Case #8

• As always, pay attention to the patient's age. The fact that the lesion did not produce symptoms and was found incidentally suggests benignancy.

• Plain radiograph shows a sharply demarcated, lucent, loculated, meta-diaphyseal lesion surrounded by a rim of sclerotic bone. The lesion predominantly involves the lateral portion of the bone and produces mild cortical expansion.

• Curettage specimen consisted of firm red-tan tissue with few small yellowish areas. Low power view showed a moderately cellular lesion composed of uniform spindle cells in a storiform pattern and scattered giant cells; .

• Spindle cells had bland appearance. Mitotic figures were easily found averaging 4 per 10 hpf. However, no atypical mitoses were identified.

• Multiple collections of foamy histiocytes (xanthoma cells) were seen throughout the lesion. Other fields showed hemosiderin-laden macrophages.

Diagnosis: Non-Ossifying Fibroma (NOF)

(fibrous cortical defect, or metaphyseal cortical defect)

• NOF is a common, non-neoplastic, self-healing lesion occuring in skeletally immature individuals, usually between the ages of 5 and 20 years. Small lesions are usually incidental radiological findings. The larger lesions occupying more than a half of the bone diameter may present with a pathologic fracture.
• Location. In most cases, NOF presents as a solitary lesion in the metaphysis or meta-diaphysis of the long bone at the knee (distal femur, proximal tibia or fibula), distal tibia and proximal humerus. A syndrome of multiple non-ossifying fibromas and cutaneous cafe au lait spots is known as Jaffe-Campanacci syndrome.
• For lesions that have the histologic features of NOF but occur in unusual locations such as pelvis, ribs or vertebrae, some authors use the term "benign fibrous histiocytoma". However, the designation remains controversial and is not generally accepted.
• GCT may enter your differential diagnosis. Remember, however, that it is characterized by the epiphyseal location and occurrence in adults.