Studies of the anterior and posterior paranasal sinuses

The anterior paranasal sinuses include the frontal and maxillary sinuses, as well as the anterior cells of the ethmoid labyrinth.

Nasomental positioning (supraoccipitoalveolar projection); allows obtaining the following data:

• The frontal sinuses are usually symmetrically located, separated by bony septa, one of which is located paramedially; their normal negative radiographic appearance should be dark gray, somewhat lighter than the orbits, homogeneous within clearly defined bony borders, displayed as a white continuous line;
• the orbits are slightly flattened due to the corresponding projection; in the lower lateral part of them, the shadows of the wings of the sphenoid bone are visible;
• the cells of the ethmoid labyrinth and their bony partitions are projected between the orbits; the posterior cells of the ethmoid labyrinth in this position seem to continue the anterior cells and are visualized in the direction (indicated by the arrow) to the superomedial angle of the maxillary sinus;
• the maxillary sinuses, located in the center of the facial mass, are the most symmetrical in location and approximately the same in shape and size; sometimes inside the sinuses there are bony partitions (complete and incomplete), which divide the cavity into two or more parts; these partitions are well visualized on radiographs; of great importance in the diagnosis of diseases of the upper respiratory tract is the radiological visualization of its pockets (alveolar, lower palatine, molar and orbital-ethmoid), each of which can play a certain role in the occurrence of diseases of the paranasal sinuses;
• the infraorbital fissure, through which the zygomatic and infraorbital nerves exit, is projected under the lower edge of the orbit; it is important in the implementation of local-regional anesthesia, and if it is deformed, in the occurrence of neuralgia of the corresponding nerve trunks;
• The round opening is projected in the mid-medial part of the planar image of the maxillary sinus (on the radiograph it is clearly visible as a round black dot surrounded by dense bone walls) and is always adjacent to the image of the sphenoid fissure.

The nasofrontal position (supraoccipitofrontal projection) allows one to obtain a detailed image of the frontal sinuses, eye sockets and ethmoid labyrinth cells.

In this projection, the cells of the ethmoid labyrinth are visualized more clearly, but the dimensions and lower sections of the maxillary sinus cannot be fully observed due to the fact that the pyramids of the temporal bones are projected onto them. It should be noted that with this arrangement, despite the good visualization of the cells of the ethmoid labyrinth, many shadows of other anatomical formations of the skull are superimposed on their image. A distinctive feature of these formations is that their shadows extend without interruption beyond the cells of the ethmoid labyrinth. The main purpose of the nasofrontal projection is to obtain a detailed image of the frontal sinus.

The lateral view allows visualization of the frontal sinus, its anterior and posterior walls, and possibly the intersinusal septum; the base of the nose and the nasal bones; the anterior cells of the ethmoid labyrinth; the outer edge of the orbit, which passes into its upper edge upwards and into its lower edge downwards; the maxillary sinus and its walls in sagittal section; the hard palate and the alveolar arch with the molars located in it; the frontal process of the zygomatic bone; the middle part of the ethmoid bone, located between the contour of the outer edge of the orbit anteriorly and the apophysis of the zygomatic bone posteriorly; the vault of the orbit; the cribriform plate; the cervical processes; the anterior arch of the atlas and a number of other structures.

The contours of the visualized structures are often presented as double lines due to the superposition of both halves of the facial skeleton. The sphenoid sinus is projected under the sella turcica. The lateral projection is important when it is necessary to evaluate the shape and size of the frontal sinus in the anteroposterior direction (for example, when it is necessary to trepanopuncture it), to determine its relationship to the orbit, the shape and size of the sphenoid and maxillary sinuses, as well as many other anatomical structures of the facial skeleton and the anterior parts of the skull base.

Examination of the posterior (craniobasilar) paranasal sinuses

The posterior paranasal sinuses include the sphenoid sinus; some authors topographically classify the posterior cells of the ethmoid bone among these sinuses.

Axial projection (vertexosubmental) reveals many formations of the skull base; it is used when it is necessary to visualize the sphenoid sinus, the rocky part of the temporal bone, the openings of the skull base and other elements. This projection is indicated for fractures of the skull base. In this projection, the following anatomical elements are visualized: the frontal and maxillary sinuses; the lateral walls of the latter and the orbit; the body of the zygomatic bone (lower arrow); the posterior edge of the lesser wing of the sphenoid bone; the ethmoid cells located along the midline, sometimes covered by hypertrophied middle nasal turbinates.

The sphenoid sinuses are characterized by considerable structural diversity; even in the same person they can be different in volume and asymmetrical in location. According to the radiographic image, they can be from very small to extremely large and extend into the surrounding parts of the sphenoid bone (large wings, pterygoid and basilar apophyses).

In addition, this projection visualizes some openings of the skull base (oval, round, anterior and posterior lacerated openings), through which the fracture line often passes in cases of skull trauma (falling on the head, on the knees, blows to the crown and occipital bone). The shadows of a part of the pyramid of the temporal bone and its apex, the branches of the lower jaw, the apophysis of the base of the occipital bone, the atlas and the large occipital opening, in which the shadow of the tooth of the second cervical vertebra is visible, are visible.

In addition to the standard projections listed above, used in X-ray examination of the paranasal sinuses, there are a number of other layouts that are used when it is necessary to enlarge and more clearly highlight any one anatomical and topographic zone.

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