Nonossifying fibroma - Orthopaedia

Tumor template based on A Clinical Guide to Primary Bone Tumors. Levesque et al.

Tumor biology and incidence

Along with fibrous cortical defects, non-ossifying fibroma, represents the most common benign lesion of the skeletal system. The incidence is estimated at 30-40% in skeletally immature individuals. Multiple lesions are seen in 8% of patients (most have the underlying diagnosis of neurofibromatosis).

Almost indistinguishable from fibrous cortical defects, with the exception of size and the extent of metaphyseal involvement. Both of these disease entities share common clinical presentation, histology, and natural history of pathology. As a result they are commonly referred to as metaphyseal fibrous defects.

Etiology

The etiology of the tumor remains unknown, however, numerous theories have been proposed. Some contend that the tumors develop from mature marrow, with a complete absence of osseous metaplasia. Others believe that they represent the manifestation of a local disturbance at the epiphyseal plate that is eventually replaced by bone.

Age

Peak age of diagnosis is in the 2nd decade of life

Gender

Predilection for males: 2:1 male to female

Presentation

Commonly, the presentation is incidental, with unrelated discovery on plain films. On occasion, patients may present with symptoms of pain and swelling that are related to stress fracture in the area of the lesion, or even a displaced fracture secondary to low-velocity trauma, as a result of the lesion acting as a stress-riser.

Physical findings

Commonly, there are no physical findings associated with the lesion; however, pain can occasionally be elicited on physical exam in the area of the defect. Pain is more common than in fibrous cortical defects due to the larger size and increased risk for pathologic fracture.

Plain films

Occupy an eccentric location in the medullary cavity of the long-bone and usually involve, but do not violate, the adjacent cortex. Radiolucent in appearance, with distinct, sclerotic margins, that tend to be scalloped. Generally, a narrow zone of transition to normal bone exists. The cortex overlying the lesion can have an "expanded" appearance, where the cortex is thinned, but is not violated. Some have attributed this expanded appearance to an absence of the normal remodeling at the metaphyseal-diaphyseal junction. No intralesional mineralization is present. Commonly, one observes a "bubbly" appearance that may be due to septae arising from ridging of the cortex.

Site

Primary sites of involvement are metaphyseal (just as in fibrous cortical defects):
Proximal tibia> distal femur > distal tibia
These locations account for >90% of all nonossifying fibromas (tibia, 43%; femur, 38%; fibula, 8%; humerus 5%)
With advancing pediatric age, the distance from the epiphyseal plate tends to increase.
The lesions can occur in the upper extremities (proximal humerus and distal radius) but they are much more uncommon. One must keep in mind that most nonossifying fibromas are discovered incidentally, therefore, age, gender, and site distributions may be confounded by rates of occurrence and rationale for radiographic evaluation in children.

Size

Length is typically greater than width. Commonly larger than fibrous cortical defects, which usually range from 1-3 cm. In bones with small diameter, the lesion may occupy the entire metaphysis.

Tumor effect on bone/Bone response to tumor

Cortical discontinuity is rarely encountered. Extraosseous extension should raise the suspicion for a tumor other than a nonossifying fibroma. Lesions have a sclerotic, well-demarcated rim. Periosteal reactions are not seen.

Bone scan

3-phase bone scan can be used to detect if the lesion is active, healing, or inactive based on the intensity of the uptake on the scan. Intense hyperemia and positive scan may suggest an associated fracture. Mild hyperemia and moderate bone uptake present during the healing phase. Normal scans are obtained when the lesion is quiescent or has fully healed.

Bone scans should NOT be routinely ordered to diagnose or manage metaphyseal fibrous defects. Use may be indicated in cases where classic radiographic features are absent.

CT Scan

CT scan may be used to verify the exact size of the lesion, identify subtle changes in lesion size over time, and determine the presence of cortical integrity or pathologic fracture.

MRI

MRI can identify a lesion with cystic components, and may be useful to present a more detailed assessment of the local osseous and soft-tissue response. Some variation in appearance has been described on T2-weighted images. All lesions tend to have decreased signal on T1-weighted images. T2 variations in high signal areas tend to stem from the varied amounts of hypercellular fibrous tissue, hemosiderin, hemorrhage, collagen, foamy histiocytes, and bone trabeculae present in a given lesion.

Differential Diagnosis

-       Fibrous cortical defect (includes a ddx of osteoid osteomas, intracortical abscesses, stress fractures, and intracortical osteosarcoma)
-       Aneurysmal bone cyst
-       chondromyxoid fibroma
-       fibrous dysplasia
-       desmoplastic fibroma.

Variant is multiple nonossifying fibroma, which is associated with Neurofibromatosis - von Recklinghausen's disease and Jaffe-Campanacci syndrome (multifocal nonossifying fibromas with . extraskeletal congenital anomalies: café-au-lait spots, mental retardation, hypogonadism, cryptorchidism, ocular anomalies, and/or cardiovascular malformations).

Natural history

Nonossifying fibroma is a benign, self healing lesion. Most undergo spontaneous regression, usually starting at the end of adolescence (as in fibrous cortical defects) and disappear by age 20-25. Due to accelerated rate of skeletal maturation, females tend to encounter earlier regression. Average time from diagnosis to complete spontaneous regression is 29-52 months (most lesions are clinically quiescent during this period of time) for fibrous cortical defects. Due to a larger size, nonossifying fibromas tend to resolve over a longer time course.
The regressive phase is characterized by trabecular bone growth beginning at the periphery of the lesion and progressing centrally, until the bone is fully reconstituted.

Malignant transformation is virtually 0%.

Pathology

Gross examination of biopsy specimens demonstrates fibrous, fleshy, and yellow or tan-brown appearance with variable areas of hemorrhage.

Histologically, these lesions are highly cellular, with fibroblastic/ spindle-shaped cells amid stromal tissue in a prominent storiform pattern. The stroma may contain multinucleated giant cells, foci of xanthomatous reaction with foamy histiocytes, and a substantial amount of hemosiderin pigment in the stromal cells. Mitotic figures or cellular dysplasia are not seen.

Diagnosis and treatment

Diagnosis most often can be made definitively based solely on the patient's history, physical examination, and plain radiographic appearance. If the patient has no symptoms, close observation with serial radiographs is recommended. Screening for multiple lesions is indicated when patient's present with history consistent with neurofibromatosis, Jaffe-Campanacci syndrome, or pathologic fracture.
A limited skeletal survey, to rule out multifocal lesions, should include AP radiographs of both tibias, fibulas, femurs, and humeri.
Observation is the mainstay of treatment. Once detected, fibrous cortical defects and small, asymptomatic nonossifying fibromas can be followed with serial radiographs. If size and appearance remain unchanged 3 months later, the patient may be followed with serial radiographs every 6 months to 1 year until regression occurs or symptoms develop. The rationale behind serial radiograph is to attempt to prevent pathologic fracture. Protected weight bearing is controversial, due to resultant adjacent disuse osteoporosis.

Large nonossifying fibromas that cause pain or swelling may be treated with biopsy, curettage, and autograft/allograft packing (Demineralized bone matrix, allograft bone chips, and ceramics all have been used successfully). This management plan is also advised in those who do not present with typical clinical or radiologic features of the lesion.

Complications

Pathologic fractures-
Most tend to be non-displaced and through the lesion; managed with casting. Following fracture healing, biopsy, curettage, and bone grafting is recommended. If displaced fractures occur, intramedually nailing is not contraindicated to achieve internal fixation.

More common in the lower extremities, composing nearly 90% of all fractures with almost 50% occurring in the distal tibia. No method exists for assessing the risk for pathologic fracture. Size has been evaluated (>50% of the transverse diameter on AP and lateral radiograph, >33mm in weightbearing long bones), however, these criterion are high unreliable in predicting fracture and need for prophylactic fixation.