Figure 1. Transverse computed tomographic images (window width = 3500, window level = 500) of the nasal cavities and frontal sinuses of a normal dog showing the 4 anatomical regions used for evaluation. (A) Region I: nasal turbinates rostral to the maxillary recess; (B) region II: maxillary turbinates at the level of the maxillary recess; (C) region III: ethmoid turbinates caudal to the maxillary recess; and (D) region IV: frontal sinus.