By: Terry R. Yochum, DC, DACBR, Fellow, ACCR and Michael S. Barry, DC, DACBR
A 10-year-old male gymnast presents with post-traumatic ankle pain following a fall from the platform bar. Radiographic examination reveals:
Figure 1. Diagnosis: Nonossifying fibroma (fibrous xanthoma) of the distal tibial metaphysis with a spiral pathological fracture.
Fibrous Xanthoma of Bone—Nonossifying Fibroma
Fibrous xanthoma of bone is a term that encompasses several lesions known under two major names: nonossifying fibroma (NOF) and fibrous cortical defect (FCD). Most researchers believe that these two entities are the identical lesions seen at different age ranges and stages of growth. Indeed, the only differentiating factor is the patient’s age, with FCD occurring in 4 to 8-year-olds and NOF seen in 8 to 20-year-olds.
The true incidence is difficult to determine since the majority of the lesions are asymptomatic and never discovered. Approximately 30 to 40% of normal children have fibrous cortical defects, with nonossifying fibroma being somewhat less common.
Age and sex distribution. The usual age range is 8 to 20 years, with the average age being 14. Males predominate in a 2:1 ratio.
Signs and symptoms. Most lesions are asymptomatic and found by coincidence when the patient is being radiographed for some other reason, usually following trauma. Large lesions, over 8 cm, often cause persistent pain and may significantly weaken the bone, allowing pathological fracture to occur, especially in active adolescents.
Location. This lesion commonly affects the bones of the lower extremity, with the distal tibia being the most frequent site. Other sites include the proximal tibia, distal femur and fibula, and proximal humerus. Most lesions and diametaphyseal and eccentric in position. The eccentric location on one side of the bone is characteristic, but is not always identifiable in some of the smaller bones, particularly the fibula or ribs.
The histologic picture of an NOF and that of an FCD are identical. This consists of a whorled bundle of spindle-shaped, stromal connective tissue cells with varying amounts of intercellular, collagenous material interspersed. Foam cells containing lipid and giant cells are frequently present.
The radiographic appearance of NOF is so characteristic that biopsy is seldom necessary. The typical lesion is solitary, radiolucent, eccentric, and generally ovoid; it often thins and may expand the cortex. The margins are scalloped and there is often a multilocular, bubbly appearance. The osteolytic area may vary from 2 to 7 cm in diameter and has a very narrow zone of transition.
Epiphyseal lesions are rare, and on occasion the metaphyseal lesion is carried by growth into the diaphsis of the long bone. Malignant transformation does not occur. Multiple NOFs do occur in association with neurofibromatosis.
NOF and FCD will show minimal to mild uptake on bone scan examination. The uptake is very low in comparison with malignant lesions and other benign tumors, such as osteoblastoma, osteoid osteoma, and aneurysmal bone cyst.
Treatment and Prognosis
Since most lesions are asymptomatic, no treatment or surgery is indicated. Spontaneous regression is the usual clinical outcome, taking from 2 to 5 years. NOFs, along with FCDs, are the only benign bone tumors known to consistently regress without treatment. As regression occurs, initially the lytic defect fills in with solid bone, leaving a dense sclerotic focus. Over a period of 4 to 5 years, this radiopaque area loses its density until it eventually blends in with the surrounding cortex.
Large, symptomatic lesions are usually treated by curettage or block excision. Those lesions with superimposed pathologic fracture may be treated conservatively by means of casting immobilization (as was the circumstance in this case presentation), and most fractures will heal, leaving the lesion still present. Occasionally, the lesion may get larger following trauma, and surgical intervention is then the treatment of choice.
Figure 2. Nonossifying fibroma of the distal tibial metaphysis. Note the eccentric geographic lesion with a sclerotic margin and endosteal scalloping, creating a bubbly matrix in the distal tibia. This appearance is very characteristic of nonossifying fibroma.
- Yochum TR, Rowe LJ. Essentials of Skeletal Radiology, 2nd ed. Baltimore: Williams & Wilkins, 1996.
- Drennen DB, Maylahn DJ, Fahey JJ. Fractures through large nonossifying fibromas. Clin Orthop 1974; 103:82.
About the Authors
Dr. Terry R. Yochum is a second generation Chiropractor and a cum laude graduate of the National College of Chiropractic, where he subsequently completed his radiology specialty. He is a Diplomate of the American Chiropractic Board of Radiology and served as its vice-president and president for seven years (1983–1990).
Dr. Michael S. Barry is a 1988 cum laude graduate of Palmer College of Chiropractic. He completed a three-year radiology residency at Logan College of Chiropractic following two years of clinical practice in Las Vegas, Nevada. He received his diplomate in radiology from the American Chiropractic Board of Radiology in 1992.