necrotizing sialometaplasia was first described by abrams et al.1 in 1973 , and since then , other similar cases have been reported . necrotizing sialometaplasia is an inflammatory , ulcerative lesion of the small salivary glands that usually occurs on one side of the hard palate , although it can also occur on the lower lip , posterior molar area , buccal mucosa , the parotid gland , tongue , and in the upper airway23 . necrotizing sialometaplasia occurs more frequently in males , with the ratio of affected males to females approximately 2 to 12 . it is histologically similar to mucoepidermoid carcinoma and squamous cell carcinoma but is a benign disease that spontaneously heals within 4 to 10 weeks . necrotizing sialometaplasia of the hard palate re - occurred on the contralateral side after 5 months . a 36-year - old woman was referred to the gangnam severance hospital ( seoul , korea ) by a private practice endodontist . the patient stated that her palate felt uncomfortable and that her throat had been swollen for a week . she had a history of smoking more than 40 cigarettes a day for 20 years and denied any other medical history . endodontic treatment of the upper left first premolar under local anesthesia with 2% lidocaine and 1:100,000 epinephrine was completed by the endodontist before the patient 's arrival to our hospital . a craterlike ulceration of 3 cm diameter , with necrotic tissue inside , was found on the left hard palate . a ) the lesion was first diagnosed as either tissue necrosis caused by local injection of lidocaine containing epinephrine or necrotizing sialometaplasia , and was treated palliatively . it was not possible to perform a biopsy at that time because the tissue was already necrotized.(fig . c ) after 5 months , the patient returned to the hospital for recurrence of the same symptoms on the contralateral side of the hard palate without any particular dental event.(fig . b ) microscopically , the palatal lesion showed diffuse necrosis of acini and ducts of palatal salivary glands ; however , the overall lobular structure of the involved gland was preserved . 3 ) based on histological analyses , the final pathological diagnosis for the palatal mass was necrotizing sialometaplasia . at the 3-year follow - up , the patient 's oral mucosa of the hard palate was normal , without any signs or symptoms.(fig . c ) this study was approved by institutional review board of yonsei university gangnam severance hospital ( irb # 3 - 2015 - 0114 ) , and informed consent was obtained . the cause of necrotizing sialometaplasia is unknown , but it is thought to result from infarctions of the salivary gland tissue125 . the causes of such infarctions may be direct injury , effects of vasoconstrictors , or injuries from needles used in local anesthesia , ill - fitting dentures , drinking , smoking , cocaine use , radiation , infection of the upper airway or allergy , intubation , surgical treatment , and systemic diseases such as sickle cell disease , buerger 's disease , raynaud 's disease , and aids2345 . shigematsu et al.6 reported that histopathological changes similar to those associated with necrotizing sialometaplasia may be observed when local anesthesia is repeatedly injected into the hard palate of mice . necrotizing sialometaplasia with ulceration may occur when tissues in the salivary glands are infarcted and the acinar cells are subsequently necrotized . brannon et al.2 reported that the risk of necrotizing sialometaplasia in smokers is about 10% ( 7/69 ) . smoking could cause infarctionsin the salivary gland by continuously stimulating the palate and inducing vascular stenosis . in a previous study , the researchers were unable to determine the cause of necrotizing sialometaplasia in 44% of the patient sample ( 30/69 ) , and the rate of recurrence was 0% ( 0/14)2 . a number of reports have concluded that the risk of recurrence is normally 0% , and that instances of recurrence on the opposite side are rare . however , histologically , tissues in the salivary glands show infarction , inflammation , granulation tissue , and squamous metaplasia of the salivary duct . because such squamous metaplasia is often observed , it may be misdiagnosed as squamous cell carcinoma , and because it is similar to mucoepidermoid carcinoma in that the squamous metaplasia is surrounded by a faint outline of necrotized acinar cells , it is easily misdiagnosed as malignant 1278 . however , despite similarities of infection and necrosis , necrotizing sialometaplasia is distinguished from malignancies because its ductal structure is preserved37 . when necrotizing sialometaplasia is misdiagnosed as a malignancy , irreversible treatment such as radical resection may follow . in contrast , some malignancies can be misdiagnosed as necrotizing sialometaplasia and subsequently go untreated . therefore , bascones - martnez et al.5 reported that incisional biopsy is recommended for accurate diagnosis , with periodic treatment until full recovery9 . the stages are not clearly separated and can progress from occurrence to full recovery without any treatment . when salivary gland tissues become infarcted and are necrotized and separated , the necrotized tissues collapse , creating a crater - shaped ulcer . the surrounding mucous membranes show secondary healing and require approximately 4 to 10 weeks for complete recovery2347 . pain may or may not be present ; however , if there is pain in the first period of ulcer formation , the use of an analgesic is recommended . because necrotizing sialometaplasia appears as an inflammatory ulcer , some doctors treat it with antibiotics or steroids , but with no reported effects on clinical symptoms7 . our patient case had a negative medical history with the exception of smoking and local anesthesia for dental treatment . thus , in the preliminary diagnosis , we diagnosed our patient with necrotized tissue caused by the blockage of the terminal blood vessels from complications of smoking and the use of lidocaine with epinephrine . after 3 weeks of follow - up , the necrotized tissues were no longer present and secondary healing of the soft tissues was apparent . five months after the first occurrence of the lesion , we observed recurrence on the contralateral side of the hard palate without any particular factors other than smoking . the second lesion was still within the initial period of necrotizing when observed , and we therefore conducted an incisional biopsy including both normal and necrotized tissues to confirm the diagnosis of necrotizing sialometaplasia . necrotizing sialometaplasia occurs unilaterally in 71% of previously - reported cases , and on both sides of the median suture line of the hard palate in 12% of cases2 . however , in our case , there was a second occurrence on the contralateral side with a time lapse between the first and second occurrences , a presentation that is thought to be quite rare . our patient was not definitively diagnosed upon the second occurrence , but the second lesion may have been caused by the patient 's heavy smoking habit , because she had experienced no dental events such as the use of local anesthesia .
necrotizing sialometaplasia usually heals within 4 to 10 weeks with conservative treatment , and rarely recurs . 
 when necrotizing sialometaplasia is present on the hard palate it may occur unilaterally or bilaterally . in this case , necrotizing ulceration occurred on the left hard palate of a 36-year - old woman after root canal treatment of the upper left first premolar under local anesthesia . 
 after only saline irrigation the defect of the lesion completely healed and filled with soft tissue . 
 after 5 months , however , a similar focal necrosis was found on the contralateral hard palate without any dental treatment having been performed on that side and progressed in similar fashion as the former lesion . 
 we conducted an incisional biopsy and obtained a final pathological diagnosis for the palatal mass of necrotizing sialometaplasia . at the 3-year follow - up , 
 the patient 's oral mucosa of the hard palate was normal , without any signs and symptoms of the condition . 
 we report a case of a second occurrence of necrotizing sialometaplasia on the contralateral side from the first , with a time lapse between the first and second occurrence .