**2. Imaging techniques**

Imaging of the paranasal sinuses should always start with CT. CT delineates both bony anatomy and possible sinonasal opacifications.

Odontogenic pathology in the upper jaw often involves the maxillary sinuses. Hence, it is of outmost importance that the upper jaw teeth are included in the image volume and that this area is included in the radiological report [1].

Post-processing of the CT images usually include only reconstruction with bone algorithm in three planes. However, in case of opacification, soft tissue algorithm offers important details of the sinus content [2].

Reconstruction with bone algorithm should be done with slices no thicker than 1 mm. Thin slices are important for evaluation of periapical tooth lucencies as seen in odontogenic sinusitis and for erosion and destruction of bone in case of malignant disorders.

Additional reconstruction with soft tissue algorithm, with 2.5-mm-thick slices, may be extremely valuable and mandatory in case of soft tissue pathology inside or outside the sinus walls. In the case of pyocele or allergic fungal sinusitis, the attenuation usually is higher than mucus [3], and a fungus ball (mycetoma) has typical scattered microcalcifications that are better presented on soft tissue algorithm. In the case of invasive fungal sinusitis, this can be diagnosed by obliteration of the fat planes outside the sinus walls that is best seen on soft tissue algorithm.

Magnetic resonance imaging (MRI) is complementary to CT when complications to infection and neoplasms must be assessed.

Low-dose CT (<20 mAs), without intravenous contrast medium, usually will be sufficient for "screening." However, if complications or malignant disease are suspected, CT should be performed with at least 50 mAs and with intravenous contrast medium administration.
