Abstract： OBJECTIVE To Analysis of CT and MRI imaging features of arrested pneumatisation of the sphenoid sinus and differentiate from osteogenic and chondrogenic tumours of the region.METHODS Retrospective analysis of CT and MRI findings was performed of 13 patients with sphenoid sinus arrested pneumatisation and 20 patients with osteogenic and chondrogenic tumours and tumor like lesions in the same period.Evaluation indicators included location,size,density,presence of expansive changes,calcification,cortical bone changes,MRI signal characteristics,signal changes after fat suppression,degree of enhancement,and statistical analysis was conducted.RESULTS Finally,the location includes the sphenoid body(4 cases),pterygoid process(3 cases)and multiple involved areas(6 cases).The arrested pneumatisation area is mainly characterized by fat density or mixed density of adipose and soft tissue.The longest diameter of the arrested pneumatisation zone is 0.8-4.1 cm.There is internal calcification(7 cases)and without bone expansive changes(13 cases).Cases with intact bone cortex(13 cases);On MRI T1WI,high signal(11 cases),equal signal(2 cases),on T2WI,high signal(10 cases),equal signal(3 cases).Decreased signal after fat suppression(13 cases),no significant enhancement(10 cases),and slight enhancement(3 cases).CONCLUSION The arrested pneumatisation of sphenoid sinus is a rare anatomical variation characterized by a mixed density of fat or soft tissue,intact bone cortex,without bone expansive changes,decreased signal of MRI fat suppression,and no obvious enhancement,which will help to differentiate from osteogenic and chondrogenic tumours of the region.