ABSTRACT
<p><b>OBJECTIVE</b>This study is aimed to observe the natural draining state of maxillary sinus, to search for the key draining location (KDL) in the natural ostium, to investigate the relation between maxillary sinus draining and sinus inflammation, and to guide the treatment of maxillary sinus opening in endoscopic sinus surgery (ESS).</p><p><b>METHODS</b>Methylene blue was used as tracer agent in this study. Fifteen cases with or without light maxillary sinus inflammation (without any treatment) were selected to observe the natural draining state and the key draining location in maxillary sinus fontanel. Eighty-nine cases with chronic rhinosinusitis, but without nasal polyp, were selected, of which the maxillary sinus mucosa restored well 6 months after ESS, to observe the draining state and modes in maxillary sinus. All patients were followed up for 12 months to evaluate the inflammation state of mucosa, and to analyze the relations between the draining mode and mucosa inflammation.</p><p><b>RESULTS</b>The KDL for maxillary sinus was located in the posterior-inferior portion of the natural ostium, close to the attachment of caudal end of the uncinate process. The draining flowed along it from maxillary sinus to nasopharynx. After conventional transnasal endoscopic operation, 15 cases showed relatively normal drainage, others displayed abnormal state and mode,including reverse draining (maxillary sinus-ethmoid sinus) , multiphase draining (outflow from front, back and lower wall of natural ostium), draining failure (with cilia transporting function of maxillary epithelium mucosae), cistern like change (maxillary sinus and ethmoid sinus formed one operation cavity, secretion accumulated in maxillary sinus) and mucosa disfunction (loss of cilia transporting function of maxillary epithelium mucosae). Inflammation was observed in 33.7% of the patients 12 months after ESS, especially in those with mucosa disfunction, draining failure and reverse draining.</p><p><b>CONCLUSIONS</b>The KDL for maxillary sinus may be located in the posterior-inferior portion of the natural ostium, close to the attachment of caudal end of the uncinate process, and the drainage mode is not affected by gravity and posture. The KDL lesion after ESS results in abnormal draining of maxillary sinus, and excessively large maxillary sinus opening may aggravate mucosa inflammation of maxillary sinus. The abnormal draining state and mode may be related with the incidence of mucosa inflammation after operation. Preserving caudal end of uncinate process and avoiding injury of KDL would be beneficial to the restoration of mucosa and lessen the incidence of inflammation recurrence.</p>