An Isolated Laminar Osteoma Arising in the Maxillary Sinus

Background

An osteoma is a benign tumor that develops through the proliferation of mature bone substance; osteomas are primarily composed of mature compact or trabecular bone [1]. The most common site of predilection is the mandible, followed by the paranasal sinuses. The anatomic location is the frontal sinus in 96% of cases, ethmoid sinus in 2% of cases, and maxillary sinus in 2% of cases [2]. Osteomas grow slowly and may spread to surrounding structures, resulting in serious complications such as orbital lesions and intracranial invasion before they are discovered incidentally during radiographic examination [3]. Additionally, most osteomas are usually contiguous with bone tissue and are rarely free [4]. In the present report, we describe our experience with a free osteoma arising in the maxillary sinus.

Case Report

A 52-year-old asymptomatic man was referred to our hospital by his general dentist who found a round radiopaque region in the right maxillary sinus. There were no special remarks in his history or his family history. His facial features were symmetrical, he had no nasal obstruction, and there was no tenderness or sensory abnormality in the right cheek or suborbital area. There was no buccal bulging of the right maxillary molar and no tenderness. Panoramic radiographs (Figure 1A) and computed tomography (CT) images (Figure 1B, 1C) showed a well-defined, round, 2.5×2 cm radiopaque mass protruding from the base of the right maxillary sinus into the maxillary sinus, with no continuity between the mass and the root of the right maxillary molar. An osteoma in the right maxillary sinus was diagnosed. We considered removing the lesion after it grew larger and symptoms occurred, but we also explained to the patient that although this was a benign tumor, there was a possibility of malignant transformation, even if rare. We further pointed out that the free osteoma might migrate to other sinuses such as the frontal sinus, in which case an extraoral approach would be necessary, and that scarring might occur outside the oral cavity. The patient provided informed consent for early removal, and the lesion was extracted using the modified Caldwell-Luc method under general anesthesia (Figure 2). A U-shaped bone window was created using an ultrasonic bone cutting device (“Piezosurgery®”) in the anterior wall of the maxillary sinus at the level of the right maxillary molar, with the periosteum attached (Figure 2A). Subsequently, an osteotomy was performed at the upper edge of the window, and the mucoperiosteal valve was elevated and opened together with the anterior maxillary wall. A white bony hard spherical mass measuring 2.7×2.3 cm, surrounded by edematous maxillary sinus mucosa, was observed in the lower part of the maxillary sinus (Figure 2B). The mass was free within the maxillary sinus when the sinus was opened, which allowed easy removal of the mass. After removal, the bone wall was fixed in position and the wound was closed with absorbable sutures. The final histopathological diagnosis was laminar osteoma, and the tumor consisted of dense laminar bone tissue covered by the maxillary sinus mucosa (Figure 3A–3C). Panoramic radiographs and CT scans taken immediately after surgery confirmed the absence of residual lesions in the maxillary sinus, and subsequent followup panoramic radiographs were obtained every year, in consideration of both the time required for a benign osteoma to recur as well as the risks associated with radiation exposure. At present, 7 years have passed since the surgery without any recurrence.

Discussion

An osteoma is a fibrous and bony lesion of the sinuses found in 3% of sinus CT scans, most commonly in the frontal and ethmoid sinuses [5]. A study of 16 000 sinus X-ray films indicated that osteomas were present in 0.4% of the radiographs. Of this small number, only 5.1% of all sinus osteomas were in the maxillary sinus [6]. Osteoma in the maxillary sinus develops slowly and is often asymptomatic. However, nasal symptoms such as swelling, pain, nasal obstruction, and rhinor-rhea have been reported due to complications of sinusitis or pressure caused by the development of the osteoma [3]. The present case was incidentally discovered on a panoramic radiograph taken during dental treatment, and there were no subjective symptoms. Borumandi et al noted the association between Gardner syndrome and osteomas, especially cranio-facial osteomas [7]. In the present case, there were no dental anomalies such as embedded or supernumerary teeth, no history of gastrointestinal diseases such as colorectal polyps, and no family history of hereditary diseases, suggesting no association with genetic diseases such as Gardner syndrome.

Various theories (developmental, traumatic, and infectious) have been proposed for the pathogenesis of sinus osteoma. Varboncove et al [8] postulated that osteomas arise from embryonic cartilage remnants or a persistent periosteum. In other words, it has been suggested that an osteoma is a post-traumatic or post-inflammatory product, and a possible etiology is the stimulation of the embryonic cartilage remnants [8]. Kaplan et al also suggested that a combination of trauma and muscle traction may be involved in the development of osteomas [9]. In contrast, it has been reported that sinusitis mostly involves only the mucosa; however, sometimes the lesions spill over to the bone [10]. It has also been reported that chronic inflammation of the periosteum deep in the mucosa promotes bone formation, which is a factor in osteomas arising in the maxillary sinus [11]. Thus, no single theory can adequately explain osteomas, and the topic remains controversial.

Maxillary sinus osteomas are slow-growing and usually asymptomatic; however, their anterior extension can cause facial deformity. Further, their continued growth can completely obstruct the sinuses and nasal cavity, leading to the development of myxomas [12]. The symptoms include pain, swelling, sinusitis, and nasal discharge. Rarely, they may enlarge into the orbit, causing diplopia, ptosis, and vision loss. Koivunen et al reported that asymptomatic, small osteomas do not require surgical treatment and can be observed on routine radiographic imaging but should be excised when they fill 50% of the sinus volume [13]. Although the present case was asymptomatic, surgery was performed to confirm the diagnosis and avoid possible future inflammation. The patient had a free osteoma that had separated from the bone of the maxillary sinus wall; however, free osteomas that are separate within the maxillary sinus are extremely rare. Yamaguchi et al reported in a Japanese paper that the possible causes of free osteoma include (1) osteoma detachment from the sinus wall due to osteoclast action on the stem, and (2) inflammatory tissue destruction due to concomitant sinusitis; but it is difficult removed via endoscopy if it is small; however, the Caldwell-Luc method is known to be used to remove large osteomas. In the present case, we also considered different approaches; that is, open surgical versus endoscopic trans-nasal excision. However, if the osteoma is larger than the natural foramen, it is difficult to remove it nasally in a single lump [14]. In addition, we thought that the lesion might remain and cause inflammation if the osteoma was crushed into small pieces and then removed endoscopically. In this case, the osteoma was large, exceeding 2 cm; thus, the Caldwell-Luc technique was selected as the treatment method. Histopathologically, osteomas are classified into 3 types: compact osteoma, consisting of dense laminar bone without a marrow cavity; cancellous to determine the cause [4]. In the present case, the cause of the migration of the osteoma could not be identified. There was no history of trauma, and the thickening of the maxillary sinus mucosa and the presence of apical periodontitis in the right upper second molar suggested the involvement of chronic inflammation. Osteoma in the maxillary sinus can be osteoma, with a marrow cavity; or mixed type, with cancellous osteoma being the most common type [15]. The present case was of a compact osteoma, which is extremely rare among free maxillary sinus osteomas.

Conclusions

In this report, we present a case of a free osteoma in the maxillary sinus that was removed using the Caldwell-Luc method. Osteoma in the maxillary sinus is very rare, and to the best of our knowledge, this is the first report in English of a free osteoma in the maxillary sinus. It was suggested that the cause of this free osteoma in the maxillary sinus may be related to maxillary sinusitis caused by tooth decay or other factors.