BACKGROUND: The aim of this study was to observe the pneumatization degree and adjacent structure of the posterior superior maxillary sinus (PSMS) and its effect on nasal cavity morphology.

MATERIAL AND METHODS: The study included a total of 103 cases whose paranasal sinus CT scans had been analyzed. The pneumatization of the PSMS and its relationship with posterior ethmoid sinus (PEs) and sphenoid sinus (SS) were observed. The effects of the pneumatization of PSMS on nasal cavity width and morphology also were evaluated.

RESULTS: 1) The PSMS was adjacent to orbit or middle nasal meatus (MNM) as type I in 5.82% of cases. The PSMS was adjacent to the orbit and superior nasal meatus (SNM) as follows: the superior part of medial wall of maxillary sinus (MMS) was not abutting on PEs as type II (4.35%) and abutting on PEs as type III (85.9%). If the type III was not accompanied by MMS shift toward medial it was identified as type IIIa (33.50%), and if it was accompanied MMS shift toward medial, it was identified as type IIIb (45.63%). The ethmomaxillary sinus (EMS) was identified as type IIIc (6.80%). The PSMS directly abutted on the SS as type IV in (3.88%). 2) The higher the degree of the pneumatization of PSMS was, the narrower the width of the upper part of the posterior nasal cavity (p<0.05 respectively).

CONCLUSIONS: The relationship of PSMS with the orbit, SNM, PEs, and SS should be identified pre-operation; it is important for safety and complete removal of retromaxillary lesions during endoscopic sinus surgery. The pneumatization degree of PSMS also should be considered as it can influence the morphology of posterior nasal cavity.

Keywords: Ethmoid Sinus, Maxillary Sinus, Nasal Cavity