The four paranasal sinuses of the head – ethmoid, sphenoid, frontal, maxillary – are visualized radiographically as radiolucent (black) areas. The presence of gray levels (varying opacities) within a sinus on a CBCT image may suggest some type of pathoses. Of all of the paranasal sinuses, the maxillary sinuses are the largest and the most important for the dental clinician due to their proximity to the maxillary alveolus.2,14
The inner walls of the paranasal sinuses are covered with a thin layer of mucosa, normally less than 1 mm thick and typically not seen radiographically.2 There are several reasons that can lead to mucosal thickening (sinusitis), varying from allergies, foreign bodies, or even odontogenic processes in proximity to the floor of the maxillary sinus (Figure 12). If such an inflammatory process crosses the floor of the sinus, it can create reactional mucosal thickening. The presence of moderate to advanced mucosal thickening (more than 6 mm) will be visualized on a CBCT scan. If maxillary sinuses are included in the field of view of the scan, the clinician must evaluate the health of the sinuses along with the patency of the maxillary ostium (the sinus-draining foramen).2,14 The cause of sinusitis should be identified and treated before a surgical procedure such as a sinus lift is performed in the area.
A dome-shaped lesion arising from the floor of the sinus, without mucosal thickening of the rest of the sinus, is characteristic of a retention pseudocyst.2 This common pathologic finding is generally asymptomatic and does not require treatment unless it enlarges to the point where it blocks the ostium.
Sinus lift procedures and foreign body removal are two important indications for requesting a CBCT scan. An antral septum may divide the sinus in two cavities; if not evaluated before surgery, it could cause major complications during the procedure. Visualization and analysis of the size and shape of an antral septum is of clinical importance when a sinus lift is desired in that area.15 Three-dimensional localization of a foreign body within the maxillary sinus by CBCT will assist in determining the best surgical approach for its removal.16