Ⅰ. INTRODUCTION
The latest WHO classification of head and neck tumors (5th edition), published in 2022, categorized fibrous dysplasia (FD), cemento-osseous dysplasia, ossifying fibroma, familial gigantiform cementoma, and osteochondroma into the Fibro-osseous Tumours and Dysplasias group. Cemento-ossifying fibroma (COF) was reclassified into Benign Mesenchymal Odontogenic Tumors1. In this category, FD and COF have different origins with the same clinical swelling pattern but different radiographic and pathologic findings. Radiologically, COF shows a number of patterns depending on the degree of mineralization of the lesion, and FD shows a ground glass pattern. Histologically, COF shows highly cellular fields with some calcified areas, and FD shows a Chinese letters/characters pattern. Treatment and follow-up methods differ depending on the characteristics of each lesion. Herein, we report a case of two adjacent lesions and the treatment method applied.
Ⅱ. CASE REPORT
A 14-year-old male was tentatively diagnosed with an ossifying fibroma on the right mandible and referred to the Department of Oral and Maxillofacial Surgery at Seoul National University Dental Hospital. The past medical history of this patient was non-specific. On intraoral examination, #45 distal eruption with #85 partial resorption was observed (Fig. 1A).
Computed tomography (CT) showed a benign fibro-osseous lesion in the right mandible (#43–46 area). In the first half of the lesion (#44 and #45), high-attenuation soft tissue was observed in the background as well as amorphous bone formation, the lesion was pushing teeth #44 and #45 mesially and displacing the right mandibular canal downward. And the posterior aspect of the lesion showed homogeneous radiopacity (Fig. 2A, 2B, 2C). Radiographically, the #44/45 lesion showed cemento-ossifying fibroma (COF), and the posterior part was similar to fibrous dysplasia (FD). Surgery was considered for the site presumed to be COF but not for the FD excitation site.
The patient underwent surgical extraction of #85 and #45 and mass excision of the right mandible under general anesthesia. After extraction of #45 and #85, the lesion was removed, with some lesion peeled off like an onion skin. The posterior part of the COF was easily separated from the posterior FD because the margin was well formed2.The outer shape was maintained after removing the lesion (Fig. 1-B, C). The specimens were sent to the Department of Oral Pathology. On histology, a thin fibrous capsule surrounding the lesion and fibrous stroma and cementum-like calcifications were observed. The specimen was diagnosed as benign fibro-osseous lesion, consistent with COF (Fig. 3).
After surgery, the patient did not experience sensory change in the right lip and mentum. At the 4-month and 10-month follow-up visits, clinical symptoms such as discomfort were not observed. The pattern of bone healing at the surgical site was confirmed on the follow-up panoramic view (Fig. 2E, 2F). Continuous follow-up is planned to evaluate changes such as rapid FD growth or need for contouring surgery in adulthood.
Ⅲ. DISCUSSION
Reports of FD occurring with other adjacent lesions are rare but do exist. FD accompanied by central giant cell granuloma (CGCG), peripheral giant cell granuloma (PGCG), or peripheral osteoblastoma (POF) as a hybrid lesion has rarely been reported in the literature. Approximately 84% of hybrid cases occur in the mandible, especially in the posterior region 3. However, such hybrid occurrences adjacent to the COF and FD which have different origins have not been reported. FD is a benign fibro-osseous hyperplastic/dysplastic disease of medullary bone, and COF is a disease derived from the periodontal ligament.
FD of the craniofacial bones is a benign, non-neoplastic, intramedullary, cellular proliferation of fibroblasts, resulting in ovate calcification of bones with unclear and unencapsulated boundaries or irregular tricuspid formation. Developmentally and behaviorally, most lesions occur in late childhood or early teens, undergo a short proliferative phase lasting 1–3 years, and then become quiescent. Asymmetry, displacement of one or more teeth, and malocclusion are frequent clinical features4.
COF is a benign fibro-osseous tumor. The WHO classifies COF as a fibro-osseous neoplasm, included among the non-odontogenic tumors, derived from the mesenchymal blast cells of the periodontal ligament, and with a potential to form fibrous tissue, cement and bone, or a combination of such elements5. COFs consisting of these elements are mostly benign neoplasms that affect the mandible and demonstrate slow, well-defined growth.
1. Radiological characteristics
On radiography, FD is characterized by homogeneous diffuse radiopacity with a ground glass appearance and is continuous with normal bone, from which it cannot be clearly distinguished. In addition, CT shows bone expansion and thin cortical bones6. Although clearly defined in FD as false boundaries that tend to be mixed with unaffected bones in fibroblasts, COF has stroma hypercellularity with a mineralized matrix possessing clear boundaries and variable proportions of tissue, such as bone and cement. Differences in opacity within the lesion appear to correlate with the duration of the tumor7.
2. Histological characteristics
The osseous component of FD usually appears as elongated trabeculae of woven or lamellar bone with irregular curves, commonly referred to as a Chinese letters/characters pattern. FD does not possess eosinophilic osteoid-like material in the periphery of the trabeculae, as frequently observed in ossifying fibromas, and does not contain the so-called brush borders in the osseous component, as in ossifying fibromas6. The most useful microscopic feature to differentiate FD from ossifying fibroma is the relationship between its margins and the adjacent normal bone. Microscopic examination reveals a fusion of FD to the surrounding bone. However, in COF, there is a clear separation of the lesion from the surrounding normal bone due to the presence of a thin fibrous capsule2. The above characteristics can easily separate the COF during surgery. In the present study, cellular fibrous stroma and various shapes and sizes of focal cementum-like dense bone calcifications were observed (Fig. 3).
3. Treatment
FD is a disease that generally does not require surgery, usually progressing from 18–20 years of age and then halting growth. Surgical reduction is usually performed for cosmetic and functional reasons8. Surgery during growth is often disappointing because relapses are common. However, if significant growth occurs in a short period of time, more active surgical intervention, including resection, can be considered. In such a case, cosmetic surgery should be considered through continuous follow-up to check deformities.
Although 50% of COF are asymptomatic, they grow slowly and can lead to facial asymmetry. The mass causes discomfort or bone expansion and possible displacement of teeth9. Therefore, surgical removal is recommended and is simple because the tumor is well-distinguished from bone10.
In the present case, COF was suspected in the area of bone expansion, internal fibrous change, and calcification observed on imaging, and the posterior glass shape appeared as cortical bone thinning. pattern indistinguishable from bone, which is a feature of FD, was identified. Because COF and FD occurred adjacently, a decision was made to remove only the COF using the appropriate surgical method, to evaluate the morphological change of the FD on follow-up, and to perform resection if necessary. In the present case, a slightly enlarged right mandible produced facial asymmetry; however, contouring of FD was not performed because the patient did not complain of aesthetic concern and growth period.
Ⅳ. CONCLUSION
Reports of FD occurring with other adjacent lesions are rare. In the present case in which FD and COF were adjacent, mass excision was performed for the COF and follow- up for FD. Adjacent lesions with different origins are diagnosis through preoperative radiologic and clinical evaluation and treatment or follow-up should be performed according to the recommendation for each lesion. Due to the lack of understanding of mixed lesions, incorrect treatment planning due to inaccurate diagnosis is possible; thus, all rare hybrid lesions should be reported in the literature for better understanding.
1. Availability of data and material
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
List of abbreviations: COF (cemento-ossifying fibroma), FD (fibrous dysplasia), CT (computed tomography)
