The sieve sinuses are hollow organs with mucous membranes attached within a bony framework, and there is usually only a small amount of thin mucus in the sinus cavities.
The sieve sinuses are located in the upper sieve labyrinth outside the nasal cavity and are divided into three groups according to the location of the sinus openings: anterior, middle and posterior. The anterior and middle sieve sinuses open in the middle nasal passage, and the posterior sieve sinuses open in the upper nasal passage.
The sieve sinuses are on both sides of the upper nasal cavity and consist of many small air-containing cavities of varying degrees of pneumatization within the sieve tubes. There are approximately 3 to 18 air-containing cavities on each side, and their arrangement, size, and extent of extension are variable and highly asymmetrical.
The sieve sinuses are highly variable, but all have some degree of development. The better developed sieve sinuses are connected to the nasal cavity with small openings, such as its air-containing cavities can be extended into the upper part of the pterygoid sinus, the bottom of the frontal sinus or the upper part of the posterior maxillary sinus and the frontal orbital area, and some can also reach the opposite nasal cavity through the nasal septum.