AAO-HNSF Primary Care Otolaryngology Handbook

HOW TO READ A SINUS CT SCAN

1. Look at the name. 2. Look at the date. 3. Look at the orientation—right versus left.

The convention of designating sides for head and neck CT scans varies from institution to institution. You cannot assume that right is right and left is left when the film is positioned so you can read the name. You must see an R or an L . There are four radiographic densities: air, fat, water, and bone . Remember this very basic principle: When two structures of the same radiographic density are adjacent, the border between them is obscured. For example, if you cannot see the right heart border on a posterior-ante- rior chest x-ray, the lung next to the heart (right middle lobe) has the same density (water density) as the heart. Likewise, pus or fluid in the sinus has the same density as thickening of the sinus mucosa . The rela- tive density of bone and other structures can be manipulated by the scan reader as either bone window (demonstrates clear bone detail) or soft tissue window (bones too bright, soft tissue easily visualized). When you view CT scans, you must look at more than one image. If you do not know what a structure is, follow it through adjacent slices, and you’ll usually be able to easily identify it. Systematically reviewing any imaging study in sequence is critical to recognizing subtle abnormalities. Although the novice viewer routinely examines the maxillary sinuses first, you should carefully evaluate the orbits, orbital walls, skull base, maxillary alveolus, nasal septum, and sinuses in order. Remember that the ethmoid sinuses lie between the orbits, the maxillary sinus below the orbits, frontal sinuses above, and sphenoid sinuses behind. You should carefully study every x-ray, magnetic resonance imaging, or CT scan that you encounter, so you can learn to recognize common anatomic variants and distinguish them from true pathology. Here are three common anatomic variants encountered on coronal CT scans of the sinuses. • Deviated nasal septum—Figure 10.1 • Asymmetry of sinuses—size, shape, and presence of septas, etc. • An air cell within the middle turbinate (concha bullosa)—Figure 10.1. Abnormalities include fluid, mucosal thickening, bony fractures, cysts, and tumors, as shown in Figures 10.1 and 10.2.

59

www.entnet.org