| disease | Ossifying Fibroma |
| alias | Ossifying Fibroma |
Ossifying fibroma is a congenital structural anomaly composed of fibrous and osteoid tissue, occurring almost exclusively in the tibia and occasionally in the fibula. This condition is often associated with anterior bowing of the tibia and follows the course of a hamartoma. It is a distinct tumor from fibrous dysplasia.
bubble_chart Pathological Changes
1. Macroscopic findings: The bone membrane appears intact, with very thin cortical bone beneath. The tumor within the osteolytic area is dense, presenting as white, yellow, or red in color. Due to fibrous material, its texture is soft but occasionally exhibits a slight gritty sensation.
2. Microscopic findings: Histologically, there are two fundamental characteristics. One is the trabecular bone surrounded by fibrous material, with osteoblasts present around it. The other is a band-like structure.
bubble_chart Clinical Manifestations
Not uncommon, but less frequent than fibrous dysplasia. More common in males. Almost always occurs before the age of 10, with the majority developing symptoms before the age of 5. Typically, it affects the tibia, and occasionally the ipsilateral fibula may be involved, but bilateral occurrence is rare. In the tibia, the lesion is most commonly found in the middle third and may extend toward either end. Additionally, it can occur in the lower third or upper third of the tibia. In the fibula, the lower third is often affected. The typical location of fibrous dysplasia in long bones is the diaphysis, rarely involving the metaphysis.
Painless, often discovered due to swelling or bowing of the tibia. Pathological fractures may occasionally occur, usually complete fractures, accompanied by pain and slight displacement.
X-ray findings generally show an eccentric osteolytic lesion within the cortical bone. The surface of the cortical bone beneath the membrane exhibits varying degrees of expansion and is very thin. The osteolytic lesion on the inner side of the cortical bone and within the medullary cavity is surrounded by a distinct sclerotic line, often resulting in narrowing of the medullary cavity. The osteolytic foci may be solitary or multiple. Involvement of the entire circumference of the tibia is rare, but if the lesion occurs in the fibula, it may affect its full circumference. Multiple lesions and/or involvement of the entire diaphysis in the tibia are uncommon.
bubble_chart Treatment Measures
Since ossifying fibroma of long bones has the potential to self-heal before the age of 5, and the recurrence rate after surgery is high, surgical treatment should not be performed before the age of 5. Between the ages of 5 and 10, surgery should be delayed as much as possible, depending on symptoms. Most pathological fractures do not require surgical treatment. The surgical indications are: ① The lesion is extensive and/or bone strength is weakened, allowing exposure outside the bone membrane and tangential resection; ② Pseudarthrosis of the tibia may require rigid bone fixation with high-strength bone grafts; ③ Severe tibial bowing may warrant osteotomy and correction after the age of 10–12.
The diagnosis is straightforward. It needs to be differentiated from fibrous dysplasia. Sometimes, it requires differentiation from histiocytic fibroma on imaging, especially when the lesion is adjacent to the metaphysis, but the histological distinction between these two tumors is clear.
