Tumor-Like Lesions

Abstract

Non-ossifying fibroma (NOF) portrays a spontaneous developmental defect in the metaphysis of cortical and subcortical bone. It consists of hypercellular fibrous tissue with spindle cells (fibroblasts) arranged in storiform or whorled patterns with enclosed multiloculated giant cells, foam cells, cholesterol crystals, and haemosiderin.

Non-ossifying fibroma and fibrous cortical defect have the same histological characteristics. The lesion is defined as fibrous cortical defect if it is limited to the cortex. The lesion is defined as non-ossifying fibroma if it is larger and exhibits extension into the medullary cavity.

Non-ossifying fibroma has an incidence of about 1%, whereas fibrous cortical defect has a much higher incidence of ca. 30% of the normal population during growth. Both lesions have a predilection for males in the first and second decades of life.

Lesions occur almost exclusively in the metaphysis of long tubular bones, the most frequently affected being the distal femur and the proximal tibial metaphysis.

Non-ossifying bone fibromas are asymptomatic and are typically discovered incidentally on radiographs obtained for other reasons. Larger lesions can occasionally produce pain or lead to pathological fractures.