Diagnosis: Cemento-ossifying fibroma (COF)
Benign fibro-osseous lesions encompass a diverse group of entities that can be seen in the head and neck area. The nomenclature for these lesions creates a great deal of confusion. According to the second World Health Organization classification, oral and maxillofacial lesions related to bone are divided into 2 distinct categories: (1) nonneoplastic bone lesions, including fibrous dysplasia; and (2) osteogenic neoplasms.1The latter category includes cementifying fibromas and ossifying fibromas. While previously grouped separately, these lesions are now thought to represent the same tumor at the ends of a continuous spectrum. Tumors in which the main mineralized component is cementum are known as cementifying fibromas. Tumors in which the main mineralized component is bone are known as ossifying fibromas. Tumors with a mixture of mineralized components are known as COFs.
Cemento-ossifying fibromas most often appear in the mandible (75%-89%) and maxilla, but they sometimes can occur in the paranasal sinuses, nasal cavity, and temporal bone.2The age at presentation is reported to range from 3 months to 72 years, with the highest incidence occurring between the third and fifth decades of life. Clinically, symptoms depend on the exact location of the lesion, although COFs may be asymptomatic. Nasal obstruction, sinusitis, headache, ocular disturbances, and proptosis can all be associated with COF of the paranasal sinuses. Extension into the anterior cranial fossa can present with meningitis.3Histologically, there are 3 basic subtypes of COF.4The first type has equal amounts of calcified material and fibroblastic stroma. The calcified structures are composed of bony trabeculae with prominent osteoblastic rims and some osteoclasts. Cementumlike bodies (also known as psammomatoid bodies) are scattered throughout the lesion. The connective tissue consists of spindle fibroblastic cells in a storiform pattern. The second type mostly consists of a storiform cellular pattern, with little bony trabeculae and often without osteobastic rimming. Psammomatoid bodies are seen scattered throughout, as in the first subtype. The third type represents a combination of the other 2 subtypes.The cellular patterns of both the first and second subtypes, including the presence of psammomatoid bodies, are seen throughout lesions and therefore represent a distinct subtype.4
The presence of a cementum-producing lesion in the paranasal sinuses leads to some confusion, as cementum does not seem to originate from the sinonasal tract. Cementum is an acellular form of bone that serves to anchor dental ligaments to the teeth. It is composed of an organic matrix (collagen fibers) with calcium hydroxyapatite crystal deposits and water. Therefore, cementum-producing lesions are thought to originate from the periodontal ligament, thereby differentiating them from lesions that develop in the sinonasal tract. Some authors argue that sinonasal cementifying lesions are the result of ectopic periodontal membrane or from primitive mesenchymal cells in the ethmoid bone.5This theory of incomplete migration, however, does not explain why COFs have been found in more distal areas, such as the tibia.6The presence of lesions outside the periodontal ligament suggests that they are derived from multipotential mesenchymal cells that differentiate into a type of osseous tissue with the same appearance as cementum.7Others contend that these lesions derive from the presence of ectopic periodontal membrane.7
Some authors consider the material seen in these lesions to be cementumlike material and not cementum. Round to oval to irregular calcified structures are prominent features in COFs and are referred to as ossicles or psammomalike spherules in those with a more laminated appearance.8Lesions containing these structures are frequently referred to as (juvenile) psammomatoid (active) ossifying fibromas (POFs), especially when they occur in the extragnathic bone. Some believe that POF is a distinct variant of COF. However, ultrastructural studies show that there are 2 types of calcium hydroxyapatite crystal deposits: one that is deposited along the collagenous matrix fibers (similar to cementum) and one that consists of extracellular deposits that are not related to any obvious fibrillar matrix (corresponding to psammomalike bodies). Electron microscopy reveals that psammomalike bodies are distinct from the laminated or concentric calcification of true psammoma bodies that are seen in other tumors (meningioma or papillary thyroid carcinoma). The calcified ossicles in ossifying fibromas are more similar to true cementum than to psammoma bodies. The World Health Organization now considers COF and POF to be synonymous.9However, one lesion that is distinct from COF is focal cementifying osseous dysplasia (FCOD), which is difficult to differentiate, but certain characteristics aid in the distinction. Radiographically, FCOD shows a close association with tooth apices or previous extraction sites, while most COFs do not show an association with either. Histologically, thick curvilinear trabeculae (“ginger root” pattern) or irregularly shaped cementumlike masses are typically seen in FCOD, whereas thin isolated trabeculae with prominent osteoblastic rimming are more commonly observed in COF.4The combination of radiographic and histologic features aides in the differentiation of COF and FCOD.
On computed tomographic scans, COFs are expansile and circumscribed by a thick shell of bone density with a multiloculated internal appearance and a content of varying density.10The psammomatoid ossicles appear radiolucent or like ground glass. On T1- and T2-weighted magnetic resonance images, COFs are hypointense to muscle. The well-demarcated bony walls are isointense to soft tissue on T1-weighted images and hypointense on T2-weighted images.10The bony wall tends to enhance with gadolinium, suggesting that it is part of the proliferative process, as opposed to a reactive hyperostosis.10In contrast, fibrous dysplasia does not show such well-defined borders.
Without treatment, COFs may behave differently depending on the site of origin. Generally, they occur in the jaw, and the stiffness of the bone tissue can stop the growth of the tumor. However, in the paranasal sinuses, they may continue to grow, eventually destroying local structures. Because of this tendency for local aggressive growth, total excision is recommended.8There is no evidence suggesting that an endoscopic approach is superior to an open approach, or vice versa, but given reports of recurrence, total resection should be the goal of treatment no matter what method is used. Despite the invasive nature of COFs, to our knowledge there are no reports of metastatic disease.2Radiotherapy has not been proved to be effective in these lesions.
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Pathology Quiz Case 1: Diagnosis. Arch Otolaryngol Head Neck Surg. 2010;136(11):1147-1148. doi:10.1001/archoto.2010.198-b