Ⅰ. INTRODUCTION
Mucoepidermoid carcinoma (MEC) accounts for approximately 29% to 34% of the malignant tumors of the major and minor salivary glands. If MEC occurs in the salivary glands, it can be found on the palate, retromolar area, floor of the mouth, buccal mucosa, tongue, and lips, but with rare occurrence in the laryngeal, nasal, tracheal, lacrimal, thyroid, pulmonary, and liver tumors.1-4 MEC can occur in children and adolescents under 20 years of age. It is the most common malignant salivary gland tumor, which accounts for 51%, and it has a slight predilection for women.2
MEC is classified as high-, middle-, or low-grade based on its histopathological features, and high-grade MEC is an aggressive malignancy with a poor prognosis.4
The treatment of MEC in the palate consists of surgical excision, and it is essential to achieve negative margins. In addition, radical surgery is the treatment option for high-grade tumor or low-grade tumor with a large size. After a surgical excision, radiation therapy is most commonly used for patients with unclear margin and high-grade tumor.5-6
Reconstructive surgery is often required due to cystic lesions or resection of malignancy in the oral cavity. Reconstruction with BFP may be considered and used to fill the small-sized to medium-sized (< 5cm) congenital or acquired soft tissues and bony defect in the palate, alveolus, and buccal mucosa.7-9 This defect include oroantral and oronasal communications after tumor resection, primary and secondary palatal cleft, and dental extraction. BFP has a body and four processes. The body is located behind the zygomatic arch. The body has three parts divided into anterior, intermediate, and posterior lobes. This is a simple and reliable flap for reconstruction, and it has an excellent blood supply and minimal donor site morbidity.10-12
In this article, we report the case of a 12-year-old female patient who had MEC on the light soft palate and underwent surgical procedures, such as resection of the site and reconstruction with BFP. Initially, we diagnosed it as a benign tumor from the clinical and radiological examinations, but the final pathology results showed MEC. Therefore, we will discuss MEC in children for precise diagnosis and treatment, as well as the usefulness of BFP for reconstruction. Additionally, some literature will serve as evidence for our treatment of the patient.
Ⅱ. CASE REPORT
A 12-year-old female patient was referred to Pusan National University Dental Hospital from the Department of Otorhinolaryngology due to a history of swelling on the light soft palate. Upon clinical examination at our clinic, a bluish and fluctuated swelling lesion was observed in the light soft palate (Fig. 1), and the patient did not have any symptom. Furthermore, the panoramic examination (Fig. 2) revealed no specific findings, and bone erosion on the light palate was not observed on CT (Fig. 3). Laboratory testing including a complete blood count, electrolyte, liver, and renal function chemistries, total protein, albumin, quantitative immunoglobulin, lactate dehydrogenase (LDH), erythrocyte sedimentation rate, ferritin, uric acid, and urinalysis was performed. She had no pre-existing general disease, was in good health, and had no alcohol drinking or smoking history.
We initially suspected a vascular lesion on the light soft palate, and we performed additional MRI for an accurate diagnosis. The results of the MRI revealed approximately 1.6 x 1.7 x 1.7cm solid and cystic mass involving the left soft palate (Fig. 4). The border of the lesion is relatively clear; therefore, there is little invasive change in the periphery, and the possibility of benign tumor is high. Although it is not common, pleomorphic adenoma or schwannoma with cystic change is possible. In the case of a malignant lesion, the possibility is low, but it is likely to be either an adenoid cystic carcinoma or a mucoepidermoid carcinoma. After that, we modified our diagnosis to pleomorphic adenoma.
Excision was planned considering general anesthesia, as well as the radiological and clinical findings obtained on January 2018 (Fig. 5a, 5b). The size of the removed primary lesion with a safety margin was 2.2× 1.6×1.2 cm (Fig. 6a), and the buccal mucosa defect was reconstructed with BFP (Fig. 5c). The light palatal defect was successfully covered without any tension or complications. The excised specimen was examined by H&E staining and by immunostaining for CK-7 and p63. Histological examination revealed a low-grade MEC composed of mucous cells lining cystic spaces with a maturation pattern (Fig. 6b). Furthermore, the resection margin of the specimen was clear. Upon immunohistochemical examination, CK-7 was found to be positive and p63 was found to be negative. Therefore, the lesion was diagnosed as a low-grade mucoepidermoid carcinoma.
After the diagnosis of the malignancy and operation, the Fluorine-18-fluorodeoxyglucose positron emission tomography/ computed tomography (F18-FDG PET/CT) was performed in order to determine the treatment plan and TMN stage (Fig. 7). Based on the F18-FDG PET/CT, CT, and MRI, there was no remnant tumor and there was no significant cervical lymphadenopathy.
Partial necrosis and inflammation of the grafted BFP was observed 2 weeks after the surgery (Fig. 8A). Epithelialization began 1 week after the surgery, and complete healing was noted within 6 weeks. The defect was completely covered without any complications (Fig. 8B). There was no evidence of distant metastasis or recurrence at every follow-up visit until 10 months after the surgery.
Ⅲ. DISCUSSION
MEC of the major and minor salivary glands is one of the differential diagnoses. It is most commonly found in the major salivary glands; however, it may also be present in the minor salivary glands. Mucoepidermoid carcinoma incidence is approximately 16% of minor salivary gland tumors, following adenoid cystic carcinoma.4-5
The incidence of salivary tumors in all pediatric patients is less than 5% every year, of which one-third is malignant tumors. One study reported that MEC accounts for 51% of all malignant salivary gland tumors and 16% of all salivary gland tumors in children.13
The incidence of MEC is very rare in children compared to adults; however, MEC accounts for 50% of salivary gland malignancy in children, which is more prevalent than adults with 12% to 23%. With the rare occurrence of MEC in children, it is still difficult to make precise guidelines about its incidence and treatment methods. In this report, we described the diagnosis, clinical presentation, molecular characterization, treatment, and outcome of children with low-grade MEC.14,15
MEC generally consists of three cell types, namely, mucinproducing, squamous, and intermediate. These cellular components consist of nest and diffuse sheet surrounding the cystic structure, and local infiltration into the salivary gland tissue, muscle, and connective tissue can be observed.16 Low grade has more mucous cells and multiple cystic structures than high grade, as well as low metastatic ability and good prognosis. On the other hand, high grade has less mucous cells, but more epithelial cells and solid islands. The middle grade is histologically intermediate.17
According to parameters and point values for each grade, MEC can be graded systematically using histologic findings. These parameters are defined as intracystic component < 20% (2 points), neural invasion (2 points), necrosis (3 points), four or more mitoses per 10 HPF (3 points), and anaplasia (4 points). Total scores of 0-4, 5-6 points, and ≥ 7 points indicate low-, intermediate-, or high-grade disease.20
The prognosis differs according to the grade of MEC. The 5-year survival rate was 98% in low grade cases because of low metastasis and aggressiveness, and 56% for high grade cases. High grade has a high recurrent tendency regardless of the origin, and it is aggressive toward metastasis to the local lymph nodes and hematogenous metastasis to the lungs and skeleton. The salivary gland tumors in children tend to be more malignant; however, they have a good prognosis, with 5-year and 10-year overall survival (OS) of 82%-98% and 82%-94%, respectively.1-4
In addition, presence factors (e.g., younger age, female gender, and major glands origin) were reported to have good prognosis, but the absence of factors (e.g., extra glandular extension, vascular invasion, mitotic rate, and necrosis) were reported to have poor prognosis.21
BFP is a special encapsulated mass of fatty tissue, and it was first described by Bichat in 1802. A lobulated mass of specialised fatty tissue was lying within the masticatory space, and it is located between the mandibular ramus and buccinator muscle, separating the muscles from each other. BFP was first used in 1977 for the reconstruction of maxillary defects caused by tumors. It is a flap that is reliable and suitable for reconstructing oral defects due to its small volume change over time. In addition, BFP procedures are used by many clinicians because of their rich vascularity, low morbidity, simple procedure, and proximity to the recipient site.7-9 BFP is composed of a body and four processes, and it has highly mobile structures. The body consists of three lobes, namely, anterior, intermediate, and posterior. The four processes (buccal, pterygoid, superficial, and deep temporal) extend from the body into the surrounding pterygomandibular and infratemporal fossae. BFP provides rich blood supply on the grafted site. It has the facial, temporal, and internal maxillary arteries, and their anastomosing branches entering the fat to form a subcapsular vascular plexus.10-11
BFP is covered with thin capsules, and it is located along the posterior maxilla. The parotid gland penetrates through the buccinator muscle at the front part of the BFP. The average weight and average volume of BFP are 9.3 g (range, 8–11.5 g) and 9.6 mL (range, 8.3–11.9 mL), respectively. BFP provides an adequate area to cover the defect in the mouth, and when properly separated from the tissue, an average size of 6 × 5 × 3 cm graft and an average thickness of 6 mm can be obtained. BFP can also cover an area of 10 cm2.8-9
can be obtained. BFP can also cover an area of 10 cm2.8-9 Complications are rare, and they have partial necrosis and excessive scarring. If buccal defects were reconstructed with large flaps, there is a risk of fibrosis and trismus. In order to prevent complications, soft or liquid diet are required until 4 to 6 weeks after epithelialization.7-8
The treatment of choice for the localized lesions is surgical excision with a clear margin. Chemotherapy and radiation therapy should also be considered as treatment options for metastatic lesions. In our patient, the lesion was initially located in the light soft palate and excision was performed. Chemotherapy and radiation therapy were not performed, and there was no recurrence after surgery.1-2
There have been no specific evidence-based guidelines for radiotherapy in pediatric MECs, thus owing to the rarity of this disease. The patients with salivary gland MECs in this case did not receive postoperative radiotherapy. Given the risks of craniofacial growth defects and subsequent risk for secondary malignancies, postoperative radiotherapy in pediatric MECs should be considered only in locally aggressive, high-grade tumors with incomplete resection.1-4
If at least some of the malignant tendencies are known at the time of the initial diagnosis, clinical examination, and radiographic imaging, radiologists and oral surgeons need to cooperate in order to establish a diagnosis and treatment plan even if the examination of the specimen should be requested by the pathology department, and a referral to an expert in this area is deemed necessary.22,23
Ⅳ. CONCLUSION
The incidence of MEC in children is rare; therefore, further studies are needed on the treatment protocol. BFP is a useful flap for reconstructing small defects in the mouth, and it is recommended because of the good results that have been reported. However, careful management, accurate diagnosis, and planning are required in order to improve the quality of life through the restoration of the oral function and esthetics after surgery considering various factors, such as sex, age, and tumor size.
