Background: Computed tomography (CT) is the preferred noninvasive method for the evaluation of osteitis in chronic sinusitis. Some scholars believe that the bone changes associated with chronic sinusitis always show high attenuation (high density) and are positively correlated with the severity of the disease. However, sinus bone remodeling is a complex process that may cause high or low attenuation. There have been few reports on the spread of osteitis. Therefore, additional research on sinus CT is necessary. Objective: To observe bony changes in chronic maxillary sinusitis (CMS) by CT and reveal the mechanism. Methods: A retrospective study was conducted in 45 patients with unilateral CMS with bony changes in the sinus walls. The patients' clinical data and CT results were analyzed and compared between the affected and normal sides. We propose the location, involvement, attenuation, and thickness method to evaluate CMS with osteitis. Results: Of the 45 patients, 40 (88.9%), 2, 12, and 7 had posterior external, medial, anterior, and superior lesions, respectively. The nasal region, sphenoid bone, palatine bone, and zygomatic arch were involved in 3, 12, 8, and 18 (40%) patients, respectively. Computed tomography indicated high attenuation in 30 (75.0%) and low attenuation in 10 (25.0%) patients; 6 (15.0%) showed new bone marrow cavities. The bone thickness was significantly different between the affected and normal sides in 40 patients (P < .001), including members of both the high- and low-attenuation groups (high-attenuation group: P < .001; low-attenuation group: P < .01). However, there was no significant difference in the thickness of the affected side between the high- and low-attenuation groups (P > .05). Conclusions: Chronic rhinosinusitis with bony changes may occur in the maxillary sinus walls and spread to adjacent bones. Both increased and decreased attenuation may occur in these circumstances. Analyzing the CT features of bone changes in unilateral CMS can improve the accuracy of disease diagnosis.