Introduction
The relative frequency of epithelial salivary gland tumors occurring in children and adolescents ranges from 3.7% to 5.5% [
1]. Moreover, the high incidence of malignancy in minor salivary gland tumors is well established. Batsakis [
2], in a review of the literature, determined that 52.3% of minor salivary gland tumors were malignant. Similar findings, of from 44% to 65%, have been reported [
3‐
8]. Therefore, the overall incidence of minor salivary gland neoplasms is low in the pediatric-adolescent age group, but in view of their high incidence of malignancy, their importance should not be underestimated.
The most common type of malignant salivary gland neoplasm of epithelial (parenchymal) origin in the pediatric-adolescent age group is the mucoepidermoid carcinoma (MEC) [
9]. Other types of minor salivary gland adenocarcinomas in this age group are rarely reported. Most of the malignant neoplasms are found in the parotid gland; only a few pediatric and adolescent cases have been well documented in the minor glands [
9]. In fact, a review of the English language literature revealed only 15 well-documented cases of MEC of minor salivary gland origin in this age group [
1,
10‐
19]. A search of the Louisiana State University School of Dentistry (LSUSD) Division of Oral and Maxillofacial Pathology archives of a 35-year period supports the paucity of malignant intraoral salivary gland tumors and the reported frequency of MECs in the first two decades of life. Therefore, the purposes of this retrospective analysis were to investigate the clinical features and biologic behavior of minor salivary gland MECs occurring in children and adolescents (from birth to 19 years of age) from the LSUSD and to compare these findings with well-documented cases reported in the English language literature.
In this study, the age of the pediatric-adolescent population was from birth to 19 years, which represents the first two decades of life. Minor salivary gland MECs from this age group were selected from the LSUSD Department of Oral and Maxillofacial Pathology archives of the period of 1 January 1969 to 31 December 2004. The Louisiana State University Health Sciences Center (LSUHSC) Institutional Review Board (#6450) approved the research protocol. Demographic and clinical information was recorded for each case, and the histopathologic slides were reviewed by one of the authors (RBB). The LSUSD MECs were histologically graded by using the criteria set forth by Auclair
et al. [
20]. The LSUHSC School of Public Health Louisiana Tumor Registry provided follow-up information for the LSUSD cases.
A search of the English language medical and dental literature was performed for well-documented minor salivary gland MEC cases in the pediatric and adolescent age group. The search was carried out in Medline for ‘mucoepidermoid carcinoma and salivary gland carcinoma’, and limits were set to human subjects under 19 years and the English language. The search was last updated in September 2011. Once studies were identified, individual articles and their references were checked for additional studies. It should be noted that although investigators have published numerous series on salivary gland neoplasms, they provide an age range only. They do not correlate the age of the patient to the location of the lesion or offer other demographic and clinical information, such as the identity of the specific minor salivary gland involved. Some of these series did indicate that at least one patient was in the first or second decade of life; however, we did not include them in this study, because they lacked adequate detail [
8,
21‐
37]. Central (intraosseous) MECs of the maxilla and mandible were not included in this study.
Discussion
Epithelial neoplasms originating in the minor salivary glands account for approximately 15% of all salivary gland neoplasms [
6,
38]. It has been estimated that about 1% to 5% of all salivary gland tumors develop in children and adolescents [
1,
8], and MEC is the most common malignancy [
5,
9,
39,
40]. In the current LSUSD series, 3.5% of the epithelial minor salivary gland neoplasms occurred in patients 19 years of age or younger; this is in close agreement with the series reported by Waldron
et al. [
38] and Kusama
et al. [
41], who found incidences of 3.7% and 5.4%, respectively. A total of five malignant salivary gland tumors, all MECs, represented 1.3% of all salivary gland tumors accessioned in the LSUSD oral biopsy service from a 35-year period, and this supports the conclusion in the literature that MEC is the most common malignancy of minor salivary glands in the first and second decades of life.
This study combined data from five LSUSD cases and 15 cases from the literature for data analysis. The majority of epithelial salivary gland neoplasms occur late in childhood, after 10 years of age [
42]. MECs are generally found between the ages of 10 and 16 years [
40,
43], which is in general agreement with this case report. In the 20 cases reviewed, 16 MECs occurred in the second decade and the overall average age was 13.5 years. We have included the case reported by Tipton [
10] of a 20-month-old with a poorly differentiated MEC; however, in view of its poor documentation, we are not convinced that this tumor is an MEC. Nevertheless, we have included it since it has been frequently referenced as such. According to Mehta and Willging [
40], MEC is the most common radiation-induced salivary gland tumor in children. None of the patients in this review had a history of radiation.
Among the 20 cases, there was a female predilection of 2.3:1. Since race was known in only 55% of the 20 cases, no further analysis of this demographic feature was undertaken. This series confirmed that the hard or soft palate (or both) is by far the most common site for intraoral minor salivary gland MECs, followed by the buccal mucosa [
39].
The histologic grade of the MEC often reflects the clinical manifestations of the tumor. Intraorally, low-grade MECs tend to be asymptomatic enlargements of prolonged duration. In this study, the average duration was five months before diagnosis; one case had a duration of seven years. Interestingly, seven of the low-grade MECs appeared as fluctuant light blue or purplish submucosal lumps, thus resembling the reactive salivary gland mucocele (mucous retention phenomenon). The reason they possess similar clinical appearances is that low-grade MECs and mucoceles possess mucous cyst formation and mucous pseudocyst formation, respectively. As Flaitz [
17] has pointed out, the differential diagnosis for a compressible or fluctuant light blue mass in an intraoral salivary gland-bearing area in a child or adolescent should include reactive and neoplastic lesions, and MEC and mucocele should be at the top of the list. Although MECs are considered rare in the children-adolescent age group, they must be considered when a lesion appears to be similar to a mucocele but is found at a site other than the lower lip mucosa [
17].
Histologically, MECs are divided into low-, intermediate-, and high-grade types, which correlate to clinical behavior. Our analysis of the five LSUSD cases was consistent with that of several other studies [
1,
11‐
19] in that all of the low- to intermediate-grade MECs originating from intraoral minor salivary glands had a very low recurrence rate and a high survival rate (100%). Recurrence in this series was less than 10%. This is in keeping with the general consensus that low- and intermediate-grade MECs have an indolent clinical course and a minimal chance for metastasis [
14]. The current series supports the opinions that MEC in children appears to be somewhat more innocuous than in adults and that the probability of death for children with low-grade MEC is essentially zero [
44]. However, others believe that malignant salivary gland malignancies in children exhibit biologic behavior similar to those occurring in adults and therefore require the same treatment principles as those occurring in adults [
45,
46]. Nevertheless, close clinical follow-up should be long-term, as outlined by April
et al. [
14], because low- to intermediate-grade MECs in this age group can recur many years after initial removal [
1,
14].
The results of this study and others [
17‐
19] suggest that low- to intermediate-grade MECs originating from intraoral minor salivary glands in children and adolescents can be effectively managed by wide local surgical excision that ensures tumor-free surgical margins. Wide surgical excision in combination with bone removal is preferred only when there is gross periosteal involvement or bone erosion by the MEC [
17,
18].
It is most likely that the treating dentist would take an intraoral radiograph or an orthopantomograph or both at the time of the initial clinical presentation. However, the treating oral surgeon would need a computed tomography scan to establish the extent of the lesion prior to surgical exploration. Prognosis of the lesion on the basis of imaging modalities has not been investigated, and to date, the only prognostic indicator is the histopathologic grading of the lesion [
14].
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
PR helped to review the clinical and histopatholgic data from the selected cases and the literature and to analyze the data. RBB helped to review the clinical and histopatholgic data from the selected cases and the literature and to analyze the data, reviewed histopathologic microslides, and confirmed the diagnoses for the cases from the LSUSD series. KGC provided the photomicrographs of the histopathologic slides. All authors read and approved the final manuscript.