ŠThe Maxillofacial Center for Diagnostics & Research
* Dedicated to Thomas Bond Jr., MD, of
Baltimore, Maryland -- Father of Oral Pathology
The osteoma is a benign neoplasm of the surface bone, usually occuring in and around the sinuses, jaws and scalp. It first occurs in young adults or teenagers and usually remains less than 2 cm. in size after years of slow enlargement. No treatment is needed except for cosmetic purposes or when the mass interfers with proper chewing and speaking. Some persons with multiple osteomas have them as part of a broader inherited disease, Gardner syndrome, which also has skin cysts and fibrous tumors, as well as many polyps in the intestines. The polyps have a strong tendency to transform into cancers.
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The osteoma is a benign neoplastic proliferation of the bony cortex. Composed of mature compact or cancellous bone, this tumor is essentially restricted to the craniofacial skeleton and is extremely rare in other bones. As with hemangioma, the osteoma may not always be a true neoplasm. Some lesions designated as "osteoma" may represent the end stage of an injury or inflammatory process or the end stage of a hamartomatous process, such as fibrous dysplasia. In certain instances, such as those arising in Gardner syndrome, it behaves much like a developmental anomaly. The common palatal and mandibular tori and buccal exostoses are not considered to represent osteomas, although they are histopathologically identical. The prevalence of true osteoma is unknown, but it is not a common diagnosis in oral pathology biopsy services.
Clinical Features: The osteoma is typically a lesion of teenagers and young adults, and there seems to be no gender predilection. The walls of the paranasal sinuses are most often involved, followed by the jawbones and the calvarium. Usually a solitary, asymptomatic, sessile or polypoid mass of the cortex (periosteal osteoma), this lesion enlarges slowly, sometimes reaching several centimeters across and resulting in facial deformity (Figure 1) or interference with masticatory function. At surgery the mass has the same consistency and color as the surrounding bone or may present as an ivory-like excrescence. Some authorities accept a medullary form of this lesion, called endosteal osteoma.
An osteoma involving the mandibular condyle may cause a slowly progressing shift in the patient's occlusion, with deviation of the midline of the chin toward the unaffected side. This condylar mass is designated osteoma by some as hyperostosis by others. An osteoma intruding into the paranasal sinuses may result in sinusitis, headache, or ophthalmologic dysfunction.
On radiographs the osteoma presents as a well circumscribed, uniformly radiopaque oval area, often superimposed over the underlying bone so as to appear to arise from the medullary spaces (Figure 2). With proper orientation the attachment to the cortical base becomes obvious (Figure 3). Some lesions show a sclerotic peripheral rim with a central trabecular pattern (Figure 4). MRI or CT scans may be necessary to establish the external nature of the bony mass.
The radiographic differential diagnosis is extensive but must include condensing osteitis (focal chronic sclerosing osteomyelitis) ,late stage central ossifying fibroma or odontoma, and idiopathic osteosclerosis. By tradition, bony masses of the palatal midline and lingual mandibular bicuspid region are called tori (torus palatinus and torus mandibularis), while multiple bony masses of the facial surfaces of the maxilla or mandible are called buccal exostoses.
A subset of persons with maxillofacial osteomas, usually multiple (Figure 4), are affected by the autosomal dominant hereditary disease, Gardner syndrome. Gardner syndrome is rare and is considered to represent a variant of familial colorectal polyposis. It is characterized by multiple adenomatous polyps of the colon and rectum (Figure 5), multiple osteomas, cutaneous epidermoid cysts (Figure 6) and subcutaneous fibromas. Multiple odontomas, supernumerary teeth, and impacted teeth are also seen in patients with Gardner syndrome, but the reported prevalence varies.
The osteoma in Gardner syndrome may occur in any bone but it is particularly common in the jaws and frontal bones, as well as in the paranasal sinuses. It is often seen in the region of the mandibular angle and all jawbone osteomas are similar in appearance and behavior to the solitary osteoma described above. The presence of multiple osteomas of the facial bones may be the first sign of this condition, hence, the patient should be evaluated for other manifestations
Pathology & Differential Diagnosis: The osteoma shows two histopathologic patterns, compact and cancellous. The compact osteoma is composed of histologically normal, dense, lamellar bone with few marrow spaces (Figures 7 & 8). The cancellous variant is composed of intertwining bony trabeculae separated by fatty or fibro-fatty marrow. Osteoblastic activity is usually minimal, but when prominent the lesion must be distinguished from osteoblastoma of the medullary spaces. Osteocytes are intact and inflammatory cells are not seen in the marrow and blood vessels are not dilated. The osteoma of Gardner syndrome is usually of the compact type.
Treatment and Prognosis:. Treatment is not required for the osteoma unless it is symptomatic or has resulted in cosmetic deformity or dysfunctional motion of the jaws. Radiographic follow-up on a 6 month schedule is recommended for two to three years, with two additional annual films thereafter. There is no malignant transformation potential, but persons with multiple lesions should be evaluation for Gardner syndrome. The major problem for patients with Gardner syndrome is a high risk of malignant transformation of bowel polyps into invasive adenocarcinoma. By age 30, more than 50% of patients with Gardner syndrome have developed a colorectal carcinoma. The frequency of malignant change approaches 100 percent in older patients. Prophylactic colectomy is usually recommended. Removal of large epidermoid cysts of the skin may be indicated for cosmetic reasons, but, as with the jaw osteomas, they have no malignant transformation potential.
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Figure 2: Osteoma of the lateral wall of the maxillary sinus (radiopaque oval) appears to be within the bone. (photo courtesy of Dr. E. LaLonde, California) [return to text]
Figure 3: Reverse image occlusal radiograph shows less dense, sessile bony mass of the facial surface of the left anterior mandible (lower right in photo). [return to text]
Figure 4: Numerous osteomas of the maxillofacial bones are seen in a patient with Gardner syndrome. [return to text]
|Figure 5: Multiple small polyps of the colon wall in patient with Gardner syndrome. [return to text]|
|Figure 6: Large epidermoid cysts from back and thigh in patient with Gardner syndrome. The keratin-filled cysts have a yellowish hue. [return to text]|
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