Fibroblastic and myofibroblastic tumors can be classified according to their biologic behavior (figure 2).

• Benign lesions:
  • Elastofibroma dorsi (figure 3): it appears at the scapulo-thoracic joint and it may be heterogeneous on imaging (fibrous and fatty tissue).
    
  • Myositis Ossificans (figure 4): it shows a heterogeneous appearance on imaging and has calcified areas.
    
  • Fibromatosis Colli (figure 5): it is found on the sternocleidomastoid muscle and it is secondary to trauma during childbirth.
    
• Intermediate lesions (locally aggressive or rarely metastasizing) (figures 6-22): Palmar (Dyupuytren) and Plantar (Ledderhose) fibromatosis (figures 11-17) and dermatofibrosarcoma (figures 18-20).
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• Malignant lesions (figures 23-27):
  • Fibrosarcoma (not otherwise specified): it is hypointense on T1 WI and iso-to hyperintense on T2 WI, with peripheral enhancement after contrast administratio.
  • Myxofibrosarcoma: it has a heterogeneous appearance with hyperintense foci on T2. Osseous involvement is frequent.
  • Other tumors that are reviewed are undifferentiated pleomorphic sarcoma, sclerosing epitheloid fibrosarcoma (figures 28 and 29), or low-grade fibromyxoid sarcoma.

Fibrosarcoma, not otherwise specified (NOS) (figures 23 and 24):

• This tumor has replaced adult fibrosarcoma in the 2020 WHO classification.
• The median patient age at presentation is 50 years.
• It arises from the tendons and fascia of deep soft tissues in the extremities, head and neck, and trunk.
• Histopathology: fibroblast fascicles with a “herringbone” architecture and variable collagen content. Although these features may resemble that of infantile fibrosarcoma, fibrosarcoma NOS has a much worse prognosis.
• CT:  isodense infiltrative or well-defined soft-tissue masses.
• MRI: Hypo- to isointense on T1 WI and heterogeneously hyperintense on T2 WI, band-likes areas may be seen (fibrous tissue, hypointense on T1 and T2 WI) and variable enhancement (predominantly peripheral).

Myxofibrosarcoma (figures 26 and 27):

• It most commonly affects older adults (60 -80 years old), with a slight male predominance.
• Most lesions arise in the extremities and limb girdles (50% are intramuscular).
• Consistency and size: soft multinodular lesions that range in size (< 10 cm).
• Histopathology: It usually consists of atypical spindle cells and fibrous septa in a myxoid matrix Long curvilinear blood vessels with perivascular cellular condensation are a specific feature.
• MRI: Heterogeneous appearance with internal hyperintense foci on T2 WI (myxoid component), fascial tail sign and intense enhacement (nodular or peripheral).

Sclerosing Epithelioid Fibrosarcoma (SEF) (figures 28 and 29):

• It usually occurs in middle-aged patients (mean age of 47 years).
• SEF commonly affects lower extremities, pelvic girdle or upper extremities.
• 80% of these tumors metastasize (to the lungs, pleura, bones and brain).
• Histopathology: polygonal epithelioid fibroblasts arranged in cords in a dense, hyalinized, and sclerotic stroma.

   

• MRI:

  • Variable SI on T1 WI and heterogeneous high SI on T2 WI.
  • Necrosis and peripheral enhancement. Enhancement indicates areas of cellularity, vascular proliferation, and peritumoral desmoplastic reaction.