1869. The Not So Simple Nonossifying Fibroma
Authors * Denotes Presenting Author
  1. Jon Olson; American Institute of Radiologic Pathology; Walter Reed National Military Medical Center
  2. Mark Murphey *; American Institute of Radiologic Pathology; Walter Reed National Military Medical Center
  3. Agustinus Suhardja; No Affiliation
  4. Eric Walker; Penn State Health Radiology
  5. Julie Fanburg-Smith; Penn State Health Pathology
  6. Mark Kransdorf; Mayo Clinic Scottsdale
To describe the radiologic appearance of unusual complications of nonossifying fibroma including stress fracture, diffuse infarction, aneurysmal bone cyst and malignant transformation that may simulate more aggressive disease.

Materials and Methods:
We retrospectively reviewed the imaging of 8 cases of nonossifying fibroma associated with unusual complications that can mimic a more aggressive disease process including stress fracture (n=5), diffuse infarction (n=1), aneurysmal bone cyst component (n=1) and malignant transformation (n=1). Radiologic studies reviewed by 3 musculoskeletal radiologists, with agreement by consensus, included radiographs (n=8), bone scintigraphy (n=2), CT (n=3), and MR (n=7). Evaluation included patient demographics; lesion location, size and margin; periosteal reaction; presence of mineralization; and intrinsic characteristics on CT and MR imaging.

Patients included 5 males and 3 females (average age 14 years; age range 8-20 years). Common locations included the distal femur (50%), fibula (25%) and tibia (25%). Lesions were centered in the metaphysis in all cases. Radiographs and CT showed a predominantly lytic lesion with a narrow zone of transition in 88% of cases with one case revealing prominent sclerosis. Nonaggressive periosteal reaction was seen in 62% of cases. A soft tissue mass was seen in only one case by MR. Fluid levels and relatively rapid enlargement were also seen in one case on MR imaging. Prominent surrounding marrow and/or periosteal cuff of edema was seen in 71% of cases on MR imaging. The signal intensity of the nonossifying fibroma was low to intermediate intensity with heterogeneity in 86% of cases on both T1 and T2-weighted MR images. One case showed diffuse high signal on T2-weighted MR and rim enhancement suggesting infection. Diffuse heterogeneous enhancement was seen in the other 2 cases following contrast administration both in the lesion and the adjacent edema.

The vast majority of nonossifying fibromas are radiographic incidental lesions without the need for further radiologic assessment. The most common complication of linear fracture is also easily recognized on radiographs. However, more unusual complications such as stress fracture, infarction and aneurysmal bone cyst formation may create an imaging appearance suggesting a more aggressive process and recognition can reduce the possibility of inappropriate treatment. These lesions only rarely undergo malignant transformation with a soft tissue mass recognized on cross sectional imaging suggesting this ominous complication.