (n = 3) or slight hyperintensity (n = 1) on T1-weighted imaging, hyperintensity on T2-weighted imaging (n = 4), with homogeneous notable enhancement (n = 3) or mild enhancement (n = 1). Five (83.3%) were found with a "fascial tail" sign characterized as thickening of adjacent fascial layer with notable enhancement. One mass showed an "inverted target" sign. Conclusion Nodular fasciitis in young adults and children is usually superficial, rapid growing, well-defined, and homogeneous, frequently with a "fascial tail" sign. Radiologically, it can resemble a benign cyst and might be easily misdiagnosed. Therefore, nodular fasciitis should be remembered in the differential diagnosis for superficial soft tissue tumor found in young adult and children.