High density shadow of maxillary sinus may be due to thickening of maxillary sinus mucosa, maxillary sinus containing purulent secretion and maxillary sinus tumor. 1. Thickened mucous membrane of maxillary sinus: mainly due to inflammation and stimulation of the mucous membrane of the maxillary sinus, resulting in thickening of the mucous membrane of the maxillary sinus. high density shadow of the maxillary sinus is shown on CT, and the clinical manifestations are nasal congestion and runny nose. 2. Maxillary sinus contains purulent secretion: mainly due to maxillary sinus infection, CT shows high density shadow of maxillary sinus. Clinical manifestations include persistent nasal congestion, headache, loss of smell and other symptoms. 3. Maxillary sinus tumor: maxillary sinus tumor is often manifested as limited mass-like high-density shadow on CT, and patients often show repeated blood in nasal mucus, and the face is deformed due to the tumor. In severe cases, it compresses the optic nerve, causing patients to lose their vision. Maxillary sinus aspiration biopsy is needed to confirm the diagnosis. If there is any discomfort, the patient should consult a doctor promptly and follow the medical advice.