The frontal sinuses are found in the nasal part of the frontal bone. They are the most superiorly positioned paranasal sinuses found above the orbits and the root of the nose. The floor of the frontal sinus forms the medial aspect of the orbital roof.

Both frontal sinuses are highly variable in size and shape and their shape and size overall depend on ethnicity and climate. However, they usually appear more or less triangular or pyramidal in adults. The typical volume of the frontal sinuses is 0.14 to 0.24 oz (4 to 7 ml).

A thin bony plate called the septum separates the left and right frontal sinuses. The frontal sinuses are drained to the ethmoidal infundibulum via the frontonasal duct. The ethmoidal infundibulum further opens into the middle nasal meatus via the semilunar hiatus.

The frontal sinuses are the last of the paranasal sinuses to develop and are often absent at birth. For some people, they never develop. The frontal sinuses usually start to develop between the ages of 4 and 7.

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Frontal sinus