A 43-year-old woman complains of periodical facial assymetry and bursting stabbing pain in the submandibular area on the right, which increases after eating spicy and sour food. Eventually these clinical presentations disappear. The patient notes periodical exacerbations. Objectively: the face is symmetrical, mouth opening is unrestricted, mucosa of the oral cavity floor is without pathologies. In the area of the sublingual fold a thickening of soft tissues can be palpated. Excretory duct of the submandibular gland produces no saliva. What preliminary diagnosis can be made?