Necrotizing sialometaplasia (NS) is a nonneoplastic inflammatory condition of the salivary glands. In 1973, Abrams et al first reported this condition.  The clinical and histopathologic features of necrotizing sialometaplasia often simulate those of malignancies such as squamous cell carcinoma or salivary gland malignancy.  All subsequent reports of necrotizing sialometaplasia stress the importance of correct diagnosis. Familiarity with necrotizing sialometaplasia and correct diagnosis are paramount in avoiding misdiagnosis and inappropriate treatment. Ischemia of salivary gland tissue leading to infarction (trauma) is the most likely cause.
A related Medscape Reference article that may be of interest is Cancers of the Oral Mucosa.
Necrotizing sialometaplasia was first reported to involve the minor salivary glands of the oral cavity, particularly those of the palate. Seventy-five percent of all cases occur on the posterior palate.  Most are unilateral, with one third occurring in a bilateral or midpalatal location. Reports of this entity in the minor glands of the retromolar pad area, buccal mucosa, tongue, incisive canal, and labial mucosa followed. In addition, necrotizing sialometaplasia is recognized in the parotid and submandibular salivary glands,  minor mucous glands in the lung,  nasal cavity, [6, 7] larynx, [8, 9] trachea,  nasopharynx, and maxillary sinus.  Similar lesions are identified in the breast; the condition is referred to as posttraumatic lobular metaplasia of the breast. 
Mesa and colleagues reported an incidence of 0.03% based on findings in 10,000 oral biopsy specimens.  However, they state that this percentage does not account for cases of necrotizing sialometaplasia that heal spontaneously without biopsy.
Necrotizing sialometaplasia is reported worldwide. Isolated cases and reviews from Europe, North America, South America, and Asia are reported in the literature.
Brannon and colleagues  reported that cases of necrotizing sialometaplasia in whites outnumbered cases in blacks by a ratio of 4.9:1. Given the ratio of whites to blacks in the United States, a significant racial predilection does not appear to exist.
The male-to-female ratio is approximately 2:1.
The average age of patients with necrotizing sialometaplasia in the Armed Forces Institute of Pathology (AFIP) registry is 47.9 years, with a range of 17-80 years. The average age is 43.1 years for female patients and 50.3 years for male patients. A case of necrotizing sialometaplasia in an 18-month-old infant is reported.
The prognosis for necrotizing sialometaplasia (NS) is excellent. Necrotizing sialometaplasia is a completely benign lesion that is most likely caused by ischemia secondary to trauma (examples of causes could be dental injection or hot liquid burn). The lesions heal on their own with or without biopsy. The reason for biopsy is to rule out cancer from their worrisome clinical presentation.
The average healing time for necrotizing sialometaplasia of the minor salivary glands of the hard and soft palates is approximately 5 weeks. The size of the lesion and whether or not bony perforation has occurred are clinical parameters that may influence the healing time.
The lesions of necrotizing sialometaplasia often are painless; less frequently, they cause pain and numbness. The clinical appearance that suggests cancer is the significant feature of this lesion. The clinical pictures show a patient with a lesion thought to be cancer who underwent biopsy and was monitored for 9 weeks. Over that time, regression of the lesion can be seen (see the images below).
Necrotizing sialometaplasia is a completely benign condition that heals on its own following biopsy.