Advanced Diagnostic Methods in Necrotizing Sialometaplasia of the Parotid Glands: An Updated Literature Review and a Rare Case Report

Abstract

Background/Objectives: Necrotizing sialometaplasia (NS) is an inflammatory condition of the salivary glands that can closely mimic malignancy. While it predominantly affects the minor salivary glands of the hard palate, it can also occur in the parotid gland, leading to potential misdiagnosis and unnecessary treatment. This study aims to analyze the characteristics, diagnostic challenges, and management of parotid gland NS through a comprehensive literature review and a case report. Methods: A systematic literature review was conducted using PubMed, including all relevant publications up to December 2024. The research strategy focused on cases of NS affecting the parotid gland. Additionally, a rare case of misdiagnosed parotid NS is presented to highlight clinical and diagnostic challenges. Results: The review identified 30 patients, with a mean age of 49 years, and a nearly equal distribution between sexes. Their etiology was primarily linked to vascular insufficiency, often triggered by surgical trauma (20 cases), tumors (1 case), vascular fragility (4 cases), smoking (1 case), or other factors (4 cases). Clinically, NS can resemble squamous cell carcinoma, presenting with neck swelling, pain, and imaging features suggestive of malignancy. Histopathological assessment remains the gold standard for diagnosis. A rare case of a 23-year-old female misdiagnosed with squamous cell carcinoma emphasizes the importance of multiparametric MRI imaging and histological re-evaluation in atypical presentations. Conclusions: NS of the parotid gland is a rare but significant diagnostic challenge, due to its resemblance to malignant tumors. While conventional imaging may suggest a neoplastic process, advanced techniques such as DWI (Diffusion-Weighted Imaging) and ADC (Apparent Diffusion Coefficient) mapping can offer valuable noninvasive insights. A multidisciplinary approach, incorporating clinical history, imaging, and histopathological assessment, is essential in order to avoid unnecessary treatment. In cases where NS is suspected, a conservative approach with careful follow-up may be warranted to prevent overtreatment.

Keywords: multiparametric magnetic resonance imaging; necrotizing sialometaplasia; parotid gland.

Figure 1

Study selection process.

Figure 2

A three-dimensional representation of the tumor and the surrounding anatomical structures, generated using 3D Slicer, an open-source platform for medical image processing and visualization.

Figure 3

MRI sections showing an apparently well-circumscribed left parotid gland mass (green arrows): axial T2 FSE (fast spin-echo sequence) (A), coronal T2 FSE (B), and sagittal MPR T1 (Multiplanar reconstruction) (C).

Figure 4

MRI axial sections showing the parotid gland mass (green arrows): (A) the axial DWI sequence demonstrating no diffusion restriction, and (B) the corresponding ADC map showing a high ADC value (1.3 × 10⁻³ mm²/s), the red circle indicates the area where the ADC value was calculated.

Figure 5

(A–J) Anatomo-pathological reasoning for a diagnosis of sialometaplasia instead of squamous cell carcinoma: The presence of cystic areas lined by squamous epithelium with focal parakeratosis and focal leukocytic infiltrate, and intraluminal keratin lamellae, is characteristic of necrotizing sialometaplasia. There is immature squamous metaplasia present in numerous ducts located at a distance from the lesion. There is mature epithelium without atypia in the “infiltrative” areas, as well as the extension of squamous nests following a pattern very similar to the tubulo-acinar architecture of the parotid gland. The “buds” of the epithelium protruding from the cyst walls are also a feature of necrotizing sialometaplasia. The stromal infiltrate is chronically inflammatory or fibrous, which is more consistent with necrotizing sialometaplasia than with squamous cell carcinoma. The immunohistochemical staining for p53, calponin, and SMA is consistent with necrotizing sialometaplasia. The Ki-67 proliferation index is increased only at the base of the epithelium in the cyst walls, and is zero in the nests of keratinocytes in the stroma.