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INTRODUCTION
Osteoma, a benign and slow-growing osteogenic tumor, is composed of well-differentiated mature bone tissue and is characterized by the proliferation of compact or cancellous bone1. Favorable sites of osteoma are the cranial vault and facial skeleton. Although the most common site of cranial osteomas is the frontal sinus, osteomas only involving frontal bone periosteum are occasionally observed2. Anthropologists have traditionally referred to small circumscribed bony lumps on the skull vault as button osteoma3. Cranial button osteoma has usually been diagnosed and treated in the Department of Neurosurgery or Plastic Surgery in Korean hospitals; however, dermatologists often encounter patients presenting with asymptomatic bony lumps on the forehead. Although button osteoma is easy to diagnose by radiological examinations such as simple radiography, ultrasonography (USG), and computed tomography (CT), dermatologists are unfamiliar with its diagnosis or surgical treatment using an osteotome and mallet. Here, we report the clinical characteristics of 10 patients with button osteomas who visited our hospital.
MATERIALS AND METHODS
This retrospective review involved the medical records of 10 patients diagnosed with button osteoma at the Department of Dermatology, Kyungpook National University Hospital, between January 2011 and August 2014. Patients' medical records included photographs, clinical information, histopathological information, and radiological images.
We analyzed demographic and clinical characteristics through medical record review, such as sex, age, sites, number of lesions, symptoms, disease duration, histopathological finding, radiological findings, and treatment.
RESULTS
Clinical features
1) Sex, age, and disease duration
Among the 10 patients, there were 9 women and 1 man. The mean age was 54.3 years, ranging from 28 to 61 years (Table 1). The mean disease duration was 60.1 months, ranging from 2 weeks to 20 years.
3) Number of lesions
All patients had only 1 bony lump on their cranial vault (Table 1). None had multiple button osteomas such as satellite, nested, or disseminated osteoma.
4) Differential diagnosis
Button osteoma of the forehead should be differentiated from cranial exostosis, ballooned osteoma, epidermal cyst, and frontalis-associated lipoma including intramuscular lipoma4. Eight patients were initially diagnosed with button osteoma, and one each was diagnosed with intramuscular lipoma and epidermal cyst (Table 1).
Histopathological findings
Histopathological findings showed compact and mature bone with lacunae (Fig. 3).
Treatment
Ostectomy with a chisel and mallet was performed for 5 patients. Under local anesthesia, skin was incised horizontally along the wrinkle line. The superficial frontalis fascia, frontalis muscle, and deep frontalis fascia were cut vertically. The button osteoma was cleaved from the skull with a chisel and mallet. Finally, a primary suture was made for wound closure of the frontalis muscle and skin incision line. Among the 5 patients who did not receive treatment, 1 is scheduled to undergo ostectomy, while the others are merely undergoing observation.
DISCUSSION
Button osteoma is not a rare disease and usually presents with asymptomatic small (rarely >1 cm in diameter) bony lumps on the parietal or frontal bone35. There is no difference in the incidence of button osteoma with respect to ethnicity3. However, the incidence between sexes remains controversial356. As for sexual preponderance in our study, button osteoma was 9 times more common in female patients than in male patients. Button osteoma commonly occurs in the second through fifth decades of life25.
However, in the present study, 8 of 10 patients were in the fifth and sixth decades of life. Although the precise etiology of button osteoma remains unknown, it may be related to trauma, infection, developmental abnormalities, etc.7.
The differential diagnosis of button osteoma includes metastatic cancer, subcutaneous hematoma, lipoma, epidermal cyst, and ballooned osteoma. Plain radiography, USG, and CT are useful for diagnosis2. Button osteoma is generally visualized as radiopaque bone lesions including the outer table of the skull8. In the present study, USG was commonly used for imaging bony anatomy, although CT is the best diagnostic imaging tool for button osteoma.
Surgical removal of button osteoma, including ostectomy, curettage, endoscopic surgery, and CO2 laser cauterization, is usually performed for good cosmesis91011. In the present study, ostectomy with a chisel and mallet was used to treat frontal button osteomas. Asymptomatic small frontal osteomas may be followed up at 6-month intervals by physical examination2. Some authors recommend asymptomatic small osteomas should be removed to prevent aggravation or rule out malignancy212.
In conclusion, this study characterized button osteoma. Korean dermatologists need to familiarize themselves with this disease. Further studies with more patients are required to confirm the present results.
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