View larger version (75K): [in this window] [in a new window]   Figure 2. A technetium Tc 99m scan disclosed evidence of an area of increased uptake in the right zygoma (arrow).

He then removed the outer table of the cortical bone covering the lesion. This revealed a circular lesion 1.0 cm in diameter composed of a gray, gritty and friable material encased by a layer of dense bone. He took a small incisional biopsy and submitted it for a frozen section.

The surgeon made a provisional diagnosis of a benign fibro-osseous lesion. He curetted and submitted the remainder of the lesion for routine histologic examination. He performed a 0.5-cm peripheral ostectomy and immediately reconstructed the defect with a block of porous hydroxyapatite.

The specimen was fixed in formalin. It consisted of firm, gritty tissue, gray-tan and measuring 0.8 x 0.6 x 1.0 cm.

Sections of the lesion revealed a well-vascularized stroma investing trabeculae of an osteoid nidus and a large area of immature bone. Extensive osteoblastic activity was apparent, with the trabeculae being rimmed by layers of plump osteoblasts (Figure 3). The surgical team made a diagnosis of osteoid osteoma on the basis of the clinical history, radiographic studies and histologic examination.

View larger version (173K): [in this window] [in a new window]   Figure 3. Closely packed bony trabeculae of the nidus contrast with the normal-appearing trabeculae in the surrounding bone (hematoxylin and eosin stain, x20 magnification).

	DISCUSSION

TOP ABSTRACT CASE REPORT DISCUSSION CONCLUSION REFERENCES

Clinically, osteoid osteoma usually is an ovoid lesion seldom larger than 1.0 cm in diameter with limited growth potential. It occurs predominantly in males. The age distribution of affected people is eight months to 70 years. Only 17 percent of affected patients are older than 30 years.³

Pain, usually deep and more intense at night, is the principal symptom of the lesion and may be present for weeks to years before surgical treatment is sought. The pain of an osteoid osteoma shows dramatic response to aspirin. This characteristic has been used as a diagnostic tool. Extremely high levels of prostaglandin metabolites (prostaglandin E₂) and prostacyclin (prostaglandin I₂) have been detected in osteoid osteomas; this phenomenon may explain its marked response to aspirin.⁴

The characteristic radiographic appearance of an osteoid osteoma is that of a sclerotic bony margin surrounding a radiolucent nidus with varying degrees of calcification. CT and nuclear medicine are reliable tools for diagnosis when radiographic findings are not specific.

Histologically, osteoid osteomas have variable degrees of calcification and are impossible to differentiate from osteoblastomas. Initially, there is a proliferation of osteoblasts and a well-vascularized spindle-cell stroma. As the lesion matures, osteoid and bony trabeculae increase.

The pathogenesis of osteoid osteomas has remained a source of controversy. Many investigators agree with Jaffe’s¹ original description that this lesion represents a benign neoplastic process. Sherman² studied 30 cases and concluded that the "solitary" nature of the lesion, the lack of signs of inflammation and the absence of systemic manifestations support the neoplastic theory. Vickers and colleagues³ reported that the small size and the self-limited nature favor an inflammatory origin. However, Zmurko and colleagues⁴ and Solarino and colleagues⁵ published reports of multicentric cases. Familial occurrence has been reported by Kaye and Arnold.⁶ This condition has been reported in numerous bones such as the femur, tibia, spine, ribs, mandible, skull and ethmoid.^7–9

Surgical removal of the lesion is the treatment of choice. Recurrence is unusual unless the nidus has been incompletely removed. Feletar and Hall¹⁰ stated that osteoid osteoma has an under-appreciated tendency to regress across time. They also suggested that the clinical and radiographic findings usually are more diagnostic than are microscopic observations.

Several problems arose in ascertaining the differential diagnosis of this case. The difficulty in making a diagnosis of osteoid osteoma was magnified when we considered the anatomical location of this entity. Lesions of the zygoma are rare. Hemangioma is the most frequently reported lesion of the zygoma, but a negative aspiration result easily eliminated a hemangioma from our differential diagnosis. The osteoid osteoma must be differentiated from osteoblastoma, sclerosing forms of osteomyelitis, ossifying fibromas, fibrous dysplasia and osteosarcoma. We used the clinical history combined with radiographic and microscopic findings to finalize the diagnosis of osteoid osteoma.

We chose to treat the lesion somewhat aggressively and to perform an immediate reconstruction with hydroxyapatite because the potential for a residual cosmetic deformity could be eliminated and a second reconstructive stage would not be required. It could be argued that the hydroxyapatite may obscure any recurrences. We think that the lesion was adequately treated; in the unlikely event that the patient should develop a recurrence, the radiodensity of hydroxyapatite should help delineate the existent bony margins.

The osteoid osteoma must be differentiated from osteoblastoma, sclerosing forms of osteomyelitis, ossifying fibromas, fibrous dysplasia and osteosarcoma.

CT-guided percutaneous radio frequency ablation has been reported as the latest successful modality for the treatment of this type of lesion.^11–13 CT-guided resection is simple and safe and seems to be more highly effective in treating this lesion than are traditional methods.^11–13

	CONCLUSION

TOP ABSTRACT CASE REPORT DISCUSSION CONCLUSION REFERENCES

 
In this article, we have presented an unusual case of an osteoid osteoma of the craniofacial bones, as well as a review of the literature and a description of the surgical treatment. To the best of our knowledge, this is the first osteoid osteoma of the zygoma to be reported in the literature. This lesion was diagnosed thanks to the care of the general practitioner, who, aware of the possibility of melanoma metastases, performed a detailed examination and identified the area of the problem, prescribed pain medication to the patient and referred him to the appropriate specialist.

Failure to diagnose a lesion is one of the most common causes for liability in our litigation-prone society. As Dr. Ronald A. Baughman, former president of the American Academy of Oral and Maxillofacial Pathology, said, "There is probably nothing dentists can do to place themselves at greater legal risk than failure to diagnose oral cancer in a timely manner."¹⁴

The general dentist always should have in mind the importance of a timely diagnosis and should perform the steps necessary to either arrive at the final diagnosis or refer the patient to the oral and maxillofacial specialist. This is even more important in patients with a history of cancer, because the most common cancer within the jaws is metastatic carcinoma.

When the dentist is dealing with a possible intraosseous lesion, the following guidelines may help:

– Identify the abnormality and compare it with the opposite side.

– Assess the radiodensity of the lesion: radiopaque, mixed, radiolucent? For example, soft-tissue lesions and cysts usually are radiolucent. Bone lesions are most commonly radiopaque or mixed; foreign bodies are radiopaque.

– Analyze the internal structure of the lesion. Is there only one cavity, or multiple large cavities like a bunch of grapes (multilocular) or small cavities with a honeycomb appearance? Is the lesion associated with a nonerupted tooth? Does it have radiopacities inside, or is its appearance that of a ground-glass lesion? All of this information is helpful. Association with the crown of a tooth usually points to an odontogenic tumor or cyst. Multilocular lesions commonly indicate benign odontogenic tumors, odontogenic keratocysts, cherubism or giant cell tumor. Honeycomb-like conditions may be hemangioma, aneurysmal bone cyst and myxoma. A ground-glass appearance typically signals fibrous dysplasia.

– Evaluate the borders of the lesion. Are they well-circumscribed, sclerotic or surrounded by a radiolucent halo? Are they diffuse or multiple? For example, benign tumors and cysts are well-circumscribed conditions, cancer usually is diffuse, slow-growing benign entities exhibit sclerotic halo, multiple myeloma and Langerhans’ cell disease exhibit multiple lesions, and many odontogenic tumors show radiolucent halo.

– Evaluate the extension of the lesion and its time of evolution.

– Assess the symptoms.

– Correlate your findings with clinical manifestations reported in the literature and a laboratory test when applicable.

An algorithm representing the maxillofacial lesions with radiographic manifestations is helpful in formulating a differential diagnosis. The data obtained by following these guidelines may lead the dental professional to a logical differential diagnosis—one that, although unusual, might point to an osteoid osteoma.