Necrotizing sialometaplasia: a malignant masquerade but questionable precancerous lesion, report of four cases

Abstract

Background: Necrotizing sialometaplasia (NSM) is an extremely rare benign lesion with an uncertain pathogenesis. The differential diagnosis of this lesion is challenging due to little familiarity with this entity and histologic similarity with carcinomas, especially mucoepidermoid carcinoma (MEC). The purpose of this study is to raise awareness about NSM, which is often overlooked or misdiagnosed as malignancy in a small biopsy.

Methods: We reviewed all biopsy materials taken from the oral cavity in a single institution in Korea from 2012 to 2018 and found 4 cases of NSM out of 726. Clinicopathologic characteristics and comparison with other lesions were discussed.

Results: Unlike previous reports, patients in our series were relatively young, and NSM was not related to smoking and not associated with malignancies, although one patient was misdiagnosed with MEC on the basis of the initial biopsy. High-grade squamous dysplasia was observed in one patient; however, all four patients showed excellent prognoses without further management.

Conclusions: A conservative approach is recommendable for necrotizing lesions of the palate in young adults to avoid unnecessary treatment. However, careful monitoring is also required due to uncertainty of premalignant potential.

Keywords: Differential diagnosis; Minor salivary glands; Necrotizing sialometaplasia.

Fig. 1

Clinicoradiologic findings of necrotizing sialometaplasia. In case 1, a bulging mass (a) in the left hard palate showing well defined high signal intentisity in T2 weighted coronal MRI (b) and peripheral enhancement and necrosis on post contrast T1-weighted coronal image (c). Case 3 showed an ulcerative mass (d) subsequently healed after 3 months (e). Case 2 also presented with a well demarcated peripheral enhancing mass in left hard palate by post contrast axial CT (f). Case 4 showed right sphenoid sinus wall defect without delineable mass in the nasal cavity or the palate (g). Two months after surgery, case 4 patient’s CT scan showed the same right sphenoid sinus wall defect (h)

Fig. 2

Representative microscopic features of necrotizing sialometaplasia in case 1. Extensive necrosis (a, × 40) with intact lobular architecture and squamous metaplasia (b, × 100). Metaplastic squamous cells without dysplasia are found in the inflammatory background (c, × 200). However, haphazardly arranged squamous cells and mucous glands causes confusion with mucoepidermoid carcinoma (d, × 100). (Hematoxylin Eosin)

Fig. 3

Necrotizing sialometaplasia associated with high grade dysplasia in case 4 (a, × 40). Marked nuclear plemorphism is evident in squamoid cells (b, × 200). These cells showed immunoreactivity to P53 (c) and high Ki-67 (d)

Fig. 4

Histologic features of a case of mucoepidermoid carcinoma (MEC). Mixed infiltration of glandular cells and epidermoid cells are characteristic of MEC (a, × 40; b, × 100). However, areas mimicking necrotizing sialometaplasia are present at the periphery (c, × 40; d, × 100)