Mucous cysts or purulent cysts of lacrimal sacitis can communicate with the septal sinus and form a septal sinus lacrimal sac fistula. When secretions are drained from the nasal cavity through the septal sinus, the cysts can shrink or even disappear and symptoms can be reduced, having the same effect as nasal drainage surgery. The exact cause of septal sinus fistula has not yet been determined. Dacryocystitis is often secondary to inflammation of adjacent tissues such as the conjunctiva, nasal cavity and paranasal sinuses, or some specific infection such as tuberculosis or syphilis. The cause is unclear in those with a primary origin in the lacrimal system. Under normal conditions, the tear duct mucosa is intact, the tear drainage is clear, the tears have some antibacterial capacity and the tear sac is not prone to inflammation. An important predisposing factor is tear retention due to obstruction of the lower lacrimal duct. At the beginning, it is not an organic obstruction, but a temporary congestion and edema of the nasolacrimal duct mucosa, while the membranous nasolacrimal duct resides in the bony duct, the mucosa is rich in blood vessels and lymphatic vessels, a little swelling can cause obstruction, so that the contents of the tear sac are retained, easy to breed bacteria, mucosa for bacterial infection, inflammation more promote congestion and edema, forming a vicious circle. If the bacteria are not virulent, the lacrimal sac continues to be chronically inflamed, eventually forming a fixed obstruction of the nasolacrimal duct. Whenever virulent bacteria enter the lacrimal sac, they cause an acute attack, mostly from the adjacent nasal cavity, paranasal sinuses, or perilacrimal tissue. The predominant bacteria in nonspecific lacrimal sac infections are Streptococcus pneumoniae, followed by Staphylococcus, Escherichia coli, and Moraxella, and to a lesser extent Pseudomonas aeruginosa or Dictyococcus gonorrhoeae.