A case of chronic sclerosing sublingual sialadenitis caused by a sublingual gland herniation through a hiatus of the mylohyoid muscle

Chronic sclerosing sialadenitis is characterized by painless and sclerosing swelling of the salivary glands. It usually occurs in the submandibular gland and rarely in the sublingual gland. A 69-year-old woman was referred to our department due to mouth swelling. At her first visit, a painless and hard mass was palpated under the submucosa of the oral cavity near the right sublingual gland. MRI showed that the mass involved the mylohyoid muscle and extended into the submandibular region. Based on various examinations, we suspected a sublingual tumor and performed a tumor resection. Intraoperatively, we observed a hiatus in the right mylohyoid muscle, and a part of the mass had ruptured into the hiatus. Histopathological examination resulted in a diagnosis of chronic sclerosing sublingual sialadenitis. In this case, we concluded that the chronic inflammation occurred as a result of stimulation to the sublingual gland, which had herniated into the hiatus of the mylohyoid muscle during functional movements of the muscle. Although there are very few reports on sublingual gland CSS, given the prevalence of mylohyoid muscle hiatus (42％-77％) and sublingual gland herniation through hiatuses (10％-32％), it is thought that there are more cases than currently reported.