Benign tumors of the anterior cranial base can arise from different locations. Intracranial tumors, such as meningiomas, can secondarily involve the cranial base and extend into the paranasal sinuses or nasal cavity. Bone tumors originating from the cranial bone include benign fibro-osseous lesions such as osteomas and ossifying fibromas. The most common extracranial tumors that can extend to the cranial base include hemangiomas and inverted papillomas. Detailed discussions on meningiomas, osteomas, hemangiomas, and inverted papillomas can be found in the relevant sections. This section focuses on ossifying fibroma.
Ossifying fibroma is a benign bone tumor that predominantly affects adolescents. The condition frequently involves craniofacial bones, with the frontal, ethmoid, and sphenoid bones being commonly affected.
Etiology
The specific cause remains unknown, and the following hypotheses have been proposed:
- Trauma may facilitate the occurrence of the lesion.
- Fibroconnective tissue undergoes neoplastic-like proliferation, leading to the formation of structures resembling bone tissue.
Pathology
Macroscopically, ossifying fibromas typically have a broad base, are hard in texture, and are encased by a thin layer of cortical bone. Their internal structure consists of dense, uniform, sand-like material.
Under the microscope, the tumor exhibits a sparse arrangement of elongated and spindle-shaped fibroblastic stroma interspersed with scattered bone islands, trabeculae, and osteoid tissue. The edges of the bone trabeculae are surrounded by osteoblasts.
The classification of ossifying fibroma is based on the proportion of fibrous and bony components within the tumor:
- Ossifying Fibroma: Primarily composed of fibroblasts, with bone-like structures and trabeculae occupying only a small portion of the tumor.
- Fibro-Osseous Tumor: Predominantly consists of bone, with varying forms of bone trabeculae that gradually undergo calcification.
Clinical Manifestations
Ossifying fibroma is often solitary, with a higher incidence in females than in males. Due to its slow growth, it is initially asymptomatic and thus difficult to detect. As the tumor enlarges, it may compress or invade adjacent structures, resulting in symptoms. Examples include cranial base destruction, exophthalmos, and displacement of the eyeball when the orbit is affected. Nasal bridge widening and facial deformities may occur if the tumor invades the nasal bones. Nasal symptoms, such as varying degrees of nasal obstruction, are common, while epistaxis is relatively rare.
Imaging Examinations
CT scans are valuable for diagnosing and assessing the extent of the lesion. Ossifying fibroma typically appears as a single round lytic lesion with well-defined margins. It displays high density, causes expansive growth into surrounding areas, and induces atrophy of adjacent bone structures. A thin hyperdense rim is often visible at the tumor's edge, and internal mineralization within the tumor varies, resulting in inhomogeneous density patterns.
Diagnosis
The clinical manifestations of ossifying fibroma lack specificity. Diagnosis primarily relies on imaging techniques such as X-ray and CT, as well as pathological biopsy. In cases where extensive bone destruction is observed and distinguishing the lesion from a malignant tumor is difficult, biopsy becomes essential.
Treatment
The only effective treatment for ossifying fibroma is radical surgical excision. The main goals of surgery are to restore organ function and improve cosmetic deformities. The surgical approach should be determined based on the location of the tumor. Complete removal of the lesion's bony shell is critical for preventing recurrence. For tumors with extensive size, excision in stages or sections can be performed.
Ossifying fibroma has a low risk of malignant transformation, estimated at around 0.4%–0.5%, most commonly observed in patients with repeated surgeries or those exposed to radiation therapy. If malignancy occurs, treatment should follow the protocols for fibrosarcoma or osteosarcoma management.