Benign Neoplasms of the Gnathic Bones

Clinical Features

Ossifying fibromas are relatively rare and are found more commonly in the mandible (90%) than the maxilla, specifically affecting the molar-premolar area. Patients in the third to fourth decades are most affected, with a high female-to-male ratio (5 : 1). Small lesions are usually asymptomatic, often incidental findings on routine dental radiographs. Larger lesions may result in significant cosmetic and functional morbidity.

Radiographic Features

Radiographic images are essential to the diagnosis, and a diagnosis should not be rendered without radiographs or their reliable interpretation. Ossifying fibromas are characteristically well-demarcated unilocular or multilocular radiolucent lesions with varying degrees of radiopacity ( Fig. 15.1 ). The radiopacities correlate with the mineralized component of the tumor. Large lesions may cause displacement of teeth, root divergence, or alterations of adjacent structures. Furthermore, a characteristic downward bowing of the mandible may be helpful in developing a radiographic differential diagnosis.

Pathologic Features

Microscopic Findings

Microscopically, lesions are composed of varying amounts of stellate fibrous stroma with diverse types and degrees of mineralized material. The fibrous tissue may be dense ( Fig. 15.2 ) to nearly acellular. The mineralized tissue may appear as cementum-like basophilic deposits, trabeculae of lamellar bone, or trabeculae of woven bone ( Fig. 15.3 ). Characteristically, plump osteoblasts are seen to rim the bony trabeculae. Rare mitotic figures may be seen, in addition to areas of pseudocystic degeneration and hemorrhage.

Ossifying Fibroma—Pathologic Features

Gross Findings

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  Lesions are well circumscribed, usually with a smooth surface

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  Easily separated from bone (“shelling out”)

Microscopic Findings

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  Variably cellular fibrous stroma with calcified tissue

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  Mineralized material may be cementum-like basophilic deposits or trabeculae of lamellar or woven bone

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  Osteoblastic rimming is noted along with mitotic figures

Pathologic Differential Diagnosis

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  Fibrous dysplasia, cemento-osseous dysplasia, active ossifying fibroma

Differential Diagnosis

Quality radiographs and a complete clinical history are required because other BFOLs may be virtually indistinguishable histologically. Radiographically, fibrous dysplasia classically appears with a radiodense “orange-peel or ground-glass” texture that blends imperceptibly into normal bone. Cemento-osseous dysplasia has a varied presentation, with immature lesions appearing primarily radiolucent and more mature lesions becoming more sclerotic and radiodense. The cemento-osseous dysplasias (periapical, focal, and florid variants) are always intimately associated with the tooth-bearing areas of the jaws. An ossifying fibroma is usually a well-defined radiolucent lesion with variable radiodensities. The BFOLS also present very differently macroscopically and intraoperatively. Grossly, cemento-osseous dysplasia is usually submitted as small mineralized, gritty fragments, the result of curetting. Fibrous dysplasia is frequently submitted in a small block or core, the consequence of sampling a lesion that is difficult to distinguish from surrounding normal bone. Finally, ossifying fibroma is generally an intact tumor mass or submitted as large fragments. It is worth noting that osteoblastic rimming is seen less frequently in the other benign fibrous osseous lesions than it is in ossifying fibroma. If no radiographic or clinical information is available, a preliminary diagnosis of BFOL may be rendered until more information can be obtained. However, definitive diagnosis is important because the treatment and prognosis of these lesions are different.

Prognosis and Therapy

Small lesions may be treated with enucleation and curettage, whereas larger lesions may require more extensive surgery with reconstruction. Close clinical follow-up is indicated to monitor the patient for recurrences.

Clinical Features

The juvenile ossifying fibromas are uncommon and are seen with considerably less frequency than their conventional counterpart. Although the trabecular variant is found most commonly in children less than 15 years old and favors the maxilla, the psammomatoid variant is generally seen in those 20 years and older and is most common to the paranasal sinuses. However, both subtypes may occasionally affect older patients. Small lesions may be detected on routine examination or patients may present with rapid, disfiguring growth ( Fig. 15.4 ).

Radiographic Features

Radiographically, the lesion presents as a well-delineated, expansile radiolucent lesion with variable focal calcifications. Lesions may demonstrate invasive growth and affect adjacent structures.

Pathologic Features

Microscopic Findings

The JTOF is characterized by a cellular fibrous background containing trabeculae of immature bone. This bone is varied in shape, often with a thick, irregular collagenous rim ( Fig. 15.5 ). Osteoblastic rimming is a feature of the immature bone. The JPOF has a variably cellular background with small spherical ossicles with distinct osteoblastic rimming ( Fig. 15.6 ). Psammomatous structures are a classic feature of this lesion ( Fig. 15.5B ), although sometimes scant. Concentrically laminated particles may occasionally simulate a genuine psammoma body. In addition, multinucleated giant cells and scattered mitotic figures are commonly seen in either variant.

Juvenile Ossifying Fibroma—Pathologic Features

Gross Findings

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  Lesions are well circumscribed, usually with a smooth surface

Microscopic Findings

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  Cellular proliferation of spindle cells

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  Trabecular variant: immature osteoid, and trabeculae of immature bone with distinct osteoblastic rimming

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  Psammomatoid variant: cementum-like psammomatous structures are variably present

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  Thick, irregular collagenous rim

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  Osteoclastic giant cells are commonly found

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  Mitotic figures are noted

Pathologic Differential Diagnosis

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  Ossifying fibroma, extracranial meningioma

Differential Diagnosis

The differential diagnosis includes the other BFOLs to include conventional ossifying fibroma. Differentiation of these lesions may require clinical, radiographic, and intraoperative data. Extracranial meningioma , especially with lesions of the maxilla, should be a consideration. The clinical and radiographic histories are helpful. The true psammoma bodies of a meningioma are different, as is the pattern of growth (whorled, meningothelial architecture).

Prognosis and Therapy

Tumors continue to enlarge if left untreated, thereby necessitating complete surgical excision. Recurrences are common (up to 58%), resulting in potentially disfiguring surgery requiring reconstruction.

Clinical Features

Central odontogenic fibromas show a predilection for women (3 : 1) and an increased incidence in the second to fourth decades. Lesions may be asymptomatic, although larger lesions may cause jaw expansion and occasional perforation of the cortical plate. The tumor is generally described as a painless mass. Central odontogenic fibromas occur more frequently in the anterior maxilla and may result in a distinctive palatal cleft or depression, considered characteristic of this tumor.

Radiographic Features

Radiographically, most central odontogenic fibromas are unilocular radiolucencies ( Fig. 15.7 ), although multilocular lesions are seen. Lesions frequently present with a well-defined sclerotic border and may be associated with the crown of an unerupted tooth. Rarely, central odontogenic fibromas may appear as mixed radiolucent-radiopaque lesions. In addition, large lesions may affect adjacent structures, move teeth, or even cause root resorption.

Pathologic Features

Microscopic Findings

There is a wide variation of histologic appearances, ranging from densely hyalinized and cellular, to loose and myxomatous, to nearly acellular ( Fig. 15.8 ). Delicate collagen fibers are occasionally identified along with fibromyxoid stroma. It is this variation that has resulted in the historical separation into two types: epithelium-poor type (formally referred to as the simple type) or epithelium-rich type (formally referred to as the WHO type). Features of odontogenic fibromas include inactive-looking odontogenic epithelium that, when present, may appear proliferative ( Fig. 15.9 ) or form irregular islands and cords. In addition, calcifications may or may not be present, simulating cementum, osteoid, or dentin. A rare granular cell odontogenic fibroma variant also exists.

Central Odontogenic Fibroma—Pathologic Features

Gross Findings

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  Encapsulated, firm, smooth yellow-white mass

Microscopic Findings

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  Wide variation of histologic appearances, ranging from loose myxomatous to densely hyalinized stroma

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  Odontogenic epithelium usually inactive, although proliferative type may be present

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  Calcifications may or may not be present

Pathologic Differential Diagnosis

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  Hyperplastic dental follicle, desmoplastic fibroma

Differential Diagnosis

For lesions that are epithelium poor, the microscopic appearance is similar to a dental follicle . Excluding a dental follicle is based on the radiographic and clinical appearance including size and location. Usually this is not a difficult distinction, and one should remember that a hyperplastic dental follicle is a very common entity, whereas the central odontogenic fibroma is exceedingly rare. A cellular central odontogenic fibroma, epithelium-rich variant, may appear similar to a desmoplastic fibroma . However, a desmoplastic fibroma does not have an odontogenic epithelial component nor is it found in association with teeth. In addition, desmoplastic fibromas generally demonstrate a locally infiltrative quality.

Prognosis and Therapy

Surgical enucleation and curettage is usually the treatment of choice. Recurrences are rare.

Clinical Features

Osteoblastoma, as a group, is a relatively rare bone lesion with approximately 10% occurring in the craniofacial bones. The mandible is affected more frequently than the maxilla, particularly the ramus, coronoid process, and condyle. The majority of cases present before 30 years of age, and there is a definite male predilection. Pain, particularly nocturnal, is a common symptom and may mimic a toothache but not relieved by aspirin.

Radiographic Features

Osteoblastomas are typically well-circumscribed, round to oval lesions that are radiolucent to radiopaque. Patchy scattered calcifications may be seen. Osteoblastomas near teeth may rarely cause resorption or displacement.

Pathologic Features

Microscopic Findings

Although there may be subtle histologic differences between osteoblastoma and osteoid osteoma, they are essentially identical. They consist of anastomosing trabeculae of osteoid in a loose fibrovascular stroma ( Fig. 15.10 ). The mineralized component usually shows noticeable osteoblastic rimming along with a characteristic basophilic appearance ( Fig. 15.11 ). Osteoclastic giant cells are usually present and may even be a predominant feature. Extravasated erythrocytes are common.

Osteoblastoma/Osteoid Osteoma—Pathologic Features

Gross Findings

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  Conventional osteoblastomas larger than 2 cm, osteoid osteoma usually less than 2 cm

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  Removed as fragments of red-brown gritty bone

Microscopic Findings

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  Anastomosing trabeculae of osteoid in a loose fibrovascular stroma

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  The basophilic mineralized component shows prominent osteoblastic rimming

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  Osteoclasts are often present

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  Extravasated erythrocytes common

Pathologic Differential Diagnosis

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  Osteosarcoma, cementoblastoma, ossifying fibroma

Differential Diagnosis

The most obvious differential diagnosis is determining whether the lesion in question is an osteoblastoma or an osteoid osteoma, determined primarily based on the size of the lesion. However, differentiating between an osteoblastoma and a low-grade osteosarcoma is most important. Osteosarcoma has atypical features which include pleomorphism, infiltrative growth, and atypical mitosis. The clinical presentation of an osteosarcoma includes pain, loosening of the teeth, and paresthesia. BFOLs are also a consideration, although these lesions generally have a distinct clinical and radiographic appearance. Cementoblastoma, which histologically may be identical to osteoblastoma, is distinguished by direct and intimate association with the tooth root.

Prognosis and Therapy

Usually conservative excision is adequate. Some large lesions may require larger resections resulting in the need for subsequent reconstruction. On rare occasions, lesions have been reported to be locally aggressive.