Introduction
Myoepithelioma is a relatively common benign tumor that exhibits various cellular morphologies. It primarily occurs in soft tissues, most commonly in the head and neck region, particularly in the salivary glands.1) Cases of intraosseous myoepithelioma have rarely been reported, with documented occurrences in sites such as the cranium, maxilla, iliac bone, vertebrae, tibia, and fibula.2,3) In this report, we aim to report a rare case of an asymptomatic myoepithelioma arising within the zygomatic bone.
Case report
A 51-year-old male visited to the outpatient clinic presenting incidental finding of a left zygomatic intraosseous mass on a CT scan. Radiological assessment for upper eyelid mass showed the ill-defined osteolytic mass at left zygomatic bone on the CT images. The patient had no significant past medical history except a prior excision surgery for an ipsilateral upper eyelid mass, which was lacrimal gland carcinoma without local and distant metastasis (T2aN0M0).
Thorough physical exam was performed. At frontal view, patient’s malar contour seemed symmetrically (
Fig. 1). Upon palpation, the contour of the zygomatic bone was smooth and painless, with no palpable lump. The CT scan showed a focal osteolytic lesion with contrast enhancement invading the body, frontal process, and temporal process of the left zygoma (
Fig. 2). Cortical thinning was observed around the mass at CT image. A surgical excision was planned for diagnostic purpose.
Fig. 1
Preoperative frontal view showing no sign of any contour deformity of left malar area.
Fig. 2
(A) Preoperative CT showing a focal osteolytic lesion (red arrow) with contrast enhancement invading the body, frontal process, and anterior zygomatic arch of the left zygoma. (B) 3D reconstruction of CT showing thinning of body and thickening of frontal process of left zygomatic bone.
A bicoronal, subciliary and upper mucogingival approach were performed to expose the lesion. The extent of excision included inferior wall of orbit, subtotal portion of zygoma including frontal process, body and temporal process considering the extensive size of the tumor. The reserved safety margin was about 1cm. To minimize functional loss, the insertion sites of the zygomaticus major, zygomaticus minor and masseter muscle, as well as the zygomaticofacial nerve, were preserved. Osteotomy was performed carefully using a reciprocating saw to avoid damaging adjacent nerve and muscles. The reconstruction was performed with the aim of preserving the volume of the orbit and the contour of the facial structure. After resection of tumor, calvarial bone was harvested for autologous bone reconstruction from outer cortex of both parietal bone. The frontal process was totally removed and reconstructed using a hinge-shaped graft. The defect of orbital surface and malar body were covered with meticulously carved graft. Firm fixation was performed with 1.2mm miniplates restoring facial buttresses.
In the specimen, grayish tissue protruded from an osteolytic hole on the posterior wall of the zygomatic body. The lateral orbital rim exhibited hypertrophy with a thickness of about 1.2cm (
Fig. 3). The specimen was sent to the pathology department for histological examination. Histopathological examination revealed characteristics of a benign tumor, with immunohistochemistry showing positive results for EMA, CK, SMA, S100, and negative results for CD34 (
Fig. 4). The patient was diagnosed with myoepithelioma based on histology with clear surgical margin. The patient recovered without complications and exhibited contour symmetry of both malar regions at the 1-year follow-up (Figs.
5,
6).
Fig. 3
The resected specimen showing osteolytic hole of body with protrusion of grayish tissue and hypertrophy of lateral orbital rim.
Fig. 4
The mass showed mixed epithelioid and surrounding spindle cell populations(A). Epithelioid cells were arranged in trabecular and tubular structures and expressed cytokeratin and epithelial membrane antigen (B,C). Surrounding spindle cells typically expressed S100 and smooth muscle actin (D,E).
Fig. 5
Gross photograph of 1 year follow up showing contour symmetry of malar region (A) Frontal view (B) Worm’s eye view.
Fig. 6
Postoperative CT of 1 year follow up showing total removal of tumor without recurrence (A) Axial view (B) 3D reconstructed view.
Discussion
Myoepithelioma is a benign myoepithelial tumor which primarily occurs in soft tissue and infiltrates the parotid gland or minor salivary glands.4) Since myoepithelioma locates intramedullary, it usually lacks distinctive clinical features and usually tends to grow slowly without pain. Myoepithelioma also have variable distribution, which can present axial long tubular bone, short tubular bone and axial skeleton.1) Thus, it is indispensable to use various radiographic and pathological modalities for differential diagnosis of myoepithelioma compared with variable epithelioid and spindle cell tumors.
CT imaging of myoepithelioma typically shows a well- circumscribed, enhancing mass with a smooth or lobulated margin. Fibrous dysplasia, which is common craniofacial benign spindle cell bone tumor, can be distinguished with expansile bone lesion with typical ground glass appearance on radiographs.
Differential diagnosis of myoepithelioma with another benign tumors such as desmoplastic fibroma, chondromyxoid fibroma and pleomorphic adenoma requires pathological evaluation since they share similar radiologic features. Myoepithelioma can express cytokeratin, epithelial membrane antigen (EMA) and S100 smooth muscle markers.5) Calponin, smooth muscle actin (SMA) and smooth muscle myosin heavy chain(SMMS-1) were also proved to be useful markers for diagnosis.1)
Since differential diagnosis is difficult based solely on clinical and radiologic features, surgical biopsy is required for pathologic evaluation. Additionally, complete excision is necessary, as recurrence might occurs up to 20% of patients.6) As the zygomatic bone significantly influences facial appearance, inadequate reconstruction after mass removal via ostectomy can cause severe facial deformity. Thus, each process of the zygomatic bone, including its prominences, body, and arch, should be reconstructed as closely as possible to their original shapes. For malar reconstruction, autologous tissue or implants can be used, including custom-made implants using 3D printing technology, considering the extent of resection. In this study, calvarial bone was harvested for autologous tissue reconstruction due to potential cost burdens and complications like infection and seroma.7) Furthermore, as known in surgeries like reduction malarplasty, rigid fixation must be performed to prevent masseter-related nonunion, and care should be taken to avoid compressing the temporalis muscle passing under the arch.8)
Removal of the masseter’s insertion can result in masticatory dysfunction. Involvement of the zygomaticofacial foramen could cause cheek numbness due to nerve injury. Since wide periosteal dissection is needed to remove zygomatic bone, patient have a risk of cheek soft tissue drooping. Also, postoperative hematoma may occur, necessitating appropriate compression dressings and drainage placement.9) Surgeons should provide sufficient explanation to patients weighing the pros and cons of surgery.
In conclusion, we report a rare case of intraosseous myoepithelioma in the zygomatic bone. Due to the challenging diagnosis of myoepithelioma based solely on clinical symptoms and imaging, surgeons should consider surgical biopsy for suspected lesions. When planning tumor removal, surgeons must choose the extent of excision and reconstruction method while considering the clinical significance of the zygomatic bone.
Ethical approval
This study was approved by the Institutional Review Board (IRB) of Inje University Busan Paik Hospital (IRB no. 2023-10-040). Written consent from the patient for the use of photographs was obtained, and the study was conducted in accordance with the principles of the Declaration of Helsinki.