Age / Sex : /

Age / Sex : 50/F
Chief complaint : Palpable mass on back, 10 days ago

Nodular fascitis

Discussion

Findings:
 Axial and sagittal T1-weighted MR images show reltively well delineated fusiform shaped soft tissue mass in supraspinous facial plane at the level of T10. It demonstrates the heterogenous increased signal intensity of the lesion on T2WI and well contrast enhancement. The central unenhanced area indicates fluid or myxoid components

Differential Diagnosis:
 Nodular fasciitis, fibrous histiocytoma, and malignant tumor such as fibrosarcoma, MFH

Pathologic Findings:
 Nodular proliferation of the spindle-shaped myofibroblastic cells. Abundant myxoid components in the central area of the mass were noted.

Diagnosis: Nodular Fasciitis

Discussion: Nodular fasciitis (NF), first reported by Konwaler et al. in 1955, is localized benign, quasineoplastic proliferation of fibroblasts and myofibroblasts that is often clinically mistaken for a sarcoma because of its rapid growth, rich cellularity, and mitotic activity. Although the cause of NF is unknown, it is likely that the fibroblastic proliferation is triggered by local injury or by a localized, nonneoplastic inflammatory process. Most patients give a history of rapidly growing mass or nodule that has been present for only 1 or 2 weeks. NF is most common in adults between 20 and 40 years of age. The most common locations are the upper extremities (48%), especially the volar aspect of the forearm, followed by the trunk (20%), particulary the chest wall and back. NF in the head and neck (17%) is next in frequency, and is the most common site in infants and children.
 Three different types of NF can be distinguished: the subcutaneous type, the intramuscular type, and the fascial type. The subcutanenous type presents about four times than any other two types. Depending upon the predominant cellular features, Price et al. distinguished myxoid, cellular, and fibrous types. Myxoid appearance predominates in young lesions, whereas older lesions have a more fibrous composition sometimes accompanied by the formation of minute fluid-filed space. Histologic subtype of NF which may relate to the age and the anatomic location of the lesion. Subcutaneous lesions tend to belong to a myxoid subtype and to be of younger age, while deeper seated lesions may be larger and older and are of a cellular or fibrous subtype. Histologic subtypes can be reflected by different SI characteristics and enhancement pattern on MRI, but the time-related large histologic variability limits the predictability of a prototype of NF on MRI. The signal in hypercellular lesions appears nearly isointense to that in skeletal muscle on T1-weighted images and hyperintense to that in adipose tissue on T2- weighted images. Highly collagenous lesions have hypointense signal on all MR images. Contrast enhancement is typically diffuse but may be peripheral in lesions with a greater extracellular myxoid matrix and central fluid-filled spaces. The differential diagnosis at MR imaging includes extraabdominal desmoid tumor, neurofibroma, fibrous histiocytoma, and soft-tissue sarcoma. In the presence of an intramuscular lesion, early myositis ossificans may be considered in the differential diagnosis, as well. The imaging-based diagnosis should be verified with an excisional biopsy. In summery, NF may be misinterpreted as a malignant lesion due to its rapid growth and aggressive nature on histology, but the correct diagnosis may be achieved by the combination of the imaging findings, location, and histology.
 
References:
1. Franz M. Enzinger, Sharon W. Weiss. Benign fibrous tumor. In: Soft tissue tumors. 3rd ed. St. Louis: Mosby, 1995; 165-199
2. X. L. Wang, A. M. A. De Schepper, F. Vanhoenacker et al. Nodular fasciitis: correlation of MRI findings and histopathology. Skeletal Radiol. 2002; 31:15
3. Dinauer PA, Brixey CJ, Moncur JT, Fanburg-Smith JC, Murphey MD. Pathologic and MR imaging features of benign fibrous soft-tissue umors in adults. Radiographics. 2007 Jan-Feb; 27(1):173-87.