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location: anterior frontal bones on either side of the midline behind the brow ridges
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 3. 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 4 or superior compartment of the frontal sinus drainage pathway 3. At this point, variant anatomy of the frontal/ethmoidal bone junction leads to two main variations:
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
Frontal sinus begin as an outpouching of the lateral nasal wall, at the level of middle nasal meatus. This outpouching then extends superomedially giving origin to the ethmoidal cells and the frontal recess. The frontal recess then pneumatized into the frontal bone 5. Development begins late in intrauterine life (at 3 to 4 months) 5. However, frontal sinus are not present a birth 6. Pneumatization develops from 1-2 years old 5.
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