Extensive maxillary sinus pneumatization.

To determine the incidence of variations of maxillary sinus pneumatization especially when it is extensive and the associated anomalies.Two hundred consecutive direct coronal paranasal sinus computed tomography (CT) scans were reviewed retrospectively. Extensive maxillary sinus pneumatization (EMSP) was defined as one in which the largest horizontal and/or vertical dimension of the maxillary sinus equalled or exceeded 90% of the corresponding diameter of the orbit. Further subtype I, II & III were defined depending on whether the pneumatization was extensive in one dimension (horizontal or vertical), two dimensions (horizontal & vertical) and by the presence of sphenomaxillary plate, intermaxillary plate or extension into frontal recess.EMSP was found in 8%, of these 7% were bilateral and 1% was unilateral. (Subtype I, II and III constituting 1%, 3% & 4% respectively).EMSP has been defined as a group and a classification proposed. EMSP will result in an atypical clinical picture, has a role in the pathogenesis of frontal sinusitis in some cases and may predispose injury to the orbit during endoscopic sinus surgery (ESS).