- location: anterior frontal bones on either side of the midline behind the brow ridges
- blood supply: supratrochlear, supraorbital and anterior ethmoidal arteries
- innervation: supraorbital and supratrochlear nerves
The frontal sinus has two chambers, one on each side, and they are almost always asymmetrical and separated by a septum. Each sinus extends superior to the medial end of the eyebrow and back into the orbital portion of the frontal bone. However, three or more chambers may be present in ~10% (range 1.5%-21%). It is divided by thin bony intrasinus septa, usually off-midline and rarely dehiscent.
Drainage from the frontal sinus tends to be more variable than the other paranasal sinuses and there is inconsistent terminology used in its anatomic description . In general, the frontal sinus outflow tract consists of a narrowing at the lower medial corner of the sinus (frontal infundibulum), where an ostium (opening) is demarcated by a small ridge of bone at the anterior sinus wall. Inferior to the ostium, drainage continues along a narrow passage known as the frontal recess or superior compartment of the frontal sinus drainage pathway . At this point, variant anatomy of the frontal/ethmoidal bone junction leads to two main variations:
- drainage into ethmoidal infundibulum, through the hiatus semilunaris into the middle meatus
- drainage directly into middle meatus
Venous drainage is via the superior ophthalmic veins.
Lymph drainage of the frontal sinus is into the submandibular nodes (cf. the overlying skin which drains to the preauricular group of nodes).
- may be absent (i.e. aplasia) or underdeveloped (i.e. hypoplasia): unilateral (4%) or bilateral (5%)
- this may be associated with a metopic suture
- may be large: extending through zygomatic processes, orbital bones, and into the squamae
They develop from anterosuperior pneumatization of the frontal recess into the frontal bone. Development begins late in intrauterine life or may start after birth (from one to twenty years), initially in the vertical segment. Pneumatization develops from 1-12 years old.