Background

This uncommon condition is usually diagnosed by the pathologist and accounts for 0.03% of all biopsy diagnoses of the oral cavity. It is more common in males with a male:female ratio of 1.5-2:1 and usually occurs in patients > 40 years old. It most commonly presents with a painful lesion of the hard palate, usually with ulceration. It is a self-limited condition and no treatment except for symptomatic relief is needed. It probably results from ischemic changes involving the minor salivary glands and thus can be found in the nasal cavity, gingiva, lip, hypopharynx, maxillary sinus, and major salivary glands. There is a primary form which usually involves the minor salivary glands of the palate and is of unknown etiology.

Under the microscope, the key microscope features are the lobular necrosis of the salivary gland tissue, preservation of the lobular architecture, squamous metaplasia of the residual ducts and acini, and temporal variability of the inflammatory cell infiltrate.

The importance in making this diagnosis rests with the pathologist distinguishing this disorder from a malignancy. The table below illustrates helpful features to make this distinction. The key point for the pathologist is a diagnosis of a squamous cell carcinoma or mucoepidermoid carcinoma of the palate should never be made until necrotizing sialometaplasia is excluded.

Differential Diagnosis of Atypical Squamous Proliferations Within the Oral Cavity

Histology	Necrotizing Sialometaplasia	Mucoepidermoid Carcinoma, Low Grade	Squamous Cell Carcinoma
Architecture/growth	Retention of lobular architecture	Haphazard, infiltrative growth	Haphazard, infiltrative growth
Cellular components	Smooth, round to oval nests of metaplastic squamous epithelium with bland cytology Residual ductal lumina with mucous cells	Admixture of mucous, intermediate,and epidermoid cells Bland cytology Irregular cell nests	Nests and cords of squamous cells with irregular outlines and variable amounts of cytologic atypia No mucin within tumor
Cyst formation	Absent	Present and prominent	Absent
Surface epithelium	May show pseudoepitheliomatous hyperplasia, usually not connected to main lesion	Uninvolved Not connected with tumor	Often dysplastic and/or in direct continuity with the carcinoma May ulcerate
Extravasated mucin necrosis	May be present Lobular infarction of salivary gland acini	Absent	May show tumor necrosis
Inflammation	May be prominent	May be prominent with mucin extravasation	May be present Association desmoplasia

Am J Clin Pathol 1977;67:315-317.
Pathol Case Rev 2000;5:221-226.

Mouth and Oral Cavity

Clinical and Microscopic Photos
Clinical and Microscopic Photos

Last Updated 4/1/2001

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