X-ray anatomy of the nasal cavity and paranasal sinuses

The nasal cavity occupies a central position in the facial skull. It is divided in half by a septum formed by the vertical plate of the ethmoid bone and the vomer. The posterior opening of the nasal cavity is divided by the vomer into two parts - the choanae. The anterior opening of the nasal cavity - the so-called piriform opening - is formed by the bones of the upper jaw and is closed at the top by the nasal bones. Paired paranasal, or accessory, sinuses are located around the nasal cavity. They communicate with the nasal cavity by means of passages, or canals, are lined with a mucous membrane and under normal conditions are filled with air, as a result of which they are clearly visible on radiographs as light and clearly defined formations.

By the time of birth, the fetus has formed the cells of the ethmoid labyrinth and has small maxillary sinuses. The development of the paranasal sinuses occurs mainly outside the womb, mainly in the first 10-14 years, and is completed by 20-25 years.

The image of the nasal cavity and paranasal sinuses is obtained on radiographs and tomograms. Tomograms produced at a small angle of swing of the X-ray tube (the so-called monograms) are especially indicative. Radiographs and tomograms are produced in direct anterior and lateral projections. Usually, the examination begins with an overview image in the anterior chin projection. It shows a pear-shaped opening, and the nasal cavity itself has the appearance of a triangular enlightenment, divided by a narrow vertical shadow of the bony septum. On both sides of it, the shadows of the nasal conchae stand out, and between them are the light spaces of the nasal passages.

Around the nasal cavity, paranasal sinuses are determined on anterior and lateral images and tomograms. The frontal sinuses are located above the nasal cavity and orbits, project onto the lower anterior sections of the squama of the frontal bone and are divided by a bony intersinusoidal septum. In addition, each sinus can be divided into several cells by additional partitions. The size of the frontal sinuses is very variable. In some cases, they are completely absent or very small, in others, on the contrary, they extend far to the sides, forming supraorbital bays. Ethmoid cells are located on the sides of the nasal septum, protrude somewhat into the cavity of the orbits and enter the superior and middle nasal conchae. On anterior images, the ethmoid cells are superimposed on the image of the main sinuses, but on lateral images they are visible in front of them, under the shadow of the perforated plate.

On radiographs and tomograms, the maxillary (maxillary) sinuses located on the sides of the nasal cavity are most clearly outlined. Each of these sinuses on the anterior images causes a clearing of approximately a triangular shape with sharp outlines, and on the lateral images - a clearing of an irregular quadrangular shape. On the anterior image, a small clearing is visible in the upper inner part of the sinus - a reflection of the round opening of the base of the skull. The sinus may not be completely divided by thin bony partitions.

Methods of artificial contrasting of paranasal sinuses have been developed. In particular, a contrast agent is introduced into the maxillary sinus by puncturing the outer wall of the nasal cavity in the lower nasal passage after preliminary anesthesia. This method is called maxillary sinusography, it is used for special indications in institutions where there is no CT scanner, in the differential diagnosis of polypous growths, cysts and tumors. In recent years, CT has begun to play a major role in the study of paranasal sinuses, including tumor lesions. Tomograms make it possible to determine the volume and prevalence of a tumor formation and the condition of surrounding tissues and cavities.