Osteofibrous dysplasia: A case report and review of the literature.

Osteofibrous dysplasia (OFD) is a rare bone tumor affecting young individuals. The differential diagnosis between OFD and adamantinoma may be challenging in some cases on imaging. We present a case of OFD and discuss the key imaging and histological findings. We also discuss the differential diagnosis between OFD and classical adamantinoma on the basis of recent literature.

Case report

A 27-year-old man presented with a complaint of a mild pain in his right leg, persisting for some months. The pain occurred mainly during the day, with some occasional pain during the night. At clinical examination, the pain was elicited by passive movement and digital compression. Leg mobility was normal.

Radiographs of his right knee and leg showed a large focal area of cortical thickening measuring 5.5 × 1.5 cm along the anterior proximal aspect of the tibial shaft (Fig. 1). Multiple roundish, radiolucent lacunae ranging from 5 to 10 mm in size were visible within the lesion, with a “soap bubble” appearance. The lesion borders were well marginated, without a transitional zone. No periosteal reaction was observed on plain films.

Figure 1

27-year-old man with osteofibrous dysplasia. Lateral (A) and anteroposterior (B) radiographs of the right proximal tibia.

Computed tomography (CT) confirmed the absence of a transitional zone and periosteal reaction (Fig. 2). On MR imaging, the lesion showed very low signal intensity on both T1-weighted and T2-weighted images. The radiolucent lacunae observed on X-rays and CT were of intermediate signal in all sequences. No invasion of the nearby soft tissues was observed. The medullary bone marrow surrounding the lesion was normal (Fig. 3).

Figure 2

27-year-old man with osteofibrous dysplasia. Axial (A) and sagittal (B) CT scan. The radiolucent lacunae have a “soap bubble” appearance (white arrows). The cortical is thickened without any periosteal reaction.

Figure 3

27-year-old man with osteofibrous dysplasia. Axial (A, B) and sagittal (C, D) T1- and T2-weighted MR images. The cortical lesion is of low intensity in both sequences (white arrows). The lacunae within the lesion are of intermediate signal on T1- and T2-weighted images.

On the basis of the imaging features, a diagnosis of OFD was made. This diagnosis was confirmed by biopsy, which was performed under CT guidance.

Discussion

Osteofibrous dysplasia (OFD), also known as ossifying fibroma of the long bones, is a rare benign tumor. OFD occurs during the first decade of the life, with a slight prevalence in males (sex ratio= 3:2) (1).

OFD is typically located at the tibial diaphysis. Rarely, OFD can be observed in the fibula (2), radius, and ulna (3). OFD is generally asymptomatic. Therefore symptomatic OFD should raise the question of an associated pathological fracture (1). When sufficiently advanced, OFD can lead to enlargement or a bowing of the tibia (1).

On imaging, the typical problem with OFD is distinguishing it from adamantinoma, a malignant bone tumor of young individuals, aged between 15 and 40 years, and typically arising from the tibia (1).

On radiographs and CT, OFD appears as a cortical thickening interspersed with multiple roundish lytic areas with a “soap bubble” appearance. Usually, neither periosteal reaction nor a transitional zone are observed around OFD (1, 2, 3). Unlike OFD, classical adamantinoma presents moth-eaten borders and extensive involvement of the cancellous bone.

OFD is generally smaller than classical adamantinomas; the mean reported size is 13.2 cm and 6.1 respectively (4). OFD is typically solitary, while fibular skip lesions may be associated with adamantinoma (1).

At histology, OFD is characterized by the presence of osteoid tissue, fibrous tissue, and a small amount of epidermoid cells (1, 3, 5) (Fig. 4). An immunohistochemical essay is mandatory in some cases to detect epidermoid cells, which are not visible on standard hematoxyline and eosine (H & E) because of their small number.

Figure 4

27-year-old man with osteofibrous dysplasia. Immunohistochemical specimen:(cytokeratin antibodies; magnification x40). Note the paucity of cytokeratin-positive cells, confirming the diagnosis of OFD (see text). OM: osteoid matrix; FT: fibrous tissue.

In adamantinoma, epithelial cells are not isolated, but large clusters of cytokeratin positive cells surrounded by fibrous tissue are visible on H & E stain and are confirmed at immunohistochemistry (1, 3, 5).

More recently, a intermediate lesion, between OFD and the classical adamantinoma—the so-called osteofibrous dysplasia-like adamantinoma (OFD/LA)—has been described (1).

In ODF/LA, the number of epithelial cells is greater than that seen in OFD. Sometimes epithelial cells are readily identifiable on H & E-stained specimens of ODF/LA. The histological differential diagnosis of classical adamantinoma, OFD/LA, and OFD depends mainly on the number of cytokeratin-positive cells present (1, 3, 5).

When a biopsy is performed, care must be taken to obtain tissue from the center of the lesion (1, 5). Indeed, it has been demonstrated that foci of OFD/LA with epithelial cells are present at the periphery of classical adamantinoma. Hence, imaging plays a key role in guiding biopsy (1, 5).

Up to 25% of OFD cases spontaneously regress at puberty. Hence, when local recurrence of OFD is seen after curettage, further surgery is generally indicated only in case of large lesions persisting in adulthood (2,7).

Adamantinoma, on the other hand, should be treated with wide local resection, often followed by reconstructive surgery (1, 5). Metastatic involvement, especially of the lung, must be ruled out on imaging.

In conclusion, OFD and adamantinoma share many common histological features but can be distinguished on imaging in most cases. Biopsy may be necessary in challenging cases.